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DEAR MAYO CLINIC: I am determined to get fit and lose weight this year. I’ve recently heard a lot about interval training. What is it exactly, and is it safe for everyone? How do I get started?
ANSWER: To improve the fitness of your heart and lungs — known as cardiorespiratory fitness — you need to exercise at a higher level of intensity than is typical for you. High-intensity aerobic interval training, also called HIIT, involves alternating periods of moderate-intensity exercise with brief periods of high-intensity exercise. Incorporating HIIT into your exercise routine can be a safe and effective way to help your body adapt to a more intense workout and become more fit.
There are many benefits of HIIT, compared to moderate-intensity exercise. For example, HIIT offers a more rapid and greater increase in cardiovascular fitness. It’s also a time-saver. The duration of exercise sessions may be shortened, since HIIT exercisers expend the same or even greater number of calories per session. In addition, people often find HIIT more interesting and engaging than moderate-intensity exercise.
To use HIIT, you need to be able to tell the difference between moderate-intensity exercise and high-intensity exercise. An easy way to distinguish between the two is with the talk test. During moderate-intensity exercise, you can talk, but you cannot sing. During high-intensity exercise, you can only say a few words before you need to take a breath. At high-intensity, you feel physically challenged, and you can only exercise for a limited time before you need to lower your exercise intensity.
Before you begin HIIT, exercise at moderate intensity only for several workout sessions until you can exercise continuously at that level for at least 20 minutes. You can use whatever form of aerobic exercise you prefer. Walking, jogging, biking or working out on an exercise machine, such as an elliptical trainer, are all good choices.
The first time you use HIIT, warm up for five minutes at a relatively easy pace. Then move to a moderate pace for about five to 10 minutes. After that, switch to a high-intensity pace for 30 seconds, then reduce your pace to back moderate for one to three minutes to allow yourself to recover completely. Repeat the high-intensity pace and moderate-intensity recovery phases two or three times during a 30-minute exercise session.
When you are exercising at the higher intensity, you should be pushing yourself, but you don't need to be working at your maximum effort. During your exercise session, you should not experience symptoms such as chest pain or discomfort, severe shortness of breath or lightheadedness. If you do, stop exercising right away. You also should not have unusual fatigue, muscle pain or joint pain that lasts a long time after you exercise. Talk to your health care provider about any of these symptoms or about other symptoms you have during exercise that seem out of the ordinary.
As you become accustomed to HIIT and your fitness improves, increase the number of times you switch between high-intensity and moderate-intensity to five or six per workout. You also can increase the amount of time you stay at the high-intensity pace to one to two minutes as you are able. Even as you become more fit, include HIIT in only two or three of your exercise sessions per week. Those sessions should not be on consecutive days.
HIIT can be used effectively by athletes, as well as people of all ages and fitness levels, including people with serious diseases, such as coronary heart disease and chronic heart failure.
Talk with your health care provider before you start HIIT, especially if you have a chronic illness, such as heart disease, lung disease, diabetes, high blood pressure, kidney disease, stroke or arthritis. — Dr. Ray Squires, Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota