It is the centripetal force due to the racquet alone that is of interest, so forget the arm mass. Dividing the Work formula by R and multiplying by 2, therefore, gives a formula for Shoulder Pull due to the racquet, in Newtons of force. See the Shoulder Pull derivation . Shoulder Crunch is the change in the centrifugal force acting on the racquet. You will recall that the Shoulder Pull due to the racquet's rotation was equal and opposite to the centrifugal force.
Impact changes the speed of rotation, and therefore the centrifugal force.
The excess centripetal force, which continues to act regardless of the impact lessening the centrifugal force it was countering, is the Shoulder Crunch. This is easily derived knowing Shock. Elbow Crunch is the excess of centripetal over centrifugal force due to impact, this excess pulling force acting at the elbow as what might be viewed as a muscle spasm. Elbow Crunch turns out to be more severe than Shoulder Crunch due to the smaller distance to the mass center from the axis of rotation. Wrist Crunch .