Circadian rhythms of activity in healthy young and elderly humans

Patterns of activity of healthy adult humans were monitored in a controlled environment for several days using a wrist-mounted ambulatory activity meter. Subjects were 15 young males, 14 young females, 17 elderly males and 23 elderly females. Substantial differences in the absolute levels and patterns of daily rest and activity across age groups were observed. The elderly subjects were somewhat more active than the young subjects overall, especially in the early morning. Consistent with their increased levels of daytime activity the elderly subjects reported less sleepiness, especially in the morning, than the young volunteers. The age groups also differed significantly on all circadian parameters. The mean acrophase (peak of a sinusoid fitted to the activity rhythms) of the elderly group occurred at 1326 hr, significantly earlier than in the young group (1513 hr). The amplitude and the mesor (mean level) of the rhythms were both greater in the elderly group. It is uncertain whether these differences reflect changes in behavior that occur as a consequence of the aging process, previously-established differences in the life styles of the different populations studied, or some other factor. These findings suggest that levels and rhythms of daily activity in healthy elderly people are often well preserved and may not deteriorate as readily as had been assumed.