In recent years, experiments examining exercise and weight loss have found that people lose far much less weight than expected, considering how many additional calories(卡路里) they are burning with their workouts.
Scientists have guessed that exercisers are likely to become hungrier and eat more after working out. They also may sit longer when not doing exercise. Together or separately, these changes could make up for the extra energy used during exercise.
To prove that possibility, scientists came up with the idea of using infrared light(红外线) to track mice's movements in their cages. Then software can use that information to analyse their daily physical activity.
So the researchers prepared special cages, putting inside some locked running wheels, and let mice roam(闲逛) and explore for four days in the cages. This provided the researchers with information about how many calories each mouse burned every day.
Then the wheels were unlocked and for nine days, the mice could run at will, and they could decide how much to eat and when to get off the wheels, walking around. The mice, which enjoyed running, jumped readily on the wheels and started to run. On and off the wheels, they could run for hours. They showed a following height in their daily energy expenditure(支出) 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 eat more. They did, however, change how they moved. They now usually jogged on their wheels for a few minutes, jumped off, rested or roamed in a while, and then climbed back on the wheels, ran, rested, briefly roamed, and it repeated. These changes in how they spent their time almost counteracted(抵消) the extra calorie costs from running, says Daniel Lark, who led the new study.
What caused the running mice to run less is still uncertain. ''But it does not seem to have been tiredness or lack of time; wheel running is not arduous for mice, and does not fill their waking hours.'' Dr. Lark says.
Instead, he says, it is likely that the animals' bodies and brains sensed the increasing energy expenditure when the mice began to run and sent out biological signals that somehow advised the animals to slow down, save energy and lose weight.
Mice will never be people, of course, so we cannot say whether the results of this would directly apply to us, Dr. Lark says. But the results do indicate that if we hope to lose more weight through, we should watch what we eat and try not to move less while we work out more.
