The Hidden Link in the Kinematic Chain: The Influence of the Tossing arm on Head and Serve Kinematics in Tennis.

The control and placement of the ball toss are critical features of the tennis serve. Whereas much attention has been given to the ball's trajectory, the motion of the tossing arm has been overlooked. This study aimed to describe the kinematics of the tossing arm and its impact on full-body kinematics and serve performance. Ten high-performance male tennis players were studied using a 10-camera, 250 Hz VICON T-series motion analysis system capturing full-body, racquet, and ball kinematics. Each participant executed ten maximum effort first serves with instructions to (i) serve normally, (ii) adduct the tossing arm early and (iii) adduct the tossing arm late. While head kinematics remained unaffected by the serve condition, the ball toss was higher and further forward in both altered conditions, increasing serve duration (p < 0.001). Players compensated by extending the preparation phase's proportion of the serve by 4.3% in both conditions. Serve trajectory was ∼3° steeper downwards (p < 0.001) in the early condition and ∼1° flatter (p = 0.020) in the late condition than participants' normal serve. In summary, alterations to the tossing arm elicited the expected changes in the serve's post-impact ball trajectory, but coaches must monitor several unintended consequences.