Investigating the Effects of Dry Needling on Hamstring Muscles Flexibility: A Randomized Controlled Trial

Introduction: Flexibility or the ability of a muscle to increase in length is an integral part of musculoskeletal characteristics and is essential in preventing musculoskeletal injuries and increasing functional levels. Hamstring muscles rupture is a common injury. One of the important factors in the occurrence of this injury is poor hamstring muscle flexibility, which because of its stiffened structure, has less ability to quickly increase in length. Some researchers have recently suggested that the dry needling technique could reduce the number of treatment sessions for hamstring muscle tightness and bring faster and more effective results. Accordingly, this study aims to investigate the effect of the application of dry needling through an acupuncture technique on hamstring muscle flexibility. Materials and Methods: The present study is a single-blinded randomized controlled trial in which 16 individuals with bilateral hamstring muscle shortness were randomly allocated into dry-needling and sham-needling groups. The sampling method was non-probability convenience. The outcome measures were the right and left active knee extension range of motion, assessed before and after the first, third, and fifth sessions of intervention. A 2-factor mixed analysis of variance was applied to determine the differences between and within the two groups. Results: Except for the group main effect, time main effect and interaction effect were statistically significant for the right and left active knee extension range of motion (P<0.001). There were differences in behavioral patterns in groups; accordingly, in the real dry-needling group, a significant difference was detected across times. However, in the sham dry-needling group, no significant difference was observed. Conclusion: The application of dry needling into motor points of hamstring muscles in individuals with bilateral hamstring muscles shortness could improve flexibility and increase the range of knee extension after 3 and 5 sessions of intervention because of the therapeutic effects of the dry needling technique in improving the muscle flexibility.