THE EFFECTS OF TECHNIQUE VARIATIONS ON KNEE BIOMECHANICS DURING THE SQUAT AND LEG PRESS 887

Abstract

The current study quantified tibiofemoral compressive force, patellofemoral compressive force, and cruciate ligamentous (ACL/PCL) tensile force during a dynamic barbell parallel squat (SQ) and Body Master (MD-117) leg press (LP) using varying stances (narrow and wide), foot angles (straight and turned out 30°), and foot placements (high and low). Ten experienced weight lifters served as subjects, using their 12 repetition maximum weight. A four camera motion analysis system collected 60 Hz video data from reflective markers positioned over bony landmarks, while two AMTI force platforms were used to collect 960 Hz kinetic data. Resultant knee forces were calculated as functions of knee angle utilizing 3-D rigid link models and inverse dynamics. Mathematical muscle models were developed and optimizations procedures utilized in order to estimate tibiofemoral, cruciate ligamentous, and patellofemoral forces. Foot angle and foot placement variations did not significantly effect knee forces. During the SQ and LP peak tibiofemoral, PCL, and patellofemoral forces were approximately 3300N, 2000N, and 4800N, respectively, and occurred near maximum knee flexion. The wide stance (WS) and narrow stance (NS) SQ generated significantly greater tibiofemoral force than both LP exercises throughout most of the knee flexion and knee extension ranges, with the WS SQ generating significantly greater force than the NS SQ. The SQ generated significantly greater PCL tension than both LP exercises, with few significant differences between stance variations. Patellofemoral forces were significantly greater in the WS SQ compared to the LP during knee flexion, while the NS LP produced significantly greater forces than the SQ and WS LP during knee extension. Peak patellofemoral forces were greatest during the NS LP. The greater tibiofemoral forces generated during the SQ may help protect the knee against excessive shear forces. No ACL tension was generated in the SQ and LP, while the SQ generally generated the greatest PCL tension. The greatest patellofemoral forces generated during the NS LP may predispose the patellofemoral joint to increased risk of chondromalacia or osteoarthritis compared to the SQ or WS LP exercises.