Are Your Interval Workouts Effective?—with Dr. Stephen Seiler

Interval workouts are often tough and many athletes finish them wondering if they were effective. We discuss how to get the most from your interval workouts with Dr. Stephen Seiler.

FT Ep. 267 Intervals with Dr. Stephen Seiler

Interval work is often hard, but many of us push through it knowing that the short-term discomfort is going to produce greater gains in the long term. But what can be harder than the intervals themselves is knowing if they are effective. Many of us latch onto hitting a specific number or percentage of VO2max, but is that truly the way to measure your interval work?  

In this episode we address that question head-on, diving into how we even define the idea of “effective” and what, if any, metrics you can use to determine the effectiveness of your session. But that leads to perhaps a more important question of how to best execute intervals and how we should be prescribing interval work.  

Joining us on this show is a fan-favorite and regular to the Fast Talk podcast, Dr. Stephen Seiler, who has made a career out of studying training adaptations and how exactly we bring about those adaptations. He addresses several key messages that he has been studying for years, including how best to target energy systems, how physiologically the interval work we do produces a signal in our bodies, and why there’s a limit to that signal.  

Perhaps most importantly, he talks about how effective training is ultimately about producing the biggest adaptive signal with minimal cost. This idea is the foundation of the polarized training approach, but may also be the best way to look at whether your intervals were truly effective or not—can you produce a large signal without having to spend the next two days on the couch recovering? Doing that is far more important than hitting a particular number.  

Joining Dr. Seiler, we hear from several top coaches talking about how they determine if their athletes’ work was effective, including Frank Overton, the owner of FasCat Coaching, Neal Henderson, the head coach for Wahoo Fitness, and Grant Holicky, coach at Forever Endurance. Finally, we hear from Dr. Stephen Cheung, another highly respected exercise physiologist.  

So, map out some time to listen to this episode—it’s long, but it’s effective—and let’s make you fast! 

RELATED: FT251: Time at VO2max: An Important Metric You Probably Haven’t Heard of 

Episode Transcript

Trevor Connor  00:05

Hello and welcome to Fast Talk, your source for the science of endurance performance. I’m your host, Trevor Connor here with Rob Pickels. Interval work is hard, but many of us push through it knowing that the short-term discomfort and sacrifice is going to produce big gains in the long term, but the one thing that might actually be harder than intervals is knowing whether or not they were actually effective. Many of us latch on to hitting a specific number or percentage of VO2 max, but is that truly the way to measure interval work?

Trevor Connor  00:31

In this episode, we address that question head on diving into how we even define the idea of effective and what if any metrics can be used to determine the effectiveness of your session, but that leads to perhaps a more important question of how to best execute intervals and how we should be prescribing interval work. Joining us today is a fan-favorite regular to the show Dr. Stephen Seiler, who has made a career out of studying training adaptations and how exactly we bring about those adaptations in our bodies. He addresses several key messages that he has been trying to convey for years including: that we really can’t target energy systems, how physiologically the interval work we do produces a signal in our bodies and why there’s a limit to that signal. Perhaps more importantly, he talks about how effective training is ultimately about producing the biggest adaptive signal with minimal costs. This idea is the foundation of the polarized training model. It may also be the best way to look at whether your intervals were truly effective or not. Can you produce a large signal without having to spend the next two days on the couch recovering? Doing that is far more important than hitting a particular number.

Trevor Connor  01:35

Joining Dr. Seiler, we’ll hear from several top coaches talking about how they determine as their athletes work was effective, including Frank Overton, the owner of Fast Cat Coaching, Neil Henderson, the head coach of Wahoo fitness and Grant Holicky, director of Coaching and Forever Endurance. Finally, we’ll hear from Dr. Stephen Cheung, another highly respected exercise physiologist. So map out some time to listen to this episode. It’s long, but it’s effective and let’s make you fast.

Rob Pickels  02:04

In our newest release of Craft of Coaching with Joe Friel, we explore the art and science of coaching masters athletes. Thanks to Joe Friel and many other coaches, there are more masters athletes than ever before and they’re taking on challenges once thought out of reach. Check out the Craft of Coaching module 11. Coaching masters athletes are guides to help masters athletes stay fast for years to come. Check out the craft of coaching at

Trevor Connor  02:35

Well, Dr. Seiler, welcome back to the show. Really excited to have you on particularly excited about this topic because this is one of those topics where I’ve come in and going, ‘I’m not sure where we’re gonna go with this. I’m not sure what the end results going to be’. Plenty of podcasts we do or I’ve done a ton of research leading in and go ‘Yeah, I know exactly the message we want to communicate’. This isn’t one of those and this is the sort of episode I love to do with you because you’re always very insightful. So I’ve done a ton of research, I have an outline, I know halfway through and be thrown both of them out and we’re going to be hearing a whole bunch of really interesting stuff that you probably haven’t thought of. So I can’t tell you how excited I am for this episode. Thanks for joining us.

Intro to Interval Training

Dr. Stephen Seiler  03:19

No thanks and no pressure, obviously. It’s a difficult topic. I mean, the easy stuff, if it was easy, we wouldn’t need to do a long podcast about it. So I do think interval training, we don’t have all the answers, but I think we can narrow the uncertainty a bit.

Rob Pickels  03:35

This is an episode I love doing with you too because unlike Trevor, I did no research, no preparation. I’m here to listen to you talk. So I’m gonna sit back, put my arms across my chest and take it away Dr. Seiler.

Dr. Stephen Seiler  03:49

Yeah, I’m ready.

Trevor Connor  03:50

I think what you’re saying, I’ve actually mentioned this a couple of times in the show and now that we have you here, I just want to actually call this out and really appreciated what you said. You were doing a symposium back, actually on Thanksgiving Day in 2022 and I was listening to the whole thing and at the very end, the moderator asked the whole group a question, that was a tough question that I don’t think there’s an answer for yet. I can’t remember what the question was aand you could see everybody trying to come up with an answer and when he got to you, you just said, ‘I think we need to be really humble here and recognize there’s probably more about our physiology that we don’t know, than what we do know’ and I appreciated hearing you saying that because this science is not complete. There is still a lot to discover and I think this discussion of intervals and what we’re covering today is probably one of those where we’re going to be doing a lot of well, ‘here’s our opinion, but I don’t know yet’.

What is Interval Training?

Dr. Stephen Seiler  04:50

I’m writing a book chapter right now and in the weeds on some issues and one of the issues is just the molecular biology and the signaling and my goodness, when you  read a contemporary review on molecular signaling and I’ve got a PhD and I feel like I’m reasonably intelligent, but I look at my eyes to start rolling back because there are so many different signaling molecules or so many different pathways. There’s so much redundancy, there’s so much crosstalk in cellular biochemistry, that it just makes chess seem like checkers, it’s very complicated. So the physiology is complex, the intracellular stuff is complex and we can accept that. I think it’s another issue to say how complicated or complex does the training prescription need to be in order to get at that adaptive process that we’re trying to achieve? So I don’t think that needs to be as complicated as many would have it to be. So that’s a starting point, let’s just start with saying, why do we even give it that name Interval Training, well, goes way back to the idea that, yeah, I could just take off running or get on the bike and just go as hard as I can until I fail and say, ‘I’m done for the day’, a continuous bout of exercise at high intensity and maybe I’ll make it for eight minutes or 15 minutes or whatever and then I say, ‘whew I’m done’, but what I do no, I break it up into pieces, I rest in between and I start stacking, I start accumulating more duration at some intensity, well, that’s interval training. That is the fundamental of it. We have said, we’re going to cut the pie into pieces, insert some rest in between and delay the fatigue rate or the fatigue curve. So that we accumulate more minutes of exercise above threshold or above FTP or whatever we you know, we decide on some dividing line or some threshold break point that we want to get above and see how many minutes we can achieve there. That’s, in a nutshell, what interval training comes down to from a just a practical point of view, but I think it’s far better for a lot of people trying to make a living by seeing how complicated they can make it by creating really fancy prescriptions of different pieces of time. 30 seconds at this power and then we’re gonna do this and then we’re gonna have 45 seconds here and then we’re gonna do it. It’s unlimited what you can create in your interval, training creat or whatever, we’ve all we’ve all got these tools, whether it’s on Zwift or Garmin or you can put in your parameters for your interval session, but the cells don’t see all that, to put it that way. So that’s, that’s one issue and then I think maybe even a bigger issue is, I wrote about this years ago, we talked about the epic workout because kind of related to the epic idea of the epic workout is the idea of the effective workout, the maximally effective interval session, what is the interval session? Is it the Steven Siler four times eight minutes? Is it the bent run a stod, 30 fifteens with three times nine minutes and 45 seconds. Four times four. There’s been all of these different magic workouts that had been espoused and often the person who did the research and publish like myself, we never said that four times eight minutes was magical at all. In fact, we tried to write that it wasn’t, but these types, any type of study that says, ‘Well, this was an effective prescription’, or maybe it appeared to be more effective than these other prescriptions. Then all of a sudden, that’s the that’s the latest magic workout.

Trevor Connor  08:43

Well, I mean, that one has a real simple answer, no matter how magical a workout is, if there is such a thing as a magical workout. If you do it for 12 months in a row, you’re gonna plateau.

Dr. Stephen Seiler  08:55

Oh, yeah or before that. Way before that, I think. Yeah. So and that brings us that’s a great segue to my next point, which is that there are no magic workouts and let’s do a little math. If you’re a three day a week athlete, that’s 150 training sessions a year. If you’re a four day a week, it’s 205. 5, that’s 250. 6, 300 sessions a year. The numbers add up pretty fast. Hundreds of training sessions and now you say ‘yeah, but Stephen, we don’t do all those interval training’. No, you don’t, I hope not, but if you’re a five day a weaker, that’s 250 plus sessions a year you’re throwing in some strings I’m not going to allow that of those 250. Let’s say at least 50 of them are going to end up being interval sessions. Right? Once a week, maybe twice a week, well, then you’re at 100 interval sessions in a year. So that’s a lot of training sessions and that’s what we have to think about is, when we talk about effective interval training, then I want us to broaden the view and say your effective interval training, we will assess that over longer timeframes than a week or a day. There’s no way to assess the effectiveness of the interval training we do, based on the one workout. As far as I can tell and when we play this game of, we’ve done this before you say take someone who’s fairly well trained, they’ve been doing this a while and in January, they have a plan and we say what would be a really nice improvement, just on some basic parameters and you say something like 5%? Well, 5% would be huge for athletes that have been in the game a long time, but let’s use 5% and then you try to say alright, 5% improvement 300 workouts, let’s divide .05 by 300 and we’ll figure out what the average improvement is per session and then you get a tiny little number that is so small, that it is smaller than the variation in all the measurement devices you have. So you can’t even detect it at that scale.

