A person's peak exercise capacity as measured on a treadmill test is a more powerful predictor of how long someone will live than risk factors such as heart disease, high blood pressure or smoking, a study says.
The study, done by researchers from the Veterans Affairs Palo Alto Health Care System/Stanford University, amounts to some of the strongest evidence yet of the importance of physical fitness.
``We're now beginning to prove the hypothesis of Darwin's whole `survival of the fittest' category, in that people who are fitter tend to do better and live longer,'' said Dr. Gary J. Balady, a Boston Medical Center cardiologist.
For the study, patients with and without heart trouble were given treadmill tests, which are routinely used to check people for heart trouble.
In treadmill tests, patients are hooked up to sensors _ including a mask to measure the amount of oxygen and carbon dioxide in each breath _ and walk on a treadmill at gradually increasing speed and angle. They continue until they are exhausted, reach their maximum heart rate, or develop chest pain or other symptom of heart disease.
The study found that a person's chances of staying alive rise 12 percent with each increase of one ``metabolic equivalent'' when exercising as hard as one can on a treadmill.
A metabolic equivalent, or MET, is defined as the amount of oxygen used by an average seated person. Two METs is very roughly equivalent to walking less than 2 mph; 5 METs to walking at 4 mph; and 8 METs to jogging at 6 mph.
Many studies have shown that fitness reduces the chance of developing heart disease and a host of other ailments, but there have been few studies of its effect on people who already have heart disease, lead author Jonathan Myers said.
The researchers looked at more than 6,200 men whose VA doctors had referred them for treadmill testing. Some had heart disease, some did not. A total of 1,256 died during the next decade or more.
When people were grouped by risk factors, the risk of death in people who could not get beyond 4 MET was more than double that of people who could get past 8 MET.
Aside from age, fitness was a better indicator of potential lifespan than any of the other risk factors checked, such as smoking, heart problems, high blood pressure, diabetes or high cholesterol.
``Whether you have heart disease or don't have heart disease going into the test, the higher you can go on your exercise test, the better you'll do in the long run. It makes a very compelling statement in that regard,'' Balady said.
Moreover, the test had nothing to do with endurance _ it was peak exercise capacity, said T. Edwin Atwood, one of the VA researchers.
``It's not how long you exercise or how long you can exercise. It doesn't have to be marathons or running,'' he said. ``Walking briskly every day for half an hour is a great risk factor modifier.''
In fact, the study found that the improvement in death rates was largest between the lowest 20 percent and the next-lowest 20 percent.
``If this data were for a drug, I can tell you the pharmaceutical company having this drug would be very, very happy. And here this is just a modification of lifestyle,'' said Eric Ravussin, a physiologist at the Pennington Biomedical Institute in Baton Rouge, La.