Abstract
This study examined the effect of the polar moment of inertia of a tennis racket on upper limb loading in the serve. Eight amateur competition tennis players performed two sets of 10 serves using two rackets identical in mass, position of center of mass and moments of inertia other than the polar moment of inertia (0.00152 vs 0.00197 kg.m2). An eight-camera motion analysis system collected the 3D trajectories of 16 markers, located on the thorax, upper limbs and racket, from which shoulder, elbow and wrist net joint moments and powers were computed using inverse dynamics. During the cocking phase, increased racket polar moment of inertia was associated with significant increases in the peak shoulder extension and abduction moments, as well the peak elbow extension, valgus and supination moments. During the forward swing phase, peak wrist extension and radial deviation moments significantly increased with polar moment of inertia. During the follow-through phase, the peak shoulder adduction, elbow pronation and wrist external rotation moments displayed a significant inverse relationship with polar moment of inertia. During the forward swing, the magnitudes of negative joint power at the elbow and wrist were significantly larger when players served using the racket with a higher polar moment of inertia. Although a larger polar of inertia allows players to better tolerate off-center impacts, it also appears to place additional loads on the upper extremity when serving and may therefore increase injury risk in tennis players.
Highlights
Since the 1980s, the physical characteristics of the tennis racket have been changed drastically by modern designs and materials
The duration was 0.9760.04 s for the cocking, 0.0960.01 s for the forward swing, and 0.2360.01 s for the follow-through of the serve
The aim of this study was to investigate the effects of the racket polar moment of inertia on dominant upper limb joint loads during the tennis serve
Summary
Since the 1980s, the physical characteristics of the tennis racket have been changed drastically by modern designs and materials. The most obvious of the substantial changes in the racket frame is an increase in head size, which accommodates more efficient offcenter impacts [1]. To control for advancements in racket design, the international Tennis Federation limited the frame size, i.e. length and racket head area [2]. Adding mass symmetrically on both sides at mid-height of the racket head increases the polar moment of inertia (Figure 1) and the racket becomes more resistant to the long-axis twisting motions that occur when the ball is impacted on the lateral portions of the racket face [1]. Players who find it difficult to consistently impact the ball in the center of the racket face may be able to increase the efficiency of their racket-ball collision by using rackets with larger polar moments of inertia [2]. There is a paucity of information on the effects of racket specifications, in particular increased racket polar moment of inertia, on upper limb joint loads under playing conditions
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