How far is individual up-down thumb movement okay?

[parishrut]

   Moving through fast passages I can hardly tell if I am actually moving my thumb individually or if my forearm rotates to accomplish the pressing of a key by my thumb. I learnt that an inferior set of muscles accomplish that movement in the thumb.

   In relatively slow passages, I can concentrate on using the forearm, but they are the fast passages which should create tension!

   I am trying to learn this fast passage right now but I get always have to get up from the piano acknowledging a minor throbbing nervous pain on the underside of my wrist. I suspect this might be arising from too much of individual thumb movement since I feel perfectly relaxed throughout, and yet the little (I don't think I should call it pain) throbbing sensation arises. It is less enough to be considered negligible but is so unusual and constant that I thought I would ask away.
   
   How far is the individual up-down thumb movement okay? What level of strain would be considered alarming, or would indicate that I am heading towards an injury?
   
   A million thanks!