Trevor Connor  11:05

To this point that you can’t measure one session. Let’s hear from Grant Holicly, who talks about focusing more on how the athlete felt and how hard they push to see if the intervals were effective.

How to know if a workout is Effective?

Grant Holicky  11:16

This isn’t going to be too much of a shock, I push my athletes put a lot of comments in. One of the things that I’m looking for immediately is their reaction to the workout. ‘I felt awful, but I pushed through’, ‘I felt like a rock star’, any of those things that is my trigger to then go dig deeper into the workout and see what they were able to do. So if they’re talking about how bad they felt, I’m looking at how resilient they were during the course of that workout. Were they able to drop to a slight little number and knock it pretty consistently? It’s interesting because I think a lot of athletes are like, ‘Oh, if I write, I felt bad. He assumed that I did bad’. If people achieve when they thought they felt bad, I’m actually more excited about the workout. When they tell me they felt great. I usually stress about the workout, then go in and look and see him really start really high and then fade maybe through the workout because they got too overconfident. So I really am looking at that feedback from the athlete first and that’s what’s telling me to go look at specific parts of that workout, but I think in general, I’m looking for consistency through the efforts, I’m looking at an ability to hold a mark, not the mark, but a mark through four intervals, six intervals, eight intervals and then maybe even use that little bit of a rise at the end, is there just a little bit in there that they wanted to just, give it a little something at the tail end?

Trevor Connor  12:41

Would you give an athlete a new interval workout? Do you just give them a power heart rate prescription or are there other things that you tell them to help them do the intervals right?

Grant Holicky  12:51

I’ll explain what I’m looking for. If they’ve never seen it before, I’m usually going to write a paragraph on the why, right? Why are we doing this and I think for me, who’s somebody that does like intensity that we’re going to play around in all the different energy systems a lot of the time. For most athletes, that’s fairly new. So giving them a roadmap of why this is in there, what we’re doing it for and then the other thing is, obviously, with my background with mental performance, I’m usually looking at a way to get them to understand how these things are inexorably tied together. Where do I want your mind at during these intervals? What is okay if you can’t perform, where do I want your head to go to or even just as simply as ‘this is gonna be really hard’. The challenge here is not necessarily can you do this, I know you can do this on the right day. How do you lean into being very uncomfortable for a period of time?

What is an Effective Workout?

Trevor Connor  13:47

So let’s take a step back and just get to the really simple question. How are we defining effective? So somebody says, I want to know if this interval workout I’m doing is effective? How do we define that?

Dr. Stephen Seiler  14:01

Yeah, then we gotta go to what are we trying to stimulate? What are the adaptive patients we’re trying to stimulate and very often, we will tend to isolate and say, well, ‘this type of training is going to target this particular type of adaptations’. High intensity exercise is going to stimulate central adaptations for example, we’re going to improve VO2 max. Well, this is unfortunately a misconception because of all that intracellular crosstalk and redundancy and multiple signaling pathways, it turns out that you can see improvements in VO2 max, if you have athletes just train at 70% of max for six weeks or untrained. You can see improvements in VO2 max with an increase in volume without any increase in high intensity and of course, you can see an effect of a bump in high intensity interval training. There’s lots of ways to achieve these different adaptations and there’s an interaction between intensity and duration. Frequency, intensity, duration, those are our three levers in any training program. So even the interval training prescription, I think we tend to overplay the intensity component of the prescription. So we use that lever to use a metaphor, we crank on that lever excessively, thinking, if I can just push harder that’s going to increase the signal strength, but the reality is that then we lose the effect of the duration component because the signal stream that we’re trying to generate in the cells ends up being a combination of amplitude and duration, if that makes sense and then you get something you call the ‘area under the curve’ in mathematics geekspeak, which is just the amplitude of the signal times the duration of the signal. So I think one of the most practical things as a take home message for interval training is, effectiveness is going to be a balance of a high enough intensity to drive, to stimulate, for example, a lot of motor units to drive, that were recruiting both type one and type two motor units, but then not so high of an intensity that we start to get this feedback inhibition, that we start to get really low pH or really high hydrogen concentration because there seems to be some inhibitory effects of that both on motor coordination, but also on signaling. So we’re trying to find this, hate to use the term, but a kind of a happy medium or a sweet spot, in terms of the relationship between how high is the high intensity and then how many minutes can I accumulate? How many minutes of duration at that high, but tolerable intensity, can I string together in order to get the stimulus that I want and then recover from it in a reasonable amount of time? Which is that added issue that in the bigger picture of interval training, if we could just isolate a single bout, then we could do all kinds of stuff, but I’ve got to get up the next morning and train again and so I need to think in terms of not only am I going to have enough stimulators effective in the moment, at turning on these molecular processes, but that the systemic stress that comes along for the ride, that it is not so overwhelming, that now the recovery clock is really stretched out and I actually end up losing training, quality and quantity, the next two days.

Rob Pickels  17:45

This was a concept that I used to discuss a lot with Neil Henderson when him and I were working together and it was something that was difficult to get an athlete to understand, oftentimes, workouts would be prescribed that were less difficult than the athlete could do and ultimate ly, what you just said was our answer. It doesn’t just matter what’s done today, it matters, what’s done tomorrow and the day after that and you can have such a gigantic signal, say on Monday, that the rest of the week, you’re not gaining anything for your body, but what really matters is what does that average or what is that stimulus over time because that’s going to be further driving adaptation and it’s okay to finish today’s interval workout, feeling like you didn’t go completely into the read completely burying yourself because ultimately, what we’re looking at is day in day out that trading consistency we know is key.

The Problem with TSS and its Relationship to Adaptation

Trevor Connor  18:40

I remember reading a study a long time ago that really caught my attention. It was a study on weightlifting, but I think a lot of what I’m about to explain applies to interval work as well. Where they had different groups doing different number of sets of the various exercises and I think they had them do it for like a week so that you would see some sort of adaptation, but they had, I think it was one group doing just a single set of the exercises and another group that did three sets of the exercises, and then a group that did six sets of the exercises and the gains that you saw, the difference in the gains between the group that did three sets and six sets was virtually non existent, but the group though did one set saw about 90% of the same gains and it was really showing with each additional set, the marginal gains got less and less and less until you hit a certain point where more sets were just doing damage and delaying your ability to recover and so I looked at that the same way in interval work of ‘Yeah, I could do more intervals, but there’s a certain point where all I’m doing is the lane, how long it’s going to take me to recover’ and I’ve really gotten most of the gains and so I remember having a conversation with somebody on our forum about this where they said they did the five by fives that I love to do and they went, ‘Well, there’s only seven TSS. So why am I doing this? Like, what am I doing wrong’ and I just went always 70 TSS with me. ‘Well, how do you get gains out of that’ and I’m like, ‘the benefits’. So the whole point of this episode is talking about effectiveness. TSS, getting as big a TSS as you can doesn’t guarantee any sort of effectiveness.

Rob Pickels  20:23

Yes, it does, Trevor. TSS stands for gains. That’s what it stands for. It’s an acronym for gains Trevor.

Dr. Stephen Seiler  20:30

Oh, man, don’t get me started. The silliest thing I ever. It’s takes so little of going into the weeds on the actual math of the TSS to understand that it is just silly. It is not a stress score, it is not a gain score, it’s not an adaption score. It’s just a load score, get used to it folks. It has none of the nuance and all of the silliness of the metrics that people make without actually understanding physiology. I’m sorry, I love those guys. I know those guys at training peaks, but that’s just silly. It is misleading for the exact example you show is that people get misled because the TSS favors duration and so you can add up TSS by just getting off the couch a bit, but but if you do a really hard to interval session, it’ll say, ‘Oh, you didn’t do very much today’, but it’s not just that. I mean, I can get the same kind of message from my Polar watch, with its algorithms as well. So there’s a lot of unfortunate mathematical misleading algorithms out there.

Rob Pickels  21:37

Is there a better way to quantify the stimulus for adaptation that occurs with an interval session or is it just one of those, It’s so complex, it’s unmeasurable at the individual workout level?

Dr. Stephen Seiler  21:50

Well, then we got to really start going into some issues on allosteric stress and what I would say, one of the wonderful things I like to do or things I think is fascinating is let’s take an interval session, let’s take five times 10 minutes and I just threw that out because a team I work with, they use that as a standard workout pretty often. So I’ve seen a lot of five by 10 minute,

Rob Pickels  22:13

You here first. Dr. Sylar says five by 10 minutes is the best workout ever.

Dr. Stephen Seiler  22:19

Exactly, yeah. This week’s famous, this week’s epic workout. No, but five times 10 minutes, they’ll be pretty high up in the in the range between they’re close to their second lactate turn point, but they’re, they’re still under control, but if I look at heart rate, it’ll drift up and if I look at ventilation, which we’re doing now, it’ll drift up even more rapidly and I can tell physiologically by looking at the relationship between their heart rate and their ventilation if they’re on the ragged edge. In the first set of 10 minutes, it’s totally comfortable for them because the breathing is quite controlled. Maybe it’s 50 breaths per minute or something like that and then by the end of their workout, they may be at 70 breaths per minute, but their heart rate hasn’t drifted up too much. It’s fairly flat, but they are working harder and harder. So what that says to me is that the stress of executing each of those interval segments is increasing. The mobilization demand is increasing. There’s a lot of reasons why that’s happening. There’s glycogen depletion, there’s changes in recruitment, we’re having to turn on more muscle to achieve the same power, the brain is sensitive to that so it’s sending parallel signals to crank up heart rate, ventilation is going up. So there is an increase in internal cost of doing that external load and it is for precisely for that reason, that the TSS is silly because what is the TSS say, for each of those 10 minute blocks? It says they’re exactly the same, it powers the same and it adds up and it says, ‘Oh, you ended up with seventy TSS. No, it’s just ridiculous and so because the cost of doing that each block, each 10 minute segment was very different and then I now have to make a judgment as a coach or athlete. Okay, could I do one more? Should I do one more? I was at 90% of max heart rate, I was at about 17 RPE and I was breathing 65 breaths per minute and this is supposed to be a threshold ish workout. Is that enough and the answer is yeah, I think so you, you’re where you need to be you’re really pushing, you’re mobilized heavily, you could survive one more I think, you could do it, but it wouldn’t make it better and in fact, it would just make this session tougher to recover from. So that’s the kind of way we’re trying to think now.

