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Do you lead an active lifestyle or a sedentary one? The question is simple, but the answer may not be as obvious as you think. Let’s say, for example, you’re a busy guy who works 60 hours a week at a desk job but who still manages to find time for five 45-minute bouts of exercise. Most experts would label you as active. But Marc Hamilton, Ph.D., has another name for you: couch potato.

Perhaps “exercising couch potato” would be more accurate, but Hamilton, a physiologist and professor at the Pennington Biomedical Research Center, in Baton Rouge, Louisiana, would still classify you as sedentary. “People tend to view physical activity on a single continuum,” he says. “On the far side, you have a person who exercises a lot; on the other, a person who doesn’t exercise at all. However, they’re not necessarily polar opposites.”

Hamilton’s take, which is supported by a growing body of research, is that the amount of time you exercise and the amount of time you spend on your butt are completely separate factors for heart-disease risk. New evidence suggests, in fact, that the more hours a day you sit, the greater your likelihood of dying an earlier death regardless of how much you exercise or how lean you are. That’s right: Even a sculpted six-pack can’t protect you from your chair.

But it’s not just your heart that’s at risk from too much sitting; your hips, spine, and shoulders could also suffer. In fact, it’s not a leap to say that a chair-potato lifestyle can ruin you from head to toe.

Statistically speaking, we’re working out as much as we were 30 years ago. It’s just that we’re leading more sedentary lives overall. A 2006 University of Minnesota study found that from 1980 to 2000, the percentage of people who reported exercising regularly remained the same—but the amount of time people spent sitting rose by 8 percent.

Now consider how much we sit today compared with, say, 160 years ago. In a clever study, Dutch researchers created a sort of historical theme park and recruited actors to play 1850s Australian settlers for a week. The men did everything from chop wood to forage for food, and the scientists compared their activity levels with those of modern office workers. The result: The actors did the equivalent of walking 3 to 8 miles more a day than the deskbound men. That kind of activity is perhaps even more needed in today’s fast-food nation than it was in the 1800s, but not just because it boosts calorie burn.

A 2010 study in the Journal of Applied Physiology found that when healthy men limited their number of footsteps by 85 percent for 2 weeks, they experienced a 17 percent decrease in insulin sensitivity, raising their diabetes risk. “We’ve done a lot to keep people alive longer, but that doesn’t mean we’re healthier,” says Hamilton.

Today’s death rate is about 43 percent lower than it was in 1960, but back then, less than 1 percent of Americans had diabetes and only 13 percent were obese. Compare that with now, when 6 percent are diagnosed with diabetes and 35 percent are obese.

Make no mistake: “Regularly exercising is not the same as being active,” says Peter Katzmarzyk, Ph.D., Hamilton’s colleague at Pennington, the nation’s leading obesity research center. Katzmarzyk is referring to the difference between official exercise activity, such as running, biking, or lifting weights, and so-called nonexercise activity, like walking to your car, mowing the lawn, or simply standing. “A person may hit the gym every day, but if he’s sitting a good deal of the rest of the time, he’s probably not leading an overall active life,” says Katzmarzyk.

You might dismiss this as scientific semantics, but energy expenditure statistics support Katzmarzyk’s notion. In a 2007 report, University of Missouri scientists said that people with the highest levels of nonexercise activity (but little to no actual “exercise”) burned significantly more calories a week than those who ran 35 miles a week but accumulated only a moderate amount of nonexercise activity. “It can be as simple as standing more,” Katzmarzyk says.

For instance, a “standing” worker—say, a sales clerk at a Banana Republic store—burns about 1,500 calories while on the job; a person behind a desk might expend roughly 1,000 calories. That goes a long way in explaining why people gain 16 pounds, on average, within 8 months of starting sedentary office work, according to a study from the University of North Carolina at Wilmington.

But calories aren’t the only problem. In 2009, Katzmarzyk studied the lifestyle habits of more than 17,000 men and women and found that the people who sat for almost the entire day were 54 percent more likely to end up clutching their chests than those who sat for almost none of the time. That’s no surprise, of course, except that it didn’t matter how much the sitters weighed or how often they exercised. “The evidence that sitting is associated with heart disease is very strong,” says Katzmarzyk. “We see it in people who smoke and people who don’t. We see it in people who are regular exercisers and those who aren’t. Sitting is an independent risk factor.”

This isn’t actually a new discovery. In a British study published in 1953, scientists examined two groups of workers: bus drivers and trolley conductors. At first glance, the two occupations appeared to be pretty similar. But while the bus drivers were more likely to sit down for their entire day, the trolley conductors were running up and down the stairs and aisles of the double-decker trolleys. As it turned out, the bus drivers were nearly twice as likely to die of heart disease as the conductors were.

A more recent interpretation of that study, published in 2004, found that none of the participants ever exercised. But the two groups did sit for different amounts of time. The analysis revealed that even after the scientists accounted for differences in waist size—an indicator of belly fat—the bus drivers were still more likely to die before the conductors did. So the bus drivers were at higher risk not simply because their sedentary jobs made them resemble Ralph Kramden, but also because all that sitting truly was making them unhealthy.

