The growing popularity of powerlifting, which consists of the squat, bench press, and deadlift, calls for biomechanically comprehensible coaching strategies. Understanding the muscle forces at work can play a key part in this endeavor. Therefore, the aim of this study was to investigate the effects of increasing intensity in the squat on muscle forces in elite powerlifters. Twenty-nine top-ranked powerlifters from the Austrian team (age: 26.1 ± 5.4 years; 1-repetition-maximum (1-RM): 2.4 ± 0.4 × body mass) performed squats at 70%, 75%, 80%, 85%, and 90% of their 1-RM. Force plates and 3D motion capture data were used to estimate muscle forces utilizing musculoskeletal models in OpenSim. Muscle forces significantly changed with increased intensity, particularly in the gluteus maximus and semitendinosus, which showed the greatest relative increase in muscle force. The vastii muscles exhibited the highest absolute muscle forces. Notably, the hamstrings, calf, and vastii muscle forces barely increased during the deepest and most challenging region of the squat (the sticking region) with increasing intensity. Furthermore, no correlation was found between the athletes' performance level and the ratio of single-joint to multijoint hip extensor muscle forces. These findings highlight the importance of focusing on hip-dominant techniques when squatting with high intensities and supplementary training for knee extensors to optimize performance.
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