Phys Ed: Why Exercise Alone May Not Be the Key to Weight Loss


Proving that possibility has been daunting, though, in part because it is difficult to quantify every physical movement someone or something makes, and how their movements do or do not change after exercise. Mice, for instance, skitter, dart, freeze, groom, eat, roam, defecate and otherwise flit about in frequent fits and starts.

But recently, animal researchers hit upon the idea of using infrared light beams to track how animals move at any given moment in their cages. Sophisticated software then can use that information to map daily patterns of physical activity, showing, second-by-second, when, where and for how long an animal roams, sits, runs or otherwise spends its time.

Intrigued, scientists at Vanderbilt University and other institutions thought that this technology would be ideal for tracking mice before and after they started exercising, especially if the technology were used in specialized metabolic-chamber cages that can quantify how much energy an inhabitant is expending throughout the day.

So the scientists fitted out cages, added locked running wheels, and let young, healthy, normal-weight, male mice loose in them to roam and explore for four days, providing the researchers with baseline data about each mouse’s metabolism and natural peripatetic-ness.

The wheels then were unlocked and for nine days, the mice could run at will, while also eating and moving around off the wheels as much as they chose.

The mice, which seem to enjoy running, hopped readily on the wheels and ran, off and on, for hours.

They showed a subsequent spike in their daily energy expenditure, according to the metabolic measures, which makes sense, since they had added exercise to their lives.

But they did not change their eating habits. Although they were burning more calories, they did not gorge on more chow.

They did, however, alter how they moved. Almost immediately after they started using the wheels, they stopped roaming around their cages as they had before the wheels were unlocked.

In particular, they stopped engaging in the kind of lengthy meanders that had been common before they began to run. Instead, they now usually jogged on their wheels for a few minutes, hopped off, rested or roamed in short spurts, and then climbed back on the wheels, ran, rested, briefly roamed, and repeated.

These changes in how they spent their time neatly managed to almost counteract the extra calorie costs from running, says Daniel Lark, a research fellow in molecular physiology at the Vanderbilt University School of Medicine, who led the new study.

In general, the running mice showed a slightly negative energy balance, meaning that they were burning a few more calories over the course of the day than they were taking in by chowing down.

But that caloric deficit would have been about 45 percent greater, the metabolic calculations showed, if they had not also begun moving around their cages less.

What prompted the running mice to roam less is still uncertain.

“But it does not seem to have been fatigue or lack of time,” Dr. Lark says.

Wheel running is not arduous for mice, he points out, and did not fill their waking hours.

Instead, he says, it is likely that the animals’ bodies and brains sensed the beginnings of an energy deficit when the mice began to run and sent out biological signals that somehow advised the animals to slow down, conserve energy, maintain homeostasis and not drop weight.

He and his colleagues would like, in future experiments, to explore how, physiologically, the rodents’ bodies sensed the changes in their energy balance and at what point they might begin to eat more. They also would like to study female, older and obese animals.

Mice will never be people, of course, so we cannot say whether the results of this and any follow-up experiments would directly apply to us, Dr. Lark says.

But the results do intimate that if we hope to exercise off excess pounds, we watch what we eat and try not to move less while we work out more.

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