Читать книгу Emotional Rollercoaster: A Journey Through the Science of Feelings - Claudia Hammond - Страница 9

When James was sixteen years old he took part in a crosscountry championship. Near the end of the race he was in fourth place, but knew that he was too tired to make the pace needed for him to win. Then something strange happened. ‘I was feeling really exhausted, but in a space of two minutes I moved into this rhythm and this beat where I felt absolutely invincible. I ran forward, took over first position and sprinted to the finish. I remember at the time I couldn’t talk to anybody; I just had to be on my own. There was just this sense of something in my body rewarding me – almost a chemical-like feeling of power.’

James had experienced something which many athletes find elusive – an exercise high. Some people exercise vigorously for years without achieving even one, but when it happens the theory is that beta-endorphins are key. Endorphin is short for endogenous morphine, i.e. morphine made by your own body. They are the body’s natural tranquillisers, which we release when we are in pain. Like morphine, they can also cause pleasure; the pain remains, but you don’t care anymore.

Is it possible that these endorphins could actually bring feelings of joy? There’s a physiological mechanism called the blood-brain barrier that protects the central nervous system by preventing most substances from crossing from the bloodstream into the brain tissues. The problem is that it’s not known whether the endorphins released into the bloodstream during exercise can actually break through the blood-brain barrier in order to have their effect on the brain. Exercise highs are hard to study systematically because it’s not an effect that can be easily quantified – who is to say what constitutes a high and what doesn’t?

It does seem, however, that exercise can affect the brain, even if the results are somewhat milder than a full-blown high and this might enlighten our understanding of the way both our minds and the rest of our bodies influence our emotions. Two or three short sessions of exercise a week can make people feel demonstrably happier, particularly if they are depressed initially. Some GPs already prescribe exercise for patients with mild depression with some success. There have even been studies showing that exercise can be as effective as anti-depressant medication. As well as the suggestion that this is due to the release of beta-endorphins there is also a theory that, like recreational drugs, exercise might cause the release of dopamine, hence we feel good.

Although research into the effect of exercise on mood might sound straightforward it’s not without its problems. For example, in some studies comparing one group who are prescribed exercise with a group not prescribed exercise, the people taking part were allowed to choose which group to be in. This inevitably introduces a bias – the people choosing exercise are likely to expect to see more positive results than those who avoid exercise. Studies have tended to allow a choice because it would be hard to persuade someone who had always detested exercise to take part in a study which might compel them to join a class. But if exercise could be shown to improve the mood of these people then it would be a powerful tool indeed. Yet another problem for the designers of these comparison studies is that factors other than the exercise itself might affect the group taking the classes. Participants might begin to feel better simply because they enjoy belonging to the group which goes to the special class. The fact that they are trying a new method of alleviating their depression might make them feel more hopeful and even the instructor’s expectations that they feel better after a session could make a difference. Any of these could have a slight improvement on a person’s mood before a single step of exercise has been done.

Despite the methodological difficulties there is some good evidence that exercise can make you feel good. The world’s first Professor of Psychopharmacology, Hannah Steinberg, has suggested that the effect of exercise could be harnessed as a treatment for drug addiction. Just as addicts use methadone as a substitute for heroin, Steinberg believes the next step might be to use exercise as a substitute for methadone, helping the brain to provide its own alternative opiates. It’s an intriguing idea, but she found it hard to persuade anyone to conduct trials.

A Danish study of just eight people addicted to drugs or alcohol found that exercise did seem to help them resist their addiction while they remained in hospital, but once they left they dropped the exercise programme and five out of the eight resumed their addiction. This study is so small of course that there could be other factors at play. The problem with using exercise in a deliberate attempt to induce feelings of euphoria is that even in experienced runners a high isn’t achieved every time. There’s also the question of whether the intensity of high could ever compare to that induced by drugs. Even if it worked on some occasions, however, it might be useful as one part of a treatment programme, with the added advantage that exercise is free and healthy.

However, it still isn’t clear whether improvements in mood after exercise are caused by the release of endorphins. People feel better after exercise even if they have been given a drug which blocks the production of beta-endorphins altogether, suggesting either that other neurotransmitters might take the place of endorphins when they are blocked or that there are other factors at work. A person might feel better after an exercise class because they are pleased with themselves for having made the effort, or perhaps they enjoy seeing themselves become fitter, or simply feel satisfied at having mastered a new routine. These could all feed through to a person’s self-esteem.

