The importance of crank length to the cyclist.

[Ripper]

I think that we really need to run a series of experiments looking at how athlete's power duration curves are influenced riding PowerCranks versus fixed cranks at a variety of hip angles. I have a pretty good idea what the experiment results would show.

What is your idea?

 

[FrankDay]

This certainly would seem to be the case with athletes riding PowerCranks as so many of them seem to have difficulty riding in the aero position with them. That would imply to me that their power would be greatly reduced while attempting to ride with tight thigh/torso angle.

Here from a Slowtwitch forum poster:

"My personal experience was that I never got comfortable in the aero position. The PC's force you to completely unweight the recovering leg, so you're bearing a lot more weight on your bits than you would on normal cranks. This was the biggest revelation to me- how much work my legs were doing supporting part of my body weight vs propelling the bike. Consequently- I was never able to ride the PC's in the aero position. I rode them for months in the offseason on my road bike but was never able to transfer them to my tri bike. "

If you would actually pay attention to reports like this a lightbulb might go on in your head. Do you think that just because this rider goes back to regular cranks the difficulty of pedaling in the TT position suddenly disappears? Or, do you think it is possible that the difficultly suddenly gets masked because now the work of getting the leg up and over the top is being done by the pushing leg, even though that means less power is going to the wheel. Or, would it seem possible that one might conclude that this person really would do much better on shorter cranks? It is just reports like this that have helped me to conclude that PowerCranks are an excellent bike fitting tool because it is not possible to know on regular cranks if one is losing much power or not. And, it is reports such as this (and my own experience) that got me to thinking about going to shorter cranks.

Edit: as they used to tell me in medical school, "listen to the patient, often they will tell you exactly what is wrong."

I think that we really need to run a series of experiments looking at how athlete's power duration curves are influenced riding PowerCranks versus fixed cranks at a variety of hip angles. I have a pretty good idea what the experiment results would show.

As long as the people are adequately trained on their PC's and as long as the fit is good on the PC's I think you will find no difference (or, even, the PC group will do better). Courtney Ogden raced on PC's at Ironman Canada a few years ago and had the fastest bike split of the day. Drew Peterson did the Everest Challenge on 110 mm PC's last year and finished in the top 10 overall.

If a cyclist is not adequately trained on the PC's they will slow you down. If the cyclist is adequately trained on them, they will not.

 

[Martin318is]

it is not possible to know on regular cranks if one is losing much power or not.

Any one of a number of pieces of kit that include spin scan can do this for you and show you very clearly what each leg is actually doing on each pedal revolution. Visit someone with a computrainer for instance...

 

[FrankDay]

Any one of a number of pieces of kit that include spin scan can do this for you and show you very clearly what each leg is actually doing on each pedal revolution. Visit someone with a computrainer for instance...

I own both a computrainer and a Velotron. Spinscan really says nothing about pedaling style, because it assumes that all the work is done on from 12 to 6 and nothing good or bad occurs from 6 to 12. To do this it combines the output of the two legs and applies it to the down leg. Pulling up on the back stroke would actually decrease the spinscan number while a large back pressure would typically increase it. I can get my spinscan number reliably above 95 at power (want to know the trick? Increase the force across the top and bottom of the stroke). Spinscan is simply a measure of smoothness. Putting a rider on PowerCranks typically increases their spinscan number about 10 points, at least while they are on the PC's. Most of the other tools used by ordinary cyclists to look at pedaling dynamics have the same deficiency.

 

[Martin318is]

I stand corrected...

Does this also apply to the Serrota Biometric Fit jig?

 

[FrankDay]

I stand corrected...

Does this also apply to the Serrota Biometric Fit jig?

I am not familiar with that device but my guess is "yes" because I am only familiar with a couple of devices that actually measure right and left pedal dynamics separately. They tend to be either only available in universities or on very expensive ($25-50k) machines. If the Garmin Vector ever becomes available hopefully that will change.

Edit: Garmin Vector isn't the only hope here. I am also aware of two other products in development that will do this, one in Europe and one in Australia. I think each of these will have the PM's in the crank arm. At least one is looking to see if the device can be incorporated into the PowerCranks.

 

[sciguy]

Courtney Ogden raced on PC's at Ironman Canada a few years ago and had the fastest bike split of the day. Drew Peterson did the Everest Challenge on 110 mm PC's last year and finished in the top 10 overall.

If a cyclist is not adequately trained on the PC's they will slow you down. If the cyclist is adequately trained on them, they will not.

Would that be Courtney Ogden who has seemed to be suffering from a series of knee injuries for the past several years? Several of us are wondering if his injuries might relate to the use either PowerCranks, shorter cranks or both.

