Effect of ball size on player reaction and racket acceleration during the tennis volley.

The purpose of this study was to examine the effect of ball size on reaction time (from ball projection to initial racket movement), movement time (from ball projection to ball-racket impact), mean rectified acceleration and vibration frequency of the racket during the impact phase (100 ms duration after ball-racket impact) of the tennis volley. Twenty-nine beginning to intermediate level tennis players performed volleys under 18 experimental conditions including variations in lateral contact location (forehand and backhand), ball type (Penn oversize, Wilson oversize, regular size), and ball speed (fast, medium, slow). A ball machine was shielded so that the subjects could not predict the ball trajectory before it was released from the machine. Outcome measures were determined using a miniature uni-axial accelerometer and a Photogate timing device. ANOVA with repeated measures and Tukey's post hoc tests were used in statistical analyses (p < .025). The reaction times for the fast speed were significantly shorter than the corresponding times for the slow speed and the reaction times for the forehand volley were significantly shorter than that of the backhand volley. The significant interaction in movement time between ball speed and ball type indicates that the benefits of the larger ball (to slow the game down) increase as the ball speed increases. No significant effect of ball type or ball speed, or interactions were found on mean rectified acceleration and vibration frequency. These results suggest that oversized balls would not cause an increased load to the hitting arm while executing a tennis volley.

Change in strength and dexterity after open carpal tunnel release.

Few studies have documented the long-term recovery of hand function after open carpal tunnel release surgery. Grip strength and manual dexterity were measured before and every five weeks up to 25 weeks after open carpal tunnel release in a sample of 11 affected wrists. Dexterity scores prior to surgery were substantially (nearly 3sd) below normative levels. There was a significant (t10=5.45, P<0.001) 37% decrease in grip strength immediately following surgery. Trend analysis of the data indicated a significant second order pattern for the decrease and recovery of grip strength, and a significant linear pattern of recovery of dexterity following surgery. The strength and dexterity tests were effective in documenting changes in function in recovery from open carpal tunnel release surgery, but grip strength and dexterity in these subjects only recovered to pre-operative levels at 25 weeks.

Grip strength and fatigue in junior college tennis players.

Change in grip strength over 30 trials was documented in two samples of junior college tennis players to assess possible fatigue. Eight men and eight women performed 30 maximum-grip strength tests with 25-sec. rests between trials. Significant positive correlations (.38 and .53 for men and women) were observed between grip strength and trials. In practical terms, grip strength did not change over 30 trials in these tennis players. The data suggested that the repetitive gripping patterns used by these players in tennis play resulted in consistent maximum-grip strengths across 30 trials.

Factors affecting force loading on the hand in the tennis forehand.

The effect of preimpact hand forces and impact location on the postimpact force loading on the hand in the tennis forehand drive was examined. Force sensing resistors and strain gauges were mounted on a midsized tennis racket. Three-dimensional cinematography was used to reconstruct the motion of the ball, racket, and upper extremity of two varsity tennis players. One subject performed fifteen strokes using his normal grip while another performed sixteen, eight with a normal grip and eight with a significantly firmer grip. Postimpact peak forces on the hand were significantly (p less than 0.01) related to force at the base of the index finger in preparation for impact and the distance the ball impacted from the longitudinal axis of the racket. Impact location and preimpact force on the hand were found to account for 66% of the variability of postimpact peak force loading in the tennis forehand drive, and are important factors related to force loading in the tennis forehand. Smaller grip forces and rackets minimizing the effect of off-center impacts should be considered as intervention to reduce the risk of tennis elbow.

Comparison of three methods of estimating energy expenditure: caltrac, heart rate, and video analysis.

This study examined the accuracy of a new device (Caltrac) in estimating energy expenditure via acceleration measurements. Energy expenditure of 20 high school students during basketball class activity (average length = 37 min) was estimated using the Caltrac, heart rate recording, and video analysis. Heart rate recording and video analysis estimates of energy expenditure were determined from heart rate, caloric expenditure curves, and an activity rating scale, respectively. The following estimates of caloric expenditure (M +/- SD) were found: heart rate recording = 196 +/- 73 greater than Caltrac = 163 +/- 49 greater than film analysis = 123 +/- 30 kcal (p less than .05). Laboratory simulations of the basketball activity revealed that the Caltrac energy expenditure was not significantly different from the actual energy expenditure (p greater than .05). The heart rate recording and video analysis estimates of energy expenditure were significantly (p less than .05) higher and lower, respectively, than the actual energy expenditure. The Caltrac is a lightweight, low-cost device that provides a relatively accurate estimate of energy expenditure in free-ranging activities, such as basketball.