A number of published studies report that prolonged sitting—as many people do daily at their jobs—is associated with risk factors such as higher cholesterol and greater waist circumference that can lead to cardiovascular and metabolic disease. Saurabh Thosar, from Indiana University, and colleagues enrolled 11 nonobese, healthy men, aged 20 to 35, who participated in two randomized trials. In one they sat for three hours without moving their legs. The researchers used a blood pressure cuff and ultrasound technology to measure the functionality of the femoral artery at baseline and again at the one-, two- and three-hour marks. In the second trial the men sat during a three-hour period but also walked on a treadmill for five minutes at a speed of 2 mph at the 30-minute mark, 1.5-hour mark and 2.5-hour mark. The researchers measured the functionality of the femoral artery at the same intervals as in the other trial. They demonstrated that during a three-hour period the flow-mediated dilation—the expansion of the arteries as a result of increased blood flow—of the main artery in the legs was impaired by as much as 50 percent after just one hour. The subjects who walked for five minutes of each hour of sitting saw their arterial function stay the same—it did not drop throughout the three-hour period—suggesting a beneficial effect of increased muscle activity and blood flow.
“Three hours of sitting resulted in a significant impairment in shear rate and [superficial femoral artery flow mediated dilation],” the researchers reported. “When light activity breaks were introduced hourly during sitting, the decline in [flow mediated dilation] was prevented.”
Thosar, S. S., et al. (2014). Effect of prolonged sitting and breaks in sitting time on endothelial function. Med Sci Sports Exerc. Published online August 18.
—Dr. Bob Goldman
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