Rob Pickels  24:47

Do you think that there are other metrics, maybe it’s not heart rate, maybe it’s not external workload, measuring that? What about like using a Moxie monitor to measure muscle oxygen saturation or what about pricking the finger 100 times during a workout and looking at a continuous lactate? Would that give more insight or even if we had that information, does that not really tell us what we need to know?

Dr. Stephen Seiler  25:13

Yeah, from a practicality standpoint, I don’t think, if we could measure continuously lactate, what it would tell us, even if we could continuously measure lactate, we would see a fairly, a quasi steady state that would appear if they start to recruit more fast twitch muscle in these kinds of some of these sessions, we might see a small increase in blood lactate actually during the session, you can’t always predict what you’re going to see from blood lactate, it depends a little bit about, their fiber type and the recruitment and so forth. So I don’t think blood lactate would help would tell us a whole lot more. Heart rate, it tells us roughly, generally, ‘yeah, this person’s working hard’ and heart rate very often will kind of with intermittent work, it’ll kind of come into a quasi steady state itself around, let’s say, 90%. Very common and then it just flat it kind of flattens out and so breathing is I found it to be interesting, just because when heart rates flattened out, breathing still going up, which is interesting to me. So we’re playing with breathing now. Moxie, the muscle oxygenation. I have played with it. Others have experimented with it. I know that there are some coaches and athletes that it informs their process, I have not been able to get enough control and have enough understanding of signal to noise on the Moxie or on the muscle oxygenation to feel like I could make useful interpretations yet. Again, I think it’s in the in the hands of the person using it and maybe there’s some things there. Unfortunately right now, if you use muscle oxygenation, you’re just looking at a small sample of tissue because it’s sending the bouncing off the wavelength of light across, maybe it goes a centimeter and a half deep or something like that, so it’s only getting a small amount of muscle and then you’re assuming that that’s representative for the whole quad, for example and I think that’s a pretty big assumption. So right now, I don’t know that these two, the Moxie would help. I don’t know that lactate would help. I still think that right now, I still think perceived exertion, I still think that just a perception of mobilization and sensitivity to that, that the good athlete can calibrate themselves to understand when they need to call it a day. If they understand that it’s not the battle, it’s the bigger picture they’re trying to achieve, that your goal is not to crush yourself.

Trevor Connor  27:51

This is a good point to hear from Neil Henderson and what metrics he looks at, which is really a more holistic view of the shape of the workout.

Measuring Perceived Effort as a Coach or Athlete

Neal Henderson  27:58

A lot of cases in the prescription, there’s the combination of a target output, power output, external power output on the bike, as well as then what we would expect is a normal response perceived effort, how hard were they working? What are their comments about that? What were the shape overall of each interval? Were they fading, were they sustaining, were they rising and then the overall interval to interval variability or changes in certain cases, we try to hit certain levels and then maintain as best we can. In other cases, we try to start off where there is a control element for the first few and potentially lift and be able to produce just a little bit more towards the end of a block of intervals. Those are a couple of the ways we’ll look at it. There’s of course, other things that we can look at, like normalized power, if somebody is doing on off intervals gives us a little bit of an insight because it’s not just the work that was done, but what kind of effort they had in recovery or not, were they unable to really pedal at all in between and so you might see a little bit of a decrease there, even though they might hit the target. Opposite of that if somebody really is feeling good and they exceed targets, but they recover better in between because they dropped that power target, they might actually be able to sit in a little bit better response to normalized power will be potentially higher than what they would have done, had they constrained that effort in the interval, but then pedaled harder in recovery. So there’s a few different ways to look at things but ultimately that subjective how the after it’s felt to the athlete relative to what the expectation set for those intervals was it prescribed.

Trevor Connor  29:36

Sounds like a very gestaltist approach. You’re looking at a whole bunch of things and how they all come together into one piece. It’s not a simple matter of your threshold powers 300. You did these intervals at 300. So you are successful. It’s a lot of things.

Neal Henderson  29:49

It is multiple things. I mean, humans are kind of complicated beings, I would say.

Sustainability of Interval Training vs Power Training

Trevor Connor  29:53

So on that note, I actually have a question for you because this is something I believe in strongly about making intervals of time, but I really want to hear your opinion because I actually read some research last night that disagrees with this. So let’s go back to that example of the five by tens, obviously an interval workout like that you’re trying to mostly hit the aerobic system, that’s where you’re trying to see your  adaptations. You pointed out that with each interval, the cost, your body gets larger. So I’ve always told my athletes, when you’re doing that sort of work, you’re doing that or the four by eights or five by fives, I almost think of the first interval as a throw away because you’re bringing in a lot of anaerobic metabolism, you’re probably not fully hitting that aerobic system. So it’s the successive intervals, the later ones, where you’re really creating that stress that’s going to produce an adaptation. So hence, I’m a big believer that the intervals need to be consistent. So if you’re using power, they need to be the same wattage every time and by the time you get to that fourth and fifth interval, you’re maximally hitting that aerobic system, but read some research last night that showed that if you let people self select their pace, where they’re not going to be consistent, they might do the first one really hard and then the next one’s become a little bit easier. Overall, people tend to go a little bit harder and tend to enjoy it more. So I’ve seen arguments for the note, ‘don’t try to be steady actually self select your pace and just kind of do what you can do’. How do you feel about that? Which do you feel is more effective?

Dr. Stephen Seiler  31:28

Well, first of all, I got to say, I hate the term anaerobic. It just bugs me. I couldn’t help it, just my blood pressure goes up, there’s two things that make my blood pressure go up and physiological discussions. One is the misuse of the term anaerobic and the other is the use of the term energy systems. They’re both just dumb and I will explain why I think they’re dumb if you want me to, but getting back to your question. Yeah, in interval session, number one, I believe you should warm up for the interval session. So if the athlete has warmed up properly and done some mobilization turned on, their musculature, got up their core temperature, they mobilized, then the first interval is not a throw away. That’s number one and I would think of it in terms of saying, Look, when you go into an interval session, you should think of it as you’re preparing your body to start a race. So you shouldn’t, unless you’re going to just say, Well, the first interval is the last part of my warmup and then you need to dictate accordingly. I mean, you need to decide on how many intervals are going to do, but it doesn’t make sense to me. For me, interval training is also partly brain training, you’re preparing the brain, you’re preparing your mind for certain kinds of stimuli that you’re going to need to be able to respond to an execute in racing. So interval training, one of the things it does as much as the physiology is it is a certain degree of stimulation towards understanding what happens when I do a fast start and so forth. So that’s part of interval training, but I would say to you, in terms of this, again we go back to this issue that, let’s say, I was going to hold 400 watts for six times three minutes, is 390 a failed workout, if I hold 390 on the fourth, fifth and six, instead of 400, almost certainly not. Or maybe 350, it depends on where in the season, and where in the preparation. I tend to think, again, thinking about sustainability because I’ve got two goals in my head and I’ve been playing with this, as I write this book, chapter, one of them is a very objective goal and that is turn on these adaptive processe. I want to stimulate adaptation, improve my threshold, improve cardiac output, things like that, but the other is, it’s got to be enjoyable and sustainable as a big picture process. If I’m going to train 300 times this year, then it shouldn’t be torture, it shouldn’t be something I dread every time I go out there. So I’ve got to look for that combination is as a meta level goal is Yeah, of those 300 sessions, maybe 75 of them is going to be are going to be really tough interval sessions type work or races, but it’s got to be sustainable and mentally kind of not defeating. It’s got to be uplifting and so I’m going to look for victories. I’m going to look for positive outcomes. So if I can always crush myself on an interval session so that every interval session ends in failure, if that’s the goal and I don’t think it should be the goal.

The Connection between Interval Training and VO2 Max Output

Trevor Connor  35:02

So I agree with you, I don’t think you can say intervals have been effective or not effective by targeting a specific number, like you said, you have to hit 400 and if you did, 390, you failed. More of what I’m talking about is, let’s say somebody does those six by three minutes and the first one’s at 440 Watts, the second one’s at 400 and by the time you get to the sixth one, they’re doing 310. So you’re seeing a big drop and they’re probably really fatiguing themselves. Can they finish that and say, I had a good workout or were they just all over the map?

Dr. Stephen Seiler  35:34

Yeah and I think there’s been some work on descending intervals and there are people who say that, ‘hey, this can be an effective strategy’. I don’t think there is a perfect strategy. Again, it’s just for the most part, it’s about accumulating work in an intensity range and turning on a lot of musculature and usually, when we’re doing interval sessions, we’re thinking in terms of trying to activate, we’re trying to activate the fast twitch motor units, we’re trying to turn on a lot of the, of the available musculature and we got to go up to the heart, the cardiovascular system, we’re going to try to, at least implicitly, we’re trying to achieve some kind of a cardiovascular load on the heart that either maintains or improves its volume. We’re trying to get this so called eccentric hypertrophy in the heart. Well, that’s another issue and the reality is that already, for most people, stroke volume is fairly close to max at a fairly low percentage of exercise intensity and we’ve known that for decades. Now, there’s some research that suggests that some athletes continue to increase stroke volume up to say, maybe 90% of max of VO2 max. So that’s part of the intensity question has always been well, how do I maximize the stress on the heart, so that the heart adapts because if I can deliver more blood deliver more oxygen, that means I’ve got the potential to have a higher VO2 max. So interval training has often been connected to VO2 max training. We’re talking a lot about muscle, but historically, I find that the big focus is often well, I’ve got to do my interval, so I get my VO2 max up, which is an interesting, it’s an interesting issue because once the athlete is already training quite a lot, the additional effect of interval training on VO2 max is actually quite small. It’s real, but it’s small.

Why VO2 Max isn’t the End All to your Output Capability?

Trevor Connor  37:39

Yeah, I actually found that really interesting. Again, I’ve seen this in a few studies where they say there’s three key attributes that really define an endurance athlete. One is VO2 Max. Second one is their threshold, particularly their threshold as a percent of VO2 Max, and then economy and then how many studies come back and say again, and again, again, particularly in higher level athletes. Besides threshold, these just don’t seem to be that trainable.

