What does progressive weakness of the posterior compartment look like?

Look at this video carefully and what do you notice? Can you see the progressive dip in the left heel as time goes on while toe walking? This is a cardinal sign of lack of endurance in the posterior compartment, in this patient’s case tibialis posterior. Your differential, in addition to lack of type one muscle fibers, insufficient vascularity or mitochondria for whatever reason would be circulatory problems as well as conditions causing progressive motor weakness like myasthenia gravis.

Fatigue testing is very important because a lot of times the problem doesn’t come out till the person reaches say a half an hour, an hour or sometimes even many miles into the run or ride. Our job as clinicians is to try to diagnose the problem to the best of our abilities. Our job also is to “exploit their weaknesses” rather than “extol their virtues”. 

If you’re getting somebody with posterior calf pain or a foot drop, or maybe somebody who gets worse over time, consider fatigue testing.