Intensity Changes Between Fast-Start and Steady Intervals, with Dr. Stephen Cheung

Dr. Stephen Cheung discusses a study comparing steady-state versus fast-start intervals, then uses Xert software to model how a fast-start interval can be much more intense.

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A rose is a rose, and a 4×8 interval session is a 4×8 interval session, right? But what if the pacing and the structure of that interval can make the intensity dramatically different? It turns out, not all intervals are created equal.

In this workshop, Dr. Stephen Cheung discusses a study comparing steady-state versus fast-start intervals, then uses Xert software to model how a fast-start interval can be a lot more intense.

The research suggests that the design of intervals can determine how much benefit or training stimulus you receive, particularly when it comes to how steady they are—or conversely, how fast you start before tapering to a desired level.


Rønnestad, B.R., Rømer, T., Hansen, J. (2020). Increasing oxygen uptake in well-trained cross-country skiers during work intervals with a fast start. International Journal of Sports Physiology and Performance, 15, 383-389.

Video Transcript

Chris Case 00:15
Welcome to Fast Talk Laboratories, your source for the science cycling performance.

Dr. Stephen Cheung 00:25
Hello, this is Dr. Stephen Cheung. I’m a professor of Brock University in Canada. And in today’s workshop, we’re going to take a look at different styles of intervals different ways of doing an interval, and whether they may end up having a big impact on the stimulus that we receive and potentially their effectiveness. We’re gonna especially look at whether doing a an interval in a very steady pattern. So for example, riding at 250 watts for the entire interval is as effective as potentially starting off with what we call a fast start type interval where you may end up going at a higher intensity early on, let’s say 280 watts, and then gradually taper down to 230 watts. The first question we need to ask of course is, does it really matter in real life, how we pace an effort? Well, I would contend that it absolutely does matter. Because if you’re in a race, if you’re in a Tour of Flanders at the base of the Koppenberg, or the patersberg, you’re not going at a steady pace for the entire interval or race effort up the hill, you’re going to be hammering all out right from the gun, and then really hang on for dear life. So in reality, most of racing is a matter of this front loaded Fast Start type of interval, where you are going all out right from early on, and then trying to hang on later on. So it absolutely is relevant. And if your whole goal and training is to simulate racing, well, then you may want to replicate those kind of efforts. And then the other consideration is even if you’re not considering trying to replicate or simulate racing, because of the higher intensity effort at the start putting you under fatigue early on, you may end up even though your overall average effort may be identical, you may end up because you’re in the state of fatigue early on actually getting more stimulus, more workout kind of effort and effectiveness as a result. So this exact question was the focus of a study by Bent Ronnestad in Norway, in 2020, in the International Journal of sports physiology and performance, they had 11 Elite male cross country skiers perform roller skiing intervals. And these are just like Trevor’s favorite five by five minute type intervals. In one of them, they had them perform the intervals in a very traditional steady state, what we call the trad here in this study, where they were going at 90% of their maximal aerobic speed throughout the entire five minutes. And then they also had them do a decreasing or this fast start type interval, where for the first one and a half minutes, they had them go at 100% of their maximal aerobic speed, and then they taper down for the final three and a half minutes to about 85% of their maximal aerobic speed. So what were the main results in this table, we see the significant differences are highlighted in bold. And the main thing that we find is that first off was the overall average speed and wattage the same in the two styles. Yes, they were, you see that there was no real significant difference at all in those. And same thing in terms of lactate values, there was no difference. They also tested their leg press power after the interval workout and again, there was no difference in terms of their absolute values and also the decrease kind of before and after the interval. So there were no significant differences in those but what they did find significantly different was the mean VO2 or oxygen uptake as a percent of VO2 peak where the decreasing style of interval actually had a slightly higher mean vo to in terms of oxygen uptake. So higher metabolic stress. And the interesting thing was even though there was this higher VO2 peak on average, there was a lower rating of perceived exertion in terms of both the Maximo RP that individuals rated these intervals that and also the mean RP so they were working at a higher metabolic rate in terms of percent VO2 yet they felt the workout to be easier.