Dr. Stephen Seiler  38:06

Yeah, well, I would say it a different way. I would say the time course of adaptation is different. You can go back to the famous study of the marathon or what was her name, now just went blank. She had the world record for years and years at 215. Well, anyway, there’s a case study of her that Andrew Jones did and what does it show over 10 years, her VO2 Max was already stable at about seven EMLs per kg at age 18 and then her lactate threshold took another four or five years to peak and her efficiency or running economy took several more years after that to peak. So there seemed to be different time courses and there’s other studies and there’s more kind of just anecdotal evidence that suggests that the first attribute that peaks out in an promising endurance athlete it’ll be their VO2 Max and often they’re hitting their they’re hitting huge numbers for VO2 Max as juniors and certainly as U23s, you know, the under 23 athletes, so they are already just really high, but then you say but but they’re not ready to compete at a very high level because they just don’t, they can’t use enough of that and maybe their efficiency is not great and we’ve seen this with some really promising athletes in Norway. Big VO2 Max already at age 19,20, but the other the lactate profile says ‘Well, yeah, but there’s room for improvement in this’, what percentage of that Max are they going to be able to maintain for a meaningful duration? So it’s important to understand there seems to be a differential time course on these adaptations and it’s not you know, black and white as to how this works, but I would just caution people to think that VO2 max is the end all because it’s probably just the start of adaptation trifecta that we’re seeking.

Designing an Effective Interval Workout

Trevor Connor  40:03

So when I actually go back, because I think you touched on something really important on what does, so if you’re trying to design effective intervals, what is important and what isn’t and you keep mentioning one that I think is really critical that in that study that everybody cites as this is why four by eights are magical. I think that was the the point of that study, you said in there, that the the four by fours, which are more what people would think of as VO two max intensity, and the four by eights, which are closer to what people would think of as their threshold intensity, that the gains were pretty similar. They didn’t really differentiate, but the four by eights, you could do a lot more time and intensity. So you might have more of a signal from the four by eights and that’s why you were saying, or giving a little bit of favoritism towards those and you brought that up earlier on this episode that it might just be about accumulating time. So is that what it comes down to or what are the other critical factors in designing effective interval work?

Dr. Stephen Seiler  41:07

I think it ends up being kind of again, you got to just put on your longer view and say it’s a little bit of a pacing issue. I’m pacing my stress in different workouts and what we’ve found when we’ve looked at high performance athletes, and if you think about the five zone intensity model within that range of up to VO2 max. So from say 55% of VO2 Max 200 and we’ll call that potentially effective and up to an aerobic max and so that means that zone three is that threshold range and then zone four is just above your just above maximum metabolic steady state or maximum lactate steady state or FTP, whatever you want to use as your nomenclature of the day and what we see is that the athletes seem to use a lot of zone four, or even transition three, four and not much zone five. They don’t go to 95% of VO2 max, they don’t go to five beats below max heart rate very much at all and I mean, I look at so many training files from exceptionally strong endurance athletes because I get a lot of these files as part of my work and I’m always astounded by how little, how few minutes in the biggest races in the world or in training, how few minutes they are actually above 95% of heart rate max. Often none zero, in tour of Launders. They’re never there and they get top 10. So this should tell us something about the fact that we’re not at view to max very often ever, in training, to be honest, but we’re at 90% a lot and so I think that has some guiding value is that we’re going to try to accumulate a lot of minutes at that 90% level and get comfortably uncomfortable with that and if we do that, it scales up the adaptations happen and it’s fairly risk sustainable and it’s recoverable. The athlete can recover from those minutes, it seems easier than they can recover from going all the way to VO2 Max. So time at VO2 Max has been used as a metric. Well, the reality is when they do that time at VO2 Max, they’re actually saving time at within some percentage of VO2 max because they have to because they’re not actually at VO2 max. You just aren’t there very long. No matter how fit you are.

Trevor Connor  43:49

There’s another way to look at interval prescriptions. That’s the question of whether it’s advancing your goals. Let’s hear Dr. Stephen Cheung talk about that.

How to Assess the Success of the Interval Workout

Dr. Stephen Cheung  43:58

I think the first thing I would look at is, did you actually complete the interval as planned? If you didn’t, if you were doing your classic five by five, Trevor and you fall off a cliff and can’t do the fourth one or the fifth one, well, that already tells you something about your physiology that you are not fit enough to do this workout or you may have paced yourself incorrectly. So I think that would be the first thing I would look at is again, did you actually complete the workout as planned and then I would say in terms of physiology is I would look at the file and say, ‘Okay, how does this fit into your overall goals’ and if you are really a crit rider and you’re doing a lot of, again, your classic five by fives, is that the right workout for you, is that building physiology the way that you need it to, to specialize for your particular racing event. So I would look at those and then I would also look at the relationship of power and heart rate. I think that is a real key to look at things like, you may have been able to do the last interval with the same power output, but my heart rate is just sky high through the roof and that tells you something also about your state of fitness and recovery. So those are all the kind of things I would look at in terms of assessing was this particular interval workout successful.

Trevor Connor  45:31

For both beginners and veterans polarized training is the best way to get and stay past year after year and this is the perfect time of year to be thinking about how polarized training can help you. In our new guide featuring Dr. Stephen Seiler explore fascinating and helpful topics, like how polarized training is different from sweetspot, how to bust out of performance plateaus, how to polarize all season, how to build durability and how to time your high intensity work. With the complete guide from Fast Talk Labs, you’ll have everything you need to polarize your training like a pro and unlock your elite. Learn more at

Repetition vs Variety within Interval Training?

Trevor Connor  46:05

So we’ve touched on the importance of duration, we’ve touched on the importance of amplitude or intensity. Another one I want to bring up and hear your opinion on this in creating effective intervals is repetition. I am one of those coaches who believes you create an interval design and then you do it for several weeks. Four, six, eight weeks and essentially perfect it and get your body used to doing it and go for the gains. I know other coaches who would say ‘no, that gets boring, so we should do a different interval workout every time you do intervals’. What’s your feeling on that? Do either of these affect the effectiveness?

Dr. Stephen Seiler  46:49

Yeah, it’s a great question. I’m somewhere in between. We had one study that we did, it was a multicenter trial and we had over 20 in each group and we did this study of the periodization of the interval training. Where we had one group trained with a typical periodization, where they intensified the interval prescription across 12 weeks. We had three, four week mesocycles and they started with four times 16 minutes and then they went to four times eight and then they went to four times four. So they were intensifying. Then we had another that was kind of a reverse periodization, where they started with four times four and then four times eight and then four times 16. So they were increasing the volume, but at a slightly lower intensity, but they were doing the same kind of workout for four weeks in a row, the same prescription like you’re talking about and then we had a third group that mixed it up. So every week they did one of each. Either two or three workouts. So they you know, it was kind of a we tried to do everything the way athletes tend to do, but they mixed it up, like you’re talking about and we couldn’t see statistically a difference in the net outcome of these different models, but it looked, if I’d have been a coach, I would have said, it looks like both the traditional and the and the reverse were a bit better than mixing it up and that surprised me, but I think it’s because of that issue you’re talking about, it’s just the execution of those interval sessions, there was more, they were just paste better because they they do them several times in a row and maybe we were pulling out extracting a little bit of extra quality because of the feedback they had from the previous session and they were pushing themselves more on the limit, maybe I can’t tell you what else it could have been because physiologically when you measured blood lactate and heart rate and those kinds of things, there were not discernible differences, but it seemed like they gave a little bit of a better effect.

Is there a difference between Intensity and Specificity?

Rob Pickels  48:52

You do still have to wonder if there is a signaling and a specificity of signaling thing going on and I understand that this is maybe theoretical and it’s very difficult to actually ascertain, but let’s say we’re choosing intensity and duration to target specific adaptations within the body. If all the work that we’re doing is focused specifically on that you would think that there would be a higher signal for that particular adaptation. When we begin really altering or mixing up the intensities and the durations, instead of working at, ‘VO2 max level’ and I did air quotes for those that can’t say me or ‘threshold level intensities’, that might create a more mixed sort of signaling biochemically and we can take this all the way back to calcium calmodulin and all of that, that’s for a different episode. I’ve always sort of looked at it in that regard, but you know, Trevor, I do think that another point to make here is as long as those workouts are potentially aimed at the same adaptation, then I think that what Dr. Seiler is talking about here still holds true. What I wouldn’t do is a big VO2 workout on Wednesday, big threshold workout on Saturday, but if they were VO2ish on Wednesday and Saturday, but maybe the intervals are just a little different, a little bit different of a percent. Like we said, it’s not about doing five by five every day, maybe one day, it’s five by five and the next day, it’s the same intensity, but you’re doing it for a longer duration with less rest, so on and so forth.

Dr. Stephen Seiler  50:36

I got to be honest, I really don’t think there’s any research that can give us a definitive answer there as to some of the really detailed issues of programming because the noise is so much bigger than the signal. If there are differences, they’re super small and then the individual variation is really big in comparison, but we do have you mentioned calcium sensitive calmodulin, the CAMPK signaling pathway and then you have the A and PK pathway. It looks like evolution has equipped us with two basic pathways that are sensitive to what’s going on in endurance training one, and there’s more, there’s redundancy, for sure, but one is is looking at the energy inside the cell is ATP going down a little bit, are we starting to get some ADP and that AMP. So we’re getting a little bit of a degradation of the of the high energy phosphates and there’s some super sensitive signaling that seems to happen around that as a, that gets co opted as a signal for adaptation and that AMPK pathway is the one that we would generally attribute this to high intensity exercise because it’s going to be you know, ATP is really well defended in the cells, but at very high intensity, you get a little bit of a drop in ATP, you get an increase in AMP enough that that ratio shifts and the data says that’s a signal and that signal goes through PGC one alpha, which is seems to be this central regulator and then induces mitochondrial proliferation and all this stuff. So intensity seems to have a dedicated signal stream, but the problem or the issue with the intensity, the ANP case signaling pathway that we would think we’re targeting that with interval training, is it’s kind of self limiting. Now, let me explain. One of the reasons it’s self limiting is that as the athlete gets fitter, that ATP to AMP ratio, it’s defended better. So you get less signal from that pathway and then the second issue, which which David Bishop has shown is that pH, if you have really low pH, meaning a lot of protons, meaning you’re really pushing the lactate, then you get inhibition of the signaling pathway. So it’s it has the self limiting features in it, that actually make a heck of a lot of sense. When you start seeing how interval training works. Yeah, you get a bump, but then it doesn’t just keep working, it doesn’t just keep getting better and it’s consistent with that signaling data that we’re seeing. How that a NPK pathway seems to work and then you go over to this other pathway that we have, that evolution has equipped us with, which seems to be related to calcium, that when you contract muscle, you there’s more calcium inside the muscle fiber because it’s used as a signal to turn on contraction and so there’s an elevated calcium level and it’s turns out that that ends up being also co opted as a signal that says, ah, if calcium is high, I’m using this muscle a lot better, upgrade the mitochondrial density and so that happens. So you got this calcium calmodulin pathway, but the interesting difference with that pathway is it’s more of a duration sensitive pathway, a volume sensitive pathway and it doesn’t seem to have the feedback inhibition problem where you get this self limitation. So on the calcium pathway, it’s kind of like just more is better.

