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The Knee Is the Victim

Because the knee is caught between the hip and the foot, it often bears the brunt of biomechanical pedaling forces, which leads to injuries. Dr. Andy Pruitt explains why.

The knee is often considered to be “the victim” within the lower body, caught between the hip and the foot. An athlete’s biomechanics and movement patterns, along with his or her bike fit, influence how the knee responds to the forces being generated at that joint.

Our Director of Sports Medicine, Dr. Andy Pruitt, has over 40 years of experience in the bike fit and cycling ergonomics industry, as well as a deep understanding of human anatomy and biomechanics. In this workshop, Dr. Pruitt addresses the many factors that influence how and why the knee can suffer under the loads of the cycling pedal stroke.

Video Transcript

Dr. Andy Pruitt  00:00

Hello, I’m Dr. Andy Pruitt, sports medicine consultant for Fast Talk Laboratories. In a previous video, we discussed specific cycling knee injuries, their locations, causes, and prevention. Today we’re going to talk about why the knee many times is the victim caught between the hip and foot.


Intro  00:29

Welcome to Fast Talk Laboratories, your source for the science of endurance performance.


Introduction to the Knee Is the Victim

Dr. Andy Pruitt  00:40

The knee is the victim. In cycling, many times the knee is caught between the hip and the foot, and we’re going to spend the next few minutes kind of talking about why that is both in perspective of anatomy, and function, and some physiology. Simple biomechanics. It’s really all it is. A lot of people say, you know, it’s just math. Well, in cycling, it’s really all about biomechanics. The bicycle is a fixed machine that is adjustable. The human is an adaptable machine, which of course then is adaptable. The knee gets caught between these adaptations, and that’s what we’re going to talk about. The hip and the foot, ankle even are many times the culprits that cause the knee injury. So, the primary lever system that pushes the bicycle down the road is a long lever of the femur, a long lever of the tibia, and then the muscles provide the block and tackle movements to move that lever system, the motor that moves that lever system. If we think about a block and tackle system out in your dad’s garage, if that rope is being pulled through that pulley in a very straightforward manner, the rope not going to wear. If that rope is being pulled through that pulley in an odd manner, then one side of that rope is going to be compressed, the other side of it is going to be overstretched or overstressed. Think about your patellar tendon, your quadriceps tendon, and your quadriceps being the muscles that actually, being the muscles, they’re actually going to move that lever system, hope that makes sense. If the knee was a perfect lever, injuries would be minimal and rare, but it’s not a perfect lever. The two condyles of the knee are two separate links and two separate sizes. From the side, they’re elliptical, they’re not round, and even the tibial plateau is not a level surface. So, we don’t get this in cycling, we get this. Even now that I’m 40 years into my career, and I know that knee over pedal spindle is not a perfect rule by any means, I still want to justify it in many ways. I think that thinking about knee over pedal spindle helps us maximize the lever system and minimize musculoskeletal adaptation. So, if we use electromyography or EMG, we can actually measure what muscles fire when, so think about this being the pedal stroke, this is the right side of the bicycle, the athlete is going away from the screen moving that way. Zone one, we start up here at 12 o’clock or the top dead center, zone one, zone two, zone three, zone four, you see zone one is by far the largest of the zones, and that is where most muscular activity happens, it’s where power is produced in the pedal stroke. The quadriceps are a knee extender, straightening the knee to push down on the pedal. The hamstrings are a hip extender, pushing down on the pedal, the iliotibial band and patellar are the lateral and medial stabilizers, respectively, and then the calf or the gastroc is pointing or stabilizing the foot. We’ll talk more about the foot soon.


Dr. Andy Pruitt  04:11

Zone two are all the same muscles working in the same way, but in a much lesser extent, because the lever system is less efficient, as the leg becomes straighter. The fulcrum is less of a power pivot, which is the patella is the fulcrum less of a power pivot, and it just can’t be as efficient as the leg straightens. So, same muscles level two, zone two, but just not to the same level of activity. Zone three, things begin to change. The leg now is fully straightened and moving up back under us, the hamstrings now are beginning to bend the knee to re-cock the leg and bring the foot back up under us, the gastroc is beginning to help, it’s a secondary knee flexor, believe it or not, It points the toe and one way helps bend the knee that next way. So, now we’re starting to bend the knee, that’s all what zone three is about, hamstrings are flexing the knee, gastroc is helping to flex the knee as well. Zone four, a lot of electromyographic activity occurs, and that those same muscles are now used in an opposite way, right? So, the quadriceps are now flexing the hip, the hamstrings are flexing the knee opposite of what they did in zone one. Obviously, the gracilis and the iliotibial band, stay the same. They’re medial-lateral stabilizers. This change in activity from knee extension, hip extension, to hip flexion, knee flexion occurs and a fraction of a second. If the average pedaling RPM 80 for the tourist, 95-100 for the elite racer guy, but at an 85 or 90 RPMs, that means that this whole thing happens in less than a second. So, we switch the whole change over from extension to flexion occurs in less than a second. So, another way to look at EMG activity is pictorially, right? So, here we’re gonna see Ryan pedal, and zone one is going to light up being the quadriceps, the hamstrings, and the calf, there you go, quadriceps, knee extension, hamstrings, hip extension, calf, plantar flexion, or stabilization of the foot. Zone two, is going to occur again, same muscular, same firing patterns, much less extent, much less efficient. Zone three, again, is the calf and the hamstring beginning to bend the knee. Then four, the big change occurs, right? The big change occurs where the knee extension, hip extension changes over to knee flexion and hip flexion. Hope that helps you see that. It’s one thing to see a graph with a lot of text, another way to see it pictorially.


