Most of us have heard that sitting is unhealthy. But many of us also have discounted the warnings, since we spend our lunch hours conscientiously visiting the gym. We consider ourselves sufficiently active. But then we drive back to the office, settle at our desks and sit for the rest of the day. We are, in a phrase adopted by physiologists, ‘‘active couch potatoes.’’
... adults spend more than nine hours a day in oxymoronic ‘‘sedentary activities.’’ For studies like these, scientists categorize activities by the number of METs they demand. A MET, or metabolic equivalent of task, is a measure of energy, with one MET being the amount of energy you burn lying down for one minute. Sedentary behaviors demand one to one and a half METs, or very little exertion.
Decades ago, before the advent of computers, plasma TVs and Roombas, people spent more time completing ‘‘light-intensity activities,’’ which require between one and a half and three METs. Most ‘‘home activities,’’ like mopping, cooking and changing light bulbs, demand between two and three METs. (One exception is ‘‘butchering animals,’’ a six-MET activity, according to a bogglingly comprehensive compilation from 2000 of the METs associated with different activities.) Nowadays, few of us accumulate much light-intensity activity. We’ve replaced those hours with sitting.
The physiological consequences are only slowly being untangled. In a number of recent animal studies, when rats or mice were not allowed to amble normally around in their cages, they rapidly developed unhealthy cellular changes in their muscles. The animals showed signs of insulin resistance and had higher levels of fatty acids in their blood. Scientists believe the changes are caused by a lack of muscular contractions. If you sit for long hours, you experience no ‘‘isometric contraction of the antigravity (postural) muscles,’’ according to an overview of the consequences of inactivity published this month in Exercise and Sports Sciences Reviews. Your muscles, unused for hours at a time, change in subtle fashion, and as a result, your risk for heart disease, diabetes and other diseases can rise.
Regular workout sessions do not appear to fully undo the effects of prolonged sitting. |
