Thumb fatigue

[i_m_robot]

Self has been practicing for a while the chopin etude 10-1

after practing for a while self feels soreness and fatigue

it is located the small muscle on top of the forearm that controls thumb movement

self has been trying for a while to figure out how to eliminate it with tempory success

perhaps self regresses without knowing 

could anyone give self some tips or suggestions, please?

[vivace]

From a little bit of personal experience I might venture to say that it sounds like you might be using too much of the abductor muscle in your thumb.

The abductor muscles are what allow your fingers to move from side to side; you will find that these muscles are somewhat difficult to move (try moving your index finger from side to side and you'll see what I mean). 

The abductor muscle works the same side-to-side motion in your thumb, though because of the placement of your thumb, the motion looks to be an up-and-down.  Using this muscle in isolation can be very tiring, and actually can cause tendonitis in the exact forearm area that you referred.

Instead of lifting your thumb only, allow your thumb to always keep in line with your forearm. In the Chopin etude, this motion will essentially create a forearm rotation both in the approach to, and out of the thumb.

I did my best to explain ...however, if you can manage to get a hold of the Taubman videos this exact problem and musical example is addressed.