Pedal Force Vectors

Dr. Andy Pruitt  07:08

Pedal force vectors are measuring how we actually pressed down on the pedal, the magnitude of the force, and the direction of the force, right? Remember, zone one is where the money’s made in the bicycle pedal stroke, these are gonna be the size of the arrow is the magnitude of force, the angle of the arrow is the direction of the force, right? So, here is where our arrows are the biggest, and there’s no angulation to force delivery, it’s perpendicular to the pedal, no power is being lost in that part of the pedal stroke. Up here, where there’s an angular delivery, some of that force is going to be skipped off the pedal, just as you skip a rock across a lake, right? It’s going to be bouncing, it’s gonna be lost, it’s not in the perfect direction that we want it. Down here, again, money’s made. What’s interesting about pedal force vectors is that if we continue to push down on the pedal at the beginning of the backstroke, is like we’re trying to make the crank arm length, right? We’re trying to push that crank arm make it longer, because we haven’t been able to convert our muscles yet to the opposite direction, it really starts to occur up here we can see there’s really less, there’s not very much magnitude, but we still have some angular forces, until we get up here to the top of zone four, where the pedal actually is weightless, the pedal is actually weightless, and we’re beginning to come over the top re-cock to deliver our force again. There’s another way to look at that, right? So, I go from a technical slide to one that might make more sense pictorially. So, again, the size of the arrow is the magnitude, the direction of the arrow is the direction of the force being delivered. Even back up in here, there’s no stock to the arrow, meaning that’s where the pedal becomes weightless, just as we get over the top. So, learning to pedal, you’ll hear coaches talk about learning to pedal a perfect circle, what they’re really talking about is being able to clear the bottom and make the leg light and weightless as soon as possible to re-cock to come over the top. Some coaches say pedal well, don’t pedal hard, and what you’re really trying to think about is moving that pedal in an appropriate direction throughout the whole pedal stroke.


Self-Selection vs. Knee Over Pedal System

Dr. Andy Pruitt  09:30

Let’s revisit the EMG slide for a second. We’ll talk about self-selection. So, self-selection versus or knee over the pedal system. When I talked about the center of rotation of the knee to be over the center of rotation of the pedal spindle. That even changes some with typography, right? If I’m riding uphill, for that straight line to occur, I may have to adjust on the saddle to keep my knee over the pedal spindle in the most efficient place. Again, this is more about weight distribution and bike handling. But if we do bike fitting from a level plane, being the neutral starting position, knee over pedal spindle gives us a position where we can scoot back as necessary, scoot forward as necessary, the train is going to change, our RPMs train is going to change our self-selected knee over pedal system position. So, it’s really important to think about this not being such a locked-in, straight line, center of rotation of the knee, over the center rotation of the pedal, that’s easiest, it’s a straight line, easy to find if using 3D motion capture, but in reality, that’s not life, right? That’s not out on the road.


Dr. Andy Pruitt  10:42

So, what does self-selection mean? There are humans with femurs that are longer, thigh bones that are longer in proportion or relation to their tibias, and the opposite can also occur a longer tibia. So, that lever system is part of the self-selection process, the thickness, and the shape of your patella or your kneecap, that is the fulcrum in the lever system, its shape, and design, as well as the trough on the front of the thigh bone, all of these are unique to the individual, and are unique to help you self-select. The knee knows where it is efficient, you’re going to move on that bike to put your knee in the most effective place. Once you’re acquired a pedaling philosophy of your own, you’re going to know where you want to be to apply power, and it’s the guy that hits the climb scoots way on the nose of the saddle, that’s self-selection. There are a lot of climbers to scoot back to use more hamstring, use more hip, that is self-selection. So, going back to zone one, two, three, four. What happens when we self-select? In a time trial or triathlon position to get really drastic and outside the box, those positions can be nine or 10 centimeters, I’ve even had one athlete 15 centimeters, knee center, and front of the pedal axle, right? That’s significant as out here, right? So, what happens to zone one, zone two, zone three, zone four, they don’t change, right? They don’t change, it may mean that zone one starts here, and ends here instead, it might mean the whole clock dial can move forward, if the knee is in front of the pedal spindle significantly. For those who have a long femur, or a more rounded thermal condyle, they may actually want to be behind pedal spindle to climb, and the clock dial is just going to move backwards, where they start zone one here and actually push across the top before they start coming down into that sweet spot. Their sweet spot is actually going to occur before it would in that neutral position. So, self-selection, if your bike fitters fighting to get that straight line perfect, it may not happen and maybe because you self-select where you want to be, knee over pedal spindle. Other part of self-selection can be the saddle, right? You may have a place on the saddle where your pelvis, your soft tissue really wants to be, and then suddenly, that’s going to dictate where your knee is or pedal system. So, there are some self-selection, that are going to occur, that you cannot see as part of a physical exam, necessarily.


Cycling as a Skeletal Protective Activity

Dr. Andy Pruitt  13:28

Okay. What makes cycling such a lifelong skeletal protective activity? We never use the extremes of the range of motion if your bike fits appropriately. We never use the extremes. So, and the hip, we’re going to use about 40 degrees of hip motion, right? We never get to the full flexion knee up to the chest, and we never get the knee pointing straight down. So, we use about 40-degrees of the available range of motion of the hip. The knee, we use about 90-degrees of available ranges of motion. The lever system is most effective when the patella can act as a fulcrum. So, avoiding the extremes, right? So, if I think about it, I’m gonna do a bicep curl, where am I the weakest? I am the weakest out here, and I am the weakest here. You’re the weakest at the extremes of range of motion. I am Popeye here in the middle of that range of motion, same way you’ve got to think about the hip and the knee.



Dr. Andy Pruitt  14:35

Ankling. Wow, have we learned a lot about ankling throughout my 40-years. We used to believe that tourists and maybe some slow RPM climbers pedaled with a level foot or even heel down, and that was, you know, that 50-75 RPMs, they were going to be more of a heel driver. We really thought that the sprinter or the higher cadence guy, you know, had more of a more of a toe point at the bottom, we believe that it was 75 to 120 RPM rider, that was a toe pointer. With the advent of three-dimensional motion capture, where we can gather true data throughout a variety of different effort levels, we now know that all cyclists use both techniques. Now, I believe that ankling is where we compensate for an inefficient lever system to be attached to a perfect circular pedal stroke, I think the ankling is where we really compensate for that. There’s a little bit of ankle motion, that helps us, we bring the toe close to the shin to get over the top of the pedal stroke, and then we’re going to point that toe and stabilize that ankle through the power stroke. So, I think we are active anklers, not heel drivers, or toe pointers, and it is a really important piece of bike fitting. I loved it when patients would come in and say, “Oh, I’m a toe pointer,” your toe pointer because your saddle is three centimeters too high, your toe pointing to accommodate for that circle, right? So, we may have to retrain them a little bit to be in a more neutral ankler to get that saddle in the right place. So, if they come in with Achilles or gastroc issues, and saddle sores, and claim to be a toe pointer, a toe pointer because their saddles too high. So, I think ankling is a really important place where we accommodate for an inefficient labor system, but it’s also a place where we can, we don’t produce much power at the ankle, but it is a place that does take important note during a bike fitting session.


Z-Plane or the Front View of the Knee

Dr. Andy Pruitt  16:52

So, we’ve been talking about the side view or the XY-plane to this point, we’re gonna now move to what I coined many years ago, the z-plane or the front view. So, what happens when the knee pushes out? So, we’re talking about this guy’s right leg, he’s writing towards you, right? So, the foot adjusts. What does that mean? We’re gonna talk about that. So, the foot has to adjust, the longitudinal arch, the long arch that everybody has in their foot is going to have to collapse, the shin bone then is going to rotate, and then knee is going to come toward the top tube. Once all those things happen, you can finally push down on the pedal. So, if you think about that, that EMG slide, right? Where all those things have to convert in zone four, to get over to the top of zone one to produce power, all that is also occurring with foot adjusting, long arch collapsing, shinbone rotating, and the knee moving in and out in a relationship, a lot going on there, right? Then finally, we get to push down on the pedal, the hip, and the core, and the launcher have to find a way to stabilize ourselves, and kind of grab onto that saddle to give that lever system something to push back against. A lot is happening in that late zone four, early zone one. So, why does all this happen? Happens because the foot is designed for walking, and running is not designed for cycling, right? It’s designed for uneven surfaces, it’s designed to accommodate and read the ground, for example, it’s also the foot as an energy storing device. As the arch collapses, it stores energy to give it back to us as we push off in running and walking. But let’s look at this demonstration here. So, we’ve got a heel strike, the forefoot is angled, it has to accommodate to the flat floor, and then the arch collapses before he can actually motivate or move to the next leg or to push down to the pedal. In cycling, we asked the foot to be a rigid lever, it is not designed to be one. So, in the early days of my career, cycling shoes were fairly flexible, there was no arch support, there was no forefoot support. Then as they move to it a little higher level the sole has got wooden, and now they’re carbon, we’ve gone from this flexible kind of terrain walking shoe to this very rigid, most of the time carbon fiber cycling shoe. We’re asking the foot to be something it is not, right? We’re asking the foot to be a rigid lever.


