Effects of string stiffness on muscle fatigue after a simulated tennis match.

We tested the influence of string stiffness on the occurrence of forearm muscle fatigue during a tennis match. Sixteen tennis players performed two prolonged simulated tennis matches with low-stiffness or high-stiffness string. Before and immediately after exercise, muscle fatigability was evaluated on the forearm muscles during a maximal intermittent gripping task. Groundstroke ball speeds and the profile of acceleration of the racquet frame at collision were recorded during each match. The peak-to-peak amplitude of acceleration and the resonant frequency of the frame were significantly greater with high- (5060 ± 1892 m/s(2) and 204 ± 29 Hz, respectively) than with low-stiffness string (4704 ± 1671 m/s(2) and 191 ± 16 Hz, respectively). The maximal and the averaged gripping forces developed during the gripping task were significantly reduced after the tennis match with high- (-15 ± 14%, and -22 ± 14%, respectively), but not with low-stiffness string. The decrease of ball speed during the simulated matches tended to be greater with high- than with low-stiffness string (P = .06). Hence, playing tennis with high-stiffness string promotes forearm muscle fatigue development, which could partly contribute to the groundstroke ball speed decrement during the game.