The Prone Scapula Retraction exercise is a very beneficial exercise for tennis athletes. The athlete faces the ground in a pushup position and slowly squeezes the shoulder blades together as demonstrated in the video. The purpose of this exercise is to help develop strength and stability in the muscles surrounding the scapula. These muscles are very important for tennis athletes to help in the prevention of shoulder related injuries. These smaller muscles that help to stabilize the scapula (shoulder blade) are very important because if they are not strong and stabilized, the smaller muscles of the rotator cuff become over active and end up performing more work than they can handle. Remember that the shoulder is a complex joint and to protect the shoulder it is important to work on improving strength, stability as well as the endurance of the muscles surrounding the joint.
For the beginner tennis player, 1-2 sets of 10 repetitions will be challenging. As the athlete develops more strength and stability this can be increased to 2-4 sets of 10-15 repetitions. It would be recommended to rest at least 60 seconds between sets.