PUBLIC-health campaigns regularly plug exercise as a sure-fire way to avoid an early grave. But that message may be too simplistic. For an unhappy few, even quite strenuous exercise may have no effect on their fitness or their risk of developing diseases like diabetes.
鈥淭here is astounding variation in the response to exercise. The vast majority will benefit in some way, but there will be a minority who will not benefit at all,鈥� says Claude Bouchard of Louisiana State University in Baton Rouge.
At the Australian Health and Medical Research Congress in Sydney last week Bouchard reported the results of a study assessing the role of genes in fitness and health changes in response to exercise. In the study, 742 people from 213 families were put through a strict 20-week endurance training programme. The volunteers had not taken regular physical activity for the previous six months. Exercise on stationary bikes was gradually increased so that by the last six weeks the volunteers were exercising for 50 minutes three times a week at 75 per cent of the maximum output they were capable of before the study.
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Previous reports indicated that there are huge variations in 鈥渢rainability鈥� between subjects. For example, the team found that training improved maximum oxygen consumption, a measure of a person鈥檚 ability to perform work, by 17 per cent on average. But the most trainable volunteers gained over 40 per cent, and the least trainable showed no improvement at all. Similar patterns were seen with cardiac output, blood pressure, heart rate and other markers of fitness.
Bouchard reported that the impact of training on insulin sensitivity 鈥� a marker of risk for diabetes and heart disease 鈥� also varied. It improved in 58 per cent of the volunteers following exercise, but in 42 per cent it showed no improvement or, in a few cases, may have got worse. 鈥淚t鈥檚 negative, but it鈥檚 true. Some people slog away and don鈥檛 get any improvement,鈥� says Kathryn North of the Institute of Neuromuscular Research at the Children鈥檚 Hospital at Westmead in Sydney.
鈥淭he fitness of some volunteers increased by over 40 per cent, but some showed no improvement at all鈥�
In the eight volunteers who showed the largest improvement in insulin sensitivity, 51 genes were expressed in muscles at double the levels of the eight people who showed the least improvement, and 74 genes were expressed at half the level. Many of these genes were a surprise to the researchers because they have not previously been linked to exercise.
鈥淲e need to recognise that although on average exercise may have clear benefits, it may not work for everyone,鈥� says Mark Hargreaves of Deakin University in Melbourne. 鈥淪ome people may do better to change their diet.鈥