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Metabolic Effects of Reduced Sitting and the Postprandial State

This is an excerpt from Sedentary Behavior and Health by Weimo Zhu & Neville Owen.

Several studies have investigated the effects on cardiometabolic biomarkers of short episodes (2- to 9-hr, single-day experiment) of prolonged uninterrupted sitting versus various manipulations of reduced sitting during the postprandial period. Although the findings from the experimental studies that have specifically addressed the cardiometabolic consequences of prolonged sitting and reduced sitting are promising, there is still a clear need for the development of further high-quality research evidence. In addition to examining the effect of longer-term exposures (i.e., weeks or months), the various perturbations in the frequency (high versus low), length (short versus long), and type (ambulation versus standing) of activity interruptions to prolonged sitting and interactions with moderate- to vigorous-intensity physical activity, dietary intake, and meal patterns need to be examined.

Furthermore, there are likely to be effects of reducing and breaking up sitting time on multiple body tissues, organs, and systems (e.g., vascular and hemodynamic mechanisms, cognitive function, musculoskeletal adaptations). Establishing the dose - response relationships among interrupting sitting, risk markers, and physiological adaptations also has the potential to inform further work in specific disease groups - for example, among patients with hypertension, peripheral artery disease, osteoarthritis, overweight and obesity, metabolic syndrome and diabetes, and cognitive impairment, and among those with elevated thrombotic risk.

Prolonged Slow Walking Post Meal

Within the work-office setting, a randomized crossover trial by Nygaard and colleagues (2009) investigated the capillary (finger-prick) blood glucose response to a carbohydrate-rich meal over a 2-hour period (see table 3.1). The study compared, in healthy women aged >50 years, uninterrupted sitting to reduced sitting achieved through initial 15- and 40-minute bouts of slow, very light walking followed by sitting. The 40-minute walking condition, but not the 15-minute walking condition, induced a significant decrease in the 2-hour incremental glucose area under the curve (AUC), leading the authors to suggest that a dose response between the duration of slow walking (and the resultant increase in energy expenditure) and reductions in postprandial glycemia may exist. However, a subsequent study by Lunde and others (2012) using a similar study design and methodologies in female Pakistani immigrants (most of whom had abnormal glucose tolerance) demonstrated reductions in the 2-hour incremental area under the curve for both the 20-minute (by 30.6%) and 40-minute (by 39.0%) walking conditions relative to the control day. A significant reduction in systolic blood pressure was also observed after the 40-minute walking condition. The discrepancies between the results in these two studies suggest that a greater workload in terms of duration of the bout of activity or in terms of energy expenditure is required in metabolically unhealthy people. An interaction between extrinsic factors (i.e., physical activity) and genetic background (Caucasians versus Asians) may also influence the dose - response relationship between physical activity and metabolic health.

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