HAMSTRING INJURIES CAUSE DIFFERENTIAL MUSCLE ACTIVITY AFTER REHABILITATION

Bourne, M. N., Opar, D. A., Williams, M. D., Najjar, A. A., & Shield, A. J. (2013). Hamstring muscle activation during the nordic hamstring exercise and the impact of previous strain injury. Medicine & Science in Sports & Exercise, 45(5), Supplement abstract number 652.

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This study determined 1) the spatial patterns of hamstring muscle voluntary activation during the Nordic hamstring exercise, 2) whether, following a return to the sport, previously injured hamstring muscles display deficits in voluntary activation compared to uninjured contralateral muscles during the NHE, and 3) whether athletes with a previous hamstring strain injury display persistent alterations in muscle morphology.

Healthy and recreationally active males (N = 10) with a history of unilateral hamstring strain injury were tested on two occasions 8 days apart (1 day) using an observational retrospective study design. Functional MRI was performed on each Ss thighs before and after 6 sets of 10 repetitions of the Nordic hamstring exercise. For all hamstring muscles (biceps femoris long-head, biceps femoris short-head, semitendinosus, semimembranosus, transverse) relaxation times were measured at rest and immediately after the Nordic hamstring exercise and cross-sectional area was measured at rest.

For the uninjured limb, the percentage increase in traansverse values for the semitendinosus was significantly greater than for the biceps femoris long-head, biceps femoris short-head, and semimembranosus. Ss with a previous hamstring strain injury to the biceps femoris long-head (N = 7) displayed a significantly lower percentage increase in transverse values compared to the uninjured contralateral biceps femoris long-head. However, there was no significant difference in the mean biceps femoris long-head observed between muscles in the previously injured and uninjured limbs.

Implication. During the Nordic hamstring exercise, the semitendinosus of healthy uninjured limbs is selectively activated. Further, previously injured biceps femoris long-head muscles display deficits in voluntary activation when compared to uninjured contralateral biceps femoris long-head muscles, which are not associated with any significant between-limb differences in muscle cross-sectional area.

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