Influence of Muscle Strength on Nordic Hamstring Exercise Performance

Abstract

Hamstring strain injuries (HSI) are one of the most common non-contact injuries in the athlete population. They can be expensive for professional organizations, as rehabilitation can cost upwards of a few hundred thousand dollars. HSIs also have a very high chance of reinjury of about 30-80%, making it important to find injury prevention methods to combat HSIs. The Nordic hamstring exercise (NHE) has been shown to reduce the risk of hamstring strain injury and reinjury in male athlete populations. Purpose: The purpose of this study was to determine how the muscle strength of the trunk extensors, hip extensors, and knee flexors predicts the knee breakpoint angle of the Nordic hamstring exercise. Methods: 20 recreationally active participants who were familiar with resistance training took part in a series of dynamometer-based strength tests with surface EMGs placed on the hamstrings, gluteus maximus, and the lumbar region of the erector spinae. Knee flexion strength, hip extension strength, and trunk extension strength were measured. Motion sensors were placed after strength testing on the shank, thigh, pelvis, and trunk to calculate joint kinematics and determine the knee breakpoint angle. Results: Mean KBPA for the 20 participants was 62.660±9.540 with no significance between strength and NHE performance (Hamstrings -0.294 p=0.208, Erector Spinae -0.281 p=0.231, Gluteus Maximus -0.251 p=0.285) as well as no significance between activation and performance of the NHE (Semitendinosus peak: -0.184 p=.436 mean: -0.221 p=0.350, Biceps Femoris peak: -0.263 p=0.263 mean: -0.344 p=0.137, Gluteus Maximus peak: -0.043 p=0.858 mean: -0.055 p=0.818, Erector Spinae peak: -0.406 p=0.076 mean: -0.418 p=0.066). Discussion: This study attempted to find the relationship between muscle strength and NHE performance. EMG data were consistent with previous research, specifically when looking at which muscle groups are most active when performing the NHE. Results may have been affected by the population used in the study, possibly confirming past studies that suggest the exercise may be population dependent. Conclusion: With no significant findings, we cannot accept our hypothesis, but future research should be done looking further into the relationship between strength and NHE performance.