What You're Probably Doing Now Is Killing You

Gretchen Reynolds, author of "The First 20 Minutes," on new fitness science

Gretchen Reynolds is the Phys Ed columnist of The New York Times.  Her new book, The First 20 Minutes: Surprising Science Reveals How We Can Exercise Better, Train Smarter, and Live Longer has just been published by Penguin. She recently answered questions from AT editorial director John Rasmus about the benefits of even small amounts of exercise, and why it's important to keep moving all day—even if you work out often. 

Q. The good news seems to be that any exercise, even small amounts, makes a positive difference. The bad news is, being sedentary is really bad for you. What happens to your body when you sit for long periods?
Multiple, unpleasant things happen inside your body if you sit for hours, without interruption. First, muscles slacken and your spine bows. Because muscles are the body's major consumer of blood sugar, if you aren't using those muscles, you start to get a build-up of blood sugar, after which both blood sugar and insulin levels are out of whack, and you have the early makings of type 2 diabetes.

Meanwhile, your body starts to produce less of an enzyme that breaks down fat in the bloodstream. So you start to get a build-up of fat in the blood; it then travels to the heart, liver, muscles and, sadly, the backside. People who sit for hours have been shown to gain weight and be at much higher risk of diabetes, heart disease and premature death than people who stand and move around frequently.

A lot of us get plenty of regular exercise, but we have jobs that keep us in front of computer screens all day. Does one offset the other? How often do you need to move around to avoid the problems of a sedentary routine?
I was personally very sorry to learn that exercise does not necessarily offset the damage of sitting. There is a peculiarly modern phenomenon known as the "active couch potato," which includes many of us. These are people, like me, who head out at lunch time and run for 30 minutes or visit the gym for an hour or otherwise dutifully work out. Then we take a cab back to office and sit the entire rest of the day. As a result, we develop the same unhealthy physiological conditions as people who exercise little, if at all. In other words, sitting for long, uninterrupted periods of time is unhealthy, even if you work out.

But the cure is almost ridiculously easy: Just stand up. The latest science shows persuasively that standing up every 20 minutes or so effectively stops the physiological processes related to inactivity. You don't have to do anything when you stand up. You can stroll to the window if you feel like it. Or do jumping jacks if you're the energetic type. But just standing up, by itself, activates the big muscles in your legs and back, and in the process, starts a whole series of beneficial physiological reactions.Your muscles pull sugar from your bloodstream and newly released enzymes incinerate the fat floating there. You'll reduce your risk for diabetes and heart disease. You may even lose weight. Studies have found that simply by standing up every 20 or so minutes throughout the day, you use several hundred more calories than if you stay seated almost non-stop.

So try to stand every 20 minutes for about two minutes, before settling at your desk again. If you need a reminder, many apps now allow you to set an alarm that will beep at you helpfully every 20 minutes.

It seems like the medical research on optimal amounts of exercise has gone back and forth over the last couple of decades. Where are we now, and why is the new evidence compelling?
Part of the problem with earlier studies about how much exercise we need is that they didn't define what the point of the exercise was. As it turns out, if your goal is be healthier—to have less risk of chronic diseases, including cancer and heart disease, to live a longer life—then you do not need a lot of quote/unquote exercise. Walking briskly for 20 or 30 minutes four or five times a week has been shown to significantly reduce your risk of developing heart disease or dying prematurely. That may sound like a tiny amount of exercise for many of us, but about a third of Americans get zero exercise of any kind, so for them, starting to walk 20 minutes on most days would have profound health benefits.

If, however, your goal is to be more aerobically fit or strong, then you will require additional amounts of, or different types of, exercise, the latest science shows. You'll need to provide your body with some degree of  'overload,' to which it adapts and you become faster, stronger and more fit. The quickest way to provide that overload is to do interval training, meaning brief spurts of hard, uncomfortable exercise followed by a short period of easier exercise and then hard/easy again. For instance, you sprint hard for one minute, then jog for a minute.

