Experimental study of coordination patterns during unsteady locomotion in mammals.

A framework to study interlimb coordination, which allowed the analysis of all the symmetrical and asymmetrical gaits, was recently proposed. It suggests that gait depends on a common basic pattern controlling the coordination of the forelimbs (fore lag, FL), the coordination of the hindlimbs (hind lag, HL) and the relationship between these two pairs of limbs (pair lag, PL) in an anteroposterior sequence of movement (APS). These three time parameters are sufficient for identifying all steady gaits. We assumed in this work that this same framework could also be used to study non-steady locomotion, particularly the transitions between symmetrical and asymmetrical gaits. Moreover, as the limbs are coordinated in time and also in space during locomotion, we associated three analogous space parameters (fore gap, FG; hind gap, HG and pair gap, PG) to the three time parameters. We studied the interlimb coordination of dogs and cats moving on a runway with a symmetrical gait. In the middle of the runway, the gait was disturbed by an obstacle, and the animal had to change to an asymmetrical coordination to get over it. The time (FL, HL, PL) and space (FG, HG, PG) parameters of each sequence of the trials were calculated. The results demonstrated that the APS method allows quantification of the interlimb coordination during the symmetrical and asymmetrical phases and during the transition between them, in both dogs and cats. The space and time parameters make it possible to link the timing and the spacing of the footfalls, and to quantify the spatiotemporal dimension of gaits in different mammals. The slight differences observed between dogs and cats could reflect their morphological differences. The APS method could thus be used to understand the implication of morphology in interlimb coordination. All these results are consistent with current knowledge in biomechanics and neurobiology, therefore the APS reflects the actual biological functioning of quadrupedal interlimb coordination.