Foot Design and Foot Activities

Dr. Andy Pruitt  19:33

Okay, let’s talk about foot design and foot activities. We’re gonna talk about forefoot angulation. I just did demonstrate this in a clearer way in a minute, but 90% of all humans have what’s called forefoot varus. This means that the forefoot is not flat to the floor, the big toe is elevated, and when I say the forefoot has to adjust the pedal this means that the foot has to find that pedal, because the forefoot varus. There’s a few of us that have a neutral flat forefoot, and even less than the outside of the foot is angled up, called forefoot valgus. The longitudinal arch, there are really four arches in the foot, but there’s really only one that would be referred to as the arch, and that is the longitudinal arch. They are meant to be an energy store, energy delivery device, where the plantar fascia or the ligament that holds up the arch, the foot collapses slightly, stores energy in that plantar fascia, and then gives it back to us like a leaf spring on toe off. However, in cycling, if we allow that to happen, that plantar fascia is going to gather energy as we’re trying to push down on the pedal, that is not weight one, we do not want the foot absorbing energy from us pushing down on the pedal.


Arch Styles

Dr. Andy Pruitt  20:53

So, there are multitudes of arch styles, I’m only going to categorize three. The cavovarus foot is that really high arched, almost rigid foot, very little arch activity in that foot. Neutral is just the foot that most of us have, 80% of all humans have a neutral arch meaning that it has given and take in both directions, it does its job, and it collects energy and gives it back. pes planus is that grossly flatfoot, we jokingly say the arch hits the ground first and these people, it really doesn’t but it is such a flatfoot that you recognize it when you see this, no there’s no arch activity here because the arch is too high, there’s no arch activity here because the arch is actually too low. Thinking about forefoot varus, it’s a hard thing to visualize. This is an athlete kneeling on a stool, and we placed a straight edge across the base of their foot. This is forefoot varus, right? The ball of the foot of the great toe is elevated off of the straight plane. So, this individual has moderate to significant forefoot varus. The neutral foot would mean this would be down here, and it would be flat. Forefoot valgus foot would be like that. hope that makes sense. This is a visual that I think really displays the amount of forefoot varus that has to be accommodated for before you can actually push down on the pedal. What are the effects of forefoot varus on the lower extremity? So, this is a skinned athlete, alright? The bicycle is removed, the saddle is removed, all the muscles and tendons removed, he’s sitting on a saddle here, the knees bent, that’s why the femur looks so short, the knees bent in front of you. So, what is the effect on the lower extremity if forefoot versus uncorrected? Here’s that medial knee travel, back to neutral, right? Again, the medial knee travels back to neutral. There’s a total lever system effect to accommodating for forefoot varus, and we’re going to slip in a big wedge under here and show what can be done to stabilize and support for forefoot varus. Arch collapse, again, the plantar fascia is in here, the ligament that holds up the arch, when it’s loaded, right? So, this guy is going to load. So, we’ve loaded the plantar fascia and it gives that energy back as the foot returns to a more neutral position. Now, in a perfect world, we would stabilize that foot with some type of arch support. So, now we can push down on that pedal and not give away that energy it would otherwise be stored in the longitudinal arch.


Longitudinal Arch Collapse

Dr. Andy Pruitt  23:57

Okay, what are the effects of longitudinal arch collapse? They are exactly the same as adapting for uncorrected, unsupported forefoot varus, right? We get the same medial-lateral knee travel, we get the same tibia collapsing toward the bike, and the solution for this is the arch support I just showed, and maybe in combination with some kind of forefoot support. Alright, another way to look at it, right? One of the themes of education to say the same thing multiple ways, and somebody will remember it. So, this is going to be another way we’re going to say and look at the effects of forefoot varus arch collapse on the whole lower extremity. Okay, so arch collapse, you see the forefoot having to adjust, and here’s the result. So, again, the knee is the victim caught between the hip and the foot, right? So, forefoot varus, arch collapse, medial-lateral knee travel, might be a good place to tell a little story. In 1985, I was the first person to ever study cycling biomechanics using 3D motion analysis. If you think about 1985, for those of you who were around, that’s also the year that the black look cleat or fixed binding cleat was introduced after the 84′ Olympics. So, there was an epidemic of knee injuries that occurred in that change from the sloppy kind of quill are slotted cleat in a toe strap with a flexible shoe, to the suddenly we clipped into the ski binding like motionless feitelson, there was an epidemic of knee injuries that occurred. So, Israeli biomechanist contacted me and said that he’d been studying running and throwing and that what I study cycling, of course, so we made an arrangement, we came to an agreement and I was responsible for studying cycling, one of the biggest questions asked at that time was how much float does a pedal system need? And one of my hypotheses was, it really depended on how much medial-lateral knee motion there was, and how much shinbone motion there was. We go back to this video, look at the shin rotation, right? Look at the shin rotation. So, I thought that I can measure the tibial tuberosity where the patella tendon attaches. So, we set up our equipment, we placed markers on all the appropriate anatomical landmarks, and lo and behold, our data said that the shin bone was not rotating. Well, we could see it rotating, but the data didn’t show up, because the landmark was skin-based, and the tibia was actually moving underneath the skin, so the marker wasn’t reflecting what was happening to the bone underneath the skin during the pedal activity, which made us then it’s still the standard today, we should now measure how far the knee moves inside or outside during a pedal stroke to help dial in the marriage of all the things that we can do, arch support, forefoot varus, cleat float, all things that we can do down here, right? To marry this system together, really it’s now measured in medial-lateral knee travel, if you’ve had a three-dimensional motion capture bike fit of any kind, of any brand, they will have talked to you about your medial-lateral knee travel. We want the knee to be a piston. We think back a few minutes we talked about that perfect lever system, and our imperfect human lever system, we want to make it as perfect as possible to minimize that rope wear and that block and tackle system, right? So, if the knees the victim, that’s going to be the tracing of an on-supported or say, traditional unsupported cycling setup between the shoe and the cleat, for example. This would be that perfect example, that perfect leverage system that we’re after. Okay, this is an actual patient in her 3D analysis, it was a multi-time world mountain bike champion. I think she won, let’s say two or three over here, and continued. She went undefeated for two years after we made this change. So, this is what you look like before. You see the figure eight knee tracings,


