A Comprehensive Kinetic and Kinematic Analysis of the Powerlifting Squat

Powerlifting squats are performed under near-maximal loads with highly individualised technique, yet how kinematics, joint loading, and muscle activation adapt across the squat cycle as relative load increases is not fully characterised. This thesis quantified the time-varying effect of intensity (%1RM) on lower-limb joint angles, net joint moments, and surface EMG during the powerlifting squat in 11 competitive athletes (Italian Powerlifting Federation) performing single-repetition squats at progressively increasing loads. Kinematics (3D motion capture), ground reaction forces (dual force plates), and unilateral EMG were segmented using barbell vertical velocity, processed via inverse dynamics (moments normalised to body mass), and time-normalised to 0–100% of the squat cycle. Load effects were estimated using functional mixed-effects regression with bootstrap rank-based 95% simultaneous confidence bands to identify robust load-dependent phases. Joint-angle adaptations were strongly phase-dependent and often reversed direction across the cycle; the largest practical changes occurred in sagittal-plane flexion/extension, reaching ~10° at the hip/ankle and ~15–20° at the knee per +10%1RM in the most affected phases. Net joint moments scaled more consistently with load: hip flexion/extension moments increased across nearly the entire cycle, while knee moments showed mid-cycle reductions consistent with a redistribution toward a more hip-dominant strategy. Peak kinetic effects occurred in sagittal-plane moments (~0.4–0.6 N·m·kg⁻¹ per +10%1RM at the hip and knee). Normalised EMG generally increased with %1RM for hip- and knee-related muscles (peak ~0.08–0.12 per +10%1RM, ≈8–12 percentage points of maximal activation), whereas oblique EMG showed no robust modulation. Overall, increasing %1RM elicited phase-specific technique adjustments but more consistent increases in mechanical and neuromuscular demand, highlighting the central role of hip extensors near 1RM.