Kinematics of treadmill galloping by cats: III. Coordination during gait conversions and implications for neural control

Abstract

Two previous reports described steady-state galloping by cats, in which the footfall pattern was invariant for a number of successive strides at one velocity. There were three such patterns: rotatory galloping, transverse galloping, and the half bound. This final report concerns mixed galloping on a treadmill, in which the cat converted from one to another of the three gallops from one stride to the next. Cinematographic measurements were taken of conversions that occurred at speeds from 2.0 to 4.6 m/sec. The conversions were in almost every instance flawless, so that each individual stride (a cycle of movement by the four limbs) was readily distinguished as a typical rotatory or transverse gallop or a half bound. Placement order of the two hindlimbs, or the two forelimbs, or both, shifted. Conversions were accomplished by an average increase of 50–100 msec, or decrease of 50 msec, from the usual 200-msec-long swing (up) duration, since stance (down) durations were unchanged. The normal swing, then, is under more flexible neural control than has previously been believed possible. From an examination of a number of interlimb timings, it was concluded that in every expression of galloping by cats on a treadmill a complete stride is demarcated by successive descents of the trailing (rear) hindlimb. This four-limb ensemble is subdivided into paired movements of the hindlimbs and also the forelimbs, each pair also being marked initially by descent of the trailing limb. Selection of left or right limbs as trailing or leading (front) may be arbitrary, may prevent fatigue in individual limbs, or could offset roll at high speeds.