Thumb independence

[peckdec]

There has been several topics about finger independence regarding other four fingers, but I didn't find any of the thumb.

For example, when I play scales, my thumb seems to be stiff and twitching, and even slowing down other fingers when using them. Overall my thumb feels quite clumsy compared to other fingers. On the otherhand if I relax it, it spreads much to the left and I would imagine it making it slower to use it again when needed (because it has to travel bigger distance). Does anyone have the same problem or a way to solve it?