The experiences of feeling fit vary greatly, ranging from a mildly pleasantsensation to intense joy, to a sense of power, to 'out of body' sensations,and sexual orgasm, writes Dr William Reville
The former world heavyweight boxing champion Floyd Patterson coaches disadvantaged inner-city youth in boxing. Achieving a high level of fitness is an essential part of the training and is the key to Patterson's strategy of getting the youngsters used to a healthy drug-free lifestyle.
Patterson believes that the feelings of well-being experienced by people who are very fit are similar to drug-induced "highs". The essential difference is, of course, that physical fitness is very good for you, whereas most drugs are very bad for you.
Many people who indulge in strenuous aerobic exercise - such as running, cycling, rowing, football, tennis and so on - are familiar with the phenomenon called "runner's high" (so called because it has been reported so often by runners). They claim that after prolonged exercise (for example, running for 30 minutes or longer) they experience a good physical and emotional feeling.
I can personally attest to this. I regularly run moderate distances (five to eight kilometres) and, after three to five kilometres, I usually feel mildly elated. This is most obvious when I run with companions and usually expresses itself through uninhibited, exaggerated and good-humoured expression of opinions.
There is no crisp definition of runner's high and no proven causes. It is generally reported as a euphoric state, with an increased sense of well-being, enhanced appreciation of nature and a transcendence of time and space. Individually reported experiences vary greatly, ranging from a mildly pleasant sensation to intense joy, to a sense of power, to "out of body" sensations, to sexual orgasm. Then again, many people who indulge in intense aerobic exercise never experience runner's high.
Running a marathon (42.2 kilometres) is an extreme feat of endurance. However, there is an even more extreme field called "ultrarunning" where athletes run distances of 80 kilometres and more. Ultrarunners can experience strange and wonderful feelings, as recounted by Yiannis Kouros, a legend in this field.
"Some may ask why I am running such long distances. There are reasons," says Yiannis Kouros. "During the ultras I come to a point where my body is almost dead. When it is very hard there is a war between my body and my mind. If my body wins I will have to give up; if my mind wins, I will continue.
"At that time, I feel that I stay outside my body. It is as if I see my body in front of me; my mind commands and my body follows. This is a very special feeling, which I like very much. It is a very beautiful feeling and the only time I experience my personality separate from my body, as two different things."
Runner's high is underpinned by physiological and psychological factors but it is unclear which factor, if either, is dominant. On the physiological side the main suspects are the glandular chemicals, endorphin and serotonin.
The word, endorphin, comes from endogenous, meaning produced within the body, and morphine, a chemical substance derived from opium that elevates mood and alleviates pain. Endorphins are chemically similar to morphine and act as neurotransmitters (involved with transmission of nerve signals in the brain).
After release from the pituitary gland, endorphin attaches to specific receptor sites in the brain, altering the brain's perception of pain and, apparently, causing feelings of well-being. Endorphin is sometimes called the "natural painkiller".
Release of endorphin is enhanced when the body is under stress and pain - for example, during heavy exercise. However, it is unclear if the elevated levels of endorphin are responsible for the positive mood change experienced in runner's high.
Uncertainties in measuring the amount of endorphin released into the brain make it difficult to distinguish its effect from that of other factors. Also, it is not clear that elevated levels of endorphin always induce a positive mood. Only about 10 per cent of people who exercise experience a distinct high and a small number even report negative emotions during exercise.
Serotonin is another brain neurotransmitter. It affects a range of conditions including appetite, migraine, depression, aggression, anxiety, mood shifts, and so on. Some drugs, such as Prozac, achieve their mind-altering effects by increasing or suppressing the activity of serotonin and some research suggests that exercise works in a similar way.
Another natural chemical candidate for precipitating runner's high is phenylethylamine (PEA), a natural stimulant produced by the body and related to amphetamines. Moderate exercise increases PEA levels in most people. People who suffer from depression tend to have low PEA levels and some researchers feel that increased levels of PEA explains why exercise has a natural antidepressant action.
On the psychological side, there is no doubt that part of the reason people who exercise feel good is because of an increased feeling of self-confidence and improved self-image. Exercise also makes people feel good because it provides a break from the hustle and bustle of everyday life.
It seems to me that, while psychological factors play a part in inducing feelings of well-being both during and after exercise, the onset of runner's high during strenuous exercise is mostly physiological in nature.
However, whatever about the precise nature of the factors underpinning runner's high, it is undeniably true that regular aerobic exercise is good both for mind and body.
Newspaper columnist and humorist, Erma Bombeck, once said: "The only reason I would take up jogging is so I could hear heavy breathing again."
If she tried it she would find that running is almost as pleasurable, and much less trouble than that other activity commonly associated with heavy breathing.