Exercised summary

It seems we have a crisis. Experts are ringing alarm bells: All over the industrialized world, there is a shortage of sleep.

In days gone by, the experts say, people used to sleep for up to ten hours a night. Today, the average Westerner gets just seven – a whole hour less than the recommended eight. And what’s worse, five percent of us get less than five hours’ sleep each night!

So our caveman and cavewoman ancestors probably didn’t sleep for eight hours a night. They also didn’t go on spontaneous and unnecessary jogs. But if there’s one thing we do know about our hunter-gatherer ancestors, it’s that they must have been extremely strong.

That’s according to primal fitness enthusiasts, anyway. Proponents of this theory believe that our ancestors’ everyday activities would have kept them fit, muscular, and lean; hunting animals would have tested their stamina, for example, and moving boulders would have required mammoth strength.

Exercise scientists are generally a peaceful bunch. But one question can have even the most placid researchers clawing at each other's throats: Can you lose weight by walking?

Until recently, it seemed clear-cut. Moderate exercise, like walking, requires energy – and when your energy output exceeds your energy intake, you burn fat. Right?

So, we’ve learned that walking can be useful. It can help you to lose weight and stay slim – and it doesn’t require very high levels of fitness. But what if you're interested in something a little more challenging – something to get your heart racing and your legs pumping? What, in other words, about running?

For novices, running can be daunting. Many would-be runners are put off for life by the horror stories of veterans – people complaining of wear and tear to muscles and joints, and all kinds of exotic injuries.

How do you picture your retirement? Whatever you envision, it’s probably unlike the lives lived by older members of hunter-gatherer societies.

Take the Hadza, the Tanzanian hunter-gatherer people we encountered in an earlier blink. While Americans walk half as much in their seventies as they do in their forties, the Hadza’s activity levels go through a much more moderate decline as they age. One result of that is that they stay fit and strong much longer than people living in the industrialized world.

We know exercise is good for us. We know we should exercise more. But now we also know why we so often find it difficult and unpleasant – because we didn’t evolve to engage in voluntary physical activity. From the standpoint of our ancestors and our evolutionary history, exercising is weird. 

That’s a fact we have to reckon with; it means that when physical activity is unnecessary or boring, we’ll probably try to avoid it. But rather than being paralyzed by that insight, can we harness it for our own benefit?