Effects of External Load on Sagittal and Frontal Plane Lower Extremity Biomechanics During Back Squats

Previous literature suggests the sticking region, the transition period between an early peak concentric velocity to a local minimum, in barbell movements may be the reason for failing repeated submaximal and maximal squats. This study determined the effects of load on lower extremity biomechanics during back squats. Twenty participants performed the NSCA's one-repetition-maximum (1RM) testing protocol, testing to supramaximum loads (failure). After completing the protocol and a 10-min rest, 80% 1RM squats were performed. Statistical parametric mapping (SPM) was used to determine vertical velocity, acceleration, ankle, knee, and hip sagittal and frontal plane biomechanics differences between 1RM, submaximum, and supramaximum squats (105% 1RM). Vertical acceleration was a better discriminative measure than velocity, exhibiting differences across all conditions. Supramaximum squats emphasized knee moments, whereas 1RM emphasized hip moments during acceleration. Submaximum squats had reduced hip and knee moments compared to supramaximum squats, but similar knee moments to 1RM squats. Across all conditions, knee loads mirrored accelerations and a prominent knee (acceleration) to hip (sticking) transition existed. These results indicate that (1) submaximum squats performed at increased velocities can provide similar moments at the ankle and knee, but not hip, as maximal loads and (2) significant emphasis on hip strength is necessary for heavy back squats.