Exercised: The Science of Physical Activity, Rest and Health

by Daniel E. Lieberman

The key lesson to digest from the starving men’s dramatically lower resting metabolic rates is that human resting metabolisms are flexible. Most critically, resting metabolism is what the body has opted to spend on maintenance, not what it needs to spend.

Such measurements indicate that nearly two-thirds of a person’s resting metabolism is spent on just three very expensive tissues: brain, liver, and muscle. Your brain and liver each consume about 20 percent of your resting metabolism, and if you are a typically strong human, your muscles expend 16 to 22 percent of your resting metabolism.

resting is not just a state of physical inactivity.

you can spend a given calorie in just five ways: growing your body, maintaining your body (resting metabolism), storing energy (as fat), being active, or reproducing.

Stated simply, we evolved to be as inactive as possible.

In fact, compared with other mammals, humans might have evolved to be especially averse to exercise.