Multiple randomized controlled trials and intervention studies consistently demonstrate that targeted stretching regimens significantly improve hamstring extensibility and lower extremity range of motion. Therefore, the claim is well-supported by the current scientific literature.
Every retrieved paper that directly tests the effects of stretching regimens on hamstring and lower extremity flexibility reports statistically significant improvements in range of motion, sit-and-reach performance, or active knee extension. There are no papers refuting the core claim, leading to a verdict of SUPPORTED.