Effects of Different Post-Activation Potentiation Strategies on Forehand Stroke Performance in Elite Squash Players: A Muscle Synergy and Time- Frequency Coherence Analysis

Background Squash is a high-intensity sport requiring rapid directional changes and explosive strokes, placing high demands on neuromuscular coordination. The forehand stroke is a key offensive action, yet its neuromuscular control mechanisms remain underexplored. Post-activation potentiation (PAP) has been shown to acutely enhance explosive performance, but its role in optimizing complex skills such as the squash forehand stroke is still unclear. Methods This study investigated the effects of three intervention modalities—deep squat training, elastic band training, and neuromuscular electrical stimulation (NMES)—on the neuromuscular control patterns during squash forehand strokes. Fourteen muscles of the lower limbs, trunk, and upper limbs were recorded using surface electromyography (EMG). Muscle synergies were extracted using non-negative matrix factorization, while intermuscular coherence was calculated with short-time Fourier transform. The number of synergies, synergy weights, activation duration, and coherence area across α, β, and γ frequency bands were analyzed using repeated-measures ANOVA or Friedman tests. Results No significant differences were found in the number of synergies (VAF > 0.9) or in activation duration across conditions (p > 0.05). However, significant differences in synergy weights were observed among groups. Squat training increased pectoralis major activation compared to band training (p = 0.040), while NMES selectively enhanced activation in deltoid, gluteus maximus, and gastrocnemius medialis. Coherence analysis showed that NMES significantly increased α- and β-band coherence in several muscle pairs, whereas squat and band training enhanced γ-band coherence between trunk–lower limb muscles. Conclusions These findings suggest that while the overall modular structure of squash forehand strokes remains stable, different interventions induce distinct neuromuscular adaptations. NMES enhances central–peripheral coupling through selective muscle activation, whereas squat and band training primarily improve kinetic chain coordination and dynamic stability. This study provides novel insights into the neural control mechanisms of squash strokes and practical guidance for training strategies.