740 EP096 – Effects of previous hamstring strain injury on the corticospinal excitability and cortical inhibition in the biceps femoris muscle

Background Previous studies have suggested that hamstring strain injury leads to activation and strength deficits in hamstring muscles. However, the effects of previous hamstring strain injury on the corticospinal excitability and intracortical inhibition remains unknown. Understanding of the mechanisms contributing to functional deficits observed in athletes with a history of hamstring injury could help develop strategies for prevention of reinjury. Objective To investigate the effects of previous hamstring strain injury on the corticospinal excitability and intracortical inhibition in the biceps femoris muscle. Design Descriptive laboratory study. Setting College athletes. Participants Ten male sprinters with a history of hamstring strain injuries. Interventions We investigated the excitability of the corticospinal pathway during isometric contractions in the biceps femoris muscle both of previously injured and uninjured limbs using transcranial magnetic stimulation. The relationship between the stimulus intensities and amplitude of motor-evoked potentials (recruitment curves) showed sigmoidal curve. We calculated the recruitment curve's maximum slope indicating recruitment gain of the corticospinal pathway, plateau value, and threshold. Additionally, we assessed the silent period duration reflecting degree of cortical inhibition, and compared each parameter between the previously injured and uninjured limbs using independent t-test. Main Outcome Measurements Primarily, the maximum slope, plateau value, threshold, and silent period duration were the measurement outcomes. Results The silent period duration of the biceps femoris muscle significantly decreased in previously injured limb than in non-injured limb (p < 0.05). Meanwhile, the maximum slope, plateau amplitude, and threshold did not differ between the limbs. Conclusions The results showed a decreased cortical inhibition of the biceps femoris muscle in the previously injured limb, indicating that athletes with such previous injuries may encounter more difficulty in controlling the muscle force output. Further research is required to examine the effects of previous injury on motor control of the hamstring muscles.