The Immediate Effect of Static Hamstring Stretching on Dynamic Balance and Gait Biomechanical Variables in Athletes With Hamstring Tightness: A Preliminary Study

Flexibility is an essential component of muscle function, and insufficient muscle flexibility may lead to muscle injuries. Decreased hamstring flexibility is one of the frequently reported risk factors for a hamstring strain and diminished athletic performance. Stretching is a commonly used intervention for increasing muscle length. There is a lack of evidence concerning the possible effects of hamstring stretching in balance and gait biomechanics. So, this study was designed to investigate the potential effects of static hamstring stretching on the range of motion (ROM), dynamic balance, and biomechanical variables of gait in athletes with hamstring tightness.

This study is a single-group, pretest-posttest clinical trial performed on semi-professional female athletes. Twelve female athletes aged 20 to 35 years with bilateral hamstring tightness received a single session of unilateral static hamstring stretching on their randomly selected side. All subjects were assessed for straight leg raise, popliteal angle (using standard goniometry), perceived hamstring tightness (using a visual analog scale). They completed single-leg standing and 15-m walking and running tasks before and immediately after the intervention. The biomechanical parameters, including gait-line length, swing duration, and stance duration in walking tasks, maximum total force and mean total force in running task, and center of pressure (COP) displacement and standard deviation during balance task were measured using OpenGo sensor insole system. The pre-post values were compared using the paired sample t-test, and the level of significance was 0.05.

The values for straight leg raise and popliteal angle significantly increased (P<0.05) compared with the baseline, while perceived tightness significantly decreased following stretching (P<0.001). The amplitude (P₌0.006) and standard deviation (P₌0.016) of COP displacement in the mediolateral direction during the single leg stance balance task were significantly decreased after the intervention. Stance duration in slow walking (P₌0.004), as well as stance duration (P₌0.012) and swing duration (P<0.001) in fast walking, were significantly decreased (P<0.05) after stretching. No change was observed in gait biomechanical variables during the running test (P>0.05).

The results of this study indicate that static hamstring stretching can be a promising intervention not just for increasing hamstring flexibility but also for improving balance ability.