How can you avoid cramping up/getting tensed up while drawing

No.5735301 ViewReplyOriginalReport
That shit happens to me even after like 20 minutes. Wrists, upper arms, shoulders. Neck after like 1 hour. Already trying to keep it loose and move out of the arm instead of having the arm on the desk and only moving the wrist but the couple times it still accidentally happens are apparently enough.
Any advice that helped you in a similar situation?