The cat step cycle: Electromyographic patterns for hindlimb muscles during posture and unrestrained locomotion

Abstract

The telemetered electromyographic activity (EMG) of select hindlimb muscles of unrestrained cats during standing, walking, trotting, and galloping have been recorded. Simultaneous cinematographic records permitted close correlation of muscle activity and locomotor behavior. In general, the pattern of extensor activity of the ankle, knee, and hip during locomotion is fairly consistent, while that of the flexors is more variable. Changes in basic EMG patterns from walk, to trot, to gallop are most evident in the two‐jointed muscles associated with the knee and hip. Progressively greater variation of activity onset and cessation can be seen among extensor muscle groups from the walk, to trot, to gallop. Co‐activation of the joint extensors and flexors, especially of the hip, at the end of the stance phase (E 3) is slight in the walk, moderate in the trot, and considerable in the gallop. These EMG changes are necessary to meet the demands imposed upon the musculature at the faster gaits, particularly galloping, which include limb rigidity as related to loading, momentum as related to the limb's directional change from the stance phase to the swing phase, and lower spinal movements. The peroneal muscles of the ankle and the gluteal muscles of the hip show extensor activity and act as joint stabilizers during locomotion. Both biceps femoris anterior muscle and biceps femoris posterior muscle show consistent hip extensor patterns at all gaits. During quiet standing, extensor activity about the knee, ankle, and metatarsophalangeal joints is evident; but the hip extensor and flexor musculature is remarkably silent. EMG data for unrestrained cats are compared to those of dogs on a treadmill (Tokuriki, '73a,b, '74; Wentink, '76) and those recorded from decerebrate cats (mesencephalic preparation) during controlled locomotion (Gambaryan et al., '71). The EMG patterns from decerebrate cats are more consistent at the walk and gallop within functional groups of muscles at the ankle, knee, and hip than the EMG patterns observed in unrestrained cats or animals moving on a treadmill.