"Previous research has revealed that increased physical activity can decrease the risk of obesity, coronary heart disease, respiratory disease, metabolic diseases like diabetes, anxiety, depression, breast cancer and colon cancer," said Elinor Sullivan, an OHSU graduate student conducting research at the Oregon National Primate Research Center. "Based on the wealth of benefits provided by regular exercise, doctors have often recommended that patients increase their level of physical activity. However, currently the factors that regulate an individual's average daily activity level, and the brain systems involved in regulating activity are not well understood. It is likely that these factors affect how easy it is for individuals to substantially increase activity through voluntarily exercise, and whether some people can more easily increase their activity than others."
To better understand the factors that can impact activity levels, the ONPRC scientists studied 17 female rhesus macaque monkeys housed in single cages compared to 12 female monkeys group housed in large pens (12 ft x 12 ft x 14 ft). The monkeys housed in large pens had more opportunities to forage for food and move around, as well as more chances to interact socially. To accurately measure activity levels, both groups of monkeys wore activity monitors attached to loose-fitting collars.
Data from the monitors in both groups of monkeys revealed that within each group there was great variability in animals' activity levels. The most active animals showed an eight-fold greater activity level than the most sedentary monkeys. However, surprisingly, individual animals' activity levels did not correspond to the size of their living area. In fact, some monkeys living in single cages demonstrated higher activity levels than monkeys living in larger housing areas.
The monkeys in the single cages were further studied for a six-month period and they showed consistent levels of activity through out this time. Sedentary monkeys remained sedentary, and active animals remained active.
A follow-up study was performed with an additional 10 monkeys, which were housed in single cages and then moved to larger group housing. Again, a high degree of individual variability was found in activity level. However, activity level did not significantly change when monkeys were moved between types of housing. Sedentary monkeys remained sedentary even when they had a great deal of space to move around in and companions to interact with, while active monkeys remained active even when they were housed in a smaller space with limited interaction with other monkeys.
"Overall, these findings suggest that it is likely to take a significant conscious effort to change one's level of physical activity and override one's intrinsic inclination to be active or inactive. To state it more plainly, if you're a couch potato, suddenly becoming active may be harder than you think," said Judy Cameron, Ph.D., senior scientist in the divisions of Reproductive Sciences and Neuroscience at the OHSU Oregon National Primate Research Center. "Our current findings build further on work we did last year showing that activity is more predictive of long-term changes in body weight than even diet. With further study, physicians may be able to gauge a person's innate abilities to become more active so they may more effectively provide options to promote weight loss -- for example, the most effective combination of diet and exercise, or the most effective type of exercise."
Future research may help reveal specifically how and when an individual's adult activity level develops. The scientists also hope to determine how genetic makeup impacts activity level, the role of childhood experience in the development of adult activity level, and how current health status such as weight and mental condition, can impact activity level. The current research indicates these are important questions to answer if people are to use the recommendation of increased physical activity as a preventive therapy for a number of serious disease processes.
"It is encouraging that wide differences in activity levels are seen in a species closely related to humans, and that activity can be monitored non-invasively so that scientists can gain a clearer understanding of the factors that lead an individual to be relatively sedentary or relatively active," added Sullivan. "These studies could also be particularly helpful in determining whether exercise in childhood has a lasting influence on adult activity levels and adult health, and if so, in identifying the types of exercise that are most effective in this regard."
The ONPRC is a registered research institution, inspected regularly by the United States Department of Agriculture. It operates in compliance with the Animal Welfare Act and has an assurance of regulatory compliance on file with the National Institutes of Health. The ONPRC also participates in the voluntary accreditation program overseen by the Association for Assessment and Accreditation of Laboratory Animal Care International (AAALAC).