Is Being Physically Active Enough to Be Metabolically Healthy? The Key Role of Sedentary Behavior

Low levels of physical activity (PA) are now well recognized as a major public health problem, implicated in cancer, cardiovascular disease (CVD), metabolic syndrome, diabetes, and early mortality (1). PA guidelines (i.e., $150 min/week ofmoderate activity or$75min/week of vigorous activity, collectively referred to as moderate to vigorous physical activity [MVPA]) are globally promoted to protect the population against the risk of developing chronic disease. But is this sufficient to promote metabolic health? The relationship between PA and health appears tobemore complex than initially thought, and another component has been attracting attention over the past decade: sedentary behavior (SB). Although they are often used interchangeably, SB is fundamentally different from physical inactivity. While physical inactivity is defined as engaging in less PA than necessary to meet the current guidelines (2), SB describes “any waking behavior characterized by an energy expenditure#1.5 metabolic equivalents (METs) while in a sitting or reclining posture” (3). Thus, individuals can be both physically active and highly sedentary (4,5). Increased time spent sitting raises the risk for metabolic syndrome (6), incidentCVD, CVD-related risk factors, and early mortality (7,8), even in people who exercise regularly. These observations raise obvious questions: Are the effects of SB independent from those of PA or simply the “other side of the coin”? What is the minimum level of MVPA needed to counteract the adverse health effects of SB? A recent harmonized meta-analysis of data from more than 1 million adults showed that high levels of PA (i.e., about 60–75 min/day of MVPA) are needed to eliminate the effect of 9 h/day of SB on mortality (9). Even if this exceeds the current PA recommendations, this observation suggests that once we reach such levels, we should be free of the effects of SB on health. In this issue of Diabetes Care,Madden et al. report that SB adversely influences metabolic health even in the presence of large volumes of MVPA (10). In this study, the relationship between objectively measured SB, light physical activity (LPA), MVPA, and metabolic syndrome risk score was examined in 54 older adults. Notably, study participants had remarkably high levels of MVPA (2.6 h/day), 2 h more than the current recommendations (2) and more than seven times that of typical older adults (11). The authors found that greater sedentary time was associated with higher metabolic risk score, independent of age and sex. They conclude that even among highly active older adults, SB is associated with increased metabolic risk (Fig. 1). Thus,MVPAandSB appear to be independent predictors of metabolic risk, as the negative health effects of SB are not fully offset by even extremely high levels of MVPA. This study adds to SB literature in several meaningful ways. Even in a population of Masters athletes reaching “ceiling levels” of PA who have likely been active most of their lives, SB is not only highly prevalent but also similar to sedentary levels of inactive older adults (11). Furthermore, SB is still strongly associated with metabolic risk. This highlights the importance of understanding and potentially intervening on both physical inactivity (too little exercise) and high levels of SB (too much sitting). This study is clinically important given that SB has been recognized as a major risk factor for many metabolic diseases (12). Studying a highly physically active group of older adults lays the groundwork for delineating the independent role of SB in the relationship betweenPA andhealth, as sitting toomuchmayhave different health implications than lack of MVPA.