Modeling Load-Driven Changes in Squat Technique Using a Moment-Limited Joint Framework

The squat is one of the most widely studied multi-joint movements in strength training and biomechanics. Although numerous experimental and computational studies have examined squat kinematics and joint loading, the mechanical mechanisms governing how squat technique adapts to increasing external load remain insufficiently under-stood. Most inverse dynamics approaches assume that the observed motion is mechanically feasible and do not explicitly account for limitations of joint moment capacity. This study proposes a computational framework for analyzing load-dependent adaptations of squat posture under increasing barbell load. The human body is represented as a multi-segment rigid-body system consisting of feet, shanks, thighs, pelvis, and torso. Joint behavior is modeled using nonlinear rotational elements with bounded moment capacity, allowing representation of elastic response followed by progressive softening when critical moments are approached. A reference squat trajectory is first generated kinematically, after which a constrained optimization procedure is applied at each motion frame to determine a mechanically admissible posture under the applied load. Numerical simulations demonstrate that increasing external load leads to characteristic modifications of squat posture, including posterior displacement of the pelvis, increased torso inclination, and redistribution of rotational demand from the knee toward the hip joint. The framework highlights joint moment capacity as a key mechanical constraint governing squat technique and provides a computational tool for studying load-dependent adaptations in human movement.