Overground locomotion in intact rats: interlimb coordination, support patterns and support phases duration.

The interlimb coordination during overground locomotion was analysed in intact rats, using the method of contact electrodes (Górska et al. 1998). It was found that in animals moving with a speed ranging from 10 to 78 cm/s (step cycles 685 to 215 ms, respectively) the interlimb coordination was characterized by homologous phase shifts close to 0.5 and much shorter diagonal than lateral phase shifts. These features corresponded to symmetrical gait with diagonal sequence and diagonal couplets (Hildebrandt 1976). Shortening the step cycle changed the gait from a walking trot (duty factor > 0.5) into a running trot (duty factor < 0.5). Correspondingly, the support patterns in the four-legged step cycles, i.e., the sequence of phases of support on various limbs changed: the support on diagonal limbs persisted but the three-limb support was replaced by one-limb support and the support on homolateral limbs by phases of flight. For each phase of support the relationship between its absolute and relative durations and the step cycle duration is being described. The paper explains the variability of support patterns described in the literature. The picture of locomotion obtained in intact rats will be used as a template for studying locomotor control deficits after CNS lesions.