The search for stability on narrow supports: an experimental study in cats and dogs.

Kinematic and coordination variables were studied in two carnivorans, one with known locomotor capabilities in arboreal substrates (cat), and the other a completely terrestrial species (dog). Two horizontal substrates were used: a flat trackway on the ground (overground locomotion) and an elevated and narrow runway (narrow-support locomotion). Despite their different degree of familiarity with the 'arboreal' situation, both species developed a strategy to adapt to narrow supports. The strategy of cats was based on using slower speeds, coupled with modifications to swing phase duration, to keep balance on narrow supports. The strategy of dogs relied on high speeds to gain in dynamic stability, and they increased cycle frequency by reducing swing phase duration. Furthermore, dogs showed a high variability in limb coordination, although a tendency to canter-like coordination was observed, and also avoided whole-body aerial phases. In different ways, both strategies suggested a reduction of peak vertical forces, and hence a reduction of the vertical oscillations of the centre of mass. Finally, lateral oscillation was reduced by the use of a crouched posture.

Steady locomotion in dogs: temporal and associated spatial coordination patterns and the effect of speed.

Only a few studies on quadrupedal locomotion have investigated symmetrical and asymmetrical gaits in the same framework because the mechanisms underlying these two types of gait seem to be different and it took a long time to identify a common set of parameters for their simultaneous study. Moreover, despite the clear importance of the spatial dimension in animal locomotion, the relationship between temporal and spatial limb coordination has never been quantified before. We used anteroposterior sequence (APS) analysis to analyse 486 sequences from five malinois (Belgian shepherd) dogs moving at a large range of speeds (from 0.4 to 10.0 m s(-1)) to compare symmetrical and asymmetrical gaits through kinematic and limb coordination parameters. Considerable continuity was observed in cycle characteristics, from walk to rotary gallop, but at very high speeds an increase in swing duration reflected the use of sagittal flexibility of the vertebral axis to increase speed. This change occurred after the contribution of the increase in stride length had become the main element driving the increase in speed - i.e. when the dogs had adopted asymmetrical gaits. As the left and right limbs of a pair are linked to the same rigid structure, spatial coordination within pairs of limbs reflected the temporal coordination within pairs of limbs whatever the speed. By contrast, the relationship between the temporal and spatial coordination between pairs of limb was found to depend on speed and trunk length. For trot and rotary gallop, this relationship was thought also to depend on the additional action of trunk flexion and leg angle at footfall.