Muscle activation during the tennis volley

Purpose: To broaden our understanding of muscle function during the tennis volley under different ball placement and speed conditions by examining the activity of selected superficial muscles of the stroking arm and shoulder (flexor carpi radialis, extensor carpi radialis, triceps brachii, deltoids, and pectoralis major) and muscles related to postural support (left and right external oblique, lumbar erector spinae, and gastrocnemius) during the volley. Methods: Seven skilled tennis players were asked to perform volley strokes under 18 experimental conditions, including variations in lateral contact location (forehand and backhand), ball contact height (high, middle, and low), and ball speed (fast, medium, and slow). A ball machine was modified so that the subjects could not predict the ball trajectory before it was released from the machine. Muscle activity was determined using surface electromyographic (EMG) techniques, and the critical instants of a volley were determined using two force platforms and two high- speed (120 Hz) video cameras. Average EMG values for different phases of the volley, defined by the critical instants, were computed. Results and Conclusions: In general, muscle activity increased with increasing ball speed. The extensor carpi radialis was more active than the flexor carpi radialis during both forehand and backhand volleys, suggesting the importance of wrist extension/abduction and grip strength. The increase in EMG levels in the forearm muscles shortly before the ball impact indicated that the subjects did not tighten their grip and wrist until moments before ball impact. Both antero-middle and postero-middle deltoids were active in most stroke phases. However, the roles of the deltoid muscles during a volley cannot be determined without knowing the actions of the other shoulder joint muscles.