Working out: It's all in the genes
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To examine those questions, scientists at the University of Missouri in Columbia recently interbred rats to create two very distinct groups of animals, one of which loves to run, while the other slouch idly in their cages. Then the scientists closely scrutinized and compared the animals' bodies, brains and DNA.
For some time, exercise scientists have suspected that the motivation to exercise must have a genetic component. When researchers have compared physical activity patterns among family members, and particularly among twins, they have found that close relations tend to work out similarly, exercising about as much or as little as their parents or siblings do, even if they grew up in different environments.
But to what extent someone's motivation to exercise is affected by genes — and what specific genes may be involved - has been hard to determine.
To find out, the University of Missouri researchers decided to create their own innately avid runners or couch potatoes, provide them with similar upbringings.
They began with ordinary adult male and female lab rats. The scientists put running wheels in the animals' cages and, for six days, tracked how much they ran. Afterward, the males and females that had logged the most miles were bred to each other, while those who had run the least were likewise paired. The pups from each group were bred similarly, through 10 generations.
At that point, the running rats tended to spontaneously exercise 10 times as much as the lazier animals.
Now, the researchers set out to determine why.Broadly, two elements are especially likely to influence whether we, as individuals, habitually exercise or not. One is physique. Animals or people that are overweight or ill, or who have poor muscle quality or tone or other physiological impediments to activity, tend to be sedentary.