On a bright afternoon in Jiangsu, China, Xin Yin acts as a personal trainer for some mice. One by one, he places the rodents on a miniature treadmill that starts slowly and gradually increases speed. These littermates are natural athletes, able to run farther with less lactic acid buildup than average lab mice.
The secret to their speed is not in their genes: the animals come from the same genetic stock as a group of control mice. And they have not received any special training. Instead, their physical condition seems to stem from their father’s exercise habits before they were even conceived. It’s a finding that suggests running could benefit not only the athlete, but also his unborn children.
“I was very surprised when I first saw the data,” says Yin, a biochemist at Nanjing University.
