Potentiated Biceps Femoris Positively Contributes To Running Economy In Recreational Runners

PURPOSE: Contribution of different muscles toward stretch shortening cycle potentiation and performance measures dictated by stretch shortening cycle potentiation is an area of active research. For example, well-established evidence shows that the medial vs lateral head of gastrocnemius is critical for greater stretch shortening cycle potentiation and its resultant enhanced motor performance. Little is known about the contribution of the biceps femoris muscle toward stretch shortening cycle potentiation. Such information is important to know because the biceps femoris is critical for athletic performance. METHODS: Secondary analysis from our cross-sectional study conducted on 19 recreational runners examined the relationship between stretch shortening cycle potentiation (via jump and leg press throw), running economy (@7 miles/hour) and muscle cross sectional area assessed via magnetic resonance imaging. RESULTS: We obtained significant correlations between the muscle cross sectional area of the long head of the biceps femoris and a) running economy (r = -0.63; p < 0.01), b) potentiated jump velocity (r = 0.54; p = 0.02) and potentiated leg press throw velocity at initial 10 ms of the concentric contraction (r = 0.512; p < 0.03). We also observed significant correlations between running economy and muscle cross sectional area of the a) Gracilis (r = -0.47; p < 0.05) and b) Sartorius (r = -0.51; p < 0.02). Our multiple regression model showed a significant relationship only between the long head of the biceps femoris and running economy (r = -0.63; p < 0.01). Our regression model yielded no other relationships between any muscle and running economy. CONCLUSIONS: Our findings provide preliminary evidence of the importance of the long head of the biceps femoris toward running economy, possibly via stretch shortening cycle potentiation. Since the long head bicep femoris is the only muscle independently related with stretch shortening cycle potentiation after controlling for Gracilis and Sartorius, and that the long head bicep femoris is the only hip extensor, it is possible that stretch shortening cycle potentiation is occurring at the hip. In addition, weak long head bicep femoris may contribute to increased risk of hamstring injury during activities that require stretch shortening cycle potentiation at the hip.