The role of lifestyle in health: the epidemiology and consequences of inactivity.

‘Sedentary activity’ constitutes an oxymoron. ‘Inactivity’ is a more appropriate term to describe the time spent in sedentary behaviours. Inactivity can be defined as a state in which bodily movement is minimal. In terms of energy expenditure, inactivity represents a state or behaviour for which energy expenditure approximates resting metabolic rate. However, the study of inactivity as a behaviour rather than an account of the energy spent in sedentary pursuits may offer a richer assessment of factors that contribute to obesity or other diseases. Inactive behaviours include television viewing, reading, working at a computer, talking with friends or on the telephone, driving a car or commuting, meditation or eating (Ainsworth et al. 1993). Historically, efforts have been made to quantify activity, to determine the validity and reliability of estimates of activity, and to determine the effects of activity on morbidity and mortality. The quantification of inactivity, and the assessment of the morbidity and mortality attributable to inactivity have received far less attention. Because inactivity has generally been viewed as part of a continuum of activity, most of the effects of inactivity must be inferred from studies of activity. Nonetheless, the adverse health effects of inactivity may be as significant as the beneficial health effects of vigorous activity. In the present brief review, we will examine the evidence that inactivity exerts effects on health that are independent of the effects of activity. We will then explore the morbidity and mortality associated with inactivity, the epidemiology of inactivity, and recommendations for change.