Fitness does not equal health

dose-response curve

Dose-response curve of hormesis.

Damaging your body through excessive exercise

I was inspired to write this on seeing a recent video (which I can’t find at the moment) of a couple of female runners crossing the finish line of the Bay to Breakers race, a 7.5 mile course. The runners literally couldn’t hold themselves upright, and crawled across the finish line, cheered on by the spectators. They were clearly damaging themselves by their excessive, for them, running.

Exercise is a form of hormesis

Exercise is a form of hormesis, which is a form of stress placed on a biological system – the body as a whole, or cells, or an organ – that results in the upregulation of stress response systems. This can include better mitochondrial function and increased numbers of mitochondria, increased antioxidant defenses, and higher levels of so-called phase 2 enzymes, which defend against toxic insults. The idea is that a small stress results in health as the organism grows stronger in order to be able to withstand these stresses.

Hormesis is the basis on which any number of inputs causes better health. It might not be going too far to say that hormesis is the very basis of health, in that any input that causes better health, inputs such as exercise, fruits and vegetables, cold showers, intermittent fasting and calorie restriction, ionizing radiation from the sun, all of these work by producing a stress, hence they work by hormesis. (It might interest you to know that fruits and vegetables are health-giving precisely because they contain small amounts of toxic phytochemicals, from which the body must defend itself, broccoli being a prime example.) The opposite of producing hormetic stress can be seen in the couch potato lifestyle that leads to obesity, diabetes, heart disease; failure to subject the body to the right amount of stress produces ill health.

Stresses can be too high

However, hormesis exists on a continuum, as illustrated in the figure above. Points 1 and 2 we might call the couch potato zone, in which there is little or no exercise, fruits and vegetables in the diet, or other stressors. Points 4 through 7 are in the hormetic zone, with the area between 5 and 6 producing the optimal hormetic effect. Points 9 and 10 are in the unhealthy area again: too much stress applied, and the organism becomes broken down due to inability to handle so much stress. Finding the optimal point of hormesis for any given stress can be difficult, but in such areas as exercise or diet, paying attention to how these make one feel can go a long way toward determining that point.

Can we pinpoint any inputs that clearly cross over into the unhealthy zone? Take a well-known toxic compound like methylmercury. It doesn’t take much for this compound to poison living things, but even here, small doses can be hormetic: see Enhanced reproduction in mallards fed a low level of methylmercury: An apparent case of hormesis. What about exercise? To my mind, a clear case of going beyond what is healthy, of applying more stress than the body can handle, and that results in damage, sometimes permanent, is marathon running. This takes a good thing, exercise, and by overdoing it, it becomes toxic.

Distance running is associated with heart damage

In young men, a high frequency of vigorous exercise, specifically running, was associated with an increased risk of atrial fibrillation. Clearly they were overdoing it. Another study found that the rate of atrial fibrillation in practitioners of long-term endurance sports was about four times the rate of sedentary controls. A long-distance run of 21 km produces biomarkers of cardiac damage in young men. And “ostensibly healthy marathon runners” have a much higher rate of myocardial damage than controls.

This is not even to mention the joint injuries caused by distance running. Runners also often overtax themselves so as to run down their immune systems, with more colds and flu as a result. This could even increase the risk of cancer. World champion marathon runner Grete Waitz died of it at age 57. Of course this is an anecdote, but it does seem possible to say that marathon running did not make her healthier, and in my opinion it may have hastened her demise. Overtraining, which almost by definition is what an elite marathoner does, is associated with increased incidence of upper respiratory tract infections and overall lower immune function. Hence cancer could be a result of prolonged overtraining.

Hormetic stress must remain in the zone of health

Many people apparently think that fitness equals health, that the more you exercise, the healthier you are. But clearly it’s possible to overdo it, and many people are. The body needs rest and recovery as well as stress, and the stress applied must not be too great, or it tips the body into a state of ill health. If you exercise a lot, and constantly feel tired, or develop colds more often than seems normal, that could be a sign that you need less exercise and more rest. (It could be a sign of other things too, such as poor nutrition.) It’s difficult to say how much is too much, but daily strenuous exercise, especially running, may cross that line. What doesn’t kill you may not always make you stronger, but weaker.

(Illustration taken from Inflammatory modulation of exercise salience: using hormesis to return to a healthy lifestyle.)

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