Abstract
PURPOSE: Leg length strongly affects the motion of the leg joints in pedaling. However, many investigations have not considered the influence induced by anthropometric factors. Therefore, we investigated the influence of leg length and segment length ratio on joint motion and electromyographic response during pedaling. METHODS: Subjects were 17 male university students (noncyclists). They performed pedaling at 60 rpm (2.4 w/kg body weight) on an electrically braked bicycle ergometer. The saddle height was adjusted to 98–100% of leg length. The relative crank length was chosen as 18% of leg length(to normalize the difference in leg length among the subjects). The foot was fixed on the pedal axis with two straps. The joint motion and surface electromyography on the left side were recorded. Segment length ratio was determined as a given segment length relative to the sum of three different segment lengths (thigh, shank, and foot) in the same leg. RESULTS: The ranges of each segment length ratio were 0.426-0.458 for thigh, 0.404-0.436 for shank, and 0.119-0.147 for foot. The results of correlation analysis on each item showed that as thigh length ratio increased, the hip and knee joint angles through a crank cycle increased (p<0.01), the velocity of dorsi flexion at a crank angle of 160-270° (denned by the top of the crank cycle as 0°) was higher (p<0.05), and the onset of muscle activation in the knee extensor was earlier (p<0.05) at 315-340°. As the velocity of dorsi flexion at 160-270° became lower, the gastrocnemius lateralis at 160-170° (p<0.05) was more highly activated with no relation to the activity of the tibialis anterior. CONCLUSIONS: The thigh length ratio nearly determined the hip and knee joint angles in the whole crank cycle and was correlated with the level of activation in the knee extensors near 0°. The results suggested that the difference of timing in the activity of knee extensors near 0°may be related to the concurrent “ankling” motion of the contralateral leg. Thus, the individual thigh length ratio determined the strategy of ankling, which may act in fixation of the ankle joint by the planter flexors or dorsi flexors. In many reports, ankling has been discussed relating to the skill of the cyclist. We concluded that the motion and muscle activity during pedaling were influenced by anthropometric factors.
Published Version
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