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Crank length - does it have an effect when standing up and pedaling?

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Crank length - does it have an effect when standing up and pedaling?

Old 02-11-15, 05:13 PM
  #26  
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Originally Posted by ESTrainSmart
I wasn't too interested in crank length until I corrected it and experienced an immediate 20-30 bpm drop in heart rate for the same speed. My pedaling technique instantly restored back to normal as well. In terms of power, there are reports of 100 watt improvements just from correcting crank length. The improvements I experienced were nothing short of massive.

The reason why I was in this situation in the first place was because I was forced to ride a completely new bike for 2014 when the tire casing of my new Conti GP4000S failed instantly after a sprint which totaled my previous bike. The new bike had a longer crank arm. I spent the full 2014 racing season unaware that my cranks were too long, but aware of major differences in my pedaling technique, cadence and heart rate.

I immediately blamed myself for the drop in performance because I didn't want to be "that person" who blamed the bike. I implemented various neuromuscular, mobility, flexibility, power lifting and strength conditioning protocols to combat the symptoms I experienced, but never saw any meaningful improvements. Changing the crank arm length instantly solved every problem I had tried to fix all year.

Sorry about that long background. I'm super passionate about this topic because of how much it affected my performance. I'm presenting my crank arm length test to a few research boards to have it studied for its accuracy.

Anyway back to your questions! When the cranks are too long, it causes the hip, knee and ankle to reach its optimal range of motion for power production too early. As a result, the rider will never feel like he or she is using their full potential throughout the power phase, especially with explosive efforts. Using a piston in an engine as an example- it's similar to the spark plug firing before the piston reaches the top. The stretch coming from either the pelvic wall, core, hip, knee or ankle musculature adds extra resistance to each pedal stroke through a co-contraction. It's like holding an active stretch repeatedly.

In terms of sprinting with long cranks, being on the drops will make things worse. A rider with long cranks will naturally favor a higher position with the hands on the hoods. If the rider forces the hands on the drops, the hips will shift forward towards the handlebars which will drastically reduce gluteus maximus activation. The reduced glute activation leads to a significant drop in power.
And how do you go about determining a person's optimum crank length, given that it's quite expensive for each individual to buy several different cranksets for personal experimentation? I notice that your 1st link states that
The results of the study suggest that each subject has a most efficient crank arm length, but it does not appear that optimal crank arm length can be predicted by leg length.
A review of crank length studies reveals that no study that I can find concludes that each person has a particular optimal crank length which is best for the all various things in which we are interested: efficiency, metabolic cost at moderate power, and maximum power:
The importance of crank length to the cyclist. - Page 183 - Cyclingnews Forum

Although the above link contains only abstracts, I have found one of the abstracted papers as a PDF download here:
https://www.google.com/url?sa=t&rct=...85761416,d.cGU

Additionally, I found another paper not listed in the cyclingnews forum and its PDF here:
https://circle.ubc.ca/bitstream/hand..._2000-0583.pdf

These papers generally conclude that cranks need not be changed from the 170mm industry standard for individuals of various leg lengths as optimum crank lengths predicted from leg length measures do not differ significantly in physiological responses from crank lengths very close to the industry standard.

This has also been my personal experience and I've never met a cyclist whose experience differed from the results in the above studies, certainly not any 20-30 beat HR difference. Unless of course your replacement bike was equipped with cranks 30mm+ longer than your usual cranks. Some, but all all of these studies do find minor efficiency losses with extremely overlong cranks.
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Old 02-11-15, 07:31 PM
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Originally Posted by Carbonfiberboy
And how do you go about determining a person's optimum crank length, given that it's quite expensive for each individual to buy several different cranksets for personal experimentation?
Im not sure what @ESTrainSmart will say, but my fitter determined this with a FitBike. He can adjust crank length and have me pedal various crank lengths and simultaneously measure power output. I do have a demonstably better power output on 165mm cranks vs 170mm cranks. I never asked what the power difference was, but I got the impression that it was not huge. But I just like the feel of the 165 mm cranks, so that's what I went with. When I got bike #2 , it had 170mm cranks already and I was going to keep them, my fitter says they're fine for me, just not optimal. That lasted all of about 2 weeks. I really just strongly prefer the 165s.
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Old 02-11-15, 11:43 PM
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Originally Posted by Heathpack
Im not sure what @ESTrainSmart will say, but my fitter determined this with a FitBike. He can adjust crank length and have me pedal various crank lengths and simultaneously measure power output. I do have a demonstably better power output on 165mm cranks vs 170mm cranks. I never asked what the power difference was, but I got the impression that it was not huge. But I just like the feel of the 165 mm cranks, so that's what I went with. When I got bike #2 , it had 170mm cranks already and I was going to keep them, my fitter says they're fine for me, just not optimal. That lasted all of about 2 weeks. I really just strongly prefer the 165s.
I'll look around. There must be a similarly equipped bike shop somewhere around here. While I don't feel any difference in power or comfort between 170s and 175s, I do like 170s better because I pedal a slower preferred cadence on the 175s and I'm used to the higher cadence. It would be interesting to see, though.
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Old 03-20-15, 08:11 PM
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Sorry for the delay. I'll try to answer all of your questions. To determine optimal crank length, I run each client through several balance exercises to evaluate flexibility and mobility at the spine, pelvis, hip, knee and ankle. If a client demonstrates compensation patterns, I use corrective exercises to restore motion to the joint. The optimal crank length correlates to the maximal distance the hip can travel without compensation. Sometimes the culprit is muscle tightness, and sometimes it's myofascial adhesions. In terms of perceived exertion, I have seen clients progress from a maximal effort to a low submaximal effort after one set of corrective exercises. There are reports of 50-100 watt improvements from optimizing crank arm length alone.

While this sounds almost ridiculous, when you consider how powerful inflexibility is, improvements much larger than 50-100 watts is feasible. For the inflexible athlete, the downward dog exercise is extremely difficult (RPE: 10/10), and oftentimes they never reach the end position. In an effort to get deeper, they maximally contract the hip flexors and core (which also usually disrupts breathing), but still fail to reach the final position. With a flexible hamstring, an athlete can reach the downward dog position without much effort. Switching from an excessively long crank to a shorter crank produces a similar change in effort by preventing one or more inflexible muscles from fighting the power phase of the pedal stroke.

Going too short can be a major problem for the competitive cyclist also, which a study identified when measuring VO2 at various crank lengths. The mechanism of limitation is caused mainly by changes in venous return and blood circulation overall. As you start to go too short, you'll start to experience symptoms common in isometric movements like wall-sits and squat pulses.

Finding the optimal crank length can mean a longer or shorter crank length. For those lucky enough to have an optimal length close to the standard 170-175mm offerings, they won't need to investigate this, but I found that there are a large number of cyclists who do not fit within this range. Here are a few rules of thumb that could mean the cranks aren't optimal:

1. The quads burnout quickly during hard seated efforts. (too long or too short)
2. The hips have to be forward in order to produce high power. (too long or the stem is too long)
3. Your natural cadence (without consciously regulating it [turn off your cadence display]) is always less than 90rpm. (too long)
4. In a seated position, the hips always rock no matter what saddle height is used. (too long)
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