Differential Activation Of Medial And Lateral Hamstring Muscles In Loading Challenges: A Pilot Study: 1615: Board #105

Hamstring strain injuries are the most common muscle injury in Australian Rules Football. 80% of these involve the lateral hamstring group. Recurrence rate on return to play is reported to be 30%. Many exercises utilised in rehabilitation treat the hamstring muscles as a single group with sagittal plane exercise. Recent studies have identified differential activation of the medial and lateral hamstring groups in cutting manoeuvres similar to those encountered in Australian Rules Football. PURPOSE: To evaluate a variety of exercise challenges to determine if differential activation of the medial and lateral hamstring muscles can be achieved during rehabilitation. We hypothesised increased specificity may better optimise activation and possibly loading of the lateral hamstring group in particular, which has little in the way of synergists over the hip and knee. METHODS: Healthy adult participants with no history of hamstring muscle injury undertook a variety of isometric exercise challenges in random order. Two of these exercises comprised resisted knee flexion (at 80° knee flexion) in 0° and 45°hip flexion. Further exercises involved a hamstring bridge on a stable or unstable surface (Swiss Ball). A single leg trunk flexion exercise was also included. All exercises were performed with neutral, internal and external rotation of the knee. Activation of the biceps femoris (lateral hamstring) and semimembranosus (medial hamstring) was measured using surface electromyography (EMG) during maximal 5 s isometric holds. RESULTS: Challenges that elicited greatest activation of the lateral hamstring group were a hamstring bridge with external rotation of the hip and knee followed by a hamstring bridge in neutral. Greatest activation of the medial hamstring occurred during prone knee flexion in 0° hip flexion and internal rotation, followed by hamstring bridging on a Swiss ball with internal rotation. CONCLUSION: This pilot study identified hamstring loading challenges that offer greater specificity in activation of the medial and lateral hamstring muscles. These challenges may be useful in targeted rehabilitation of the lateral or medial hamstring muscles. In interpreting our findings it should be noted that activation levels do not necessarily correspond to muscle loads.