Motor control mechanism underlying pedaling skills: an analysis of bilateral coordination in the lower extremities

In the field of competitive cycling, non-traumatic injuries arising from muscle fatigue have been recognized as a significant problem. Although muscle coordination of the lower extremities is key to achieve high efficiency in pedaling, only a few prior studies have quantified the bilateral coordination of both legs. This quantification could contribute to the understanding of how enhanced pedaling skills may help to reduce muscle fatigue. The aim of this study was to investigate the mechanism underlying inter-lower limb coordination, which should serve to extend the understanding of pedaling skills further. First, 11 healthy males were instructed to pedal for 30 s under a 150-W exercise load and at cadences of 70, 90, and 110 rpm. Next, we investigated the synergistic activity—known as muscle synergy—of both the left and right legs based on the time frequency components of surface electromyography, along with the crank rotation angle during the pedaling exercise. The results indicate that the muscle synergy of bilateral muscle coordination reflects the motor adaptation to pedaling rate during cycling, and the functional roles of the left and right legs differ with changes in cadence and cycling experience. In conclusion, the motor control mechanism underlying pedaling skills is explained by the bilateral muscle coordination related to actions, such as pushing a pedal down using one leg, while pulling the other pedal up using the other leg during pedaling. This conclusion casts doubt on investigations into the efficiency of the pedaling done by a single leg.