In this month’s MSSE, I am directing attention to three articles that address the interaction of physical activity and sedentariness.
First, Benatti and Ried-Larsen review the effects of interrupting prolonged spans of sitting with periods of physical activity. One conclusion was that punctuating prolonged sitting with even low-intensity physical activity such as standing and light ambulation could prove beneficial for physically inactive persons. However, the studies included also suggested that greater metabolic health benefits accrued with higher physical activity intensity during the breaks. Furthermore, some studies suggested that healthy physically active individuals, as well as people with type 2 diabetes, would optimize metabolic health benefits by interrupting prolonged sitting with physical activity at a higher rather than lower intensity during the breaks.
Slightly at odds with the implication about type 2 diabetics are findings from an original research study reported by Falconer et al. They used isotemporal substitution regression models to explore the impact of reallocating one level of activity for another while holding total time constant. Their results imply that engaging in relatively small increases in light-intensity physical activity, or even reducing the duration of inactive periods, may provide improvements in body composition and metabolic health in people with newly diagnosed type 2 diabetes. The importance of the study is that it suggests that lifestyle interventions in patients with type 2 diabetes may be effective in improving health by incorporating increased daily activities even at intensities that do not contribute to accumulation of moderate to vigorous physical activity (MVPA).
Finally, Katzmarzyk et al. studied physical activity and sedentary time in an international sample of children. They employed a rigorous design and a standardized data collection procedure across 12 countries spanning a large range in economic development. Physical activity and sedentary behavior were measured objectively using accelerometry, and heights and weights were directly measured in over 6,500 ten-year-old children. The results suggest that both physical activity and sedentary behavior are correlates of obesity; however, the association with sedentary behavior was not independent of physical activity. The optimal threshold for MVPA identified in this study was 55 minutes per day, which supports global physical activity guidelines that call for 60 minutes of physical activity for children and youth.
In toto, these studies continue to reveal strong support for the health benefits of even mild physical activity. Further, they add information for consideration in the ongoing deliberation of whether the amount of time spent sedentary each day is an independent health risk factor, separate from the amount of physical activity.
L. Bruce Gladden