What is HIIT?

WHY HIIT? High Intensity Interval Training

A HIIT session often consists of a warm up period of exercise, followed by three to ten repetitions of high intensity exercise, separated by medium intensity exercise for recovery, and ending with a period of cool down exercise.

The high intensity exercise should be done at near maximum intensity. The medium exercise should be about 50% intensity.

The number of repetitions and length of each depends on the exercise, but may be as little as three repetitions with just 20 seconds of intense exercise.

There is no specific formula to HIIT. Depending on one’s level of cardiovascular development, the moderate-level intensity can be as slow as walking.

A common formula involves a 2:1 ratio of work to recovery periods, for example, 30–40 seconds of hard sprinting alternated with 15–20 seconds of jogging or walking.

The entire HIIT session may last between four and thirty minutes, meaning that it is considered to be an excellent way to maximize a workout that is limited on time.

A version of HIIT was based on a 1996 study by Professor Izumi Tabata. (We love our Tabata) The study used 20 seconds of ultra-intense exercise (at an intensity of about 170% of VO2max) followed by 10 seconds of rest, repeated continuously for 4 minutes (8 cycles).

The exercise was performed on a mechanically braked cycle ergometer. Tabata called this the IE1 protocol. In the original study, athletes using this method trained 4 times per week, plus another day of steady-state training, and obtained gains similar to a group of athletes who did steady state training (70% VO2max) 5 times per week.

The steady state group had a higher VO2max at the end (from 52 to 57 mL/(kg•min)), but the Tabata group had started lower and gained more overall (from 48 to 55 mL/(kg•min)). Also, only the Tabata group had gained anaerobic capacity benefits.

It is important to note that in the original study from 1996, participants were disqualified if they could not keep a steady cycling pace of 35RPM for the full 20 seconds of work.

Implications for popular exercise regimes that advertise as Tabata training should include overall analysis of the original study.


HIIT technique can be applied either as a separate exercise plan in case that you are in a hurry, or as an intense complement to your existing plan. HIIT training can literally have hundreds of forms.

Depending on your objectives, combine exercises, tools and time intervals to obtain the optimal result.

For example: 20 seconds of intensive workout and 10 seconds of rest. Whole process shall be repeated for 4 minutes.


According to a study by King, HIIT increases the resting metabolic rate (RMR) for the following 24 hours due to excess post-exercise oxygen consumption, and may improve maximal oxygen consumption (VO2 max) more effectively than doing only traditional, long aerobic workouts.

Tabata’s 1997 study concluded that “intermittent exercise defined by the IE1 protocol may tax both the anaerobic and aerobic energy releasing systems almost maximally.”

High-intensity interval training has also been shown to improve athletic performance. For already well-trained athletes, improvements in performance become difficult to attain; increases in training volume may yield no improvements.

Previous research would suggest that, for athletes who are already well-trained, improvements in endurance performance can be achieved through high-intensity interval training.


Long aerobic workouts have been promoted as the best method to reduce fat, as it is popularly believed that fatty acid utilization usually occurs after at least 30 minutes of training.

HIIT is somewhat counter intuitive in this regard, but has nonetheless been shown to burn fat more effectively. There may be a number of factors that contribute to this, including an increase in resting metabolic rate.

HIIT also significantly lowers insulin resistance and causes skeletal muscle adaptations that result in enhanced skeletal muscle fat oxidation and improved glucose tolerance.

In young women, HIIT three times per week for 15 weeks compared to the same frequency of steady state exercise (SSE) was associated with significant reductions in total body fat, subcutaneous leg and trunk fat and insulin resistance.

Before you step on that treadmill to do an hour’s worth of running, ask yourself why am I running? If it is lose weight and burn fat, reconsider and do 20 minutes of interval training and you’ll see a faster result and a toner body to boot.


The term HIIT is now as common-place as the term ‘functional’ within the fitness world. But are you really HIITing the mark? High Intensity Interval Training should be just that, high intensity. But what does this mean? Well, it is difficult to find a universally agreed upon definition of the level you need to reach before really working at high intensities.

Within the aerobic energy producing zone, this would likely be 80-100% of maximum heart rate. Intervals performed at this level could likely be sustained for several minutes or longer.

Within the anaerobic energy producing zone you have the sub-categories of lactic acid/glycolysis and alactic/creatine phosphate energy producing pathways. For the former, working at an intensity of 100-120% maximum heart would likely allow an interval to be sustained for around one minute.

As interesting comparison elite 2,000m rowing tests on an ergometer, taking between 320 and 460 seconds, is dependent upon the functional capacity of both the aerobic and anaerobic energy pathways, with the relative amount of energy derived from anaerobic metabolism being 21-30%.

If using intervals where the power output is extremely high i.e. 120-200% heart rate maximum, the intervals are likely to last just a few seconds, perhaps up to 30s, and so the inverse link between intensity and duration of work becomes all the more obvious; the harder you work, the shorter the interval!

HIIT is popular for many reasons and justifiably so:

1. Time efficiency

2. If your goals if fat loss, burn the same Kcals in a shorter amount of time

3. Perhaps reduce your risk of insulin resistance and diabetes with better hormone sensitivity

4. Increase both your aerobic and anaerobic fitness at the same with varying work and rest ratios within an interval session

5. Set fitness challenges which are fun to monitor and track e.g. how many reps of a move can you complete across all of your intervals

6. Set workouts which are easy to progress e.g. shaving or adding just 5 seconds at a time to you rest and or work intervals respectively

7. Make your intervals sport specific if you are a keen athlete – these can meet the work/rest demands of your sport.

Have fun with HIIT sessions – use varying pieces of equipment such as battling ropes, light weights and medicine balls (as well as body weight), and if you don’t have a specific goal per se’, then play around with those work/rest phases to develop well-rounded fitness overall.

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