Ideally this article should begin with a mathematical model--an equation. On the left we should put together contributions and expenditures in terms of hours, money and effort. On the right we should enter the profits in terms of years of life, money and quality of life. Unfortunately it is not that easy. The literature is comprehensive but also not complete. At the request of the British Department of Social Welfare, Fentem & Bassey went through the literature on exercise and health--1 334 references (4), and were unable to draw up any conclusion in the form of a mathematical equation. They could only make a declaration which they called "The case for exercise" (10). Lack of scientific proof should not stop us from drawing probable conclusions. In the article below we set out our reasons for the conclusions we have arrived at. In brief, the conclusion should be: "exercise is healthy and health is profitable".