Trevor Connor  54:28

Anybody who’s interested check out episode 264. We actually talked in detail about a review from Dr. Larson that details these two pathways in a really elegant way.

Calmodulin and Duration of Training 

Rob Pickels  54:39

Yeah, no, definitely. Great call out, Trevor, thank you. When I have traditionally thought and listening to you speak now Dr. Seiler, it popped an idea in my head and that’s what I want to ask you about. When I’ve traditionally thought about calcium calmodulin has always been in long duration. When we talk about duration, we’re talking about the number of hours that are accumulated at a relatively low intensity, but if we think about how the body grades force during exercise, when you move from base to tempo to threshold and you’re increasing your intensity, you’re recruiting more and more motor units, moving away from slow twitch or including slow twitch but also bringing in more fast twitch fibers. If we think about duration, is there a duration component with the calcium calmodulin system, as we recruit fast twitch fibers for longer, meaning does longer intervals at higher intensity, the duration there, released more calcium than say fast twitch fibers help adaptation there. We talked about the you know time a greater than 90% of VO2 Max is potentially important in a previous episode, we’ll show notes that it was about Dr. Ronstadt research because it’s recruiting fibers that otherwise don’t really get recruited very often. Again, more duration. Can we look at this calcium calmodulin in all of these or is it really just those really long duration slow twitch fiber efforts, multiple hours at zone one?

Dr. Stephen Seiler  56:17

I would say probably you can look at it as part of all the training sessions because the calcium elevation it’s always there when we turn on muscle. So it is a signal stream that’s always there. Now, I’m not the molecular biologist. So I will quickly defer to others like David Bishop and those who are working directly with this, but I think the redundancy that we see, when they start going into the weeds on the molecular signaling suggests to me that there’s a tremendous amount of overlapping in the signal streams and so I think that is one of the things if there’s a take home message for today and I think if there’s a take home message for some of the stuff I’m writing right now, it is that we really need to try to get away from this siloing that we think that we tend to do, and say, well, ‘this kind of training has this particular effect and this kind of train has this particular effect in the body’ because the more we look at the data, the more we look at the signaling. That’s not how it’s working. It’s very interconnected and one of the favorite words of Trevor this functional symmorphosis that I’m sure you’re gonna crack, but I’m not sure functional symmorphosis is even the right theory to use, but there is connectedness in the sense that the training that we do that we think is improving stroke volume and cardiac output is also improving molecular level signaling in the mitochondria and in the muscle fibers. So there’s, there’s coordinated movements, and I’ve said to people, ‘Look, you basically never see an athlete with a super high VO2 Max, it’s got a pathetic threshold intensity’ because those two things almost can’t happen. If you’re doing enough training to get this one. You almost cannot have a really bad threshold. So they there tends to be co-coordinated movement of these adaptations, but there’s emphasis differences, for sure. So I’m not trying to say you throw out the training intensity zones, but I’m saying that there’s a lot of crosstalk, there’s a lot of interactive effects. For example, glycogen depletion is a modifying signal for these other signaling pathways, reactive oxygen species, we haven’t even talked about Ross, you know and apparently, Ross is part of the mix because if you give athletes antioxidants, heavy antioxidant loads, inhibits adaptations. So something is happening related to Ross. It may be a redundant mechanism, but there are a number of mechanisms that are cross talking with each other, they’re interconnected and right now we’re just talking about mitochondria. We could also talk about angiogenesis, building more capillaries, we could talk about hypertrophy of the heart, eccentric hypertrophy, which says, we want to increase volume and we want to make the walls thicker, but but just thick enough so that we maintain the appropriate ratio between volume and thickness. That so called eccentric hypertrophy that we get in the heart. So all of this is happening and kind of a coordinated way and there’s redundancy of the signals.

Symmorphosis and our Instinctual Determination

Trevor Connor  59:40

We had talked about this a while ago. So maybe I should just give the one, two minute summary for anybody who didn’t hear that episode and also let people laugh at me for mispronouncing this, but the symmorphosis, this is the idea that no system or part in a process in our body is overdeveloped. So if you think about oxygen delivery or oxygen consumption, you have to breathe in oxygen to your lungs have to be able to take in that oxygen, then that oxygen has to be transferred from the lungs to your blood, then it has to go to your heart and your heart has to pump it to the muscles, then the muscles have to be able to take the oxygen out of the blood. So there’s multiple steps here and the idea is, why have your heart have an amazing ability to deliver oxygen to pump this oxygen, if you have a really poor ability at the muscle level to take out that oxygen, then that’s just a waste. To make the body efficient, you want all these different steps to be about equivocal so that one isn’t much better than the others. So what you’re getting at is adaptation is going to hit all steps. So it’s not going to just develop one is going to develop all of them. So if you improve one, you improve all and that means that you don’t have one step that’s overbuilt and kind of pointless.

Dr. Stephen Seiler  1:00:59

Yeah and we can even go a little deeper into this and I kind of like to think in terms of evolution and try to understand, can I explain things from any kind of an evolutionary framework and Daniel Lieberman, I guess he’s still at Harvard, he’s done a lot of this issue of what is our evolutionary background, what are we good at and it seems to have been that we were these persistence hunters. The one thing physiologically that Homosapiens are good at, is just slow running and not fast running, definitely not swimming, but slow running because of our ability to get rid of heat and persist, we could eventually run down the antelope or whatever and it’s been tested, it’s doable, humans can do it, there’s been experiments, anthropological kinds of experiments to say, yeah, we can do this and so that suggests that, okay, something about our evolution suggests that we have some advantages and that we can handle this low intensity exercise for long periods of time and so there seems to be probably some adaptive advantage there that we can turn that on fairly quickly, but the other thing that is interesting is, is that, as you alluded to, we are super efficient, meaning that if the body doesn’t produce tissue or produce adaptations, that it doesn’t need because they’re so darn costly. You know, making more mitochondria or building more muscle mass or building our big brains that are costly enough to feed. So the body is super efficient. So you have these tendency towards a low intensity advantage that we can scale up adaptations really quickly, we seem to have some pathways that work well, but if we quit training that regresses really quickly and both of those seem to have evolutionary, you might say, explanations for how this tends to work and so I think there’s parsimony, now we’re starting to see, we can almost track it all the way from from an evolutionary model through molecular signaling to signal versus stress management. If we get out on the on, the more the daily grind of training, now we have to say, Yeah, we’re trying to induce molecular signals, but the process of running or cycling in the heat or hard intervals, it induces a systemic stress response. So now, what ends up I think, being the reason we have the need for intensity distribution and issues like that is really about signal distress. It’s about managing that over time.

Thrifty Gene Hypothesis

Trevor Connor  1:03:48

I think the key evolutionary theory that poles in here is the Thrifty Gene hypothesis that we evolved in a time when we are constantly struggling to get enough calories to consume enough calories to make up for the calories that we were burning and so our bodies were designed if you don’t use it, get rid of it because muscle mass requires energy. The bigger stronger heart requires energy. So why require that energy unless you’re using it?

Dr. Stephen Seiler  1:04:15

This brain requires a heck of a lot of energy.

Trevor Connor  1:04:18

Right, exactly.

Dr. Stephen Seiler  1:04:20

20% or so.

Trevor Connor  1:04:22

That was because we were mostly foragers and scavengers. I love this theory because it explains so many things that if you think about them, they wouldn’t make sense otherwise, like why do we lose muscle mass? Being stronger fitter faster is obviously was important in those times when you’re fighting off a lot of predators. So why in the world would you want to lose muscle mass? Well, it’s because muscle mass requires energy. Look at lions and tigers. They were top of the food chain getting enough calories was generally not an issue for them. They don’t have the sort of muscle loss if they don’t train that we have.

Managing Stress by using ‘Reps and Reserve’ Training

Dr. Stephen Seiler  1:04:57

Yeah, I’m careful, I don’t want to offend people with certain views, but I do think that understanding that evolutionary heritage and understanding where all of these signaling molecules, how they have emerged and understanding that is useful. I try to think through the logic of it all, the cellular logic, but then, I think those old guys, you’re talking about evolution, I need to know something about training tomorrow, then I’m going to fast forward and move to this issue of signal versus stress. If you asked me what is effective interval training? Then I’m going to answer effective interval training over time will be the interval training that induces a large signal for adaptations in these various affected organs, the heart, type two fibers, angiogenesis, buffering capacity, but at an affordable cost. At an affordable stress cost over time. I can afford to go a bit into the into the red on a hard day, but I can’t go into the red every day, then the bank account, then I go bankrupt, then the energy, then I’m in trouble. Back to that idea of a recovery clock and on average, if I’m going to have a sustainable process, my athletes need to be essentially recovering every 24 hours, on average. Now, that means I can do some tough withdrawals, I can do some extra withdrawals on some days, but then I’m gonna have to have some, what do you call them? Easy days and we’re back to this and then I can make some decisions about how much is it worth and a law of diminishing return, which we always see with these training sessions and training programs, is in strength training, they would call it the ‘reps and reserve’. They even have that terminology they use and you can almost use the same terminology for your interval session. If I give to you a six times four minute interval session, then I might say to you, I want you to do this and you’re leaving one rep in the tank because I’m trying to pull you back just a little and say, you’re gonna do this so that you could do seven reps, seven times four, or eight times four, but you’re doing six, but you do it as if you’re going to do seven or eight and then we’re going to stop at six. That’s a kind of a reps and reserve idea that builds in just a little bit of a stress management buffer.

Dr. Stephen Seiler  1:04:57

We actually had that conversation, I can’t remember when it was, but we had Brent Bookwalter on the show and he talked about every once in a while. It’s really fun to go to failure with interval work, but he said, ‘that’s fun. I don’t say it’s smart’ and he said, ‘most of the time, I want to leave something in the tank because I’m concerned about what I need to do the next day’.