Dr. Andy Pruitt  28:45

we made all the biomechanical corrections in her footwear and were able to get her to look like this. So, not only is this protecting the knee, but it’s also producing more power. This is a waste of energy. This is not a waste of energy.


Pelvic Width and Choosing the Right Saddle

Dr. Andy Pruitt  29:07

Okay. Pelvic width is really key to choosing the right saddle. There are retail systems out there for measuring ischial tuberosity, those are your sit bones, right? So, if I’m sitting on grandma’s hard chair, I’m going to be sitting on my sit bones. That’s why I’m going to slump to kind of get off of them a little bit. But in cycling, we measure the sit bones, but we actually sit in front of them. At the moment, there’s not a perfect way to measure pelvic size or angulation. At the moment, I think there are several in the works, I know there are several in the works, but at the moment we’re going to measure ischial tuberosities and choose our saddle discussion, and salad choice beginning with that measurement. So, pelvic width plays a huge role. Why? If I’m looking for bony support on my saddle, and my saddle is too narrow for example, I am going to shift to one side or the other to get some bony support. So, when I shift one side to another, I have created a huge biomechanical change. I am suddenly low on one side, and high on the other side, right? I’ve created a functional leg length inequality, for example. Now, what if my saddle is too wide? I am going to scoot forward to find an appropriate place to support my pelvis, I’m gonna scoot forward in the more narrow part of that saddle, with that due to my knee over pedal spindle, right? Pushes my knee in front of the knee over pedal spindle, so pedal or excuse me, pelvic width, and choice makes a huge role in your biomechanics.


Stance Width

Dr. Andy Pruitt  31:00

Stance width. So, a guy named Bill Ferrill, who invented the fit kit back in the early 80s, New England Cycling Academy, Bill coined the term cue angle. What he was really talking about was stance width. The q factor is a measurement of the angulation at the knee, we’re gonna talk about varus valgus knees here in a second. So, but cue angle is really an anatomical measurement of the human. What Bill was alluding to was stance width and its effect on knee angulation. So, if you’ve got a valgus or knock-knee individual, with a stance that is too wide, it’s going to exaggerate their knees coming to the top tube. So, he was a proponent of adjusting stance width to help improve the effectiveness, to get that straight line pedal stroke. Knee varus valgus, we’re going to talk about, foot and ankle.


Dr. Andy Pruitt  32:06

Tibial torsion, supination, pronation, forefoot varus, are variants that can occur anatomically and are across the board all fit well under the bell-shaped curve of normal. Now, if I’ve got tibial torsion, think about tibial torsion. It’s like someone grabbed a washrag and wrung it out, so I’m grabbing my knee, I’m grabbing the ankle, and I’m twisting them. For some reason, genetically, some people have greater tibial torsion than others. The tibial verum is another one where the tibia is actually bowed in a varus manner like parentheses. You see, I was at a bike race this weekend and I saw this poor lady, I wanted to go pat her on the back, apologies to her about her biomechanics, but she had valgus knees, so she was very knock-kneed, and to accommodate for that she had these huge tibias that look like parentheses, and it was all to get her foot back under her knee. So, tibial Verum, tibial torsion, are variants that you can find in the tibial shaft itself. Pronation is a word that in the running community got a bad rap, pronation was a bad way to stop pronation. Well, pronation is that normal foot activity of the arch collapsing, storing energy, and giving it back to us. Supination is that rigid, high flat where the arch is way up high, that’s a supinated foot. Again, variations all within the bell-shaped curve of normal, and we have to consider those as bike fitters, and of course, forefoot varus, or neutral, or valgus are things we need to consider as well.


