Grippers Make My Thumbs Sore

[nagual]

I've noticed since a while back that for some reason my thumbpad muscles get sore when I only do grippers. This strikes me as somewhat odd, since I can do pinch workouts after gripping with my pinch strength intact.

First I thought it was the combination of gripping and pinching, but when I stopped pinching altogether, I still got sore.

Can it be that the setting of the grippers train the pinch that much? I mean it is sort of a pinch when using the other hand to help set the gripper...