Task-related differences in distribution of electromyographic activity within peroneus longus muscle of spontaneously moving cats.

In the hindlimb muscle peroneus longus (PerL) of cats, electromyographic activity (EMG) was recorded from anterior and posterior regions during voluntary motor behaviour. In spite of the fact that this muscle is composed of units that all exert their forces in the same direction, the intra-muscular EMG distribution differed in a marked and reproducible way between different types of motor behaviour. Anterior as well as posterior regions were both strongly active in relation to the swing-phase of stepping. In comparison to this stepping-activity, there was a marked predominance of posterior PerL activity during hindlimb standing (or take-off for a jump) and an equally pronounced predominance of anterior PerL activity when the cat was preparing to land from being lifted (or at the end of a jump). It is suggested that these task-associated differences in EMG distribution reflect topographical aspects of the intraspinal organization of motor tasks.