Knee joint loading in the open and square stance tennis forehands

Abstract

Sandamas, Paul 2013. Knee joint loading in the open and square stance tennis forehands. Department of Biology of Physical Activity, University of Jyväskylä. Master's Thesis in Biomechanics. 80 pages.

The aim of this study was to calculate and compare the resultant forces and moments in the knee joint of the open and square stance tennis forehands. An additional aim was to incorporate the ground reaction forces to shed light on the role of the lower body in aiding pelvic rotation in these two different forehands.

The two types of forehand strokes hit by 7 right-handed university team level tennis players were filmed and the ground reaction forces on each foot were measured simultaneously. A link segment model of the lower limbs was used along with the inverse dynamics approach to calculate the resultant joint forces and moments in both knees during both the forward swing and follow-through phases of the shot. The ground reaction forces and resultant knee joint forces and moments of the open stance (OS) strokes were compared with those obtained for the square stance (SS) forehands.

Although the average swing times, peak racket velocities and peak transverse plane pelvic velocities were similar, significant kinetic differences (P<0.05) were recorded in the knee joints between the strokes. The SS created greater abduction moments in the left knee during the forward swing and follow-through (0.7 and 0.95 Nm/kg) than the OS (0.2 and 0.32 Nm/kg), respectively. The largest external rotation moments were found in the SS left knee during the follow-through (0.31 Nm/kg) and in the OS right knee prior to impact (0.24 Nm/kg). Despite this, significantly (P<0.05) greater ground reaction torque (TZ) was generated by the right leg in the OS stroke before impact (0.27 Nm/kg), than by the left leg in the SS during the follow-through (0.09 Nm/kg).

The data did not support the hypothesis that the peak knee external rotation moments would be greater in the square stance. Analysis of the ground reaction forces together with the knee kinetic and pelvic motion data suggests that the square stance utilises the forward step as an aid to pelvic rotation, whereas; the open stance relies more on the extension, abduction and external rotation of the right leg to aid pelvic rotation.