Dr. Andy Pruitt  33:44

If we look at a knee straight on, most people under the bell-shaped curve of normal are going to have 4-12 degrees of valgus, meaning that if I dropped a plumb line from the middle of my hip to my second toe, straight line, the knee is going to fall slightly inside of that line. Again, a straight line, hip, second toe, on a valgus knee is going to fall inside of that line, 90% of all humans have a valgus knee. Again, it can vary from 4-12 degrees. Women have a slightly higher incidence, higher degree of valgus than men do. Neutral is a straight knee, I mean it is straight, if you want to be a cyclist and you were born with a neutral knee alignment, and a long femur, you were born to be a cyclist, add in up big max VO2, you got it all going. We think about a guy named Greg LeMond, who is the last American to win the Tour de France, at least legitimately, he had neutral aligning, meaning that both condyles of his femur were the same length. There was no rotation that occurred at his knee, he had a really long fever and a gigantic VO2 max, he was born to be a cyclist, for sure.


Dr. Andy Pruitt  35:09

Verus knee again, got that palm line from the hip to the second toe, that knee is going to fall outside of that straight line. If you’ve got valgus knees, like my lady I saw at the bike race, valgus knee with significant tibial Verum or torsion, that combination is quite deadly.


Non-Knee Factors That Affect Functional Knee Alignment

Dr. Andy Pruitt  35:30

Non-knee factors that affect functional knee alignment. Again, saddle too wide, to narrow, and that’s self-selection and you’re looking for soft tissue relief, and you’re looking for skeletal support, and you are going to self-select on that saddle. LLD, leg length discrepancy, leg length discrepancies can be a lot of things, it can be real, it can be that your femoral segments or your tibial segments are actually different lengths from each other. Were rarely seeing X-ray measurements that are perfect millimeter, for millimeter. So, most of us have some kind of minuscule asymmetry there. It can also be a pelvic asymmetry, that acts as a leg length inequality. The pelvis is made of three bones, they don’t all have to be mirror images of each other. So, if the right one is slightly different than the left one, it can create a functional leg length inequality.


Arch Collapse

Dr. Andy Pruitt  36:33

Arch collapse. So, if we got one foot that’s pronated, one foot that’s supinated, or one that’s a high arch, one that’s a low arch, as you stand, your hips are going to be offset. So, you’re going to have created a leg length inequality, because of arch collapse. Why does the weak glute med? So, the gluteus medius is a muscle, is where your six-gun sits, right? If you’re a cowboy, you get your six-gun. Yep, that’s where your gluteus medius is. It is a stabilizer to the law extremity at the far upper end. And if the weak glute med is weak, that knee is gonna have a tensity, you’re going to go into a little bit more collapse, and again, a functional leg length inequality.


Muscular Imbalance

Dr. Andy Pruitt  37:19

Muscular imbalance, wow. So, you’ve got a tight hip flexor on this side, and a tight hamstring on this side, and they do this to you. Again, it’s going to create this, this asymmetry, if you will, and then again, the one arch low, one arch high is that asymmetrical foot alignment.


Dr. Andy Pruitt  37:37

So, let’s talk about varus and valgus knees again. So, I don’t remember when it, 20-35 years ago, I was trying to develop an off-bike test that I can visualize what their biomechanics were going to do for me once they started pedaling. So, they’re pedaling at 90 RPM, it’s a little hard to see it, right? This was the original 3D motion capture machine right here. So, you had to catch this or at least visualize it before they got on the bike. So, the 1/3 knee bend is something we do. So here, again, tibial tubercle, the bone right or the knee, second toe, that is going to be a virtually straight line, and that is a very efficient pedal stroke, right? So, he’s having very little going on. Now, I have to put a caveat here, and this is the same individual demonstrating for us the three different knee alignments. It’s difficult for you to go home and pretend to be valgus if you’re not and pretend to be varus if you’re not, but for demonstration purposes, it’s good to go. So, this guy, neutral and straight. This guy, this is a valgus knee where the knee is projecting inside, so if I were to stop it and hang that plumb line, that plumb line is gonna fall inside of the foot, that is a valgus knee again, most people I don’t know the exact number, I’m going to be comfortable saying 80% of people have this kind of 1/3 knee bend, where there’s a little bit of foot accommodation, a little bit of arch accommodation, and the knee is going to move down and in. Varus is the knee plumbline is going to fall outside of the foot. This is hard for our model to actually demonstrate for us, you can see him struggling to produce a varus knee because he doesn’t have a varus knee, but for demonstration purposes out here, in the middle of the pedal stroke, his knee is gonna fall outside of that foot.