Dr. Stephen Seiler  1:07:55

It’s okay. I mean, I’ve heard this conversation from Renato Carnavon. He’s coached all the Kenyans. He said, every once in a while, they just decided they were going to have fun, as you say, just fly, you know, on an interval session and then he’d say, ‘Okay, that’s all right, but we’ll just have to deal with the repercussions’ meaning we’ll just hold back a little bit the next couple of days. It’s okay, but as long as you’re able to accept that in your training and say, ‘Man, I really pushed hard, I went, I have to or no reps in reserve. I’m struggling, and I built in an extra rest day or an extra low intensity day. Okay, no worries, it’s sustainable. So it doesn’t have to be a disaster when your athlete goes off the reservation a little bit. In fact, it can be a sign that they’re thriving, I would say that they have the energy to do that occasionally, but if they do it every day, they’ll go in the hole pretty quickly if they don’t understand the overall math they’re trying to regulate and they’re trying to pace themselves over a longer timeframe. I think that’s one of the things that typifies, you might call them these, these ‘savvy endurance athletes’ that they figure that balancing problem out pretty well.

Can we target specific energy systems?

Trevor Connor  1:09:12

So you’ve already answered this question, but I just want to ask this to see if I can make it just storm out of the room. So you think the…

Dr. Stephen Seiler  1:09:20

Energy systems.

Trevor Connor  1:09:21

Yes, even better than that?

Rob Pickels  1:09:24

I looked at the outline and said, ‘Well, we’re skipping that section’.

Dr. Stephen Seiler  1:09:28

I’m happy to explain to you why I hate it.

Trevor Connor  1:09:31

Do you think we can target specific energy systems with our interval workout, particularly the anaerobic energy system?

Dr. Stephen Seiler  1:09:39

Here we go. All right. I’m gonna try to not explode in my head. My blood pressure just squeezes up. No, the reason I am so against this term is that it implies this again, this siloing that says I’m either using this system or I’m using this system. It is one energy system. There’s one, it is a single system, elegantly coordinated so much that if you do anything for more than about three seconds, every part of the system is starting to unwind and unfold and adapt and respond. It’s one system. Okay? If I die tomorrow, that’d be one of the things I’d want to leave you with. There’s one energy system, beautifully coordinated and connected.

Rob Pickels  1:10:39

That’s on your gravestone. It was one system.

Dr. Stephen Seiler  1:10:43

There was only one energy system. You gave me an aneurysm with this. No. So it’s like your hybrid car. Right? You know, it’s interconnected. The battery use of the battery versus use of the combustion engine, they’re connected. They are not independent of each other and that’s how energy systems work, the energy system we have and that’s also the reason my other hated word is anaerobic. You’re not, you’re essentially never anaerobic. This idea that you suddenly don’t have oxygen is stupid. It’s wrong. Let’s get rid of it. We’ve been trying to get rid of it for decades, but it just keeps persisting. Oh, I went anaerobic. No, you didn’t. You went glycolytic, you had a dramatic increase in glycolysis rates, which ends up causing, you know, there’s competitive movement of, of these two carbon molecules or to you know, into the mitochondria and out and sometimes it becomes lactate, sometimes it becomes pyruvate. There’s competition there. That’s nothing to do with oxygen. That is a glycolytic rate issue. That’s why I don’t like the term anaerobic and I don’t think many physiologist do.

Misuse of the term Anaerobic

Trevor Connor  1:11:57

So now you’re touching on one that really bugs me, I hate it when people refer to anaerobic glycolysis because my point is glycolysis is always anaerobic, it’s just sometimes the end product, pyruvate, goes into oxidative phosphorylation. Sometimes it has to be transported out of the cell as lactate taken up by other tissue, but it still ends up going in.

Dr. Stephen Seiler  1:12:19

There’s the oxygen independent part and the oxygen dependent part. I guess that would be the way I would use that term and just get rid of anaerobic because it just has these implications of I’m suddenly holding my breath at the cellular level. No, you’re not and if we can get past that because I think it would help us understand interval training as well. So now I have ranted on my two of my big pet peeves that will go on to my gravestone

Trevor Connor  1:12:47

I actually wanted to ask you about that, so I’m glad we did that, but I think…

Rob Pickels  1:12:52

No, but seriously, can you answer the question?

Trevor Connor  1:12:56

I do think the other important point, which you’ve already answered is it was a an old school notion that you could have interval work that very, very specifically targeted one aspect of our physiology and I think what you’re getting at is, well it can have this particular interval work can be a little stronger in this area than that interval work. Really all interval work is hitting most processes.

Lactate Buffering and increasing Buffering Capacity

Dr. Stephen Seiler  1:13:24

Yeah, and let’s take an example is, if I am a middle distance athlete or I’m preparing for some really high intensity intermittent type of racing, that I might try to do some very dedicated sessions to what we might call ‘lactate buffering’. Trying to build up my buffer capacity and that’s a fairly fresh fruit type of adaptations, I can increase the bicarbonate buffering capacity, with some very targeted sessions, I can get a little bit of a bump in that capacity and maybe tolerate a bit higher degree of hydrogen ion accumulation because I can buffer it and get rid of it via ventilation. So that might be kind of a high intensity, I might do it three or four week period with this kind of training and that’s going to be on that really that high intensity end, above VO2 max. So yeah, there’s some nuance here. Within the interval training spectrum, we can definitely have emphasis areas, but even if I were doing that, so called anaerobic capacity training, I would be getting stimuli for other adaptations, but it’s a costly kind of training. That would be a good example of a type of training, where I’m trying to build up buffer capacity, I’m gonna have to really hit the, the intensity high to try to push lactate metabolism, push hydrogen accumulation up so that I get that signaling effect. Well, it’s going to be costly. It’s going to be a high stress workout, it’s going to suck, it’s going to hurt. It will induce a big autonomic response. So it’s not going to be the kind of thing I’m going to do every week, throughout the year, it would be wasteful. Going back to this idea of, if we don’t need the adaptations, it’s too energetically demanding to maintain it and that’s a great example is really being topped out on your buffering capacity is so costly, that you’re going to use that as a peaking strategy. That would be the kind of interval training you would do at very specific times to get the bump in buffering capacity and then except that it will fade back out when you stop doing those workouts, but you can’t afford to do those workouts every week, they’re too darn tough systemically. Whereas those 90% intervals four times eight minutes, they’re on the interval spectrum, they’re easier to recover from and they give you some of that buffering effect and a lot of the other effects so they they’re kind of a better trade off.

Optimization vs Maximization

Trevor Connor  1:15:57

So that brings up a question and I’m gonna theorize a little bit here. Yes, you can target a little bit, but for the most part, a lot of interval work is hitting a lot of the same stuff. Is the goal here with interval work less to specifically target and more to consider which interval type work produces the maximal gains with the minimal cost? So is it about just finding which, is it optimization in use at these terms versus maximization? So you just brought up an example of interval workout that might have some gains, but there’s a real cost to that interval work? So how often do you want to do it? Should we really, when we think about interval work, focusing on the ones that go, This produces a really big signal for adaptation, but the cost isn’t that huge and I think, the more I think about it, that’s why I’ve been such a big fan of the four by eights and the five by fives because we’ve seen produces a big adaptive signal, but as you said, you don’t walk away from those being absolutely wiped, you can keep training the next day. So it’s big signal, minimal cost.

Dr. Stephen Seiler  1:17:10

You can light yourself up with those, but it depends on your mindset and I use my daughter as an example, she, she would do the four times eight, or even, we’d just fulfill the whole thought, we might start at three times eight and then we go to four times eight and then five times eight. So we use the accumulated duration, but when when I first started having her do these, she raced them. So you will have athletes that treat every interval session as a kind of a personal race against the previous version of themselves and that is not sustainable. It will bury you. If you think that every time you do that key workout, that standard interval workout. So the advantage of the standard interval workout is of course, that it’s you know, you get this pacing understanding you can execute it well, the disadvantage of it is, is you’re constantly comparing with previous sessions. So you get this feeling that I need, I want it to be better, I want it to be better every time and that may happen when you’re a fairly young athlete and everything’s going in the same direction, but once you get at a fairly high level, every interval session is not going to be a new personal record. So that is the big concern.

Trevor Connor  1:18:30

I have that conversation with athletes all the time where they’re doing a particular interval workout, normally, the first few times they do it, the power is going to go up just from the learning effect, but then they have that first session where the power is lower, and they contact me and they go, ‘I was 10 Watts lower what’s going on? What’s wrong?’ and I’m sitting there going, ‘you had a burrito for dinner last night? I don’t know why, why do we care’.

Dr. Stephen Seiler  1:18:53

Or now we’re actually where you belong, you’ve actually gotten the first fast phase of the adaptation you’ve paced, you learned in some pacing, we’ve gotten all that out of the way. Now let’s get down to the hard business of slowly getting this up. 10 Watts on averages is a really mean for the updation. So a lot of that, like you say, it’s just learning how to pace the workout. I listened to a podcast you guys did on pain and certainly the conversation and learning how to deal with some of that probably influences interval execution. So part of the improvement in the interval session performance may be just, you know, dealing with better doing a better job of dealing with the signals that are coming to the brain and how we’re how we’re feeling. So there’s a number of things that that are not just cellular adaptations going on here. There’s brain adaptations as well and they’re meaningful, I think. It’s real. That’s also part of it.

Trevor Connor  1:19:55

This is a good place to hear from Frank Overton he talks about the importance of looking long term into your interval work, will also identify the success in individual sessions.

