Active Voice: MVPA Protects Against Excessive Sedentary Behavior
By Mark D. Peterson, Ph.D., M.S.
Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.
Dr. Mark Peterson, an ACSM member, is a physiologist, activity epidemiologist, and research assistant professor at the University of Michigan-Medicine, Department of Physical Medicine & Rehabilitation. His work is devoted to the treatment/prevention of obesity, sarcopenia, and functional motor deficit. He is also funded by the National Institutes of Health (NIH) to study mechanisms of metabolic dysregulation and muscle pathology among individuals with cerebral palsy (CP), and to identify behavioral interventions to prevent these secondary outcomes.
This commentary presents Dr. Peterson’s views on the topic of a research article he and his colleagues have authored and which appears in the June 2014 issue of Medicine and Science in Sports and Exercise® (MSSE).
Excess dietary consumption and failure to meet the recommended 150 minutes of weekly moderate-to-vigorous physical activity (MVPA) have received extensive attention in the literature, as underlying factors that place individuals at risk for obesity and chronic disease (for further information, see 2010 Dietary Guidelines for Americans and the ACSM/AHA joint recommendation on physical activity and public health). However, and especially during the past few years, the topic of sedentary behavior (SB) has received equal research emphasis as a modifiable predictor of cardiometabolic diseases and early mortality. The bulk of this work has demonstrated a strong link between time spent sitting down, such as occurs during television viewing, and increased risks for negative health outcomes. Numerous large cohort studies have demonstrated an association between sitting time and risk, even after adjustment for self-reported MVPA. These findings collectively suggest the following important public health messages regarding the interplay between lack of physical activity and health deterioration: (1) physical activity and exercise cannot protect against the negative consequences of excessive SB, and/or (2) individuals who engage in large volumes of SB are at exaggerated risk because they are also less likely to engage in any physical activity.
The study of SB as a distinct concept, rather than the mere absence of MVPA, is an important area of research. However, since the definition of sedentary behaviour has evolved over the last decade, there has been some confusion about ways to distinguish it from physical inactivity. Previously, being sedentary meant merely a lack of MVPA. And yet, in his recent research report in MSSE, Dr. Peter Katzmarzyk presented evidence of a strong negative association between time spent simply standing and the risk of mortality – supporting the notion that even light physical activity is a potentially viable target of intervention.
This message is extremely important and provides the foundation for lifestyle modification and public health interventions, particularly among individuals who are both physically inactive and participate in excessive daily sitting. However, what remains to be sufficiently understood is how different combinations of objectively measured, intensity-specific physical activity and sedentary patterns contribute to protection against or potentiation of cardiometabolic disease risk.
Indeed, and as suggested by Dr. Katzmarzyk in his SBM commentary last month, “One could easily imagine a situation where someone is meeting the physical activity guidelines but spending a large fraction of the day sitting.”
Towards that end, and using accelerometry data from over 5,000 adults, the results of our study reported in MSSE, showed that time spent in SB was not a predictor of metabolic abnormalities when MVPA was accounted for. Adults with the highest MVPA (~43-48 min/day) across SB tertiles did not differ markedly in prevalence of obesity, adiposity, and/or serum cardiometabolic risk factors. However, less than this amount of daily MVPA was associated with substantial elevations of risk. Interestingly, we also found a significant trend of decreased time spent in lifestyle moderate activity across lower tertiles of MVPA, such that individuals with the highest MVPA also tended to spend more time in lifestyle moderate activity than adults in the lower tertiles of MVPA. Therefore, it is quite plausible that a combined tendency toward higher MVPA and lifestyle activity may provide substantial additive health benefits, regardless of the amount of time spent in SB or light activity. These findings certainly do not discount the value of fragmenting sitting time with light activities, as there are many high-risk populations who may not be able to engage in the recommended amounts of physical activity (e.g., frail older adults, congenital or acquired motor disabilities, etc.). It does, however, support the relative value of MVPA, independent of SB, to attenuate risk.