Evaluation of Movement Smoothness of the Upper Limbs in a Ball-Bouncing Task with Changing Speeds

Abstract

The purpose of this study was to compare the variability muscular activities and movement smoothness of the upper limbs during the speed-increase phase of a basketball-bouncing task between experienced basketball players and novices. Participants were nine college basketball players and six novices. The participants were instructed to synchronize their bouncing movements with an auditory signal (100 bpm), and bouncing the ball as fast as possible when a light-emitting diode signal was turned on. During the bouncing task, two-dimensional body kinematics was recorded using a high-speed camera at 100 frames/s and the number of angular jerk (derivative of acceleration) zero-crossings was calculated. The variability of muscular activities was acquired by surface electromyography signals obtained at the shoulder, elbow, and wrist muscles. A muscle co-contraction index (CI) was calculated on the based on the activities of the flexor and extensor muscles of each joint.

The experienced basketball players showed a smaller CI and a smaller number of the angular jerk zero-crossings in the wrist muscles than the novices. These results indicate that the experienced basketball players bounced the ball more smoothly with lower joint stiffness than the novices. In contrast, the novices have “jerky” movements and higher co-contraction than the experienced basketball players in the speed-increase phase. These results suggest that experienced basketball players can control the speed of the ball with lower co-contraction and produce smoother bouncing movements in the speed-increase phase of the task than the novices.