Regular Stretch Does Not Increase Muscle Extensibility: a Randomized Controlled Trial

The purpose of this randomized controlled trial was to determine whether regular stretch increases hamstring muscle extensibility. Sixty healthy individuals were randomly allocated to an experimental or a control group. The experimental group attended supervised stretch sessions where they stretched the hamstring muscles of a randomly allocated leg for 30 min five times a week for 6 weeks. The control group did not attend any stretch sessions during this period. No participants withdrew from the study. A purpose built device was used to measure passive hip flexion during a straight leg-raise manoeuvre with the application of a standardized and non-standardized stretch torque. The stretch intervention did not increase passive hip flexion when measured with a standardized stretch torque [mean treatment effect=-1 degrees; 95% confidence interval (CI)=-3 to 2 degrees]. It did, however, increase passive hip flexion when measured without a standardized stretch torque (mean treatment effect=10 degrees, 95% CI=6-14 degrees). Six weeks of sustained 30-min daily stretch does not increase the extensibility of the hamstring muscle of healthy individuals. It does, however, improve stretch tolerance leading to increased joint range of motion without any actual improvements in muscle extensibility.