Sitting the rest of the day wipes out the benefit of an hour of vigorous exercise

Adding to the evidence demonstrating the marked metabolic impairment caused by sitting most of the day (and the benefit of sit-stand desks), research recently published in PLoS One (Public Library of Science) shows that the benefit of a full hour of exercise is wiped out by sitting the rest of the day. The authors state:

"Epidemiological studies suggest that excessive sitting time is associated with increased health risk, independent of the performance of exercise. We hypothesized that a daily bout of exercise cannot compensate the negative effects of inactivity during the rest of the day on insulin sensitivity and plasma lipids."

In particular, insulin sensitivity takes a big hit:

"Experimental data from studies in rodents, as well as data from cross-sectional studies in humans, suggest that excessive sitting time is associated with adverse changes in circulating lipids and insulin sensitivity. Recent intervention studies also showed that short-term reduction of daily PA negatively affects insulin sensitivity...These data suggest that inactivity may have negative effects on insulin sensitivity independent of energy balance."

Furthermore...

"Several lines of evidence indicate that physical inactivity can lead to skeletal muscle insulin resistance and possibly to lipid abnormalities...current guidelines provide no guidance how, besides the 150 minutes of moderate to vigorous PA/week, the other 9930 minutes of the week should be spent. In the present study we tested the hypothesis that the negative metabolic effects of excessive sitting cannot be compensated by 1 hour of daily physical exercise."

They shrewdly designed their study to discriminate the effects sitting, light activity and exercise:

"We used activity monitors that measure 24/7 energy expenditure and posture allocation, enabling us to distinguish the effects of sedentarism from minimal daily physical activities. Under free living conditions, sitting time, physical exercise and daily energy expenditure were manipulated in healthy volunteers in three well controlled experimental conditions in order to determine the independent effects of excessive sitting on insulin sensitivity and circulating lipids."

They measured insulin sensitivity (oral glucose tolerance test, OGTT) and plasma fasting lipids after their subjects performed 4 days of either sitting 14 hours per day (sitting regime); sitting 13 hours per day and substituting 1 hour of sitting with vigorous exercise for one hour (exercise regime); and substituting 6 hours of sitting with 4 hours of walking and 2 hours standing (minimal intensity physical activity (PA) regime). The results were striking:

"Area under the curve for insulin during OGTT was significantly lower after the minimal intensity PA regime compared to both sitting and exercise regimes. Triglycerides, non-HDL cholesterol and apolipoprotein B plasma levels improved significantly in the minimal intensity PA regime compared to sitting and showed non-significant trends for improvement compared to exercise."

In other words, one hour of vigorous exercise did very little if the rest of the day was sedentary, while walking around and standing a large part of the day was clearly beneficial. The authors observe:

"A sedentary lifestyle has become a major health threat in our affluent society. Current guidelines on the prevention of cardiovascular disease promote at least ½ hr moderate to vigorous physical activity (MVPA) at least 5 days/week. They do not answer the question if, when DEE [daily energy expenditure] is held constant, such short bouts of exercise can compensate for the negative metabolic effects of inactivity. The present study, performed under free living conditions, suggests that 1 hour of daily physical exercise cannot compensate for the negative effects of inactivity on insulin sensitivity and plasma lipids if the rest of the day is spent sitting. Vice versa with nearly identical DEE reducing sitting time by walking/standing was more effective in improving insulin level and lipid parameters than 1 hour of moderate to vigorous bicycle exercise. This novel observation may have important health policy implications."

Could there be a better argument in favor of using sit-stand desks as a monumental public health measure? The authors conclude:

"One hour of daily physical exercise cannot compensate for the negative effects of inactivity on insulin sensitivity and plasma lipids if the rest of the day is spent sitting. Reducing inactivity by low intensity activities such as walking at a leisurely pace and standing is more effective than physical exercise in improving these parameters in sedentary subjects. Our study suggests that in addition to health interventions that stress the importance of spending enough energy to maintain a neutral energy balance, a minimal daily amount of non-sitting time should also be promoted."