Biomechanical Changes To Protect That Knee From Being a Victim

Dr. Andy Pruitt  39:43

So, how do we affect biomechanical change to protect that knee from being a victim? Right? What is your bike fitter, your physical therapist, your physician, whether it’s a medical fitter or performance fitter, what do they do to put you in this most advantageous position to not only protect the knee but also make it the most effective power producer? Well, shoe choice. Low hanging fruit, let’s go with low hanging fruit first, right?


Shoe Choice

Dr. Andy Pruitt  40:09

Shoe choice. So, modern shoes have moved to rigid nylon plastic or to carbon fiber. When I first started there was a rubberized and then became wood, so shoes have definitely come a long way. The first thing, is to take that flexible foot and make it a rigid lever. Any cycling shoe is going to act in that manner. Any cycling-specific shoe is going to help give you a rigid, rigid lever in replacement of that flexible lever. Footbeds are going to address arch collapse, but as a wedge built into it, it can address forefoot design, usually, that’s a varus support of some type in the footbed. So, this combination is incredibly important low-hanging fruit that should be addressed in any bike, either whether that’s a medical bike fit or a performance bike.


Pedal Choice

Dr. Andy Pruitt  41:07

So, pedal choice, whether it be a medical or performance bike pedal choice is crucial. What needs to be considered? The size of the pedal, and whether you want a big platform or small platform. If you use a walkable shoe, you’re probably gonna want a bigger platform, if you’re going to use a smaller platform, then you’re going to use a more rigid shoe, you just have to be able to transfer that power. If these two guys are right, right? So, if you’ve got the footwell represented within the shoe, you don’t really need much flow, I mean, three or four degrees is all the float you’re going to need if these guys are dialed in. Our pro athletes, most of the time use zero degrees of float, because their bike fit is perfect, and their biomechanics are most likely near perfect, that’s how they’ve gotten that level of athleticism. They can get by with zero degrees of float, when the paddle wears, the cleat wears, they probably have one or two degrees of float that was unintentional, but there as well. So, absolutely.


Dr. Andy Pruitt  42:19

Now, if we measure from the crank arm to the middle of the pedal platform, standard pedals are 53 millimeters, there are pedals out there that are 50 millimeters, and there are pedals out there that go all the way up to 64 millimeters. So, we have quite a large range, where we can adjust for stance width. So, petal size, float, stance width, all need to be considered there. Sometimes, you can do some of this canting at the pedal, depending on the brand of the pedal. So, there are biomechanically intended pedals out there where you can actually count the pedal, instead of doing it at the shoe or in the footbed.


Saddle Choice

Dr. Andy Pruitt  43:05

Saddle choice. Incredibly important. Saddle choice, position, and design. We’re looking for skeletal support with a modicum of soft tissue support. In my experience, too much skeletal support leads to ischial bursitis, hip bone bursitis, some skeletal soreness, even saddle sores. But too much soft tissue, soft tissue support leads to erectile dysfunction, urinary dysfunction, labile scarring, we don’t want to go there either, right? So, we got to find this balance when skeletal support and soft tissue support. There are saddles out there designed purely for skeletal support, and there are saddles out there that balance those two, and men and women saddles, there’s a lot of overlap. So, if a women’s saddle fits best for a guy, buy it, it doesn’t have a pink flower on it, but there are designs that go both ways. I know many, many, many successful women who ride men’s saddles without an issue, and I know a lot of guys even at the pro tour level who ride a women’s saddle. I think they ought to be unisex and ubiquitous, and that’s kind of what I pushed for in the industry.


Stretching and Strengthening

Dr. Andy Pruitt  44:16

Stretching and strengthening. Can we affect biomechanical change? You bet, because as I said earlier, one weak muscle group called the gluteus medius if it’s weak, can affect your whole lower extremity alignment. So, stretching and strengthening can absolutely affect a biomechanical change.


Dr. Andy Pruitt  44:33

Core strengthening. Just think about if your core is weak as it can’t stabilize on the saddle, and you’re doing a lot of rocking and you can’t, you’re going to affect a bad biomechanical output. So, stretching and strengthening absolutely can affect a biomechanical change. What if I’ve got one tight hamstring, right? And that knee doesn’t want to extend quite as much as the other one. then I’m going to move to that side to protect that hamstring, I’m going to create a leg length inequality, I’m going to have two different knee flexion, dead bottom center. So, stretching and strengthening. Absolutely, especially under the guidance of a PT can really affect biomechanical change.



Dr. Andy Pruitt  45:16

Injury. Wow, yeah, duh, right? So, if I break my leg, and it heals either longer, or shorter, or with a rotation, I have affected biomechanical change. Degenerative injury, degenerative change, or arthritis, or aging. Wow. So, if a knee becomes arthritic, that joint space is actually narrowing, and what if the inside of my knee is more arthritic than the outside of my knee, I’ve created an angulation, that knee is not natural. So, degenerative change absolutely can create a biomechanical change. Obviously, surgery of any kind, foot surgery, knee surgery, hip and back surgery, all of those potentially have changed the way you sit on your bicycle.


