• aging;
  • insulin;
  • lean body mass;
  • metabolic rate;
  • physical activity

The purpose of this study was to examine the relationship of age to body composition, glucoregulation, activity, and energy expenditure in male and female rhesus monkeys. The animals were studied in three groups, young adults (YA, 7–9 years), middle-aged adults (MA, 13–17 years), and older adults (OA,>23 years) adults. OA had a lower ( P<0.05) lean body mass than the YA and MA. OA also had the lowest values (P<0.06) for energy expenditure (kJ/minute). Age-related differences (P<0.05) were observed in time spent resting and moving. The OA spent the most time resting and the least time in vertical movement. There was a trend towards an age-related decrease in acute insulin response to glucose, while other glucoregulatory parameters were not changed with age. These results are similar to findings in humans, providing further evidence that the rhesus monkey is an appropriate model of human aging.