Effects of the hamstring group on knee joint stress during jump landings

The focus of this project was to examine both experimentally and mathematically the mechanical loadings to the knee joint during jump landing activities and determine if the inclusion of the hamstring group in the biomechanical model caused an increase in knee joint forces. Previous studies only included the gastrocnemius. Five healthy and active male subjects were involved in this study. Experimental protocol consisted of three test conditions composed of ten trials each involving a stair descent from a riser height of 15 cm and jump landings from heights of 50% and 100% of the subject's maximal vertical jump height. Ground reaction forces and kinematic data were obtained. A biomechanical model of the knee joint was developed to include the mechanical characteristics of the hamstring group and this model was used to analyze the knee joint kinetics. It was determined that there was an increase in antagonistic muscle activity provided by the addition of the hamstring group to the biomechanical model and a subsequent increase in patellar tendon force was also observed. A patellar tendon force increase of 6.1%, 5.30%, and 4.0% for conditions one, two, and three respectively were when only the gastrocnemius was included into the model. However, an increase of 4.9%, 6.5%, and 8.5% for conditions one, two, and three respectively were observed with the inclusion of the hamstring group.