A decrease in habitual physical activity accompanies old age in mammalian species and in healthy man.74,142 This is not simply a consequence of a parallel decline in exercise capacity, and factors other than those which limit aerobic capacity and endurance performance must be involved.143 Moreover, most old people remain at least moderately active.144 Everyday activities may require cardiorespiratory and muscle performance which is much nearer the maximum in elderly individuals than in younger people and further reduction in reserves by, for example, illness, will more readily cause disability.
Regular moderate activity is sufficient to mitigate declining exercise capacity and muscle performance and conditioning programmes may well confer additional benefits even at advanced ages. Exercise remains good for you regardless of age. A suitable programme is one of moderate to high workrates, involving large muscle groups and performed for 15–30 minutes every other day.145 The intensity is best guided by heart rate, for which a variety of formulae have been proposed.146
The complex interaction of physiological factors influencing muscular performance has been illustrated. Only when these physiological processes are disentangled and better defined will we elucidate the molecular mechanisms which underlie age-associated changes. It is not yet possible to define the relative importance of intrinsic and extrinsic influences, but the proportion of the decline in VO2 max which is directly attributable to intrinsic aging is smaller than is usually assumed, probably less than 50%.147 While the most critical determinant of VO2 max in young subjects is probably cardiac output,148 we now recognize that in elderly people the balance shifts; muscle performance, changes in blood distribution and peripheral microvascular capacity become ever more important determinants of exercise performance and should command increasing research interest.