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Why is Exercise Good for You? Why pain leads to gain?

Run your car hard and it breaks down. Run your body hard and it picks up. Dr John Bohannon investigates to find out why pain leads to gain.


Exercise is supposed to be good for you. In fact, according to decades of scientific research, failure to exercise can kill you. Those who indulge in a couch- and car based way of life are much more likely to get bagged by the big killers: cardiovascular disease, diabetes, cancer. And yet, from a mechanical point of view, exercise is self-abused. Microscopic muscle fibbers rip, toxins flood your bloodstream, organs slosh and collide, skeletal joints bump and grind.

Ask any engineer how to maximize a machine’s life span and he or she will give the same advice: Use it gently and it will break more slowly. The second law of thermodynamics- which says in essence, that every system tends to run down- is bad news for machines.

Paradoxically, the opposite advice applies to the human machine: Use it too gently and it will break down more quickly.

We don’t disobey the laws of thermodynamics, of course; instead we work around them by eating, excreting, and shedding heat. The net result is that we constantly rebuild ourselves while exporting our damage to the environment around us. Keeping that process going requires that we remain active.

The optimal level of human activity was shaped by our evolution, a quirky solution to the specific challenges faced by our Palaeolithic ancestors. (Many scientists argue that the most common serious illnesses of the industrialized word, the “diseases of affluence,” are due to a mismatch between the circumstances of modern and Palaeolithic life.)

Hunter-gatherer days are plenty of long distance walking and running, and full off other physical exertions, such as butchering carcasses, scraping hides, climbing trees and dancing.The ancestral lifestyle is equivalent to cross-training for endurance sport like triathlons.

Studies that compare athletes, moderately active people, and full-on couch potatoes back the claim that “virtually any measurement we can make improves with exercise and gets worse the more sedentary we become.




The bodies of athletes read like a physiology wish list. A regimen of regular exercise improves arterial functions, blood lipid profiles, intracellular ionic concentration, insulin sensitivity, and heart function- all of which seem to account for the disease- reducing aspects of exercise. Physical activity is even associated with lower risk of Alzheimer’s. Moreover, some exercises are recommended for people with disabilities and those who have special needs. Through their NDIS plan, they could get a personal therapist or trainer to achieve their fitness and wellness goals.

There’s no denying that exercise is necessary for health, then, and that it makes you smart and happy to boot. But that still doesn’t address the root of the question: How does exercise do all this? What are the mechanisms that connect a 10-mile run and say, the failure of a mutant cell to run amok and form a tumour? For now, there is only one grand unifying theory for how exercise does its magic. It invokes a phenomenon called hormesis. (I know, it sound like an exotic massage “therapy,” but it’s real biology.) Hormesis is a theory that attempts to explain why, in very small doses, toxic substances can actually have a positive affects on heath. For example, after imbibing trace amounts of the deadly poison dioxin, animals have a better change of survival when exposed to a full dose. Shower animals in low doses of radiation, wait 24 hours, and then blast them with gamma rays. Those that were pre-exposed have a lower risk of dying of cancer. Hormesis is a nutshell: That which does not kill us makes us stronger.

The starting point for the hormetic theory of exercise is that intense physical activity is a source of toxins. By gushing oxygen through your system and accelerating you metabolism, you produce molecular by-products in your blood and tissues, especially free radicals, atoms with unpaired electrons that wreak havoc on DNA

So, yes exercise damage the body even at the molecular level – but by exposing your body to small doses of this toxins through exercise you stimulate a vast emergency network generating antioxidants to mop up free radicals, enzymes to repair broken DNA, and hormones to boost immunity. Exercise every day and hormesis keeps your body vigilant. Over the long term, that might prevent disease.

That sounds reasonable, but doesn’t it seem bizarre that humans are designed to damage themselves in order to remain healthy? We also could wonder: why don’t we have a physiology that functions equally well in active and sedentary lifestyles?

Well, evolution didn’t design us that way. A more flexible physiology would surely be more complex, more metabolically expensive, and hence less efficient. Evolution cannot look forward to anticipate future behaviours. It could not have seen cars and couches on our horizon.

Perhaps it is incorrect to think of exercise as a drug that people give themselves to boost heath. Rather, lack of exercise – inactivity- is like a disease that causes heath to decline.

So science has so pretty solid explanations of why exercise is good for you, and some quite solid numbers on how good it is for you. But as any reputable researcher can tell you, statistics reveal nothing about the individual.

All I can do is star my next workout, knowing that I’m doing my best to be the person evolution designed me to be.

By Dr John Bohannon

Discover presents - The Body Magazine / 2008

Adaptation by Tomás Würst

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