YMMV,

Hugh

 

[acoggan]

Prove that statement when one is considering what happens in the aero/TT position. While Martin's study did show a small variation over a large range one can assume his subjects were mostly upright (he did not specify), since he was measuring maximum power. If one were to repeat that study with cyclists in the TT position my guess is the results would be skewed even shorter and with larger variation. And, if one were to repeat that study looking at sustainable power in the aero position vs crank length I would expect the results to be skewed even shorter. Unless you can prove your above contention with real studies I would suggest that you are extrapolating from upright position data what you expect and simply blowing a lot of hot air our way through your computer keyboard. I mean, you do sayWhy on earth wouldn't you think that wouldn't have an effect on the amount of power they might be able to generate? And, if it did, why wouldn't it be a "panacea", at least for them?

1. The subjects in Jim's studies were all experienced cyclists, who were free to adopt whatever thigh-torso angle they felt allowed them to generate maximal power for a very short duration while seated (naturally, I had my hands in the drops). I would therefore argue that it is quite likely they did so, i.e., "body wisdom" is a powerful influence...this is, after all, why you see pursuiters invariably creeping onto the nose of their saddle late in race, or (more relevantly) why steep-seattube-angled TT/tri bikes were invented in the first place. Thus, while it is possible that cranks even shorter than 145 mm might (or might not) be better when a rider is forced to assume an overly-acute thigh-torso angle, that is really putting the cart before the horse...the goal is to maximize power:CdA, not just minimize CdA, so you never want to adopt a position that compromises your power *unless* you know that the improvement in CdA is worth it.

2. In keeping with the above, I have measured my both my CdA and my sustainable power in a wide range of aero of positions while using a wide range of crank lengths. What I have found is that if I go too low, my power drops more than my CdA, and shortening the cranks by up to 22 mm doesn't help.

3. Panacea (n): a. A remedy for all diseases and ills; cure-all. b. An answer or solution for all problems or difficulties.

 

[acoggan]

Then, would you agree, that pedaling technique is not "natural"? That what we do in pedaling a bicycle depends mostly on how we were taught when learning and not what God has predetermined, through evolution, is best for us?

On the contrary: pedaling is an extremely "natural" motion, in that 1) we activate the same muscles in essentially the same sequence as when walking or running, and 2) even pedaling backwards has very little effect on this pattern. IOW, we pedal using essentially the same evolutionarily-designed motor program as we use during upright bipedal locomotion, with very little learning either necessary or beneficial.

 

[acoggan]

Expanding on above statement. Martin's research results are based on natural pedaling techniques where max torque is applied with a vertical downward force between 2 -4 o'c and where only the lower body is used. With this technique changes in cadence are easier to make in keeping with the change in crank length. But if you are using a technique which can almost double the cumulative torque from each pedal stroke by starting max torque around 11 o'c, where forward and downward pedal forces are used, which uses both the upper and lower body in generating the crank torque and which works best using the higher gears, I don't believe you would get the same 'change of crank length' results.

Back to your same ol' schtick, I see. Thank goodness...I'd start to worry that the world was coming to an end if you or Frank ever deviated from your "performance art".

 

[acoggan]

IMO Frank has a fair point, here, in that the results of Martin's study may well have been different with riders in the TT position.

Not for me (or, apparently, Chris Boardman).

It depends what exactly you mean by large, of course, but I'm surprised you haven't thought it worthwhile to field test longer cranks. 190mm instead of 170mm would get your knee 4cm higher relative to your hip at the top of the pedal stroke (assuming you move both saddle and pads down 2cm), so if there were no adverse impact on power production, this might be expected to give a small but perhaps worthwhile aero gain.

At the risk of giving away too much information: Your feet and lower legs are a far greater source of aerodynamic drag than your thighs, which are 1) far closer to horizontal, at least at the top of the pedal stroke, and 2) drafting, to at least some degree, behind your arms. Longer cranks therefore don't provide a significant aero advantage, but do move you that much closer to the "tipping point" with respect to the minimal acceptable thigh-torso angle (which for me is at the point that my thighs almost contact my lower ribs...not because of any interference effect or restriction of breathing, that's just a consistent reference point).

 

[acoggan]

As long as the people are adequately trained on their PC's and as long as the fit is good on the PC's I think you will find no difference

What happened to the 40% improvement?

 

[sciguy]

It is just reports like this that have helped me to conclude that PowerCranks are an excellent bike fitting tool because it is not possible to know on regular cranks if one is losing much power or not. And, it is reports such as this (and my own experience) that got me to thinking about going to shorter cranks.

