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Have you wondered why it's hard to start an exercise program? Researchers studying monkeys have found that whether you're active or not seems to be a pretty deep-seated habit. This ScienCentral News video has more.
"Some monkeys are very sedentary during the day and other monkeys are up to eight to 10-fold more active, day after day after day," says OHSU's Judy Cameron, a professor of behavioral neuroscience.
As they reported at the annual meeting of the Society for Neuroscience, the researchers put motion-measuring devices on adult monkeys' collars to monitor their daily activity. "These are three-way accelerometers measuring movement in all three directions," she explains. "[They are] about the size of a wristwatch, so they can be very non-invasively put on a collar of an animal and the animal is very comfortable wearing them." This allowed the researchers to record the animals' activities twenty-four hours a day.
Cameron and her colleagues decided to study monkeys because of their similarity to humans. It's difficult to translate activity studies done in more common lab animals, like mice, into meaningful information for people. "Rodents like to run for hours and hours at a time, and they may run thousands of rotations a night. It's hard to know what that's equivalent to in people — would it mean running a huge number of miles a day?" Cameron says. "So you want to use a species that would be more comparable to humans." As she explains, monkeys have similar patterns of natural movement to people, which include playing, sitting around, and socializing.
It's sometimes difficult to get a direct picture of human activity level because doing studies in humans can influence their behavior. Most of us don't want to be perceived as unhealthy or inactive so we might try to do more exercise if someone was watching. But as Cameron says, "We don't think that the monkeys understand what the activity monitors are for."
The researchers wondered whether sedentary monkeys might become more active if they were housed in a larger space with more other monkeys to play with, and whether active monkeys might become more sedentary in a smaller living space. They were surprised to find that the housing condition had no influence on activity level. "An active individual may be very, very active when it's in a large space with a lot of room to run around and lots of playmates, however it stays active even when it's in a smaller space with less to do," says Cameron. And even with more space and more to do, sedentary simians stay sedentary.
Cameron says that's important because no matter how much they munch, the active monkeys don't gain weight. "You would expect that the more food that they eat, the more obese they would become, But that turned out not to be the case," she says.
In addition to looking at how much energy the monkeys used, the researchers kept track of how much food they ate. Based on those two factors, they were also able to calculate each monkey's base metabolic rate — meaning, how much energy it needed just to keep its body's basic functions going. What they found is that neither metabolic rate nor food intake were strong predictors of weight gain — while activity levels were. As Cameron explains, "So when you think of that, it means that an active individual would be less likely to gain weight no matter how much food they were eating. And that's exactly what we saw."
This makes it even more important to get into the swing of regular exercise, even if it is against your nature. Cameron and her colleagues are now planning studies to figure out whether this set tendency to be active or sedentary is caused by genes or early environment. If it proves to be related to early behavior — such as exercise levels as a child — there may be ways to help children avoid growing into sedentary adults. They also hope to identify whether some kinds of activity are easier to get involved in for those of us who aren't active types .
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