Can't point you to studies and hate using myself as n=1, but my saddle far forward lead to adductor overuse, tightness and longus tearing later during IM run. Likely in the large context it matters but saddle height, saddle fore-aft and cleat location have equal impact on recruitment. No expert here and could be entirely wrong.

With my bike fit went from 200 cranks to 175's now. Moved the seat like 100mm back. Raised the seat. Now I can spin the powercranks unlocked in aero on the trainer.
Spun 150mm cranks for a few days, might even try 140's. It takes a LONG time to collect enough data to show any trend.

I also changed my rpm focus from like 90 to 70.

So as you say, there are lots of variables to consider.

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Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

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I don't know about any experimental studies but I wrote about the importance of geometry a while back in my blog (in the sig).

Turns out you can calculate the torque profile at each joint required to put out a specific pedal force profile with leg limb data (length and moment of inertia). Unfortunately these parameters vary among individuals and people will have different experiences so it's hard to say a universal truth in the matter.

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I like analyzing things - http://engineeringfitness.org

GCN has a "science lite" video about it:


https://www.youtube.com/watch?v=eMAxH_Ud8YE

The conclusion is that it doesn't really matter and that comfort (and aerodynamics I guess, even though they don't mention it) should decide.

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Citizen of the world, former drunkard. Resident Traumatic Brain Injury advocate.

I tried as low as 150 but settled on 160. I found the 150 put a lot more load that ultimately stressed my lower back. The shorter cranks helped alleviate the issues I was having with my hip flexors in an ironman I was still having at 165.

Could the lower back issue have been caused because you had the front lowered too much?

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Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

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Muscle utilization is a red herring.

Could you explain? With research to back it up obviously.

My premise is that 1cm of crank length change doesn't matter in terms of muscle utilization, so it would be hard to cite research to prove a negative, but my opinion is not baseless. I am basing this off of about 1500 fits on a dynamic fit bike with adjustable cranks, and before that another 1500 or so fits without adjustable cranks. Out of all of those fits, I've heard some version of, "this muscle seems to be working more/less/better/worse." a couple hundred times. Never once did that subjective assessment of muscle recruitment actually matter enough to inform the fit.

Early on, I spent a good bit of time trying to figure out the how's and why's of those subjective impressions, before I learned to largely ignore them and focus on the things that seemed to actually matter in guiding a rider into great positions. Please note I am not arguing against a rider's subjective impressions during a bike fit, as they are actually a large part of the process. I am arguing against subjective impressions regarding specific muscle recruitment. These impressions are almost never as they seem to be, and will generally fade to the background pretty quick IF we have developed a great position through proper use of the fitters eye, tools, and the riders subjective assessment of comfort and power producing ability.

So I would suggest to not focus on the details of what muscle is doing how much, and rather look to the bigger picture such as "Do I pedal better here?" If you pedal better, the muscle recruitment is almost certainly better. Start with overall impressions of power and comfort, and you will reverse engineer yourself into proper recruitment.

I agree with finding freestyle's comments about the subject, but I think I can add a little more to your question(although like he said, probably doesn't matter)

If you go shorter and move forward there is a definite portion of the workload that transfers to the hamstrings or back of your legs. I can't tell you how many times I have showed roadies the forward TT position and after awn early hard effort their hamstrings are hammered. I myself will get this same feeling after a long layoff or switching from road to tri positions. I actually did a two man TT champs with a solid bike guy set up in a good forward position, one he had never really ridden. He smoked the course, but hammy's were toast afterwards. I'm pretty confident that a week or two in that position would have gotten rid of that( strengthening normally unused or lightly used muscles) and all would be good.

But to the point it didn't seem to matter too much even in this first hard effort, but of course it would have had he had to run afterwards, so some weeks training in that position with shorter cranks would be advised. (-;

To just in a fit, a very short amount of time, try something like crank length and ask, well, how does it feel, makes no sense.
I have ridden 200's to 150's now in a month. After a few minutes, I adjust. I have been testing for 80 minutes just about every day, measuring HR
at different RPM levels, with fixed power, in and out of aero. I still do not feel I have enough data to draw conclusions yet. But to think anyone can tell
how a change like crank length, and then fit, might impact them without a lot of training with different fits makes no sense.

