Author(s): PÜRZEL, A., KAUFMANN, P., KOLLER, W., PÖHLMANN, L., BACA, A., KAINZ, H., Institution: UNIVERSITY OF VIENNA, DEPARTMENT OF SPORT AND HUMAN MOVEMENT SCIENCE, Country: AUSTRIA, Abstract-ID: 255

INTRODUCTION:
The squat in powerlifting is executed under standardised conditions, yet elite athletes exhibit marked inter- and intra-individual variability in movement patterns, challenging group-based interpretations of squat mechanics [1]. Musculoskeletal (MSK) modelling allows for detailed estimation of muscle forces (MF) [2]; and although certain general patterns of MF adaptation with increasing intensity have been described, substantial variability in individual force production strategies persists across athletes [3]. Consequently, investigating individual MF contributions rather than group means is essential for athlete-specific technique and training optimisation.
METHODS:
3D motion capture and ground reaction forces were recorded from 29 elite powerlifters (age: 26.1±5.4 years; 1-repetition-maximum (1RM): 2.4±0.4xbody mass (BM)) performing squats at 70 to 90% 1RM. Personalised MSK-models based on the “Catelli”-model [4] were used to estimate MF in OpenSim [2]. Peak forces were normalised to BM and used to calculate MF ratios between hip and knee extensor muscles. Individual MF ratios and changes in MF ratios (i.e., slopes) were derived in order to visualise inter-individual strategies with increasing intensity during the concentric phase and the sticking region. This region is defined as the interval between the initial maximal upwards velocity of the barbell and its first local minimum [5] (i.e. the most challenging part of the squat).
RESULTS:
The knee-to-hip extensor MF ratio decreased significantly from 70% to 90% 1RM (1.25 (IQR 1.16-1.49) to 1.18 (IQR 1.11-1.30); p<0.001). This shift was driven primarily by greater contributions of the single-joint hip extensors (p<0.001). The average change in MF ratio with increasing intensity was negative and significantly different from zero (-0.004±0.005; range: −0.012 to 0.007; p<0.001), indicating a systematic shift toward greater hip-extensor involvement at higher loads. Individual MF relationship changes showed marked heterogeneity (ICC=0.017): 44.8% of the athletes with a hip-dominant pattern at 70% 1RM were becoming even more hip-dominant as intensity increased. 41.4% of athletes shifted from knee- to hip-dominant strategies, whereas knee dominance or reductions in hip dominance were rare (6.9% each).
CONCLUSION:
Individual muscle force strategies varied markedly across athletes. Overall, squats became increasingly hip-extensor-dominant with rising intensity, mainly due to greater involvement of the single-joint hip extensors. Knee extensor dominant strategies were rare. These findings highlight the need for individualised technique and training adjustments. Considering individual muscle-force contribution strategies may help optimise squat performance.

Literature:
1) Kristiansen et al., Hum Mov Sci, 2019
2) Delp et al., IEEE Trans Biomed Eng, 2007
3) Pürzel et al., Scand J Med Sci Sports, 2025
4) Catelli et al., Comput Methods Biomech Biomed Engin, 2019
5) Van den Tillaar et al., J Hum Kinet, 2014