Relationship between knee extensor moment arm and running performance in endurance runners

We previously reported that a longer knee extensor moment arm (MA) is associated with better sprint performance because of increase in knee extensor torque during sprinting. In contrast, a shorter MA is a useful in decreasing energy consumption in muscles, potentially by mitigating the length changes of muscles during joint rotations. In this study, we examined whether a shorter knee extensor MA would be related to better running performance in endurance runners. The knee extensor MA and quadriceps muscle volume (MV) in 42 endurance runners and 14 untrained subjects were measured using magnetic resonance imaging. The knee extensor MA was significantly shorter in endurance runners than in untrained subjects. The knee extensor MA, but not quadriceps MV, was significantly correlated with personal best 5000-m race time in endurance runners. These findings suggest that a shorter knee extensor MA may be advantageous in achieving superior running performance in endurance runners.