High intensity interval training or HIIT is defined as short, intense, unsustainable bursts of physical activity, paired with intervals of quick rests. This type of intense training causes a sort of metabolic disturbance which can result in the body burning calories at a higher rate up to 48-72 hours later. HIIT can also increase metabolism, reduce insulin resistance, improve cardiac function, produce faster gains in endurance levels than steady state cardio training and can be an effective way to recruit/build type 2 fast twitch muscle.
This type of training can be done anywhere and usually doesn’t require equipment and may be more efficient in terms of time commitment. This type of training also burns more fat effectively than typical endurance cardio. The body has to heal after this type of training so it is not recommended that you perform HIIT every day – usually it is recommended to perform this type of training a maximum of 1-3 days per week (it’s important to note that more is not better).
This training program involves intense work periods that are performed at 80% to 95% of a person’s estimated maximal heart rate which is the maximum number of times your heart will beat in a minute without overexerting yourself. The recovery periods may last as long as the work periods and are usually performed at a rate of 40% to 50% of a person’s estimated maximal heart rate. The workout involves alternating between the work and recovery periods.
HIIT can be modified for people of all fitness levels and people with various medical conditions including being overweight and people with diabetes. HIIT workouts can be performed using various methods of exercise including bodyweight exercises, strength exercises, cycling, walking, swimming, or running or group fitness classes. HIIT workouts tend to burn more calories than traditional workouts and you can burn more calories during the post-exercise workout period. During the excess post exercise, oxygen consumption or EPOC which is generally about a 2-hour period after an exercise bout where the body is restoring itself to pre-exercise levels and using more energy. HIIT workouts tend to generate about 6-15% more calories burned during the EPOC period which adds to the overall workout energy expenditure.
HIIT workouts are more exhaustive than traditional steady state endurance workouts. A longer recovery periodis often needed. If you are going to start HIIT type training workouts it may be beneficial to start with one HIIT training workout per week and then as you feel ready for a greater challenge add a second HIIT workout during the week while still making sure you spread out the workouts and never do them on back to back days.
When developing your own HIIT program you need to consider the duration, intensity and frequency of the work intervals and the recovery intervals.
What should my rest and active HIIT intervals feel like? How do I know if I’m working hard enough?
Intervals during the high intensity work period should be performed at > 80% of your estimated maximal heart rate. The work period should feel like you would describe your workout as being hard to very hard. If you use the talk test as your guide it would be very difficult to carry on a conversation. The recovery period should be performed at 40-50% of your estimated maximal heart rate. This type of exercise would be described as comfortable, to help you prepare for your next high intensity work interval.
One example would be to do a ratio of 1:1 which may be a 3-minute hard work or high intensity period followed by a 3-minute recovery period. 20 on and 10 off is very popular. Another training protocol is where the exerciser does about 30 seconds of sprint or near full-out effort which is followed by 4 to 4.5 minutes of recovery. This type of combination can be repeated 3-5 times. These exercises are typically performed in shorter bouts.
If you are considering giving HIIT a try make sure you are cleared by your physician or take a physical activity readiness questionnaire in order to determine if it is appropriate for you to begin this type of training.