Leg automaticity is stronger than arm automaticity during simultaneous arm and leg cycling

- Subjects performed simultaneous arm and leg cycling.
- Leg cadence variability was barely affected when the subjects attended to arm cycling.
- Arm cadence variability increased when the subjects attended to leg cycling.
- Automaticity of leg cycling is stronger than that of arm cycling.

Recent studies indicate that human locomotion is quadrupedal in nature. An automatic rhythm-generating system is thought to play a crucial role in controlling arm and leg movements. In the present study, we attempted to elucidate differences between intrinsic arm and leg automaticity by investigating cadence variability during simultaneous arm and leg (AL) cycling. Participants performed AL cycling with visual feedback of arm or leg cadence. Participants were asked to focus their attention to match the predetermined cadence; this affects the automaticity of the rhythm-generating system. Leg cadence variability was only mildly affected when the participants intended to precisely adjust either their arm or leg cycling cadence to a predetermined value. In contrast, arm cadence variability significantly increased when the participants adjusted their leg cycling cadence to a predetermined value. These findings suggest that different neural mechanisms underlie the automaticities of arm and leg cycling and that the latter is stronger than the former during AL cycling.