The problem with assessing the effects of exercise on health are many. However, one of the main problems is that it is very difficult to determine cause and effect with regard exercise and body weight. It is known for example that healthy normal weight people exercise more than obese and unhealthy individuals. However, while it is tempting to suggest that it is the exercise that is the cause of the good health and normal body weight, it could just as easily be that obesity and ill health prevent exercise due to the excessive body weight and fatigue these phenomena cause. Many studies have shown associations between exercise and weight loss, but little useful information can be determined from correlative data, beyond basic associations. Clinical trial data is more useful, but often the exercise that is prescribed to obese individuals also comes with dietary changes and so again it is difficult to determine the actual cause of any effects. The usefulness of exercise in health is therefore surprisingly controversial.
If exercise was a cause of good health, it would be expected that athletes would live longer than non-athletes. However, there is no data to suggest that participation in sport throughout life increases longevity.
To highlight the problems of such research it is interesting to consider a recent study published in the American Journal of Clinical Nutrition investigating the differences in exercise amount between different groups of people. In the study subjects were divided into groups based on body mass index and health status. One group was normal weight subjects with good health, another group was obese subjects with good health and the last group was obese subjects with poor health. The health of the subjects was assessed by measuring blood glucose, high density lipoprotein cholesterol, hypertension, triglycerides and insulin resistance. Those who were unhealthy could be said to have the main characteristics of the metabolic syndrome, centering on the development of insulin resistance. The amount of exercise performed by the subjects was measured by wrist worn accelerometer and estimated through self reporting. It is important to note that the subject were elderly and aged between 60 and 82 years.
It is likely that mild exercise such as gardening, walking, and the occasional exertion are required for good health. Most people can obtain this level of activity by leading an active lifestyle. Performing endless physical activity in the form of sport does not appear to be required for good health. Although it does improve fitness in the short term.
As expected the normal weight individuals performed the most exercise. This corroborates what most studies show. However, it does not mean that the exercise was the cause of their lower body weights or their good health,. It could just as likely be that either their low body weight or good health facilitated their higher exercise capacity, or it could be that some other factor was involved. Interestingly the obese subjects in good health performed more exercise than those with poor health. However, it is again not possible to draw a solid conclusion from this data. As the subjects with poor health had the symptoms of metabolic syndrome, and as these symptoms particularly insulin resistance decrease the capacity for exercise, it might be that these individuals simply have a very poor tolerance to exercise. A lack of exercise for example is not the cause of malaria, but people with malaria do not exercise a great deal. Exercise clearly improves fitness, but its role in health is not well established and may have been exaggerated.
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