If you've jumped on the high-intensity interval training (HIIT) bandwagon, you know it involves alternating short bursts of intense activity with longer intervals at a much lower intensity. Athletes traditionally use interval training to improve performance for sprints, and fitness enthusiasts use it to burn calories in a short period of time.
HIIT is intense, so you only need short workouts of 20 to 30 minutes. Herein lies its advantage in terms of calorie burn. You scorch a lot more calories in these short workouts than you would going at a moderate intensity for the same period of time. Plus HIIT turns on certain fat-burning mechanisms that help lean you out quicker than always jogging at an easy pace.
Calculate your calorie expenditure during interval training using a heart rate monitor. The exact number depends on your age, size and intensity level.
Heart Rate Minimums
Calorie expenditure formulas often use your heart rate to determine your calorie expenditure rate. This approach is most accurate when your heart rate is greater than 90 and less than 150 beats per minute, or bpm. This requirement makes it important to keep your heart rate above 90 bpm during the "easy" bouts of your interval training.
To calculate your calorie burn using your heart rate requires you to wear a heart rate monitor. You can use one with a chest strap, arm strap or the latest technology that reads your pulse right from your wrist. Most heart monitors today include a heart rate recorder as a standard feature. This allows you to obtain your average heart rate for the duration of your interval training workout.
To do the actual workout, you may need something like a treadmill or stationary bike. But you can do intervals on a running track or with calisthenics, such as burpees and high knees.
Do Your Workout
Put your heart monitor on and perform some type of light exercise to get your heart rate above 90 bpm as a warm up. You'll then being your interval workout, for sprint intervals, for example, you might run one lap around the track at full speed followed by another lap at a recovery pace. Go for 20 to 30 minutes total -- depending on your stamina and the time you have to commit to exercise. Complete your interval training and turn your heart rate recorder off.
The calorie expenditure formulas require your average heart rate during the interval training session in bpm and the duration of the session in minutes. They also require your age in years and your weight in pounds.
The following equation from the Journal of Sports Sciences calculates the calorie expenditure for women:
Calories = [(0.074 x Age) + (0.4472 x Heart Rate) – (0.05741 x Weight) – 20.4022] x Time / 4.184.
Men use the following equation:
Calories = [(0.2017 x Age) + (0.6309 x Heart Rate) – (0.09036 x Weight) – 55.0969] x Time / 4.184.
So, if you're a 35-year-old woman who weights 180 pounds and worked out with an average heart rate of 140 bpm for 30 minutes, the equation would look like:
[(0.074x35) + (0.4472x140) - (0.05741 x 180) - 20.4022] x 30/4.184
and you'd have burned approximately 247 calories.