This sort of thing is true for a lot of instruments. For guitar, a lot of players get into the bad habit of pinching the neck with their fingers and thumb, and moving their wrist when they strum. This can lead to injury at worst, but more common is a cramp or complaining about barre chords. You should use your elbow and a steady, fixed wrist to pull your fingers against the frets with just enough pressure to avoid buzzing, the thumb shouldn't be applying pressure at all, and you should be strumming from the elbow.