High intensity interval training (HIIT) is a form of cardiovascular exercise that has been found to improve overall
conditioning, boost metabolism, and burn fat.
It has been a part of the training of serious athletes for a long time
and has become increasingly popular with more casual exercisers in the past few years.
HIIT entails alternating short bursts of high intensity anaerobic
exercise, making your heart work much harder, interspersed with more moderate levels of
recovery. It requires high motivation because it is very physically demanding and therefore not for everyone. But if you already exercise regularly and are looking to ramp up your exercise program, HIIT may be just the thing for you.
The American College of Sports Medicine (ACSM) tells us that high intensity intervals should be performed at about 80 to 95%
of capacity or maximum heart rate. It
should feel like you are exercising hard or very hard, to the point where it
would be difficult to carry on a conversation.
In contrast, recovery
intervals should be done at about 40 to 50% of maximum heart rate, a low enough level to
allow you to recover sufficiently to move on to the next interval. Note: older people may require a longer
recovery period.
HIIT can be done with almost any form of aerobic or cardio exercise including walking, running, biking, swimming, or elliptical training.
Benefits
According to Wikipedia and ACSP, based on research, HIIT has numerous benefits:
- Improved blood pressure and cardiovascular health,
- Improved insulin sensitivity (important for diabetics or pre-diabetics),
- Reduced abdominal fat
And according to the ACSP, not only do HIIT workouts burn more calories during the workout itself, but also afterwards compared to regular cardio workouts that don’t involve high-intensity intervals.
Safety Concerns: Who Can Practice HIIT?
HIIT is not appropriate for people who have been largely sedentary, at least until they “establish a foundational level of fitness” (ACSM). People with cardiovascular conditions (e.g., hypertension, high cholesterol, or who smoke), diabetes or obesity should not attempt HIIT without being first evaluated by a physician and cleared for exercise.
Before beginning HIIT, you should be able to exercise at least 20-30 minutes at 70-85% of your maximum heart rate [see below for maximum heart rate].
The whole exercise period can last from 20 to 60 minutes. There is no generally agreed upon specific formula for length or ratio of the high intensity intervals versus the recovery periods. In what I read I saw that the ratio can range from 1:1 (equal length intervals of intensity and recovery) to 1:4 (recovery periods last 4 times as long as intervals, e.g., 30 seconds at 80 to 90% followed by 2 minutes of recovery).
The exact ratio depends on person’s level of fitness, with serious athletes better able to have longer high intensity intervals and shorter recovery periods. People who only have a short period to exercise like HIIT because the high intensity can be a way of getting a lot of benefit in a relatively short time frame.
How often should you engage in HIIT? Because it takes longer for your body to recover completely from HIIT, no more than three times per week is recommended. Depending on your conditioning, you might want to start out with once a week and gradually move up to three times per week. You can, and should, customize HIIT to your own fitness level.
Starting an HIIT Program
The whole exercise period can last from 20 to 60 minutes. There is no generally agreed upon specific formula for length or ratio of the high intensity intervals versus the recovery periods. In what I read I saw that the ratio can range from 1:1 (equal length intervals of intensity and recovery) to 1:4 (recovery periods last 4 times as long as intervals, e.g., 30 seconds at 80 to 90% followed by 2 minutes of recovery).
Begin each HIIT session with at least 5 minutes of warm up and 5 minutes of cool down. The graphic below depicts a sample schedule if you are interested in trying HIIT:
How often should you engage in HIIT? Because it takes longer for your body to recover completely from HIIT, no more than three times per week is recommended. Depending on your conditioning, you might want to start out with once a week and gradually move up to three times per week. You can, and should, customize HIIT to your own fitness level.
Maximum heart rate and exercise
According to the Centers for Disease Control, maximum heart rate is determined by subtracting your age from 220 (in my case 220 - 66 = 153 beats per minute). Vigorous exercise is performed at 70 to 85% of your your maximum heart rate. Therefore HIIT would be considered extremely vigorous at 80 to 95%. Moderate activity is considered to be 50 to 70% of your max heart rate.
My HIIT Program
About three times per week I have been doing 6 to 10 intervals during a 35 to 40 minute period of exercise on an elliptical machine. I warm up first for at least 5 minutes. My intervals last from 30 to 45 seconds, and I get my heart rate up to 80 to 90% of the maximum, 122 to 138. I follow each high-intensity interval with a recovery interval of 2 to 4 minutes at 50%, although my heart rate stays pretty high, 100 to 110. I have been enjoying it. It makes an otherwise pretty boring session of cardio a lot more interesting by setting up challenges.
If you are already exercising pretty regularly, give it a try!
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