Activities have been confused

EDITOR—Glass et al have concluded that in elderly people “social and productive activities that involve little or no enhancement of fitness lower the risk of mortality all cause as much as fitness activities do,” and that “activity may confer survival benefits through psychosocial pathways.”1 The study design, however, incorporates a misconception that pervades many studies into physical activity.

Neither high levels of cardiorespiratory fitness nor participation in vigorous activities that promote cardiorespiratory fitness are necessary to decrease morbidity and mortality. The main health related variable is the volume, rather than the frequency, intensity, or duration of the activity. Whether the activity is planned (as in sport), or incidental (as in gardening), is obviously immaterial. The body does not care whether the physical activity is undertaken as sport, exercise, hobbies, translocation, or household chores.

In this study, most activities categorised as social and productive can entail significant levels of incidental physical activity. Of the 11 activities mentioned, only day or overnight trips and playing cards, games, or bingo are likely to be completely sedentary. The risk is high that this analysis is seriously confounded by the presence of health enhancing physical activities in all three categories. Glass et al are obviously aware of this as they have omitted “shopping” and “gardening” from one of the analyses. We cannot, however, discount the possibility that all the activities categorised as productive (gardening, preparing meals, shopping, unpaid work, paid work, and other employment) might incorporate significant amounts of physical activity. Significant risk reduction is achieved at a level of 150 kcal/kg/day of expenditure of energy through activity.2 This level is embodied in current health related guidelines for physical activity, 3 4 which recommend 30 minutes of brisk walking per day. Sufficient energy expenditure can be just as easily accrued through incidental physical …