What makes people run?

Why do 11 per cent of Americans and tens of millions of people around the world tie on running shoes and clock their weekly kilometres? The three most recent presidents of the United States have put in time as runners (and earlier this year, one candidate, Mike Huckabee, trained for the Boston Marathon while campaigning for the U.S. presidency). The president of France, Nicolas Sarkozy, is a runner. And beyond the vast army of ordinary joggers, it can sometimes seem as if the entire planet is trembling beneath the footfalls of ultramarathoners, ironmen, and other endurance athletes.

Runners also make the news by dying while running - two died in the 2006 Los Angeles Marathon, another during unseasonably hot weather at the 2007 Chicago Marathon, and yet another a month later, when 28-year-old Ryan Shay died of heart failure during the US Olympic Marathon trials. So the question is asked not just in puzzlement but sometimes in anger and sorrow: What makes us run?

The answer, according to a controversial body of research, is that our passion for running is natural. A small group of biologists, doctors, and anthropologists say our bodies look and function as they do because our survival once depended on endurance running, whether for long-distance hunts like the one Liebenberg witnessed or for racing the competition across the African savanna to scavenge a kill. The prominent science journal Nature put the idea on its cover, with the headline "Born to Run". And in his book Why We Run (HarperCollins, $19), the biologist and runner Dr Bernd Heinrich argues that something exists in all of us that still needs to be out chasing antelopes, or at least dreaming of antelopes. Without that instinct, "we become what a lapdog is to a wolf. And we are inherently more like wolves than lapdogs, because the communal chase is part of our biological makeup".

Anyone who has put in some kilometres knows how good running can feel, once it stops feeling bad. But beyond the way it feels, medical evidence also suggests that humans are built for endurance exercise. In response to a good training program, for instance, the left ventricular chamber of the heart can increase as much as 20 per cent in volume. The chamber walls thicken, too. So the heart fills up faster and pumps more blood to the rest of the body. The coronary arteries also change, dilating more rapidly to meet the body's demand for oxygen. Endurance exercise won't make anyone live forever. But it seems to make the cardiovascular system function the way the owner's manual intended.

In the skeletal muscles, increased blood pressure causes new capillaries to emerge. The mitochondrial engines of the cells ramp up to consume energy more efficiently, helped along by an increase in the production of various antioxidants. These changes in the heart and extremities together typically boost the maximum amount of oxygen the body can consume each minute by 10 to 20 per cent. For men who used to become short of breath slouching to the fridge for a beer, VO2 max can increase even more. Lapdogs start to function like wolves.

More surprisingly, the brain responds as if it was built for endurance exercise, too. Everybody knows about the runner's high, that feeling of euphoria thought to be triggered by a rush of endorphins to the reward centres of the brain, usually near the end of a good, long workout. (Running for dinner, as part of a hunt, could very well amplify that effect; in essence, a love of running could lead to more ample dining opportunities.) But researchers have discovered lately that exercise affects the function of 33 different genes in the hippocampus, which plays a key role in mood, memory, and learning. By stimulating growth factors, exercise also produces new brain cells, new and enhanced connections between existing cells, new blood vessels for energy supply, and increased production of enzymes for putting glucose and other nutrients to work.

People who exercise regularly perform better on some cognitive tests: Run more, think better, hunt smarter, eat better. Exercise also seems to buffer the brain against neurological damage, reducing the effects of stress and delaying the onset of Alzheimer's and other diseases. Most significant, exercise helps prevent and alleviate depression, which afflicts one in five Australians at some stage in their lives and costs the national economy $3.3 billion a year in lost productivity. In fact, studies suggest that exercise works as well as pharmaceutical antidepressants, and that the effect is "dose dependent" - that is, the more you exercise, the better you feel.

For the full length version of this article, pick up the August Men's Health. Also check out the magazine for the "4 Secrets To Running Forever," and "Evolution Of The Running Man."