It's posts like this one that brings to mind the old expression "cures what ails you" often associated with snake oil salesmen........oooops

Hugh

 

[Ripper]

Personally, I'd go a step further and go to an experienced bike fitter and have them do an assessment and any adjustments for you. Unless you are trying something dramatic, you should be able to make most of the changes on the one day - if done correctly. Changing Q Factor is theoretically a minor change but it depends what your starting point is. In my own case, my position had seemed fine but on inspection I was already irritating the ITB. Any movement of my feet closer together would have made this worse.

So I ran a little experiment. Keep in mind my baseline was a position that an experienced fitter helped me with.

I moved the cleats so my feet came inwards about 3-4 mm each. After a slight tweak to saddle height and a very slight tweak to saddle fore-aft, the position is comfortable and I have ridden and raced with it for 5 days now. The power is the same (using a power meter on the indoor trainer), although the feel is better, possibly because my feet are now more 'over' the pedals.

Obviously, I am not testing in a wind tunnel, so take this with a grain of salt - the position seems to be faster. Looking at average power for segments of road has yielded faster speeds, given highly similar conditions (in terms of wind, temp, time of day).

Felt great in the race too.

Just thought I'd share the experiment results

 

[coapman]

On the contrary: pedaling is an extremely "natural" motion, in that 1) we activate the same muscles in essentially the same sequence as when walking or running, and 2) even pedaling backwards has very little effect on this pattern. IOW, we pedal using essentially the same evolutionarily-designed motor program as we use during upright bipedal locomotion, with very little learning either necessary or beneficial.

Correct, your objective in natural pedaling is to apply a vertically downward force to the pedals. Nothing could be easier and so it continues today. What you are forgetting is that this natural motion was established at a time when cleats were unheard of and it was only possible to apply torque in that manner. Cleats provide the medium for delivering highly effective forward force to the cranks as they move through 12 o'c. How are the muscles used to generate this maximal forward force:: If you stand with your back against a wall and then slide downwards to an almost seated position. You then apply a force to that wall as if attempting to force it backwards, using one leg at a time. On the bike you need resistance to counteract this force and this is where the arms come into the action. You also need the correct bike set-up, but it's as simple as that.

 

[coapman]

Correct, your objective in natural pedaling is to apply a vertically downward force to the pedals. Nothing could be easier and so it continues today. What you are forgetting is that this natural motion was established at a time when cleats were unheard of and it was only possible to apply torque in that manner. Cleats provide the medium for delivering highly effective forward force to the cranks as they move through 12 o'c. How are the muscles used to generate this maximal forward force:: If you stand with your back against a wall and then slide downwards to an almost seated position. You then apply a force to that wall as if attempting to force it backwards, using one leg at a time. On the bike you need resistance to counteract this force and this is where the arms come into the action. You also need the correct bike set-up, but it's as simple as that.

I forgot to mention that when attempting to apply that force to the wall, you keep the entire sole of your shoe on the ground.

 

[FrankDay]

Two crank length anecdotes to report from this weekend.

1. Racing in his first ever bike race Mike Clark won it using 145 cranks.

2. Dave Campbell won his age group at the Wildflower Olympic distance triathlon using 200mm cranks. He is 6'5" though, which helps.

How much did the crank length they choose help or hurt their performances is unknown but a win is a win and I'll bet both are very happy with their choice.

 

[FrankDay]

Here is another crank length anecdote from this weekend. Did my first expo of the year at the Wildflower triathlon.

For awhile now I have set my crank length on my demo bicycles to 145 to make it easier for potential customers to have success in pedaling the product but long enough that if feels like regular pedaling but let most still still experience having a lot of difficulty. I had two bikes set up and I decided to set one up with 130 cranks and then have customers to ride both and see if they could tell me which one was easier and if they could tell what the difference was.

1. about 90% of them said the 130 were easier right away. 100% said the 130 were easier when comparing being in the aero position.

2. None could guess or feel difference between the cranks until I told them.

I thought it a particularly good demonstration as to why they ought to be experimenting with crank length.

 

[CoachFergie]

I thought it a particularly good demonstration as to why they ought to be experimenting with crank length.

About as much use as shuffling the deck chairs on the Titanic when compared to the real research that has been performed on crank length.

 

[sciguy]

About as much use as shuffling the deck chairs on the Titanic when compared to the real research that has been performed on crank length.

Yes, but Frank has some nice shiny new adjustable PowerCranks that will make it sooooooooo easy to do the experiment Gosh fun science for everyone!


Hugh

 

[FrankDay]

Would that be Courtney Ogden who has seemed to be suffering from a series of knee injuries for the past several years? Several of us are wondering if his injuries might relate to the use either PowerCranks, shorter cranks or both.

YMMV,

Hugh

Of course I don't know all the details but I have told Courtney over and over that he pretty much needs to stop running (and the use the PC's maintain his running fitness) until he is completely healed. It seems, he, like many, believe that one must run a lot to run well so he has, I believe, pretty much ignored my advice here. I think though he may finally be paying attention. The only injury the PC"s can cause in an athlete is an overuse injury from trying to do too much too fast. That isn't an issue with Courtney. Nothing slows an athlete down more than an injury.

