Most elderly people have some kind of regular daily activity, usually closely connected to their daily habits. A six-graded scale for classification of physical activity is presented. Persons with a low physical activity also usually perceive their physical strain as rather light or moderate. There is a reduction with age in muscle volume, muscle strength, and aerobic capacity which are rather parallel. From a muscular point of view there are only moderate qualitative changes up to the ages around 70; at higher ages there will be a tendency to more marked changes in muscle structure. The maximal aerobic power as well as muscle strength can be increased by physical training also in the elderly. At least up to the ages around 70 there will be an adaptation in muscle structure and enzymatic capacity. In very well-trained 70-year-old men high levels of oxidative enzymes are found together with high maximal aerobic power capacity. A positive attitude should be taken towards physical exercise for prevention and rehabilitation also in the elderly.