Effects of Different Approach Directions and Sizes of Selected Tennis Forehand Strokes on Knee Biomechanics

Tennis is a global sport and knee injuries are prevalent, ranging from acute to chronic and minor, to severe. Different directional movements and speeds involved in tennis may lead to a higher chance of injury due to changing loading rates at the knee. This study investigates effects of diagonal and lateral forehand strokes with step or lunge on kinematics and kinetics of the knee on the dominant leg during simulated tennis play. Ten National Tennis Ranking Program (NTRP) players level 4.0 upwards were recruited for the study. A motion analysis system was used to obtain three-dimensional joint kinematics, and force platform to collect ground reaction force (GRF) data. Players performed five trials in four conditions, lateral step, lateral lunge, diagonal step, and diagonal lunge, using a forehand stroke for all four conditions. A two-way repeated measures ANOVA was used, with post-hoc comparisons, with significance set at 0.05 a priori. The results from the study show that there were no significant differences of peak knee extension moment, peak knee abduction moment between the diagonal and lateral forehand shots, either with a step or lunge, or peak abduction moment between approach size in both directions. However, there was a significant difference in knee extension moments depending on approach size in the lateral and diagonal direction, with the lunge approach in each direction being significantly higher than the step. Further study may be required to determine what approach steps and direction movements are more appropriate for players of a standard below NTRP level 4.0, and for a knee OA population.