 

[FrankDay]

1. The subjects in Jim's studies were all experienced cyclists, who were free to adopt whatever thigh-torso angle they felt allowed them to generate maximal power for a very short duration while seated (naturally, I had my hands in the drops). I would therefore argue that it is quite likely they did so, i.e., "body wisdom" is a powerful influence...this is, after all, why you see pursuiters invariably creeping onto the nose of their saddle late in race, or (more relevantly) why steep-seattube-angled TT/tri bikes were invented in the first place. Thus, while it is possible that cranks even shorter than 145 mm might (or might not) be better when a rider is forced to assume an overly-acute thigh-torso angle, that is really putting the cart before the horse...the goal is to maximize power:CdA, not just minimize CdA, so you never want to adopt a position that compromises your power *unless* you know that the improvement in CdA is worth it.

You can argue whatever you want but the fact remains that Dr. Martin did not measure nor comment on the body position used by his subjects so, it is simply supposition on your part. Even you agree that hip angle at TDC can affect power. Hip angle changes as one goes lower in front and it can affect power. You write above: "the goal is to maximize power:CdA". Someone needs to do a study on this, don't you think?

2. In keeping with the above, I have measured my both my CdA and my sustainable power in a wide range of aero of positions while using a wide range of crank lengths. What I have found is that if I go too low, my power drops more than my CdA, and shortening the cranks by up to 22 mm doesn't help.

Thanks for that anecdotal report as it applies to you. I seem to be getting a lot of reports to the contrary. Wouldn't it be nice if we knew what "science" says about how this might apply to a wider population.

 

[FrankDay]

On the contrary: pedaling is an extremely "natural" motion, in that 1) we activate the same muscles in essentially the same sequence as when walking or running, and 2) even pedaling backwards has very little effect on this pattern. IOW, we pedal using essentially the same evolutionarily-designed motor program as we use during upright bipedal locomotion, with very little learning either necessary or beneficial.

Let me get this straight. Are you saying that just because life on earth evolved to efficiently do repetitive reciprocal antagonist muscle activation to efficiently walk, chew, wing flap, or run that cycling is "natural" because we get to invoke that spinal reflex?

But, to go a step further, are you saying that because people learn to use, essentially, the same pattern in cycling that we do in walking or running, that this means this has to be the most efficient cycling pattern simply because it is related to the most efficient running or walking pattern? If so, do you have any studies that back up this contention? Really? Why on earth would a pattern (walking/running) that only allows actual propulsive force application for 0.2-0.5 of the time be optimal for an "invented" pattern that allows power application for 100% of the time? Adapting the walking/running pattern is, of course, the "easy" and obvious way to go if one wants to learn to cycle. There is, of course, zero evidence it is the best or only way to go if one wants to optimize the method.

 

[Caruut]

Here is another crank length anecdote from this weekend. Did my first expo of the year at the Wildflower triathlon.

For awhile now I have set my crank length on my demo bicycles to 145 to make it easier for potential customers to have success in pedaling the product but long enough that if feels like regular pedaling but let most still still experience having a lot of difficulty. I had two bikes set up and I decided to set one up with 130 cranks and then have customers to ride both and see if they could tell me which one was easier and if they could tell what the difference was.

1. about 90% of them said the 130 were easier right away. 100% said the 130 were easier when comparing being in the aero position.

2. None could guess or feel difference between the cranks until I told them.

I thought it a particularly good demonstration as to why they ought to be experimenting with crank length.

So until they had some outside information steering them towards a certain outcome, they had no idea that there was any difference? For a guy who talks a lot about science, you ought to know what that means.

 

[FrankDay]

So until they had some outside information steering them towards a certain outcome, they had no idea that there was any difference? For a guy who talks a lot about science, you ought to know what that means.

Huh? The only outside information these folks had came from riding the bike. The shorter cranks actually looked longer to the casual observer because of the grass being taller around the one bike making the pedals seem closer to the ground. A couple of riders I guess had seen what their friends had said. All I did was ask them to ride two bikes with PowerCranks, one after another, and I asked them if they could say if one was easier than the other? In most cases it was obvious one was easier than the other because they were having much less trouble riding the cranks. In a couple of cases I couldn't see any difference by the rider said the shorter cranks were easier. In a few cases the riders did not see a difference.

Anyhow, I reported what I did and what I observed. If you think it is all hooey I guess you can figure out a way of better reproducing the "experiment" to see if you get a different result. After these little "experiments" I would use the results to talk to them as to why we think it important that they experiment with crank length if they want to optimize their results.