How to measure Power Output

Frank Overton  1:20:04

I think the first thing that we look at from intervals, we asked the athlete how they felt, there’s a felt good, but it was really hard type of reporting and then there’s minutes felt awful and I didn’t make that much power type of reporting. So we look at average power, normalized power, we cross reference those with what the athlete says about the intervals. One other thing that we look at is comparative analysis between similar length intervals over time. So if they’re doing VO2 max intervals, are you averaging higher VO2 max intervals for five minutes from three months ago or from three years ago. Athletes, they would just like to know if they’re improving, are they making more power? So we’d like to tell them if they are or they are and I love intervals for that because you can measure the power output and say you did this much more than the last time or not and I want to understand if the athlete gave it their best effort and did they really dig in and bust it out or did they kind of just, eh, phone it in. So we have little tricks to understand that without having to ask them every single time, but that’s just getting to know the athletes. So that’s really important. Sometimes it doesn’t really come through in the data, you can look at little things in the data, though. If they’re doing a five minute interval and they’re in the last one and the power starts to dip and low and then 20 seconds from when the interval has to be done, does it like ramp back up because they just were like, ‘I’m almost there’. So you can look at that and I mean, it’s pretty obvious to me what happened, they were getting close to the end, they were like, I want to give it my best effort and you can see that power go up or on the other hand, did they just start going down and they just kind of gave up. So we look at that in the power output and then they may say that in the how they report those intervals, but I think a lot of that, how they felt about the workout and then how they performed as it the data shows goes towards if we deem that workout successful or not. I mean, there’s like doing the workout, there’s doing the workout, as well as you can. Are you all in every single day are you just, you’re just like trying one day a week? So we look at that to determine if workouts successful or not. It depends also on the goals of the athlete, a lot of athletes, a lot of amateur athletes, I think it’s just a success to get them to do the workout. So we as coaches may use their goals to let them know, Hey, you’re doing great, you know, you don’t have to like extract your heart and lay in a ditch after every single interval workout, that’s probably not going to be sustainable for years and years. So we do like to think about sustainable training for athletes that’s going to net longer term gains than going crazy for a couple of weeks and so a couple of different ways to let athletes know that they did it right.

Rob Pickels  1:23:19

Hey, listeners, it’s Rob pickles. co host of Fast Talk, we have some exciting news to share. Fast Talk is now on Patreon. Patreon is a social platform that helps us keep creating the Fast Talk podcast you know and love. As a Fast Talk supporter, you can help us stay independent, just log on to and search for Fast Talk podcast. Personally, I’ve really loved creating Fast Talk, being able to share a little bit of myself with you every week has been a lot of fun and I’m happy that I’m able to give back to a community that means so much to me. I’m inspired every day by your emails, comments and feedback and I’m constantly looking for ways to improve the podcast experience for our listeners. Honestly, we couldn’t do any of this without all of you. So thank you for your support and thanks for listening.

Where do you land on the interval work spectrum?

Trevor Connor  1:24:06

So we are getting to an hour 25. So as much as I could go another two hours with this conversation, I think we need to start winding it up and I want to hit both of you with a question before we get to the take homes because when we came into this episode I was really interested in where are we going to land on this spectrum. So there’s a spectrum of how to approach this high intensity or interval work from on the one end mand I’ll tell you this is where my first mentor was, he never did interval work in his life. He did training races. So on this end is the, it all does the same thing. It really doesn’t matter as long as you’re accumulating time and intensity. Just do it doesn’t matter. Go to a training race. Do whatever workout you want to do, just accumulate time. Who cares? In the middle you have that, o, you need something structured, but it is all kind of doing the same thing. So you can mix it up, you can have a little bit of fun, do this interval workout one day do that interval workout another day, which is what you see in a lot of these programs and then I would say the other extreme is the pick a workout, it needs to be structured, you need to execute it effectively and do it for eight weeks until your eyes fall out. So that’s kind of the spectrum. Where do you guys land and Dr. Seiler let’s start with you and then Rob, I want to hear your opinion?

Dr. Stephen Seiler  1:25:34

Well, I’ve got the gray hair to show that I’ve been around a while and I feel confident I can say that I’ve seen all three of those, that entire spectrum, I’ve seen athletes that have achieved great success with all of it and if I go out to the extreme recently, Nils von der Pol, the athlete who the speed skater who did some really bizarre training with five hard days and then or five days in a row of training always taken two off. If you looked at his interval training sessions, he did the exact same thing for weeks and weeks and weeks and weeks on end and it was just incredible what he did some of the power outputs and so he’s on that end and then you’ve got some of the great athletes of our decades past, probably like Eddie Mercs would have trained himself into shape with racing. So I think we’ve seen all of those and we’ve seen in the middle and we’ve seen natural intervals and Fartlek and so I think that tells us that there is a great deal of redundancy, there’s a great deal of just doing the work in that signaling process and that maybe we should give ourselves a break on trying to find the magic in this issue. It may be though that individual athletes with their individual psychology and with maybe their individual morphology and fiber type may respond better just partly because of personality to one regime or the other and that’s okay, that’s great. If we can zero in on that and for example, just giving them enough autonomy, to say, You know what, I need you to accumulate 30 minutes of hard work, but you decide how you do it today. If you want to do it as six times five or if you want to do it as, I don’t know, 10 times three or if you want to do a Fartlek and you got to accumulate over an hour. Thats okay, but I need 30 minutes of hard work where your heart rates roughly at 90%. Go for it. That would be a way and give the athlete a feeling that Oh, I’m getting to actually make some decisions here and that can actually for some of them actually release positive energy with that autonomy. So that’s in that mix.

Physiologist vs Coaching

Rob Pickels  1:27:49

For me, I think of this question, Trevor, from the perspective of a physiologist and then also from a coach and I think I give two different answers, depending on what that is. The physiologist in me says, there’s diminishing returns, kinda like you described earlier with your weightlifting example. I think the most bang for your buck comes from just training in a manner that the vast majority of what you’re doing is at low intensity and a small bit of what you’re doing is at high intensity. Following a structure like that, it gets you a lot of the way there. In this situation is not really describing exactly what that high intensity is, as Dr. Seiler said, it could be a whole range of different things. That gets you most of the way there. I don’t know, 70% 75. I’m making numbers up. I do think that the next step beyond that now becomes Okay, let’s be a little bit more specific about the signaling that we’re trying to induce. Maybe certain intensities are going to recruit certain fibers, they’re going to cause certain changes within the body. If we are focused on what that is, then maybe we’re able to induce adaptation in a more specific manner, kind of like how Dr. Seiler described the different ways of periodization, earlier in this conversation, the mixed, while it wasn’t statistically different, might not have been as efficacious. I do think that if you go beyond that, we have even smaller returns now. Where do exactly this workout to this second, exactly this number of times? I don’t know, maybe that’s slightly better. Maybe it’s slightly worse, but at this point, I think that we’re now getting to the additional benefits are getting quite quite small and maybe we’ve gone beyond what’s practical, but the coach in me, you know, looks at this from the athlete side of things and that is, what the heck do they like to do? Why are they doing the sport? What are they trying to achieve? Those often become much bigger questions than the exact duration of this interval and I’m glad you said this earlier, Dr. Seiler, I always chuckle when you have a coach that prescribes the most complex workout in the world to the second and it has nothing to do with the body and everything to do with them. Just trying to think they’re smart because if I can prescribe such a specific workout, I must really know what I’m doing. Dude, it doesn’t matter, it really, it doesn’t matter, but some athletes, like my wife needs exact and if you tell her run 11 miles, she will run back and forth in front of the house to hit 11 miles. Where I’m like, you could’ve stopped at 7 and a half. What do I care, it’s no different. So you have to know your athlete because if you’re opposed to the athlete, if the athlete wants exact and you refuse to give them exact, trust me, that relationship isn’t going to work out very well and vice versa. Some athletes need agency over their training. Others want to 100% just trust the coach and listen to them. So it goes both ways for me, Trevor, what do you think?

Finding the right type of Interval Work

Trevor Connor  1:30:59

I’ve kind of gone on a whole journey of this. As I said, my original mentor, he’d never did intervals in his life he was all about, he set up a Tuesday night training race and a Thursday night time trial and that’s how he got his intensity. In my first couple of years, that’s what I did too. I went years without doing intervals. So I was very much on the just go hard. Then went to the other extreme of the no, we have to design a specific workout. I was never into the complicated, I just like you, Dr. Seiler, I like my five by fives or Tabata workout, but something that was relatively simple so that the athlete could execute it, but then I was like, here’s your workout, you’re doing this for five to eight weeks and you don’t do anything else I have now probably landed in the middle part of it’s the recognizing that actually, they really all do generally hit the same sort of place. That said, I’m still going to say if I’ve got a crit rider that I’m coaching and a time trialist that I’m coaching, I’m not going to give them exactly the same work, there is going to be some overlap, but I’m going to give that time trialist more long threshold work. I’m going to give that crit rider a little more of the short high intensity and some sprint work and it might just be mental, learning how to deal with those particular types of pain so they can handle it in their event, but what I’ve really gotten to now is the, once I’ve made that decision, getting to know the athlete and what resonates with them. I have seen that, I have some athletes that all they want to do is interval work. If I sent them to a training race, that would be a torture for them. I have other athletes that the interval work is the torture and they would love to do a training race. So I look for the type of work that it’s in the general area that I want the work to be in and that they’re going to enjoy and it’s going to resonate with them.

Rob Pickels  1:32:54

Trevor, you know how I do so much base riding on the trainer?

Trevor Connor  1:32:56


Rob Pickels  1:32:57

Yeah, the name of that workout is ‘baservals’. Just so you know.

Dr. Stephen Seiler  1:33:01

I have a baservals right workout too. I did it last night, two hours, but the most I might do three hours. This one, I just fluctuate every five minutes between 180 Watts and 225. 225 is just under my first threshold. 180 just feels relaxed and so I just bounced back and forth for three hours or two hours.

Rob Pickels  1:33:21

Pretty much where I am. Yep, exactly.

The difference between Interval Training and Racing

Dr. Stephen Seiler  1:33:23

Baservals, but one thing I would say, Trevor is when we go to this idea of racing, as you know, I would say, while you were doing intermittent work, you were doing interval training during the race because cycling is extremely intermittent in nature, but the difference I would say that I find interesting about racing versus prescribed interval session is, as you would be quick to point out, in a race, you’re trying to be maximally efficient. So you’re trying to actually minimize energy costs, you’re trying to lick from the others plate. So  your behavior is actually designed to reduce pain to reduce your own stress and then use your engine at the exactly right moment. That’s a different mentality than the five times five that says you don’t get to do that you have to do this work. You don’t get to try to maneuver around it and I think if you do too much of just using races, maybe you miss out on some of that discipline that you need to push yourself with the structured interval. So I think a mix might be useful.

