David Sandler

Correlation Analyses and Regression Modeling between Isokinetic Testing and On-Court Performance in Competitive Adolescent Tennis Players

Tennis requires skill, physical attributes, and strategy. Ball velocity and placement are two of the most important components in winning the faster-paced modern game. Although isokinetic testing has been used to evaluate physical characteristics and injury potential in tennis players, few studies have compared isokinetics and on-court performance. Such a comparison would help establish links between speed-specific properties of functioning muscles and stroke production and could affect overall training strategy. This study compared isokinetic peak torque (PT), average power (AP), and total work (TW) during specific testing patterns correlated with ball velocity or stroke accuracy during the service, forehand, and backhand and developed predictive equations for each stroke using these variables. Thirty-five players, aged 13–18 years with at least 4 years playing experience, were evaluated using internal and external shoulder rotation, leg extension, and diagonal throwing motions. Ball velocity was measured using a radar gun. Accuracy was evaluated on the basis of shot position and depth. Significant correlations were found between ball velocity and a number of isokinetic variables, while no significant correlations were observed with shot accuracy. Significant isokinetic variables for each stroke were entered into regression models. One isokinetic speed sufficiently predicted ball velocity for each stroke, since no increase in predictive capacity was observed with the addition of other isokinetic parameters. We conclude that isokinetics at testing speeds between 1.57 and 4.71 rad·s-1 can effectively predict ball velocity, but not accuracy, and that our results may be helpful in planning strategies for training and rehabilitation.

PEAK POWER, GROUND REACTION FORCE AND VELOCITY DURING THE SQUAT EXERCISE PERFORMED AT DIFFERENT LOADS

This study examined the changes in peak power, ground reaction force and velocity with different loads during the performance of the parallel squat movement. Twelve experienced male lifters (26.83 ± 4.67 years of age) performed the standard parallel squat, using loads equal to 20, 30, 40, 50, 60, 70, 80, and 90% of 1 repetition maximum (1RM). Each subject performed all parallel squats with as much explosiveness as possible using his own technique. Peak power (PP), peak ground reaction force (PGRF), peak barbell velocity (PV), force at the time of PP (FPP), and velocity at the time of PP (VPP) were determined from force, velocity, and power curves calculated using barbell velocity and ground reaction force data. No significant differences were detected among loads for PP; however, the greatest PP values were associated with loads of 40 and 50% of 1RM. Higher loads produced greater PGRF and FPP values than lower loads (p = 0.05) in all cases except between loads equal to 60–50, 50–40, and 40–30% of 1RM for PGRF, and between loads equal to 70–60 and 60–50% of 1RM for FPP. Higher loads produced lower PV and VPP values than lower loads (p < 0.05) in all cases except between the 20–30, 70–80, and 80–90% of 1RM conditions. These results may be helpful in determining loads when prescribing need-specific training protocols targeting different areas of the load-velocity continuum.