Stand Up for Your Health

Worse yet, experts say that 60 to 90 minutes of daily exercise may not counteract the effects of sitting all day. In fact, Hamilton says, the biochemical reactions slowed by sitting are completely different from the ones that are activated by your daily workout. The biggest difference between thin and fat people is not how much they eat or exercise, but how much they sit, according to James Levine, MD, an obesity researcher at the Mayo Clinic. In a now famed 2005 study, Dr. Levine placed mildly obese and lean participants with similar, fairly healthy diets in sensored "magic" underwear that recorded their body position every half second. The thin people spent a whopping 120 fewer minutes every day sitting, and the overweight people would have burned an average of 350 more calories if they'd engaged in as many non-exercise-related activities (i.e., puttering around). The take-home message: Sitting can have just as great an effect on your weight than eating or exercise, all because our metabolism engine is fueled by constant little movements.

Sitting messes with your back
Your powerful abdominal, pelvic, and leg muscles evolved to do the work of supporting your 100-plus pounds of organs and bones. "But when you sit, you're placing most of your weight directly on the spine and pelvis instead," explains Andrew Hecht, MD, co-chief of spinal surgery at Mount Sinai Medical Center. You're also forcing the natural S-curve of your spine into a C-shape, which isn't strong enough to take the pressure. "Imagine resting a heavy weight on top of the letter S or C," says Galen Cranz, PhD, author of The Chair: Rethinking Culture, Body & Design. "Which is going to collapse more easily?"

Sitting shortens your life
How's this for a case against being on your bum? A long-term study published in the American Journal of Epidemiology in 2010 followed nearly 70,000 healthy women and their daily habits for 14 years. After adjusting for risk factors including body mass index and smoking, researchers found that women who spent six hours a day sitting had a 37% increased risk of dying versus those who spent less than three hours a day seated. Also, death rates from cardiovascular disease were 2.7 times higher in women who sat six or more hours a day, regardless of how much they exercised or weighed. Yes, sitting literally kills.