Radial extracorporeal shock wave therapy modulates hamstring stiffness and flexibility in young males with hamstring tightness: a randomized controlled trial

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 P FDR   P FDR  = 0.008, moderate effect | r | = 0.350). Between-group comparisons revealed significantly greater improvements for rESWT in all three measures (all P FDR  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 ( P FDR  = 0.091). Regarding muscle stiffness, significant group × time interactions with large effects occurred across all hamstring sits (all P FDR  η²  = 0.200-0.410). Both groups exhibited significantly reduced stiffness immediately post-intervention (all P FDR   P FDR   P FDR   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.