The rotator cuff which is a group of muscles that stabilizes the shoulder joint and provides rotational movement. The shoulder joint can be thought of as a ball and socket, and has a wide range of motion. Together, the joint and rotator cuff make the movements possible that lift the arm and rotate it to facilitate overhead serves in tennis. Tennis players who use strong, forceful strokes generate about 4,000 watts of power with each serve, or a force equivalent to 5 horsepower.
Causes
The muscles of the rotator cuff are the supraspinatus, infraspinatus, teres minor and subscapularis. These muscles stabilize the shoulder joint as well as lift the arm and rotate it.
The supraspinatus functions to lift the arm away from the body the first 10 to 15 degrees. Further lifting requires the work of the deltoid muscle, which is not part of the rotator cuff but forms the round contour of the shoulders. Internal shoulder rotation, or rotation of the arm toward the center of the body, accelerates the arm during the swing. This motion is carried out by the subscapularis muscle. External shoulder rotation --- rotation of the arm away from the center of the body --- slows the arm down after impact. The infraspinatus and teres minor muscles provide external rotation.
Symptoms
In the swing preceding impact with the ball, internal rotation accelerates the arm. According to Dr. Bruce Elliot, an Australian biomechanist, most of the power on a serve comes from internal shoulder rotation. The infraspinatus and teres minor muscles --- the external rotators --- contract to slow down the motion in the follow through phase. The external rotator muscles are smaller than the internal rotators, so training is essential to protect the shoulder from injury.
Treatment
Although rotation of the shoulders provides a good amount of the force behind an overhead serve, the muscular action begins in the legs, then the pelvis and trunk, then on to the shoulders through internal rotation. This is known as the kinetic chain. Bending or flexing the knee has been shown to relieve stress on the internal rotators of the shoulder during an overhead serve, although research is still ongoing.
Conclusions
Each muscle in the rotator cuff plays a role in lifting the arm, the stroke and follow through for an overhead serve. The shoulder joint alone produces 13 percent of the kinetic energy and 21 percent of the force exerted in overhead serves.
References
- Wake Forest University Sports Medicine; Rotator Cuff Tendonitis in the Tennis Player; Stephen Wiley
- MedlinePlus; Rotator Cuff Tendinitis; August 2009
- American Academy of Orthopaedic Surgeons; Shoulder Impingement/Rotator Cuff Tendinitis; February 2011
- STMS; The 4000 Watt Tennis Player; W. Ben Kibler; 2009
- "British Journal of Sports Medicine"; Biomechanics and Tennis; 2006
Member Comments