Size of Biceps Femoris Long Head Muscle Is Related to Running Economy in Male Recreational Runners

Although the hamstring muscles play an important role in running, very little is known about the individual contributions of each hamstring muscle (biceps femoris_{long head}, biceps femoris_{short head}, semitendinosus, and semimembranosus) toward running economy. As such, our study examined all the muscles in the hamstring to provide insight into which muscles contribute the most to running economy. Such information can provide insight in designing precise exercise training programs for enhancing running performance. Secondary analysis from our cross-sectional study conducted on 23 male recreational runners examined the relationships between stretch shortening cycle potentiation (via leg press throw), running net VO₂ (inverse of running economy) (at 11.3 km/h), and maximum cross-sectional area of biceps femoris_{long head}, biceps femoris_{short head}, semitendinosus, and semimembranosus was assessed via magnetic resonance imaging. We obtained significant correlations between the maximum cross-sectional area of the biceps femoris_{long head} and log₁₀running net VO₂ (r = −0.52; p < 0.05). Our multiple regression model showed that the maximum cross-sectional area of biceps femoris_{long head} but not stretch shortening cycle potentiation predicted log₁₀running net VO₂ (r = −0.52; p < 0.01). We found no other relationship between any other hamstring muscles and log₁₀running net VO₂. Our findings provide preliminary evidence of the importance of the biceps femoris_{long head} toward running economy. This may be due to the preferential activation of efficient slow twitch muscle fibers of the biceps femoris_{long head}. Additionally, we noted that the biceps femoris_{short head}, semitendinosus, and semimembranosus muscles were not related to running economy in recreational male runners.