Anatomical Bike Fitting

Dr. Andy Pruitt  46:06

My philosophy is really based around anatomical bike fitting, that anatomical positioning. I want the bike to look like you, not you look like it or look like your hero, I want the bike to represent and support you. Sometimes that is an accommodation that might need to be made. I think there’s a physical therapy philosophy that we want to accommodate the bike less, we want to change the body, not the bike, and there’s probably a blend of that’s going to come together and happy marriage. Sometimes accommodations are temporary. I’ll give you a really good example. She was an ex-world time trial champion, who I was riding behind as we were preparing for the World Championships, and she was all the way off to one side of her bike, I said, “Do you have back pain, do you have saddle pain, what’s going on? She says, “My genitalia are just suffering terribly. I’m really sore, and I’m moving off to the side of the bike.” So, I did a quick exam. She had a functional leg length inequality. At the time, we put in a lift and little wedge for her, ride at Worlds, she wins, everybody travels home they go back to wherever they came from, I met up with her again several months later, riding behind her, I didn’t remember which side she was off to at Worlds but come to find out she was off to the other side. The accommodation was a temporary one for her. So, she straightened up got through Worlds great, but as she no longer needed it, it kind of pushed her to the opposite side. So, for her that accommodation was temporary. For many people, accommodation like a lift, or cant, or arch support, is a permanent accommodation.


Minimizing Adaptations

Dr. Andy Pruitt  47:59

Again, making the bike look like you, we want to minimize that adaptation. Why? Adaptation in the musculoskeletal system, especially in the tinnitus system is a bad thing, we want to accommodate up to a certain level of toughness, but we don’t want to over accommodate where it’s going to wear out. Your coach may talk to you about it, we’re going to break you down this week so that your muscles can get stronger and accommodate and you come back stronger. That’s healthy accommodation. An unhealthy accommodation is one where we’re not supporting the athlete on the bike correctly. We want the bike to be fit-neutral for that experience. That means that different bikes may have slightly different positions. Road bikes, gravel bikes, commuter bikes, they’re all going to be very close to each other. Your town bike may be a far more upright position to look at traffic, it may have more skeletal support on the saddle, more sit bone support, less soft tissue support, it may have a more open torso angle, so a neutral for the experience. The downhill racer, the guy that rides in the all-terrain park, I don’t care if his knees over his pedal system, he needs his body in a place where he can control his bike in the air, control his bike to land, use the body English, so it’s gonna be a lot of self-selection that goes in that particular all-mountain or downhill position. Time Trial and triathlon, I’ve already said that their knee can be 9-15 centimeters in front of that neutral position, that is the exception to the range of motion rule. If we go back to our hip and knee range of motion slide, I said we avoid the extremes of range of motion in cycling, and that’s why it’s so good for us. Triathlon and time trial are the exceptions to that rule to get aerodynamic, we’re going to close that hip torso angle to be more aerodynamic, and we’re going to be closer to that end range of hip motion. There are ways to accommodate for that, crank arm length, there are ways to accommodate for that closure, but neutral for the experience is really key.


Dr. Andy Pruitt  50:26

I have danced around some potential corrections, the truth of the matter is that potential corrections are far too many, and far too specific to gather, and kind of delivery to you in a generic format. There are all kinds of support that can happen, there are all kinds of arch support that can happen, there are all kinds of adaptations for tibial torsion, tibial verum in the saddle, how many saddles are out there? That’s how many choices there are for the correct saddle selection. So, there are just far too many potential corrections to address those here, they shouldn’t be addressed with you and your medical and or performance bike fitter.


Dr. Andy Pruitt  51:12

Just kind of a quick review of anatomical positioning as measured by 3D motion capture, and what you should expect when you go to a bike fit to eliminate this knee victim situation. We want a good on and off-the-bike evaluation of your anatomy and your biomechanics. We need to understand the effect, what effect your foot varus or valgus what effect your anatomy and biomechanics have on the pedal stroke. We need to effectively determine the need for an orthotic. To me, the word orthotic is a corrective device. I think generically people think about orthotics is something you put in your shoe, but they don’t have to be, a corrective device or corrective support is orthotic. Actually, I think a cycling shoe is the original cycling orthotic is taking that flexible foot and helped it turn it into a rigid lever. So, the very first cycling orthotic you got was your rigid cycling shoe. We want to understand the need for adjustment in the stance width, we need to affect defined a house dance with is gonna affect your lower extremity biomechanics. We want to compensate for leg length inequality if it actually exists. So, here’s 3D motion capture, kind of our last little review. We’ve got the subject, we’ve taken all of the supportive activities out of his shoes, over here we’ve made his shoes biomechanically correct. Here we have that figure eight pedal stroke, the knee is definitely going to be the victim here. Over here, we’ve created that perfect linear pedal stroke.


Dr. Andy Pruitt  52:56

I hope you found today’s video useful. If you’re having any issues with your knees and would actually like to speak with me, you can schedule a consultation at