Aerobic Exercise Capacity May Be Genetic

Some people may be born to run, but a new study shows many of us may have to work a bit harder at the gym to compensate for the laziness of our ancestors.

Researchers found rats that came from a long line of inactive rats were born with more heart disease risk factors (search) than rats that were born into a family of athletic animals.

Although the two groups were all descended from the same group of laboratory rats, the inactive rats were the product of 11 generations of rats bred to have a low tolerance for aerobic exercise. These rats are described as having a low aerobic exercise capacity, which is the inability of the body to use oxygen efficiently and generate the energy needed to exercise for long periods of time.

“We found that rats with low aerobic capacity scored higher on risk factors linked to cardiovascular disease -- including high blood pressure and vascular dysfunction," says researcher Ulrik Wisloff, PhD, professor of cellular and molecular exercise physiology at the Norwegian University of Science and Technology in Trondheim, Norway, in a news release.

Researchers say many studies conducted in humans show that low aerobic exercise capacity is associated with a higher risk of death due to heart disease. Therefore, increasing aerobic exercise capacity is important to anyone who wants to reduce their risk of heart disease or stroke.

"The reality of having a genetic determinant of our existence is that there are some people who are born with less ability to take up oxygen and transfer energy than others," says Steven Britton, professor of physical medicine and rehabilitation at the University of Michigan, in the release. "These people may have to work harder and will never reach the level of a professional athlete, but almost everyone can improve their aerobic capacity and health status with regular exercise."

Born to Run?

In the study, which appears in the Jan. 21 issue of the journal Science, researchers studied 11 generations of rats bred to have either a low or high exercise capacity.

By generation 11, the high-capacity rats were able to run continuously on a treadmill for 42 minutes, on average, before exhaustion forced them to stop. In contrast, the low-capacity rats could only manage an average of 14 minutes on the treadmill before stopping.

Researchers found the overall difference in running capacity between the two groups was 347 percent.

But they say the most important finding of the study was that low exercise capacity was also closely associated with higher levels of various risk factors for heart disease and diabetes, such as higher elevated fasting sugar, triglycerides (a blood fat (search) linked to diabetes and heart disease), higher insulin levels, and abdominal fat.

"It's important to remember that, as a result of artificial selection over 11 generations, our low-capacity rats have an abnormally low concentration of proteins required for energy production that may underlie the development of common diseases in humans," says Britton. "And, while our results are intriguing, future research will be needed to prove a direct cause-and-effect relationship between mitochondrial function (protein required for energy production) and disease."

By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Wisloff, U. Science, Jan, 21, 2005; vol 307: pp 418-420. News release, University of Michigan Health System.