Joint Power is a scalar term computed at:
Power = [Mx,My,Mz] . [wx ,wy,wz]
Power = Mx.wx + My.wy + Mz.wz
but it has become common in the biomechanics community to resolve Power into a segment coordinate system.
Joint Power requires a “Joint” to be created because Joint Angular Velocity is the relative angular velocity between the two segments intersected by the Joint.