While researching a book on exercise and the brain, John Ratey learned that intense exercise releases a hormone that burns belly fat and adds muscle fibers. So the Harvard Medical School psychiatrist swapped out 40-minute jogging sessions on the treadmill for something less time consuming but more vigorous: Twice a week, he now jogs for a total of 20 minutes and includes five exhausting sprints of 20 to 30 seconds apiece. After a month, he was amazed at the results. "I didn't change my diet, and I spent less time on the treadmill," he says. "But all of a sudden, I was 10 pounds lighter."
Who wouldn't like to get a greater return on the time invested in exercise? The good news is that it's entirely possible. Science is increasingly pointing the way to the most efficient methods of working out. Meanwhile, trainers and coaches have their own trade secrets for saving time. Which is good, because none of us have any to spare. "Many of the people I work with are time starved," says Todd Durkin, a trainer and conditioning coach in San Diego. "They don't have an hour a day to work out."
Being more productive begins before you even break a sweat. A good workout requires planning. "The biggest mistake people make is that they don't determine what their goal is, both big picture and for today," says Carol Espel, national director of group fitness and Pilates at Equinox Fitness Clubs. Unless you're training for a specific event, your goals are probably to boost your aerobic endurance, strength, or both—and, of course, to burn calories. And the window for doing all that starts to shrink the minute you begin spinning your proverbial wheels. "I saw two girls at the gym walking around saying, 'What am I going to do?' " says Teddy Bass, a Los Angeles-based personal trainer. "Have that in mind before you go to the gym," he says.
So, you know what you're planning to do today, and now you want to warm up. You may be surprised to learn that you can probably skip the stretching. A comprehensive review of previous research published last fall found that muscle stretching doesn't reduce post-workout muscle soreness in healthy adults. Other studies suggest it doesn't prevent injuries, either. "If people eliminated that downtime...and spent 15 more minutes on lifting weights or cardiovascular exercise, there'd be more benefit to their health," says Stacy Ingraham, an exercise physiologist at the University of Minnesota. Stretching is intended to improve your range of motion, she says, but you can do that instead by lifting weights, which also builds strength. (The exception: If you have been very inactive and are starting an exercise routine, you may need to increase your range of motion over time before exercising.)
Start slowly. But just because you're not stretching doesn't mean you can skip a warm-up entirely. "Whenever you do any activity, you need to progressively begin," says Ingraham. "The pace at which you'll be doing the majority of the workout is not the pace you should start at." So pedal, jog, or swim more slowly for three to 10 minutes. Do the same warm-up before strength training.
OK, you're warmed up and ready to go. Let's say it's an aerobic exercise day. (For general fitness, the government recommends either 30 minutes of moderate aerobic exercise most days of the week or 20 minutes of more vigorous exercise three times a week, in addition to strength training twice a week.) Rather than doing a long stretch of steady exercise, you can follow Ratey's example and take advantage of interval training, a term for "alternating periods of high- and low-intensity exercise," says Martin Gibala, a physiologist at McMaster University in Hamilton, Ontario. That may mean bursts of more intensive exercise lasting between 30 seconds and three minutes, followed by recovery periods of as little as a few seconds or as long as 15 minutes, he says. By working at a higher intensity, you're forcing your body to adapt to different conditions, bringing benefits that exercising at a steady pace doesn't provide. And the jumps from minimal to high effort and back down again may improve fitness more than simply plugging along at a medium pace.
In addition to improving aerobic fitness, interval training can burn more calories in a shorter time. There's also some evidence that intervals trigger a mechanism that helps the body burn more fat and possibly even boost metabolism more for some period after the workout ends. For the already fit, the key to getting these benefits is to go hard during those intense periods. "In my 30 seconds, I'm grabbing onto the treadmill, and I'm out of breath," says Ratey. (You shouldn't be able to carry on a conversation during the sprints.) High-intensity exercise is rougher on your body, so limit intervals to twice a week, and take a rest day in between. And be careful of overuse injuries, which tend to crop up during intense exercise. To round out your regimen and meet experts' recommendations, also do some steady aerobic activity one or two days a week.
Intervals aren't just for hard-core exercisers. They've even been used (under careful medical supervision) with heart patients. One study published last summer in Circulation found that interval training improved aerobic capacity and other markers of health for heart failure patients. And Darren Warburton, an exercise scientist at the University of British Columbia, separately found that interval training aided the health of patients with coronary artery disease. He's now investigating whether the same holds true for type 2 diabetics. Still, if you're not accustomed to exercise at all, are older than 60, are at risk of heart problems, or have arthritis, consult a doctor before you start.
For those already exercising regularly, there are simple ways to incorporate interval training into a workout. "If your mode of exercising is walking around the block, walk faster in between two light poles and then back off for the subsequent two light poles," says Gibala. The same concept works in the pool, on a bike, or on a rowing machine.
Even on days devoted to strength training, there are ways to cut workout duration. If you go to a gym and can't avoid its busiest times, learn how to use all the equipment. That will give you more options if your usual machine or weight bench is occupied, says Valerie Waters, a trainer whose clients include the überfit Jennifer Garner. If you're unfamiliar with what's there, book one or two sessions with a trainer and indicate that you want in your limited time together to learn how to use the equipment, she says. Moreover, don't be intimidated into waiting around for a machine when someone else is just sitting there sweating on it. "It's absolutely appropriate to ask, 'How many more sets do you have?' and if they say three more, it's completely appropriate to say, 'Can I work in?'" says Waters.
Go low-tech. Better yet, find yourself a corner of the gym—or your home—and just use free weights and your own body weight. Free weights torch more calories and work more of your body, especially if you use the larger leg muscles. "Doing a squat with 10-pound dumbbells is better than sitting in a leg extension machine," says Equinox's Espel. And focus on moves that use more than one joint and more than one muscle group, like a squat that goes immediately into a shoulder press, says Waters.
She and other trainers are also big fans of mixing aerobic and strength training to get a combined workout. Such "circuit training," in which you move through a series of vigorous exercises with little or no rest in between, "lets you knock out two things at once," says Durkin. You can set up your own circuit, perhaps with advice from a trainer, by intermingling resistance exercises with stints on a bike or treadmill. Many gyms have circuit training classes, too. Most also have shorter, 30- or 45-minute classes that are designed to incorporate both cardio and strength training; you can let the instructor do the planning for you.
Whatever you're doing, don't skip the cool-down to save time. Your body needs a gradual ramping down of exercise to return it to its normal state, and stopping on a dime can cause blood to pool in your legs and make you dizzy. But you don't need to stretch, says Ingraham; it doesn't work any better after exercise than before. So save the extra five minutes for thinking about what you'll accomplish with tomorrow's workout.