Impact of moment arm on torque production of the knee extensors in children.

The joint moment arm (MA) dimension is related to joint torque in adults. However, this relationship remains unexplored in children. In this study, we aimed to determine the relationship between MA and joint torque of the knee extensors in this young population. The quadriceps femoris muscle volume (MV) and knee extensor MA in 20 preadolescent boys (age: 10.7 ± 0.9 years) were measured using magnetic resonance imaging. The knee extensor isometric and isokinetic torques were measured using a dynamometer. The isokinetic torque measurements were performed using slow and fast angular velocities at 60°/s and 180°/s respectively. The knee extensor torque-producing capacities were assessed as the knee extensor isometric or isokinetic torque per the quadriceps femoris MV. The quadriceps femoris MV correlated significantly with all three knee extensor isometric and isokinetic torques (r = 0.513-0.804, p < .05 for all). The knee extensor MA also correlated significantly with the three knee extensor isometric and isokinetic torques (r = 0.701-0.806, p ≤ .001 for all). Furthermore, the knee extensor MA correlated significantly with all three knee extensor torque-producing capacities (r = 0.488-0.701, p < .05 for all). These findings suggest that in addition to adults, greater MA plays an important role in achieving higher joint torque production of the knee extensors in preadolescent boys. This study is the first to determine the impact of MA dimension on joint torque production in children.

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