The harm to leg arteries caused by sitting for hours can be easily reversed with hourly 5-minute walks, according to new research published in Medicine & Science in Sports & Exercise, the official journal of the American College of Sports Medicine.
Sitting for prolonged periods is associated with risk factors for cardiovascular and metabolic disease, such as higher cholesterol levels and greater waist circumference. Because muscles are slackened when sitting, they do not contribute to pumping blood to the heart. This causes blood to pool in the legs, damaging the endothelial function of arteries and impairing blood vessels' ability to expand.
In the new study, 11 healthy, non-obese men aged between 20 and 35 years took part in two randomized trials.
In the first trial, the participants were required to sit for 3 hours without moving their legs. How well their femoral artery - the large artery in the thigh - was functioning was measured using a blood pressure cuff and ultrasound technology. Readings were taken before the study commenced, and at the 1, 2 and 3-hour marks.
In the second experiment, the men again sat for 3 hours, but also walked on a treadmill set at a speed of 2 mph for 5 minutes at the 30-minute, 1.5-hour and 2.5-hour marks. Again, the researchers measured how well the femoral arteries of the participants were functioning.
The researchers found that, while sitting, the dilation and expansion of the participants' arteries were impaired by up to 50% after just the first hour.
However, there was no decrease in arterial function among the participants who walked for 5 minutes each hour. The researchers think this is because the increase in muscle activity aided blood flow.
Americans sit for 8 hours a day, on average
"American adults sit for approximately 8 hours a day," says study leader Saurabh Thosar, a postdoctoral researcher at Oregon Health & Science University. "The impairment in endothelial function is significant after just 1 hour of sitting. It is interesting to see that light physical activity can help in preventing this impairment."
"There is plenty of epidemiological evidence linking sitting time to various chronic diseases and linking breaking sitting time to beneficial cardiovascular effects, but there is very little experimental evidence. We have shown that prolonged sitting impairs endothelial function, which is an early marker of cardiovascular disease, and that breaking sitting time prevents the decline in that function."
Recently, Medical News Today reported on a study published in the British Journal of Sports Medicine, which suggested that reducing the amount of sitting time could protect DNA and even prolong lifespan.
The researchers behind that study found that reduced sitting time is linked to lengthening of telomeres - the protective "caps" at the end of chromosomes that prevent their genetic code from unraveling or clumping together.
Other studies in 2014 have suggested that standing - rather than sitting - during work meetings indirectly benefits work performance in organizations where knowledge-based working is important, and that walking boosts creative thinking.
Also, in June, researchers involved in the Behavioral Sleep Medicine Program at the Feinberg School of Medicine at Northwestern University in Chicago, IL, found that people who are late to bed spend more time sitting and are less motivated to maintain an exercise schedule.