Every time I hear the word shims, or see shims on a cycling shoe, I tend to cringe. Shims seem to be in high usage these days for bike fits. I've never understood the usage of the shim. Well, maybe one time I did. I had a cyclist who had a lower leg accident and shortened the leg by over an inch. If the cyclist did not have the shim, he sat completely off the side of the saddle. Adding the lifts/wedges to rise that leg to match his other was important. Other than that, after over 1000 fits, I have not seen the usage of shims provide any benefit.
Let's take a look at it how I see it. I want the body to function and move as smooth as possible. If there is a particular action that does not look right, I start to analyze why. What muscle imbalance is there? Any current or past injury causing this to occur? Is the cyclist sitting crocked on the saddle? The questions start to find an answer. And most times it becomes an argument of the what came first, the chicken or the egg. Is the cyclist sitting crocked on the saddle because their psoas (your psoas attaches in front of your body from posterior spine to the front of your iliac crest of your hip) is tight pulling them forward or do they not like the saddle, so they are sitting crocked to not irritate anything off "underneath". Then it causes their knee to flare out, make a funny circle upon return to the top of the stroke. Any way you slice it, it needs to be corrected.
This situation has crossed my schedule a few hundred times. And at least half of those times the cyclist had a shim put in to not let their knee flare out during the pedal stroke. To me, this is just a band-aid. It just starts to divert the issue somewhere else. My recommendation would be to correct the pedal stroke visually and neurologically.
Let's take this triathlete I saw recently. Overall the fit was not bad, however needed some tweaking. After chatting about mechanics, and what was failing him, the shims under the cleats seemed to point out issues. A year previous with a different fitter, shims were put in to not let the knee flare out. However, under visual review, the knee was still flaring out at the top of the pedal stroke. Here's how I see it.
Your feet are the start point of balance and fit. Stand on both feet. If you rotated your foot and put most of its weight on the outer part of the foot, you'd see your knee swing out. You would also see this if your piriformis or psoas was tight. What was done a year ago was put shims under the foot to keep the foot rotated out and not fall back in while pedaling. Well, those shims eventually caused the ilipsoas to tighten more, rotate the right SI joint forward and shut off the gluteus maximus from functioning. Ultimately, this caused the athlete's ITBand to be tight on the run. So, instead of supporting an imbalance such as this, let's try to solve it through correct proprioceptive work and corrective actions.
I took the shims out and moved the cleats to be in the same position on each shoe, so that the first point of contact is equal. We also discussed retraining the pedal stroke by applying the power/pressure down the middle of the shoe (almost more medially) and keeping the pelvis square on the saddle. One main problem was that the gluteus maximus was not firing or supporting the leg (partially due to the tight psoas muscle). The cyclist was suggested to complete glute activation exercises on a daily basis. Here is the outcome after one training session of 2 hours:
- no hip flexor issues, basically at all
- a bit of twinginess for 15 seconds is all the athlete reported
- stayed in aero 50% more than he would have and even climbed a bit in aero, which he didn't normally do at all
- his butt stayed in one spot the entire ride, even coming back into the saddle after standing
- his right foot tracked properly
- he ran, with short intervals, directly off the bike for 30 minutes, no issues
At the time of this writing, we are going to start looking at saddles. His previous saddle was no issue, however he is realizing that he was moving around a lot on the bike, so the saddle never bothered him. Now that he is in one spot on the bike and able to stay in aero, he will venture onto a new saddle. The hip flexors are tight still when he gets out of the water in a race and jumps on the bike. The plan for that is to lessen the aero position, and start doing training sessions that implement out of the water transitions to bike at race power.