Author(s): SAKAMOTO, Y., PATAKY, T.C., Institution: KYOTO UNIVERSITY, Country: JAPAN, Abstract-ID: 2296

INTRODUCTION:
Squat is one of the most commonly performed exercises in strength training, conditioning, and rehabilitation [1,2]. While “ideal” forms are often instructed, factors such as skeletal ratios and hip morphology can substantially affect movement strategies [3,4]. Previous studies have primarily focused on local constraints or final posture, with limited attention to effects of kinematic strategies during descent to maximal flexion. The purpose of this study was to examine how differences in initial movement instruction influence subsequent kinematics and joint load distribution throughout the squat.
METHODS:
Twenty-one healthy male adults (age 24.0 ± 4.0 years; body mass 61.9 ± 7.8 kg) performed squats under three conditions: Normal, Knee-initiated, and Hip-initiated. Each trial consisted of a 3-s descent, 3-s hold, and 3-s ascent. Three-dimensional motion capture, force plates, and surface electromyography (sEMG) were used to collect data. Repeated measures ANOVA and Friedman tests were applied to time-series data.
RESULTS:
Movement instructions successfully changed descent-phase kinematics, with significantly increased hip or knee flexion contributions during the first 0–10% of descent for their respective conditions. In the descent phase, Hip-initiated condition delayed knee and ankle flexion, whereas Knee-initiated condition delayed hip flexion but accelerated ankle flexion. During the hold phase, Knee-initiated condition showed significantly larger Center of Pressure (CoP) sway (95% ellipse area and anterior-posterior [AP] standard deviation) compared to Normal. By the end of descent, joint angles in Hip- and Knee-initiated conditions tended to converge toward Normal, but cumulative joint moments (integrated over time) established at the start persisted throughout the descent. Ascent-phase kinematics showed no notable differences between conditions.
CONCLUSION:
Initial movement strategy substantially influences descent and hold-phase kinematics and joint load distribution, while ascent-phase kinematics are largely unaffected. Even when final posture appears similar, internal states may differ depending on early movement patterns. Increased CoP sway in Knee-initiated movements suggests that initial strategy is critical for both performance and injury prevention. These findings highlight the importance of considering early movement processes, in addition to final posture, when defining individually optimized squat strategies.
REFERENCES:
1) Schoenfeld BJ. J Strength Cond Res. 2010
2) Bashir et al. PLOS ONE. 2022
3) Myer GD et al. Strength Cond J. 2014
4) Song K et al. J Orthop Res. 2022