Aging and physical mobility in group-housed Old World monkeys

Abstract

While indices of physical mobility such as gait speed are significant predictors of future morbidity/mortality in the elderly, mechanisms of these relationships are not understood. Relevant animal models of aging and physical mobility are needed to study these relationships. The goal of this study was to develop measures of physical mobility including activity levels and gait speed in Old World monkeys which vary with age in adults. Locomotor behaviors of 21 old ([Formula: see text] = 20 yoa) and 24 young ([Formula: see text] = 9 yoa) socially housed adult females of three species were recorded using focal sample and ad libitum behavior observation methods. Self-motivated walking speed was 17% slower in older than younger adults. Likewise, young adults climbed more frequently than older adults. Leaping and jumping were more common, on average, in young adults, but this difference did not reach significance. Overall activity levels did not vary significantly by age, and there were no significant age by species interactions in any of these behaviors. Of all the behaviors evaluated, walking speed measured in a simple and inexpensive manner appeared most sensitive to age and has the added feature of being least affected by differences in housing characteristics. Thus, walking speed may be a useful indicator of decline in physical mobility in nonhuman primate models of aging.

Fig. 1

The measurement of walking speed. Marks were made with indelible markers at visible points on various structures throughout the home pens. Each landmark was given an identification (e.g. A, B, C….), and distances between landmarks were measured. Every time a subject passed a landmark they were timed with a stopwatch until they passed another landmark, and time and landmarks were recorded. Walking speed was calculated as distance/time

Fig. 2

Body weight (BW) of young and old adult female cynomolgus, bonnet, and African green monkeys. There was a significant age by species interaction in which older African greens appear lighter than younger, whereas older macaques appear heavier than younger macaques

Fig. 3

Activity levels of young and old adult female cynomolgus, bonnet, and African green monkeys. Activity levels were measured by the per cent of time spent locomoting (traversing space with at least three continuous steps), and did not vary significantly by age

Fig. 4

Types of physical activity of young and old adult female cynomolgus, bonnet, and African green monkeys. Climbing (4a), leaping/jumping (4b) were recorded as frequency per hour. Old monkeys climbed and tended to leap and jump less than younger monkeys

Fig. 5

Walking speed (cm/s) of young and old adult female cynomolgus, bonnet, and African green monkeys. The average of the first five samples of walking speed is depicted. Older monkeys walked 20% more slowly than young monkeys