Too Little Exercise and Too Much Sitting: Inactivity Physiology and the Need for New Recommendations on Sedentary Behavior

Abstract

Moderate- to vigorous-intensity physical activity has an established preventive role in cardiovascular disease, type 2 diabetes, obesity, and some cancers. However, recent epidemiologic evidence suggests that sitting time has deleterious cardiovascular and metabolic effects that are independent of whether adults meet physical activity guidelines. Evidence from "inactivity physiology" laboratory studies has identified unique mechanisms that are distinct from the biologic bases of exercising. Opportunities for sedentary behaviors are ubiquitous and are likely to increase with further innovations in technologies. We present a compelling selection of emerging evidence on the deleterious effects of sedentary behavior, as it is underpinned by the unique physiology of inactivity. It is time to consider excessive sitting a serious health hazard, with the potential for ultimately giving consideration to the inclusion of too much sitting (or too few breaks from sitting) in physical activity and health guidelines.

Figure 1

For an individual who sleeps 8 hours per day, the remaining 16 hours are typically filled with domestic and work duties. For this hypothetical “physically active” adult, a 45-minute exercise session of brisk walking prior to work ensures that the minimum level of purposeful exercise (30 minutes per day on 5 days per week) is achieved early in the day. However, this person then sits during the drive toCurrent Cardiovascular Risk Reports RK02-4-2-01 fig. 1 work, at the computer before lunch, during lunch, at the computer after lunch, during the drive home, at dinner, and while watching TV. This492 pts. W/48 pts. D (41 × 7) hypothetical person may spend up to 95% of his waking hours sitting. However, because this person walked briskly for a sustained periodAuthor: Hamilton et al. Editor: Ginny Artist: TE of at least 30 minutes, current public health guidelines consider him “physically active.” The term active couch potato or exercising couch potato is probably more appropriate.