Exercise as something undertaken deliberately is not natural. Animals and humans in a natural habitat don’t exercise; their physical activity is a byproduct of life activities, such as hunting, gathering, mating, fighting, or fleeing predators.
We modern humans exercise deliberately, we expend energy with the end of improving our health and getting our bodies in better shape.
But what counts as exercise? This is actually an interesting question.
Suppose you’re a trained distance runner, and on an off day you decide to take a two-mile walk because you’re tired of sitting around the house, and need some refreshment. Does that count as exercise?
No, it does not, because it won’t result in any improvement in your health. It doesn’t provide enough of a stress to cause the body to increase its aerobic or muscular abilities.
Now, suppose you’re a 90-year-old man who’s in ill health, mostly confined to your comfy chair, and you do the same two-mile walk. Does that count as exercise?
Yes. It will result in a stress on your system that will cause a physiological reaction that will, ultimately and if repeated enough, result in better health.
Exercise must be of sufficient intensity relative to the fitness of the person exercising.
A two-mile walk can be healthful even for someone who’s already in good shape/health, because it means that the person is not sedentary, and being sedentary causes insulin resistance and an increased risk of death, even if exercise is done during other times. But it doesn’t count as exercise in the sense of increasing fitness.
To count as exercise, the activity must in some way push the limits of what a person is capable of.
A just-published study looked at a group of swimmers, who were divided into three groups. One, a control group, did nothing; a second swam at high intensity, low volume; and a third swam at low intensity, with high volume.1
The high-intensity group performed swimming at 6 to 10 all-out intervals of 30 seconds each, with two minutes rest between each bout.
The low-intensity group swam continuously for one hour.
Both groups did this three times a week, for 15 weeks. Then they measured the swimmers’ insulin sensitivity, a prime marker of the effects of exercise.
Only the high-intensity swimmers saw an improvement in insulin sensitivity. For the low-intensity swimmers, the result was zero change.
Clearly, the low-intensity, high-volume swimming barely counts as exercise. It wasn’t intense enough to result in an improvement.
I don’t do much swimming, but my impression is that most people who swim for exercise do it like the low-intensity group. Only less volume. That’s probably doing little for their health.
How can you know whether your exercise has enough intensity to result in improvement?
The way to know is that the exercise should leave you gasping for breath and wishing you could stop.
Cardiorespiratory or aerobic fitness is highly correlated with health.2 High cardiorespiratory fitness apears to be way more important for health than traditional cardiac risk markers such as lipids, and more important than body mass index.
Cardiorespiratory fitness is usually measured by VO2max, which is the body’s maximal uptake of oxygen in milliliters per kilogram of body weight per minute. A calculator will let you input a few bits of information about yourself and it will estimate your VO2max. This is a legit operation from the K. G. Jebsen Center of Exercise in Medicine at the Norwegian University of Science and Technology.
The calculator estimates my fitness, a VO2max of 51, as on the level of an average 31-year-old. I’m disappointed: the average 31-year-old these days is a mess — sedentary and overweight. Other sites say that level makes me highly fit — for my age.
But ideally there should be no age-related decline in VO2max. If you think that that’s normal, then you’re just buying into the notion that there’s nothing much you can do about aging, that decline is inevitable.
If you read this site much, you already know that I reject that notion.
So it’s true what everyone says about exercise: it’s very good for you, and you must exercise to be in good health.
But what is VO2max? In reality, it’s a measurement that’s affected by several components, such as maximum heart rate, cardiac output, hemoglobin, lung capacity, and the level and quality of mitochondria and energy-producing enzymes.
To get VO2max to an optimal level, all of these must be functioning properly.
For this to happen, exercise must strain your current ability. Then your body will develop its capacity beyond its current limits.
Notably, exercise that doesn’t train the whole body will not give the best results in terms of VO2max. While running can improve the heart muscle, it raises aerobic enzymes only in the legs.
High-intensity weight training comes very close to being a perfect exercise. Not saying you can’t or shouldn’t do anything else, but you probably won’t need to. High-intensity interval training is another great way to improve fitness.
As for walking, swimming, or other low-intensity activity, go ahead and do them if you enjoy them. I do. I walk daily, and swim in the summer.
But I don’t fool myself that this is greatly improving my cardiorespiratory fitness. They’re enjoyable activities that make me feel better, nothing more.
For those who are not in good shape, such as the elderly and the infirm, walking is a great thing to do and will improve cardiorespiratory fitness.