Influence of stance width and toe direction on medial knee contact force during bodyweight squats

Squats are frequently performed to strengthen the quadriceps (Quad) and gluteus maximus (GM) in sports and clinical fields. Since the squat itself produces a large knee contact force, clarifying the relationship between the squat techniques and the knee contact force is important. However, the influence of different squat techniques on the medial knee contact force (KCFmed), which would result in knee disease, remains unclear. This study aimed to investigate the influence of various squat techniques on KCFmed during bodyweight squats. Since muscle strengthening by the squat is inevitable, we additionally aimed to explore the effect of a different squat technique on the quadriceps (Quad) and gluteus maximus (GM) forces. Twelve healthy adults performed squats with different stance widths (narrow stance, NS; middle stance, MS; and wide stance, WS) and different toe directions (0° of forefoot abduction - NEUT and 30°forefoot abduction - OUT). The KCFmed, Quad force, and GM force were computed using a musculoskeletal model with marker trajectories and ground reaction forces. The KCFmed in NS was significantly larger than that in MS and WS, and KCFmed in OUT was significantly larger than that in NEUT. The Quad force in OUT was significantly larger than that in the NEUT, and the GM force significantly became larger as the stance width became narrower. These findings suggest that squats in MS and NEUT may be suitable for reducing KCFmed while maintaining the Quad and GM forces.