Bike Fit Changes: Stable Feet | Mobile Hips

When we make bike fit changes, we expect something to change, right?  It makes sense that we're after certain changes and an expert bike fit ought to elicit changes for the better.But this begs a question:  Do all changes happen to the same degree?  Do all areas of the body adapt the same amount and at the same time?For many years I've had the benefit of using infrared motion capture, which allows me to see very minute changes, measured down to the millimeter and degree, after even small alterations to the bike setup.  More recently, saddle pressure technology has given me specific data on how the pelvis is moving and where it's loading the saddle, which fills a blind spot in the infrared data.  So when I make changes to a client's bike position, I can see very quickly and very accurately, what parts of the fit change right away and what areas adapt more slowly over time.Over the years I've noticed some consistencies, and recently some research appears to back this up.First, when altering a rider's position, ankle motion seems to not change much at all -- even after raising the saddle a lot, the ankle will often adhere to the same amount of movement it did before the change.  It's not that changes at the ankle don't occur -- they just are more subtle and slow to adapt.On the other end of the spectrum, pelvic motion often changes immediately and sometines drastically.The most interesting part is that after a few weeks of riding both of these seem to normalize -- the pelvic motion calms down and I see its movement stabilize, while the ankle, not changing much at first, slowly begins to adapt and change its overall range of motion and movement pattern.Some new research appears to support this idea.  In the journal put out by the American College of Sports Medicine (www.acsm.org) called Medicine & Science in Sports & Exercise, an article by Barratt, Martin, Elmer, and Korff looks at the effect of changes crank arm length has on experienced cyclists.  The article is titled:Effects of Pedal Speed and Crank Length on Pedaling Mechanics during Submaximal CyclingThey measured changes in joint kinematics, angular velocity, among others, when riders had their crank length changed to varying degrees from 150 mm to 190 mm in length. Here's a brief except from the article:"Conversely, crank length–dependent changes in ankle joint excursions were smaller (Figs. 1A and 2A). Consistent with this finding, changes in ankle angular velocities across pedal speeds and crank lengths were negligible (signified by small effect sizes; Figs. 1B and 2B). It has previously been shown that the plantarflexors stiffen the ankle joint to allow for energy transfer from the proximal to distal segments (12). Our results suggest that this requirement to stiffen the ankle joint is accomplished by relatively constant ankle kinematics across crank lengths (Figs. 1A, B, 2A, and B). In addition, we found significant differences in extension and flexion velocities of both the knee and hip joints across pedal speeds, which is consistent with previous findings (23). Our results thereby confirm that pedal speed is related to the shortening velocities of the muscles spanning the knee and hip but not the ankle joint."I know that reading into a paragraph standing alone like that can be difficult because there's little context around it, but what it's essentially saying is that when different crank lengths were tested (from 150 mm to 190 mm) many variables at the knee and hip exhibited significant changes while the ankle remained constant because the main goal at the ankle is not to flex or extend and apply more force to the pedal but rather to be held still so that the larger muscles in the upper leg and butt can do the work.It makes sense then that if the ankle doesn't change much when we do something as drastic as changing crank length by up to 40 mm, that it's unlikely to change much when we make changes to saddle position for instance during a bike fit.The ankle remain pretty static because no matter what position we're in, it's job remains pretty much the same = stay rigid so more power from larger leg muscles can push down.This idea also matches pretty well with a recent article I wrote on solving foot pain on the bike which discusses that there's little penalty to moving the cleats further back on your shoe -- this merely shortens the lever around the ankle that the calf muscles have to stabilize and puts them at a greater mechanical advantage.  This just makes it easier for the calf muscles to hold the ankle still so that the bigger muscles can do their work more efficiently.Why do we care?  This information is critical for any bike fitter, or anyone wanting to fit their bike better, to understand.  Any time there are bike fit changes made to the cleats, pedals or saddle position especially.  We need to be very careful about expecting to make too much change at the foot or ankle immediately because of the possible unintended consequences that might occur at the knees and hips.  It makes a good case for making the smallest effective change, or practicing what I call minimum effective dose bike fitting.I'm interested what questions this brings up for you?  Feel free to leave a comment or send me an email on this topic...