## 4 Discussion
This suggests a reliance on core stability to compensate for lower limb force production deficiencies, leading to reduced power output, which affects stroke speed and accuracy. This pattern indicates a potential risk of kinetic chain breakdown and may be biomechanically linked to tennis elbow injuries [47]. During the FT phase, the elite group exhibited higher activation of the LBF and lower activation of the RTA and RES (\(p<0.05\)). This suggests that they predominantly depend on the biceps femoris for stability, promoting post-stroke balance and seamless movement transitions. This activation pattern aligns with the \"eccentric-priority strategy\", in which eccentric hamstring control mitigates peak joint reaction forces by 19%, improving movement recovery efficiency by reducing reset time by 230 ms. Conversely, the amateur group displayed greater activation of the RTA and RES alongside lower LBF engagement, indicating a stronger reliance on lower leg muscles for compensation and insufficient biceps femoris control over the lower limb. This lower-leg-dominant pattern corresponds with the \"distal compensation hypothesis\", characterized by an ankle-focused stabilization strategy. These findings imply that elite players refine eccentric control of the biceps femoris during the FT phase, enabling more efficient post-stroke body adjustments. In contrast, excessive lower-leg reliance in amateurs may compromise post-stroke stability and delay movement recovery, potentially affecting preparation for the next shot. The elite group exhibited a more refined muscle synergy pattern throughout all phases of the open-stance forehand stroke. They efficiently engaged larger muscle groups (rectus femoris, biceps femoris, gluteus maximus) to generate power while reducing dependence on smaller muscles (tibialis anterior, plantar flexors). This approach improved movement stability and may help enhance kinetic chain coordination during stroke execution. In contrast, the amateur group displayed a more dispersed muscle activation pattern, lacking clear phase-specific characteristics. Their core stability and lower-limb coordination were comparatively weaker, particularly during the BS and FT phases. These limitations could hinder force generation efficiency and disrupt overall movement stability. Although this study did not directly measure movement stability or force output, previous research has indicated that refined muscle synergy patterns contribute to improved athletic performance [24; 28; 48]. Therefore, the elite group's more synchronized muscle activation pattern may reflect a neuromuscular control strategy that facilitates improved stroke coordination and movement efficiency. Furthermore, the elite group exhibited more refined neuromuscular control throughout the FS and FT phases, which may contribute to more coordinated and technically consistent stroke execution. Conversely, the amateur group displayed inconsistent muscle activation patterns and higher variability in movement adjustments, potentially affecting coordination and energy transfer efficiency. To enhance performance in amateur athletes,targeted training of the gluteus maximus and quadriceps can increase lower limb power contribution during strokes while reducing over-reliance on smaller muscle groups. To address deficiencies in FT control, strengthening the biceps femoris can improve post-stroke balance and center-of-mass adjustments, thereby enhancing stroke fluidity and stability. This study analyzed muscle synergy patterns in athletes of different skill levels using EMG data, revealing the role of muscle activation patterns in stroke execution. Several limitations related to the study population and design should be acknowledged. The sample size was relatively small and included only male players. Differences in participants' age, playing experience, body composition, and BMI were not explicitly controlled, which may have introduced variability and limited the statistical power.