Physical exercise is proposed as a highly effective means of treating and preventing the main causes of morbidity and mortality--most of which are associated with aging--in industrialized countries. Low physical fitness is an important risk factor for cardiovascular and all-causes morbidity and mortality; indeed, it is even a predictor of these problems. When properly measured, the assessment of physical fitness can be a highly valuable indicator of health and life expectancy and, therefore, should be performed routinely in the clinical setting. Individually adapted training programs could be prescribed based on fitness assessment results and an adequate knowledge of patient lifestyle and daily physical activity. Such training programs would allow people to develop their maximum physical potential, improve their physical and mental health, and attenuate the negative consequences of aging.