The fitness world touts high-intensity interval training, or HIIT, as a way to pack more punch into your workouts. And for good reason. Its many benefits include weight loss, increased metabolism and improved heart and lung function, but they don't come easy. The target heart rate zone of a HIIT workout is 80 to 95 percent of your maximum heart rate.
HIIT refers to any manner of exercise during which short bursts of intense activity are followed by periods of recovery at a low or moderate intensity. An example is doing sprint intervals during a jog. High-intensity intervals can last anywhere from 5 seconds to 8 minutes. The recovery periods are typically as long as or longer than the high-intensity periods.
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These intense periods of effort followed by recovery allow you to blast your heart rate up and burn more calories than you would during a steady-state moderate-intensity workout. This method also causes physiological adaptations that result in an increased metabolic rate post-exercise and accelerated increases in cardiovascular fitness over steady-state cardio.
Read more: Interval Training on a Stationary Bike
Maximum Heart Rate
Your heart rate should increase during exercise, but it also has a ceiling on how high it can safely go, known as your maximum heart rate. This is the number of times your heart can beat in a minute during exercise without overexertion.
In general, your maximum rate drops as you get older. You can estimate your maximum heart rate by subtracting your age from 220. A 35-year-old, for example, has an estimated maximum heart rate of 185 beats per minute, while a 50-year-old's max heart rate is 170.
A number of factors can affect your maximum heart rate, including your overall health and any medications you are taking, so you'll need to see a doctor if you want to determine your exact maximum heart rate.
During high-intensity bursts in interval training, you should push your heart rate as high as you can safely take it. Generally, that's about 80 to 95 percent of your maximum heart rate, according to American College of Sports Medicine. A 35-year-old, for example, should aim to get his heart rate up to between 148 and 175.
While many pieces of gym equipment will measure your heart rate while you exercise, they are not as accurate as using an individual heart rate monitor. You can also judge the intensity by how the exercise makes you feel. Exercise of that intensity should quickly make you break a sweat and make your breathing deep and rapid. During exercise of this intensity, you shouldn't be able to speak more than a few words at a time.
Working out near your maximum heart rate can be dangerous if you have certain health conditions. If you have heart disease, high blood pressure, arthritis or are over 60, you should avoid interval training without a go-ahead from a doctor.
If you're just starting an exercise program, high-intensity interval training also might be too strenuous for you. You should be able to sustain activity at about 65 percent to 75 percent of your maximum heart rate for at least 30 minutes before you try higher-intensity exercise. When you start interval training, you may want to try just one or two short bursts at the higher heart rate, and build gradually to more complete interval training.
Read more: 5 Myths About HIIT