Hamilton came to call this area of science “inactivity physiology” while he was conducting studies to determine how exercise affects an enzyme called lipoprotein lipase (LPL). Found in humans as well as mice, LPL’s main responsibility is to break down fat in the bloodstream to use as energy. If a mouse (or a man) doesn’t have this enzyme, or if the enzyme doesn’t work in their leg muscles, the fat is stored instead of burned as fuel.

Hamilton discovered that when the rodents were forced to lie down for most of their waking hours, LPL activity in their leg muscles plummeted. But when they simply stood around most of the time, the gene was 10 times more active. That’s when he added an exercise session to the lab-rat routine and found that exercise had no effect on LPL. He believes the finding also applies to people.

“Humans sit too much, so you have to treat the problem specifically,” says Hamilton. “The cure for too much sitting isn’t more exercise. Exercise is good, of course, but the average person could never do enough to counteract the effect of hours and hours of chair time.

“We know there’s a gene in the body that causes heart disease, but it doesn’t respond to exercise no matter how often or how hard you work out,” he says. “And yet the activity of the gene becomes worse from sitting—or rather, the complete and utter lack of contractile activity in your muscles. So the more nonexercise activity you do, the more total time you spend on your feet and out of your chair. That’s the real cure.”

“Your body adapts to what you do most often,” says Bill Hartman, P.T., C.S.C.S., a Men’s Health advisor and physical therapist in Indianapolis, Indiana. “So if you sit in a chair all day, you’ll essentially become better adapted to sitting in a chair.” The trouble is, that makes you less adept at standing, walking, running, and jumping, all of which a truly healthy human should be able to do with proficiency. “Older folks have a harder time moving around than younger people do,” says Hartman. “That’s not simply because of age; it’s because what you do consistently from day to day manifests itself over time, for both good and bad.”

Do you sit all day at a desk? You’re courting muscle stiffness, poor balance and mobility, and lower-back, neck, and hip pain. But to understand why, you’ll need a quick primer on fascia, a tough connective tissue that covers all your muscles. While fascia is pliable, it tends to “set” in the position your muscles are in most often. So if you sit most of the time, your fascia adapts to that specific position.

Now think about where your hips and thighs are in relation to your torso while you’re sitting. They’re bent, which causes the muscles on the front of your thighs, known as hip flexors, to contract slightly, or shorten. The more you sit, the more the fascia will keep your hip flexors shortened. “If you’ve ever seen a guy walk with a forward lean, it’s often because of shortened hip flexors,” says Hartman. “The muscles don’t stretch as they naturally should. As a result, he’s not walking tall and straight because his fascia has adapted more to sitting than standing.”

This same effect can be seen in other areas of your body. For instance, if you spend a lot of time with your shoulders and upper back slumped over a keyboard, this eventually becomes your normal posture. “That’s not just an issue in terms of how you look; it frequently leads to chronic neck and shoulder pain,” says Hartman. Also, people who frequently cross their legs a certain way can experience hip imbalances. “This makes your entire lower body less stable, which decreases your agility and athletic performance and increases your risk for injuries,” Hartman says. Add all this up, and a person who sits a lot is less efficient not only at exercising, but also at simply moving from, say, the couch to the refrigerator.

There’s yet another problem with all that sitting. “If you spend too much time in a chair, your glute muscles will actually ‘forget’ how to fire,” says Hartman. This phenomenon is aptly nicknamed “gluteal amnesia.” A basic-anatomy reminder: Your glutes, or butt muscles, are your body’s largest muscle group. So if they aren’t functioning properly, you won’t be able to squat or deadlift as much weight, and you won’t burn as much fat. After all, muscles burn calories. And that makes your glutes a powerful furnace for fat—a furnace that’s probably been switched off if you spend most of the day on your duff.

It gets worse. Weak glutes as well as tight hip flexors cause your pelvis to tilt forward. This puts stress on your lumbar spine, resulting in lower-back pain. It also pushes your belly out, which gives you a protruding gut even if you don’t have an ounce of fat. “The changes to your muscles and posture from sitting are so small that you won’t notice them at first. But as you reach your 30s, 40s, 50s, and beyond, they’ll gradually become worse,” says Hartman, “and a lot harder to fix.”

So what’s a desk jockey to do? Hamilton’s advice: Think in terms of two spectrums of activity. One represents the activities you do that are considered regular exercise. But another denotes the amount of time you spend sitting versus the time you spend on your feet. “Then every day, make the small choices that will help move you in the right direction on that sitting-versus-standing spectrum,” says Hamilton. “Stand while you’re talking on the phone. It all adds up, and it all matters.”

Of course, there’s a problem with all of this: It kills all our lame excuses for not exercising (no time for the gym, fungus on the shower-room floor, a rerun of The Office you haven’t seen). Now we have to redefine “workout” to include every waking moment of our days. But there’s a big payoff: more of those days to enjoy in the future. So get up off your chair and start nonexercising.