Walking is, at least for people like me, the perfect exercise. Just this morning I walked 11 kilometers. Most other kinds of exercise result in strain and injury, especially to joints. Pascal Picq points out in his book (reviewed earlier) that slow, long-distance running and walking is something that humans do much better than any other species, especially the ones like cheetahs that can run much faster but only for short distances. And even older humans, who are no longer athletic in other ways, can run or walk for long distances; geriatric marathon runners are actually quite common, though often unnoticed because they finish last. But they finish.
Walking is slower than running, which means that the walker is less likely than the runner to trip over or step on things in the path or, if so, to sustain injury from them. An injury can take an old body a long time to recuperate from. I have required physical therapy for things that, as a younger man, I would hardly have noticed.
Walking is almost perfectly aerobic. That is, your muscles can keep working for long stretches of time because your circulatory system can provide them with all of the oxygen that they need (that is what aerobic means). And the body can also keep itself cool during long walks.
There are three ways that an object, such as your body, can keep cool even while generating body heat during exercise.
- The first is through what is called radiant heat transfer. Your body emits invisible light, just off the red end of the spectrum, which is why it is called infra-red. It is, in fact, a kind of energy and to lose this energy means you will cool off. How much energy you lose is not completely under your control. It depends on your environment and how hot you are. Deep space is almost at absolute zero, and when you lose infra-red light into outer space—even into a clear blue sky—it is gone forever. You cannot speed it up or slow it down. This is why you feel a chill if you sleep out in the open, but not if you sleep under a tree or a roof. The tree or roof is not at absolute zero.
- The second is sensible heat transfer—sensible as in the fact that you can feel it. Your molecules conduct some of their energy to the air, that is, if the air is colder than you are, which is usually the case. You have some control over this. You can alter the amount of surface area you expose to the air by curling into a ball (to hold in the heat) or extending your arms (to release it). There is always an unstirred boundary layer of air next to your skin, especially when that air is trapped inside of fabric. To cool off, wind is your friend.
- The third is latent heat transfer—from the evaporation of water. Water constantly evaporates from you, especially from your invisible sweat. Your sweat glands allow water to evaporate before it has a chance to become visible on your skin or clothes. People who have defective sweat glands easily overheat. Again, wind is your friend—it not only blows away sensible heat but also water vapor.
You cannot do much about radiant heat. But walking or slow running allows sensible and latent heat to keep you cool. I need the exercise for my body but also to keep my mind active. I will walk all I can for as long as I can. If someday I can only hobble, I will still be healthier for having walked (around 90 kilometers a month) as much as I do.
