DOES CRANK LENGTH MATTER?

Does crank arm length matter in a time trial position?
A letter of observation from Curtis Cramblett, PT, CFMT, CSCS, Level II Cycling Coach; after returning from Garmin Team Camp, December 2010. 

I just came back from the Garmin professional cycling team camp in Grand Cayman Islands where some great discussions happened regarding crank length. Research is starting to suggest that changing crank lengths by 2.5-5mm does not change power for endurance athletes. This has also been true in my experience. Athletes, without trying, increase their cadence, making up for the slight loss in leverage. The benefits of shortening up your crank length on a time trial bike, is that as your knee and your hip come over the top of the pedal stroke, your hip and your knee have to bend less. Keeping the angles closer to what they are on your road position, and making it easier to keep the momentum over the top of the stroke. That’s a very good thing if you consider your hip has to bend so much more in a time trial position, while your torso angle comes down, in order to get very aerodynamic. When this drop in torso closes up the hip angle, basically you increase hip bend and the amount of stretch to your hip muscles in the back, including your hamstrings. Additionally this puts the muscles in the front of the hip, the hip flexors, at a much more shortened position and when muscles gets very short, they have a harder time contracting.  

David Zabriski, Curtis Cramblett

Curtis Cramblett, Christian's Van De Velde

In summary, as crank length goes down, we are still trying to figure out how much is still efficient for most people. As crank length goes down the decreased hip and knee bend at the top makes it easier to clear the top of pedal stroke, and thus allows less bumping of your knees into your chest. For most cyclists, a feeling of easier breathing comes with that, keeping them appropriately positioned over the top of the pedal. For those triathletes out there, it also seems to make it easier to then hop off the bike and transition into your run. So there's not enough good research yet, however the cutting edge thought these days, is to consider having 2 different crank lengths; one for your road bike and one for your time trial bike - where the time trial bike is shorter. 

Many will suggest that getting used to one and then switching over to the other is detrimental, because you’re use to a certain pedal circle. However my experience, and other avid cyclists experience, suggests that it’s a lot easier to get used to a smaller circle than it is to get used to a more bent hip angle, closed hip angle and it’s easier to keep your power levels higher with a more open hip angle where you’re fighting this pedal at the top of the stroke. Gives us something to think about, and I would suggest you checkout Slowtwitch.com, look up crank length, there are some nice discussions going on there, and I think you will see a lot more cyclists and triathletes; when in time trial positions, choosing to shorten up their cranks in the next couple years.
— Curtis Cramblett, PT, CFMT, CSCS, Level II Cycling Coach. Revolutions In Fitness.