Bike Fit Case Study

November 20, 2014 | by Dr. Jess

Occasionally we like to take the opportunity to educate our fellow cyclists and runners on what we are seeing in the Press Play Performance Lab.   What is to follow is one of our most recent cycling analyses to walk into our office.   In this case, we would like to highlight how we use biofeedback to help one's performance on the bike.  Unfortunately, what you don't know can cause a leak in power.

History and Findings

A Cat 2 racer came in for a bike fit with a goal of regaining symmetry in his pedal stroke. He has observed a loss of power in his left leg when pedaling, especially when fatigued. During the physical exam, we found his flexibility to be within normal limits except for the left hamstring and hip flexor. His squat was very strong, but when he broke 90 degrees his left hip shifted forward due the mobility issues.  While performing a single leg squat he demonstrated pelvic instability bilaterally. When pedaling with a single leg he pedaled smoothly on the right side but had difficulty getting over the top of the pedal stroke on the left side.

When we began data collection, we found his saddle pressure to be symmetrical, but contrary to his sensations, he produced more peak force on his left leg (Left peak force averages about 200N while right avg about 140N). Also of note, he did not demonstrate a smooth transition on the bottom of the pedal stroke as seen on the force time plot below, especially with the right leg.

GP Manager

The next step would be to perform sEMG on his muscles to determine if muscles in his legs are firing properly and in correct order.  We have often seen muscles not relax during part of the pedal stroke due to dysfunctional firing sequencing.  Above, we can see his left foot does not unweight the pedal as much as his right foot and thus probably the reason he has trouble coming over the top of the pedal stroke.  Along with the data we collected, sEMG would give us more information to further understand his symptoms.

Corrections

In addition to retraining his pedal stroke, we raised his bars by 1 cm to open up his hips and give his hamstrings a break. This change allowed him to relax his arms and actually decrease his frontal area improving the aerodynamics of his position.   As you can see in the post-fit Force Plot, he demonstrates better transition bilaterally and his right/left peak forces are more symmetrical.  Left peak forces average about 200N and the right averages about 180N.  Right peak forces improved by about 40N. You will also notice we eliminated the double peaks on the bottom of the force-time plot indicating a more efficient transition at the bottom of the pedal stroke.   This is a much improved pedal stroke bilaterally, with more work to do.

GP Manager

He left with homework to increase functional mobility and stability of his left leg and pedal drills.  He will return for a follow-up within a month to retest foot and saddle pressure in which we expect to see a more symmetrical pedal stroke due to better hip flexibility, pelvic stability, and adaptation to fit and pedaling technique. 

We go where the data drives us.

- Mitchell and Jess

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