CIRCADIAN AND INDIVIDUAL VARIATIONS IN DURATION OF SPONTANEOUS ACTIVITY AMONG ANKLE MUSCLES OF THE CAT

This article concerns the spontaneous motor behavior of cat hindlimb m uscles and muscle regions using 24-h electromyographic (EMG) recording s. Previously, we found marked differences in average daily ''duty tim e'' (i.e., the percentage of total sampling time filled with EMG activ ity) between different muscles, or muscle portions. We have now analyz ed systematic differences in duty time between (i) highly active (midd ay) and relatively inactive (midnight) periods, and (ii) individual ca ts. Differences between cats seemed to be associated with differences in motor habits. The midnight reduction in activity was particularly s triking for muscles with a high midday activity. Quantitative differen ces in spontaneous activity (duty time), as compared between active an d inactive periods of the day or among individual cats, were associate d with marked qualitative alterations in the distribution of activity among the sampled muscles, i.e., these quantitative differences could not be described as a simple up-or downscaling of general motor activi ty. (C) 1998 John Wiley & Sons, Inc.