Dr. Stephen Cheung 05:07
Sometimes when you’re presenting group data can kind of mask or distort individual responses. So Ronnestad also presented the individual responses here in this graph for the mean VO2, when doing the traditional on the left versus the decreasing style of interval on the right. And what we see there in the dashed lines is that eight out of the 11, individuals had quite a significant increase in their mean VO2 in the decreasing style of interval compared to the traditional. So it’s pretty good representation that the mean responses do seem to represent the individual responses also. So let’s drill down further now into the actual five minutes of work itself. Recall that the two interval styles was the decreasing interval, the first minute and half was at 100% of maximal aerobic speed. And then it tapered down the last three and a half minutes was at 85% of m a s, whereas the traditional interval was at 90%. Throughout, we see this play out in the oxygen consumption data over those five minutes, we see, in the first two minutes, there was a significantly higher oxygen uptake, with the decreasing style of interval. And then in the final two minutes or so there was just a slightly higher oxygen uptake on average, with the traditional style of interval. But overall, you can see kind of the relative difference between those two areas, you see where the main effect was, the main reason the mean oxygen uptake was higher with the decreasing style of intervals was because it got driven up higher early on in those first two minutes. So now let’s go to the exert software system and look at one of the workouts it’s called gasoline and on the face of it is somewhat like a three by eight minute interval workout only instead of being steady state it is that repeatedly decreasing style of interval where over each eight minute set, there are four reps where you start off with a higher intensity and then you gradually taper down, higher intensity again, taper down higher intensity taper down higher intensity taper down. So it is a much more stochastic type of effort, even though it is a relatively long eight minute interval. So here is a record of one of my actual performances of the gasoline workout This was done indoors on my trainer, and you will see that the whole workout is about an hour and 15 minutes. And it is a pretty tough challenging workout you have the MPA or maximum power available dropping over each time about 250 watts or so from 1100 watts down to about 850. And also the exert strain score, or XSS is pretty high for the workout in considering it’s only 75 minutes, we accumulated 128 XXS. So overall, you can see this is based on my fitness signature peak power 1110 watts, high intensity energy of 21.9 kilojoules and threshold power 231 watts. So let’s zoom in on one of those efforts. And specifically, this was the third of the three, eight minute efforts. And you see that pattern of decreasing intensity, play out every two minutes, there was that little bit of spike, you see the red kind of shading in the power profile about every two minutes, and then it dropped down to right around my threshold power. Overall, the average power output was 252 watts, which if you look at it is 109% of my threshold power. And this is pretty typical of intervals that are recommended for around five to 10 minutes timeframe of about 105 to 110% of threshold power. My heart rate was pretty good and steady throughout. Within a minute it had increased to that 146-148 range and it stayed pretty steady there throughout. And you see again, that purple line is the maximum power available MPA, it dropped from its fresh level of 1,110 down to 860 watts over that eight minute of effort.

Dr. Stephen Cheung 09:50
So now let’s use exert software to model a steady state effort versus a decreasing type of intensity effort. So the first one we’ll look at is a steady state effort of eight minutes at an intensity of 110% of threshold power. This is again modeled on my fitness signature. The key things I want to look at is, first off, let’s look at the MPA. Again, they will drop from 1110, down here, in this case to 889 watts at the end of eight minutes, and that the total exert strain score accumulated over those eight minutes is 20. And this is done in equivalent power 254 watts. So equivalent power is modeled very similar to normalized power. Now, let’s look at an eight minute interval modeled within that gasoline kind of idea of four by two minutes of decreasing type efforts. And here, the thing to notice is that the average is roughly the same 110% threshold power. Actually, if you look at the equivalent power, again, very similar normalized power, it is actually a little bit lower instead of 254 watts, it is at 249 watts. But the big thing is that the total exert strength score is actually higher went from 20 in the steady state model, to 25 XSS, and also the MPA has dropped instead of 889 watts down to 834. So what this shows is that there is significantly more fatigue being built up over the course of that eight minutes. And it really comes down to each of those initial early, harder efforts, causing more fatigue, and therefore causing you to accumulate more exert strain score, and essentially force your body to be in a deeper state of fatigue, and end up with a greater level of stimulus as a result. So what have we learned from this analysis? I think the big picture takeaway is that not all intervals are created equally. And that you can actually design an interval of the exact same overall work and also the same duration. But it can be quite different in terms of the stimulus that it provides based on the way that interval is designed and paste. So in this example, I think the decreasing style of interval can create a lot more stimulus for you because it puts your body in the greater state of fatigue over each one. And I think another benefit is that there’s less monotony both in terms of neuro muscular recruitment, and also mental monotony, I know for me that I can’t stand steady state efforts, I’m a very bursting type of writer and I love nothing more than Tabata style intervals. So in terms of a long interval, something like this gasoline style of continuously decreasing intervals and four sets of them over the course of one eight minute effort really gives me something to look forward to knowing that it’s gonna get easier in a way over the course of each two minutes. I think the other benefit is that it also replicates race efforts better in terms of going hard at the base of a hill, for example, and then still being able to sustain power over the course of the entire hill. The key message, though, is that as Ronnestad pointed out, this was one single acute effort. And this isn’t a longer to know study. So we don’t know necessarily whether overall, this is going to lead to better long term gains from these decreasing style of intervals compared to steady state ones. So here’s the reference that we talked about today from Bent Ronnestad. I hope this workshop gives you some insight into design of an interval and also encourages you to play around with how you design your intervals in your workouts. So what kind of intervals work best for you? Are you a very steady state type of rider in terms of longer intervals? Or do you prefer to have these kind of bursting type of efforts built into them? What do you feel makes it work better for you one way or the other? I’d love to carry on this conversation with you in the forum. So please feel free to discuss this there. In the meantime, I’m Dr. Steven Chung and I will see you next time.

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