Sitting on a chair, attach one end of a piece of elastic tubing to the net post, doorknob, or another stationary object. For supination (shown here for the R arm), grasp the tubing in the right hand and wrap it around the hand several times. Rest your forearm on your thigh and position yourself so that there is tension on the band with your palm facing the floor. Without moving your upper arm or body, rotate the forearm so that the palm is facing upward in the end position.
Perform 2-3 sets of 15 repetitions of each exercise. If you have time constraints, make sure you perform the exercises with your dominant arm.