Trevor Connor  1:34:35

That’s a really good point and I should have brought that up as well. So that’s something my mentor was Glen swan. That was a lesson that he taught me. I think it was he that said to me, ‘during the week, I race hard on the weekends, I race smart’ and you saw that in the Tuesday night race. He would actually yell at people that would just sit in the field, well wouldn’t yell but he would tell them stop doing that. People who just sit In the field and conserve and you’d see him in the race right off the gun, he would attack. He’d be out there for like a minute the field would catch him, he would recover for 30 seconds, then he would attack again and the first race of the season, he would actually get popped because the fitness wasn’t there and he was doing that so much, but each week, he would do that more and more until about the third of the fourth week, he would finally just ride away from us and win the race, but his philosophy was, you go to that training race to race hard.

Rob Pickels  1:35:29

Yeah, Trevor, I have an article on our website that I wrote last year maybe, about how to use Zwift races as training exactly like this, going into the race with a purpose, knowing what you’re going to do. Is it going to be sit on the front for X amount of time and then recover, but yeah, that takes a little bit of structure into an otherwise unstructured environment.

Dr. Stephen Seiler  1:35:48

We could go into the weeds here, but Trevor, you taught me a little bit about Zwift and about being willing to set your ego to the side and pop into a race after you’ve already done some work or I started doing the opposite. I didn’t have quite the ability to, I had to keep my ego intact. So I would first race. I’m Fifty Seven, I mean, I needed everything I could get in the race, but then I actually have had these Zwift races, where after I gave myself a five or 10 minute cooldown and then I did some more interval work because I’ve already turned on a big stress response, I might as well get a strong interval workout out of it because before that, I just had the 20 Minute race. So there’s different ways to use combinations, I think of a more reactive training, which would be the races and then proactive where you are kind of doing some planned effort. So I think there’s different ways to go at this and bottom line for all of this, I think we’re coming down to is there is no magic workout and we shouldn’t look for it, we should think about sustainability. Have fun, get a good strong signal, but be able to wake up the next day and train again with a smile.


Trevor Connor  1:36:58

Which brings us to light might be the most anticlimactic part of the show because we might have already done all this, but our one minutes. Do we have anything left to say or did you just give yours?

Dr. Stephen Seiler  1:37:10

Yeah, people are probably tired of me talking. So I think I’m done.

Rob Pickels  1:37:14

For me, I just want to re emphasize and maybe I think, Trevor, this should be the title of the episode. It’s okay to leave something in the tank. That you don’t have to go to negative ability, it’s okay to push yourself hard, but leave a little bit of something left there.

Trevor Connor  1:37:32

So I think my take home is going back to something you said at the very start of the show Dr. Seiler that I definitely want to touch on again, which is you said you’re not going to get a discernible adaptive signal out of a single workout. So I agree completely, find what works for you find the balance, keep it fun, find something that’s hard, but then my recommendation is once you find that thing, give it four weeks, see what it does for you because you’re not going to know for four to six weeks, if you’re getting gains out of it or not and my only warning is saying oh, this week, I’m going to try to training rates approach and then next week, I’m going to try these particular intervals and then the following you’re going to try those intervals, you have no way of knowing what is working for your body or what isn’t. So find it, if it’s a training race is great. Do four weeks of training races, see what happens for you. Give it the time.

Dr. Stephen Seiler  1:38:30

Yeah, I agree and four weeks is a really good minimum kind of block and we’ve seen so much that if it’s gonna happen, it often will start happening in four weeks. You’ll start seeing something. That’s a good call and the other thing is, you just said there that I was fascinated with this guy Von der Pol that Nils, the speed skater, he said, I would do like hill repeat running once every six weeks and then I never understood if it was making me better because I didn’t do it often enough. I quit doing stuff like that, which I think is refreshing too is look at all your trainings. Are you doing some just random stuff, just this off the wall type of training every once in a while because you think somehow it’s going to have a magic effect? Probably it’s not at all and more likely it just gets you hurt or it just kind of waste of energy, clean out the random stuff and focus on the essentials and that may be an energy saving kind of or direct you in the in a functional way.

Trevor Connor  1:39:32

Well, Dr. Seilar always a huge pleasure having you on the show.

Dr. Stephen Seiler  1:39:35

Well, it’s always fun to be here. I’m always also happy if you don’t refer to Jay Z or any rapper that I don’t know, so I’m just glad we’ve moved past that.

Trevor Connor  1:39:46

I think we settled on we’re gonna call you AC DC now.

Rob Pickels  1:39:49


Trevor Connor  1:39:50

You like your 70s metal?

Dr. Stephen Seiler  1:39:52

I gotta tell you a story. I have Spotify and I have these different sets of songs that I listen to during Zwift sessions. All of the sudden, I get this playlist and I did not ask for it, I didn’t search for it and it said ‘Gym Hits for Older Men’.

Trevor Connor  1:40:13

Oh no.

Dr. Stephen Seiler  1:40:14

Yeah AI had just and it was AC DC, I mean it was a good list I got to admit, but I just I just like you gotta be kidding me I’ve been just AI has categorized me now this old man. Oh man I was pissed. Don’t get me started on Spotify.

Trevor Connor  1:40:39

That’s bad titling.

Dr. Stephen Seiler  1:40:42

Gym Hits for Old Men.

Trevor Connor  1:40:46

Well like I said, one of my saddest days was I was in a rental car and I was just trying to find a radio station I could listen to and I found this easy listening station and I kid you not they played an AC DC song and I’m like, when did AC DC become easy listening?

Dr. Stephen Seiler  1:41:04

Well, I put this out on Twitter that you know I had been targeted as the Old Man Guy and then this guy wrote back said what does that mean, it was like 20% Hard Rock and 80% Easy Listening. Okay, I deserve that. So anyway, we do the best we can.

Trevor Connor  1:41:25

That was another episode of Fast Talk. Subscribe to Fast Talk wherever you prefer to find your favorite podcast. Be sure to leave us a rating and a review. The thoughts and opinions expressed on Fast Talk are those of the individual. As always we love your feedback. Tweet us at @fasttalklabs or join the conversation at Learn from our experts at or help keep us independent by supporting us on Patreon. For Dr. Stephen Seiler, Frank Overton, Neil Henderson, Grant Holicky, and Rob Pickels. I’m Trevor Connor. Thanks for listening!



Agnol, C. D., Turnes, T., & Lucas, R. D. D. (2021). Time Spent Near V˙O2max During Different Cycling Self-Paced Interval Training Protocols. International Journal of Sports Physiology and Performance, 16(9), 1347–1353. Retrieved from 

Cao, M., Quan, M., & Zhuang, J. (2019). Effect of High-Intensity Interval Training versus Moderate-Intensity Continuous Training on Cardiorespiratory Fitness in Children and Adolescents: A Meta-Analysis. International Journal of Environmental Research and Public Health, 16(9), 1533. Retrieved from 

Coffey, V. G., & Hawley, J. A. (2007). The Molecular Bases of Training Adaptation. Sports Medicine, 37(9), 737–763. Retrieved from 

Edge, J., Eynon, N., McKenna, M. J., Goodman, C. A., Harris, R. C., & Bishop, D. J. (2013). Altering the rest interval during high‐intensity interval training does not affect muscle or performance adaptations. Experimental Physiology, 98(2), 481–490. Retrieved from 

Gibala, M. J., & Jones, A. M. (2013). Physiological and Performance Adaptations to High-Intensity Interval Training. Nestlé Nutrition Institute Workshop Series, 76, 51–60. Retrieved from 

HELGERUD, J., HØYDAL, K., WANG, E., KARLSEN, T., BERG, P., BJERKAAS, M., … HOFF, J. (2007). Aerobic High-Intensity Intervals Improve V˙O2max More Than Moderate Training. Medicine & Science in Sports & Exercise, 39(4), 665–671. Retrieved from 

Hesketh, K. L., Church, H., Kinnafick, F., Shepherd, S. O., Wagenmakers, A. J. M., Cocks, M., & Strauss, J. A. (2021). Evidence-based vs. social media based high-intensity interval training protocols: Physiological and perceptual responses. PLoS ONE, 16(9), e0257685. Retrieved from 

Kellogg, E., Cantacessi, C., McNamer, O., Holmes, H., Bargen, R. von, Ramirez, R., … Astorino, T. A. (2018). Comparison of Psychological and Physiological Responses to Imposed vs. Self-selected High-Intensity Interval Training. Journal of Strength and Conditioning Research, Publish Ahead of Print(NA;), NA; Retrieved from 

Laursen, P. B., & Jenkins, D. G. (2002). The Scientific Basis for High-Intensity Interval Training. Sports Medicine, 32(1), 53–73. Retrieved from 

Menz, V., Marterer, N., Amin, S. B., Faulhaber, M., Hansen, A. B., & Lawley, J. S. (2019). Functional Vs. Running Low-Volume High-Intensity Interval Training: Effects on VO2max and Muscular Endurance. Journal of Sports Science & Medicine, 18(3), 497–504. 

Nimmerichter, A., Eston, R. G., Bachl, N., & Williams, C. (2011). Longitudinal monitoring of power output and heart rate profiles in elite cyclists. Journal of Sports Sciences, 29(8), 831–839. Retrieved from 

Seiler, S., Jøranson, K., Olesen, B. V., & Hetlelid, K. J. (2011). Adaptations to aerobic interval training: interactive effects of exercise intensity and total work duration: Effort-matched interval training. Scandinavian Journal of Medicine & Science in Sports, 23(1), 74–83. Retrieved from 

SYLTA, Ø., TØNNESSEN, E., SANDBAKK, Ø., HAMMARSTRÖM, D., DANIELSEN, J., SKOVERENG, K., … SEILER, S. (2017). Effects of High-Intensity Training on Physiological and Hormonal Adaptions in Well-Trained Cyclists. Medicine & Science in Sports & Exercise, 49(6), 1137–1146. Retrieved from 

Thomas, K., Stone, M., Gibson, A. S. C., Thompson, K., & Ansley, L. (2013). The effect of an even-pacing strategy on exercise tolerance in well-trained cyclists. European Journal of Applied Physiology, 113(12), 3001–3010. Retrieved from 

Wen, D., Utesch, T., Wu, J., Robertson, S., Liu, J., Hu, G., & Chen, H. (2019). Effects of Different Protocols of High Intensity Interval Training for VO2max Improvements in Adults: A Meta-Analysis of Randomised Controlled Trials. Journal of Science and Medicine in Sport, 22(8), 941–947. Retrieved from 

Yang, M., Meng, D., & Mejarito, C. L. (2023). RECOVERY METHODS FOR ATHLETES DURING HIGH-INTENSITY TRAINING. Revista Brasileira de Medicina Do Esporte, 29, e2022_0649. Retrieved from