Radial extracorporeal shock wave therapy modulates hamstring stiffness and flexibility in young males with hamstring...

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.

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.

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  < 0.001). The control group improved significantly only in SRT (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  < 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 (P_FDR  = 0.091). Regarding muscle stiffness, significant group × time interactions with large effects occurred across all hamstring sits (all P_FDR  < 0.001, η² = 0.200-0.410). Both groups exhibited significantly reduced stiffness immediately post-intervention (all P_FDR  < 0.001); however, only the rESWT group maintained significant reductions at 5 minutes post-intervention (all P_FDR  < 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 P_FDR  < 0.05).

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.