There was a time when most scientists and coaches thought that interval training could only be undertaken safely and effectively a few times a week. But a series of new studies by Canadian researchers have shown that ALL of your exercise can be interval training—in which case, you can get all of your exercising done in about 30 minutes a day and still get huge fitness gains. In practice, this type of training involves a five-minute or so warm-up, on a stationary bike or jogging, followed by one minute of hard exertion (think of it as least an 8 on a 'discomfort' scale of 1 - 10), followed by a minute of easy exercise, repeated five times. Cool down for five minutes, and you're done. In the Canadian studies, this brief regimen, practiced at least four times a week resulted in big gains in aerobic capacity and leg strength, along with reductions in blood pressure, bad cholesterol and even, hurrah, weight.

You used to be a pretty committed endurance athlete, and I understand you've cut down somewhat. Why is that? Do you notice a difference?
I'm a fine example of someone whose exercise goals have shifted as my life has changed. I have a family now and busy work responsibilities. I've also got a bit of a been-there-done-that attitude toward competition. I've run marathons and 10Ks and raced bikes. There was a time when becoming fitter and more race-ready was my primary goal from exercise. Now I want to be healthy. I want to set a good example for my teenaged son, in part by being around when he is, himself, competing. So I've cut back on the amount of exercise that I do. I still run almost every day. But I run three or four miles at a pleasant pace, with some intervals thrown in occasionally, just to remind myself that I could be fast if I really felt like it. And I do notice a difference. My exercise isn't as tiring as it once was, so I seem to have more energy and willingness to do other, easy activities throughout the day. I garden. I help at my son's school. I stand up a lot. And my health is good. I haven't gained weight, even as I've cut back on my workout mileage pretty substantially. My blood pressure and cholesterol levels are good (due in part, too, to my genetic good fortune in having healthy parents). My heart is strong. My muscles still respond to what I ask of them. And I'm not getting injured, which I suspect that I would be if I were trying to train for a marathon now. I don't plan ever to stop exercising. But I'm happy with the amount and type that I do now and it's answering my needs. I think that that's what we all should hope for from workouts.

This is kind of a chicken and egg question, but is exercise a cause of better health in itself, or does it have to have some other impact—like weight control—first?
There's a continuing debate in the physiological community about fitness and fatness: which matters most? And, based on a wealth of new science, the answer appears to be fitness. In essence, if you have to choose whether to worry most about your weight or about fitness, go with fitness. In large-scale studies at the Cooper Institute in Dallas, researchers have shown that overweight men with above-average aerobic fitness lived longer and had much less risk of heart disease than those who were less fit, even if they were relatively svelte. That's not to say that you shouldn't try to achieve or maintain normal weight. Being fat is unhealthy; there are physiological effects associated with having lots of fat cells in your body that are best avoided. But if you really have difficulty losing weight, and many people do, then it's especially important that you maintain your fitness. By that means, you can lessen the unhealthy effects of extra weight, to some degree.

Also, exercise is the only proven method for keeping weight off, once you've managed to shave the pounds. Experiments in mice show that exercise resets the body's sense of how much you should weigh and so it won't try so hard to get you to eat and regain lost pounds.

What's the baseline amount of exercise that everybody needs every day, or every week? Should you break it up during the day, or do it all at once?
The baseline amount of exercise is, frankly, any, as study after study shows. The human body is genetically built for motion, even if that motion is only standing up. But the current expert guidelines suggest accumulating 30 minutes of moderate activity at least five days a week. 'Moderate' activity in non-science speak means walking. That amount of exercise will keep you quite healthy. You do not need to accumulate those 30 minutes in one chunk, either. A number of studies have proven that 10 minutes of walking 3 times a day confers the same benefits as an unbroken half hour of exercise. Can't find 10 minutes to work out? Walk around your office for 5 minutes and repeat that 6 times during the day. Even that tiny commitment of time and energy can potentially lengthen your life.