Publications

Introduction: The hamstrings are essential for sports and daily activities, yet high stiffness and reduced flexibility increase injury risk. Existing relaxation techniques may be ineffective or impractical in clinical settings. This study investigated the immediate effects of radial extracorporeal shock wave therapy (rESWT) on hamstring stiffness and flexibility in individuals with hamstring tightness, providing preliminary evidence for its therapeutic potential for hamstring tightness.

Methods: In total, 131 participants with hamstring tightness were randomized to receive either active rESWT (n = 66) or sham control intervention (n = 65). Flexibility was assessed using the sit-and-reach test (SRT), active knee-extension test (AKE), and active straight leg raising test (ASLR), measured pre-intervention and 5 minutes post-intervention. Muscle stiffness was measured using MyotonPRO at 25% (upper), 50% (middle), and 75% (lower) of the line connecting the ischial tuberosity and the medial/lateral femoral epicondyles, evaluated pre-intervention, immediately post-intervention, and 5 minutes post-intervention.

Results: For flexibility, the rESWT group demonstrated significant, large-effect improvements in SRT (|r| = 0.738) and ASLR (|r| = 0.848) performance, along with a reduction in knee-extension deficit (AKE, |d| = 1.584) (all PFDR < 0.001). The control group improved significantly only in SRT (PFDR = 0.008, moderate effect |r| = 0.350). Between-group comparisons revealed significantly greater improvements for rESWT in all three measures (all PFDR < 0.001; moderate-to-large effects: SRT |δ| = 0.373, AKE |d| = 1.858, ASLR |δ| = 0.683). Notably, post-intervention SRT raw scores reflecting final performance showed no significant between-group difference (PFDR = 0.091). Regarding muscle stiffness, significant group × time interactions with large effects occurred across all hamstring sites (all PFDR < 0.001, η² = 0.200-0.410). Both groups exhibited significantly reduced stiffness immediately post-intervention (all PFDR < 0.001); however, only the rESWT group maintained significant reductions at 5 minutes post-intervention (all PFDR < 0.001). The rESWT group exhibited significantly lower stiffness than the controls both immediately and 5 minutes after intervention at the 50%/75% semitendinosus and 75% biceps femoris (all PFDR < 0.05).

Conclusion: rESWT produces immediate and 5-minute short-term reductions in mid-to-lower hamstring stiffness and improves hamstring flexibility, suggesting potential for the immediate management of hamstring tightness.

Keywords: flexibility, hamstrings, radial extracorporeal shock wave therapy, rehabilitation, stiffness

This study found that rESWT may yield immediate effects in young males with hamstring tightness. It could reduce muscle stiffness in the mid-to-lower hamstring regions within a 5-minute short-term and improve hamstring flexibility, as reflected by SRT, AKE, and ASLR. Additionally, although there were no significant between-group differences in post-intervention raw SRT scores, the rESWT group showed substantially greater improvements in change magnitude than the control group. These findings tentatively suggest that rESWT has potential benefits for relieving hamstring tightness, modulating muscle mechanical properties, and enhancing posterior lower-extremity chain flexibility. Limited by the immediate and 5-minute short-term observation period and single sample source, issues such as the long-term efficacy and optimal intervention parameters of rESWT still require further validation through large-sample, long-term follow-up, multi-parameter controlled randomized studies. In future research, we will conduct long-term efficacy follow-ups, expand the sample sources, and combine other assessment methods (such as shear wave elastography or electromyography) to provide more comprehensive objective evidence for the effect of rESWT on improving hamstring tightness.