The dangers of a leading sedentary lifestyle are widely known, but a recent study published in the Journal of Applied Physiology suggests that sitting for more than 13 hours per day may entirely nullify the metabolic benefits associated with exercise.
"Inactivity Induces Resistance to the Metabolic Benefits Following Acute Exercise," published Feb. 14, assessed the metabolic health of 10 regularly active University of Texas graduate students who were asked to become temporarily sedentary.
Researchers first measured each subject's activity habits and aerobic fitness levels. Then, for four days, the subjects were asked to restrict themselves to no more than 4,000 daily steps with 13 hours of sedentary behavior, such as sitting on a couch.
The subjects also consumed fewer calories during this period, according to the study. This helped control body weight and ensure any measurable metabolic changes were largely related to inactivity, not diet.
On the fifth day, the subjects visited the university's human performance lab where they consumed a special milkshake comprised of ice cream and half-and-half. The researchers then monitored their insulin, triglycerides and blood sugar and insulin for the following six hours to see how each variable would respond to the milkshake—a sudden injection of fat and sugar.
Finally, the researchers had the subjects repeat the same process for another five days. However, on the second round's fourth night, the subjects were asked to run briskly for an hour on a treadmill. Then, on the fifth day, they again consumed the heavy milkshake and were re-evaluated.
The researchers reported little to no change in the subjects' triglycerides and blood sugar levels after their treadmill run (day 10) when compared to those levels without a treadmill run (day five). In both cases, the subjects exhibited tired, inefficient metabolisms.
The study's abstract states: "These data indicate that physical inactivity creates a condition whereby people become resistant to the metabolic improvements that are typically derived from an acute bout of aerobic exercise."