A somewhat sedentary lifestyle combined with regular exercise is turning us into what physiologists are calling ‘active couch potatoes’–and that exercise, no matter how vigourous, doesn’t appear to be counteracting the negative effects of that sedentary lifestyle.

In rats, this lifestyle was found to produce “unhealthy cellular changes in their muscles” and increase insulin resistance and fatty acid levels in their blood. In conclusion: a mostly sedentary lifestyle is bad for us, regardless of exercise habits.

[Studies have shown] that, to no one’s surprise, the men who sat the most had the greatest risk of heart problems. Men who spent more than 23 hours a week watching TV and sitting in their cars (as passengers or as drivers) had a 64 percent greater chance of dying from heart disease than those who sat for 11 hours a week or less. What was unexpected was that many of the men who sat long hours and developed heart problems also exercised. Quite a few of them said they did so regularly and led active lifestyles. The men worked out, then sat in cars and in front of televisions for hours, and their risk of heart disease soared, despite the exercise. Their workouts did not counteract the ill effects of sitting. […]

Decades ago, before the advent of computers, plasma TVs and Roombas, people spent more time completing ‘light-intensity 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. […] 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’. […] 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.

via Waxy