Kinematic and EMG reactions to imposed interlimb phase alterations during bipedal cycling.

Strong 'neural constraints' synchronizing the step cycles of bilaterally paired limbs in decerebrate cats have been revealed by forcing those limbs to step at different speeds. To determine if humans operate under similar restrictions, we studied subjects pedaling a bicycle ergometer whose coupled cranks imposed continuous change upon interlimb phasing. Unlike the cat, the EMG timing patterns of each leg proved to vary little as a function of phase. Phase change did induce fluctuations in average EMG signal energy, but these were highly idiosyncratic to each muscle. Nevertheless, leg kinematic trajectories remained confined to narrow bounds well within biomechanical limitations. We thus suggest that the trajectory of each leg is actively regulated during pedaling, although the interlimb neural constraints apparent in decerebrate stepping are absent.