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Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

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Lions don't lose sleep worrying about the sheep

Respectfully, "quickly" is exactly how changes in fit coordinates are best and most commonly made. The whole premise behind modern dynamic fit bikes is that a rider can tell very quickly how changes in seat height, setback, reach, drop, crank length, saddle selection, etc effect the fit. And that their subjective impressions, tempered by the fitters experienced eye, is the correct answer. I can set your seat height in 5 minutes. Why would it take months to set your crank length? Once you bring a bunch of other metrics into the process, and convince yourself that months of testing is required to reach a conclusion, you are no longer doing a bike fit, you are chasing ghosts.

Crank length is about hip angle and pedaling efficiency.
As far as muscle recruitment goes: If this is a new fit different muscles will feel "weird" for a while.
But, and here's a big one, one a tri bike - a bike you'll have to run off of - you want to load the quads more because you don't run with your quads. You run with your glutes and hamstrings - if you're running correctly.
Finally, you can search with Google Scholar to find peer-reviewed information on crank length and how it relates to riding/pedaling.

we shall see.

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Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

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Thank you. So well said and to the point. You will never convince the one with too much time on his hands and a need for attention, but you hit the nail on the head.

We've done two studies in my lab. This one would be the one that best addressed your question.
Effects of Pedal Speed and Crank Length on Pedaling Mechanics during Submaximal Cycling.
(PMID:26559455)

• 

Barratt PR 1 , Martin JC ,Elmer SJ , Korff T
Medicine and Science in Sports and Exercise [10 Nov 2015, 48(4):705-713]
Abstract
During submaximal cycling, the neuromuscular system has the freedom to select different intermuscular coordination strategies. From both a basic science and an applied perspective, it is important to understand how the central nervous system adjusts pedaling mechanics in response to changes in pedaling conditions.To determine the effect of changes in pedal speed (a marker of muscle shortening velocity) and crank length (a marker of muscle length) on pedaling mechanics during submaximal cycling.Fifteen trained cyclists performed submaximal isokinetic cycling trials (90 rpm, 240 W) using pedal speeds of 1.41 to 1.61 m·s(-1) and crank lengths of 150 to 190 mm. Joint powers were calculated using inverse dynamics.Increases in pedal speed and crank length caused large increases knee and hip angular excursions and velocities (P < 0.05), whereas ankle angular kinematics stayed relatively constant (P > 0.05). Joint moments and joint powers were less affected by changes in the independent variables, but some interesting effects and trends were observed. Most noteworthy, knee extension moments and powers tended to decrease, whereas hip extension power tended to increase with an increase in crank length.The distribution of joint moments and powers is largely maintained across a range of pedaling conditions. The crank length induced differences in knee extension moments, and powers may represent a trade-off between the central nervous system's attempts to simultaneously minimize muscle metabolic and mechanical stresses. These results increase our understanding of the neural and mechanical mechanisms underlying multi-joint task performance, and they have practical relevance to coaches, athletes, and clinicians.

Thanks Jim!
That was the answer I was looking for, so the increase in crank length increased hip extension work increased, so as suspected the glutes were doing more of the work?

Link doesn't work,

Was this the one where you looked at rer?

I always prefer citing that one (for st or basically IM athletes) as opposed to the 30 second power, which others sometimes post.

Thanks,

You're welcome. Yes, but for power averaged over each joint action, the only comparison that was significant was hip flexion which produces a tiny fraction of total power. The rest were only trends, not significant effects.

No, that was McDaniel et al with metabolic cost but without biomechanics.

Trends is good enough for me!
Am I correct in reading that essentially it was only really the 150 that reduced the hip extension power, and 165 to 190 were largely similar? This has been my exact finding, 165 to 175 felt exactly the same. But dropping to 155 felt very different

Feel, feel. I was down that rat hole for years. I can use a 150 to 200 crank and push the same power. I am trying to gather data for things I can measure, rather than feel, which has not helped me on the bike in the past.

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Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

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Lions don't lose sleep worrying about the sheep

When you are gathering data are you sat up on a turbo.
If so it means very little imho as this doesn't represent aero position on the road, one bit.