Comparison of a Low Load Eccentric Training Protocol and a Static Stretching Protocol on Hamstring Muscle Flexibility

The purpose of this study was to compare eccentric strengthening to static stretching for increasing hamstring flexibility. Sixty-three asymptomatic participants were recruited via convenience sampling. Nineteen participants did not meet the inclusion criteria, thus leaving 44 participants. Inclusion criteria included hamstring tightness defined using the passive knee extension test (PKE). Exclusion criteria included a history of any lower extremity injury, including hamstring injury, within the past 12 months. Participants were randomized into one of three groups: Nordic Hamstring Exercise (NHE) eccentric group, static hamstring stretching, or control group. Hamstring flexibility was assessed, via the PKE, at baseline, 3 weeks, and six weeks. Between and within group differences in hamstring flexibility were assessed using a mixed model ANOVA. The analysis yielded a significant time x group interaction (< 0.05). At six weeks, both the static stretching and eccentric group had greater improvements in flexibility compared the control group (p < 0.001). This study adds to the body of research by demonstrating the positive effect of eccentric training on gross muscle length. It revealed the NHE results in similar increases in hamstring flexibility when compared to static hamstring stretching. As a result, either stretching or eccentric training can be used effectively to address hamstring flexibility deficits.