Finally there is the social interaction. If a person is at home feeling depressed, then visiting the gym with other people might provide a break from that isolation. If you use a drug to block the production of beta-endorphins, the improvement in mood after exercise still occurs, suggesting that endorphins might have nothing to do with the process.

In the Department of Kinesiology at University of Wisconsin-Madison there are treadmills, weight machines, exercise bikes, free weights and a swimming pool. While human guinea pigs pump iron every flutter of their heart can be measured. Outside there is even an arboretum where volunteers cut down the undergrowth while wearing transmitters which allow the scientists indoors to measure their heart rates. After they’ve finished the work, their levels of anxiety and depression are measured. With the help of this equipment and a team of volunteers, Professor William Morgan has developed a theory which might explain why exercise can make you feel happy – he calls it the distraction hypothesis. It is appealingly simple; exercise makes us feel good merely because it distracts us from the worries of the day. He found that although people do experience a decrease in anxiety as a result of vigorous physical activity, the effect soon wears off and within twenty-four hours you’re back to where you started. Therefore regular exercise could be a way of topping up your joy and keeping a lid on anxiety. Too much exercise, however, can have the opposite effect. In experiments where swimmers progressively increased their training sessions from 3,000 metres a day to 12,000 metres a day, the athletes gradually became more depressed. Once they began to decrease the distance they swam, their mood slowly returned back to normal.

There is some more good news for people who prefer to sit still. Professor Morgan also found that when he asked people to sit in a quiet room in a comfortable old leather armchair or lazyboy, as he calls it, for the same length of time as an exercise session, they felt just as good afterwards.

A final theory of why exercise might make you feel good is the thermogenic hypothesis – the idea that you feel happy after exercise because your body temperature has increased and that it is this high temperature which is responsible for the release of beta-endorphins, which in turn make you feel good. Not surprisingly, research in this area began in steam baths and saunas in Scandinavia. In one study back in 1972 the volunteers who took part had a twenty-minute sauna followed by a ten-minute shower for which they were paid in cash and in beer. Before and after the sauna the mood of the volunteers was measured. Beforehand two of the twenty male volunteers had warned the experimenters that they didn’t like saunas and indeed four people did find the sauna so stressful that they had to be let out early. However, overall people did feel less anxious after the sauna, but so did the control group who had undressed, sat waiting on a bench for twenty minutes and then had the ten-minute shower.

More recently William Morgan’s team have tried to determine whether it’s the exercise per se or the rise in temperature which makes people feel good after exercise. He found that if the whole body is heated mood can improve for up to twenty-four hours and in the bloodstream at least, levels of beta-endorphins rise. The team have come up with ingenious experiments in an attempt to establish the answer such as getting one group to exercise dressed in everyday fitness gear while another group exercised clad in warm clothes, a hood, gloves, a surgical mask and two blankets. Despite the rise in body temperature, not surprisingly the hot group ended up feeling more anxious than the others, rather than less. Another approach is to prevent the exercise from increasing the body’s temperature by lying in a cold bath for half an hour before exercising. It was found that if a person’s body had been cooled beforehand their temperature remained low and they felt no better after exercise, whereas the people whose bodies had not been cooled did feel happier after exercise, suggesting that it could be the rise in temperature, not the exercise itself, that makes people feel better.

Another way of testing this theory is to prevent body temperature from rising with exercise by doing that exercise under water, but when this was tried with scuba divers they still felt better afterwards, suggesting that it’s not the warmth that’s doing the trick. At the University of California Shawn Youngstedt and his team put volunteers on exercise bikes under water with their heads poking out above the surface. There was no improvement in mood after exercising, but the researchers do warn that this might have been due to the novelty of the task or anxiety caused by having their oesophageal temperature taken – a procedure involving the insertion of a tube up the nose and down into the throat. Other experiments have involved exercising while wearing a scarf filled with ice and even having a rectal temperature taken before, after and (somehow) during exercise. In this study anxiety did decrease after the exercise session, but perhaps the participants were simply relieved that it was over. So it seems that exercise can make people feel good, but we’re still a long way from knowing exactly why.