Short bursts of activity beat nonstop exercising

Even if you enjoy aerobic workouts, you probably wish that they took less time. Good news: New research shows that you can get all of the metabolic and cardiovascular benefits of aerobic exercise in about 60 minutes a week.

The secret is high-intensity interval training (HIIT) where you exercise ­intensely for one minute and leisurely for another minute, working up to a total of 20 minutes three times a week. How it works…

NEW THINKING

For years, the American College of Sports Medicine has advised Americans to walk, bike or get other forms of ­moderate-intensity aerobic exercise for at least 30 minutes, five days a week. That’s two-and-a-half hours—minimum.

HIIT can be a refreshing change. You do the same activities (walking, biking, stair-climbing, etc.), but you do them hard—ideally at 80% to 90% of your estimated maximal heart rate. On a 1-to-10 scale, you’ll rate the exertion between 7 and 8 (compared with about 5 for conventional aerobic workouts).

Here’s the good part. After just 30 to 60 seconds of pushing yourself, you take a break. During the recovery phase, you keep moving, but at a leisurely pace—a slow walk, slow pedaling on the bike, etc. You rest for the same length of time that you exercised—between 30 and 60 seconds. Then you push yourself again. Each on-off cycle is one interval.

Exercise scientists used to think that HIIT was helpful mainly for athletes or very fit adults who wanted to take their fitness to an even higher level. But new studies suggest that this technique can be equally effective—and, in most cases, equally safe—for just about everyone who is in reasonably good health.

IMPORTANT BENEFITS

For our recent study, we recruited 41 “regular” people who typically engaged in aerobic activities only two or fewer times a week. After they completed preliminary tests and questionnaires, they completed a single workout that involved HIIT (one minute on, one minute off, for a total of 20 minutes), conventional high-­intensity aerobic ­exercise (20 minutes)…or conventional moderate-intensity aerobic exercise (40 minutes). Each participant did all three workouts, in a randomized order, separated by about one week.

At the end of the study, 24 of the participants said that they preferred HIIT, compared with just 13 who preferred conventional, moderate-intensity aerobic workouts. The remaining four people preferred the conventional high-intensity aerobic workout.

This is an important finding because people who enjoy exercise are more likely to keep doing it. Just as important, the study showed that nonathletes are able to do HIIT. Mixing the high-intensity “challenges” with frequent rest breaks boosted their confidence.

Other benefits…

Higher metabolism. You actually burn fewer calories during an HIIT session than you would during a standard aerobic workout. But HIIT elevates your basal metabolic rate for up to 24 hours after the workout. You burn more calories post-exercise than you normally would.

Researchers at McMaster University in Hamilton, Canada, studied ­participants who followed a 20-week program of conventional aerobics and others who followed a 15-week HIIT program. The first group burned 48% more calories per session than the HIIT group, but the HIIT group burned 900% more fat over the 15 weeks than the first group burned in 20 weeks.

Cardiovascular health. A number of studies have looked at the effects of HIIT in patients with heart disease. They found that participants had better outcomes—improved blood lipids, less insulin resistance, more elastic blood vessels, etc.—than those who did ­traditional workouts.

Improved fitness. The body’s ability to use oxygen is among the best measures of cardiovascular health and longevity. People who do these workouts have improved peak oxygen uptake after as little as two weeks.

Important warning: There’s some evidence that the resting component makes HIIT safer than traditional aerobic workouts for people with heart disease or other chronic conditions. But any form of vigorous exercise can be risky for those with health problems. Get the OK from your doctor before trying it.

A TYPICAL WORKOUT

To do an HIIT workout, you first need to pick your activity. It could be walking, biking, swimming, jogging, stair-climbing or any other form of aerobic exercise. After that…

Warm up. Take three to five minutes just to get ready—with slow walking, easy pedaling, etc.

Do a “speed” session. If you’re new to HIIT, I recommend limiting your initial speed sessions to 30 seconds each. You can increase the time each time you work out. Your goal will be 60 seconds.

As discussed above, you want an exertion level that you would rate as a 7 or 8 out of 10. If you’re not sure if you’re pushing hard enough, use the talk test—you should have just enough wind to blurt out a short word or two. If you can speak an entire sentence, increase the exertion.

Now take a break. The recovery phase will last just as long as the exertion phase. If you exercised for 30 seconds, rest for 30 seconds. As noted above, “rest” doesn’t mean doing nothing. You’ll keep doing the activity, but at an easy pace—say, between 15% and 20% of your maximum ability (1 or 2 on a 0-to-10 scale).

Immediately start the next interval. After resting, repeat the speed part of the exercise. Do it for 30 seconds…recover for 30 seconds…and so on.

Increase the intervals. I advise people who are new to HIIT to complete a total of four intervals. If that feels like too much, you can do just one or two, increasing the number when you feel ready. In our studies with nonathletes, we started with four intervals during the first session. We added one interval during each subsequent session until they reached a total of 10. We found that most people adjusted quickly.

Three times a week. Because these workouts are more intense than a conventional, moderate-intensity workout, you don’t want to do them every day. Your muscles need time to recover. ­Every other day is optimal.

Be flexible. The typical HIIT workout involves a 1:1 ratio—one minute of exertion followed by one minute of rest. But there’s nothing magical about this ratio. For someone who has been sedentary for a long time, I might recommend a 30-to-60-second exertion phase followed by a two-minute or even a four-minute break. In general, the more intensely you exercise, the more rest you’ll need. Your body will tell you what you need.