Coordination between arm and leg movements during locomotion

To evaluate the contrasting dynamical and biomechanical interpretations of the 2:1 frequency coordination between arm and leg movements that occurs at low walking velocities and the 1:1 frequency coordination that occurs at h igher walking velocities, the authors conducted an experiment in which they quantified the effect of walking velocity on the stability of the frequenc y and phase coordination between the individual limb movements. Spectral an alyses revealed the presence of 2:1 frequency coordination as a consistent feature of the data in only 3 out of 8 participants at walking velocities r anging from 1.0 to 2.0 km/h, in spite of the fact that the eigenfrequencies of the arms were rather similar across participants. The degree of interli mb coupling, as indexed by weighted coherence and variability of relative p hase, was lower for the arm movements and for ipsilateral and diagonal comb inations of arm and leg movements than for the leg movements. Furthermore, the coupling between all pairs of limb movements was found to increase with walking velocity, whereas no clear signs were observed that the switches f rom 2:1 to 1:1 frequency coordination and vice versa were preceded by loss of stability. Therefore, neither a purely biomechanical nor a purely dynami cal model is optimally suited to explain these results. Instead, an integra tive model involving elements of both approaches seems to be required.