Acute Effects of Static Stretching and Its Combination with Menthol Gel on Squat Jump Performance at Two Initial Knee Joint Angles
(Yi Peng, Ming Li, Hao Li, Xinpeng Gao)

This study investigated the effects of static stretching (SS) and its combination with menthol gel on lower limb muscle activation, synergistic patterns, and squat jump (SJ) performance at two knee starting angles (90° and 120°). Twelve participants completed a randomized crossover protocol across three sessions, each involving SJ trials under different intervention conditions. Data were collected via a 3D motion capture system, EMG, and a force plate. EMG data were analyzed using principal component analysis and amplitude calculations, while jump height, ground contact time, peak ground reaction force (GRFpeak), and the rate of force development (RFD) were derived from kinematic and kinetic data. Results showed no significant changes in average EMG amplitude with SS or menthol gel (p > 0.05). However, SS at 120° significantly altered muscle synergy (p < 0.001, d = 2.02), increased jump height (p = 0.002, d = 0.59), and reduced ground contact time (p = 0.005, d = 1.15), GRFpeak (p < 0.001, d = 1.59), and the RFD (p < 0.001, d = 1.47). Menthol gel offset these changes. Additionally, joint angle influenced all performance metrics (p < 0.05). These findings suggest that while SS can enhance jump height at certain joint angles, it may hinder explosive force output, and combining it with menthol gel can mitigate such drawbacks.