High Intensity Interval Training, known commonly by the acronym HIIT, has become exceptionally popular in the last 5-10 years. I think of HIIT as a distinct type of training, but the term has become synonymous with traditional circuit training.
Interval Training describes any form of exercise where there are periods of effort followed by periods of recovery. Intervals are not inherently high-intensity. For example, a newcomer to running might start their training with 2 minutes of running followed by 3 minutes of walking (for 25 minutes). The 2 minute intervals of running need not be high intensity because this training session is designed to gently expose the runner to a manageable amount of stress (more musculoskeletal than cardiovascular). The runner’s body will adapt to the stress, and over time, the runner will be capable of running for longer.
However, Interval Training allows for high intensities because of the short durations of effort and the imminent opportunities to recover. Recovery periods need to be long enough for individuals to catch their breath and rest their muscles. For HIIT, I prefer at least a 1:1 work to rest ratio, e.g. 1:00 of exercise followed by 1:00 of rest. Recovery periods need to be earned, so individuals need to push themselves hard during intervals. There should be plenty of sweat, heavy breathing, muscles fatiguing and minimal chat. To achieve these high intensities, appropriate exercises should be performed. Running, cycling, rowing and swimming are fantastic for HIIT. Traditional, full-body exercises like mountain climbers, burpees and star jumps can also work. You can even have fun with prowler exercises, battle ropes and tyre flips. However, you will struggle to achieve the required intensity with exercises that target small muscle groups, like sit-ups, bicep curls and bridges.
In my opinion, workouts with short recoveries and only moderately difficult exercises do not constitute HIIT. Instead, they are traditional circuit training workouts. In circuit training, individuals perform a variety of exercises in a sensible sequence with minimum recovery so that both aerobic fitness and strength are trained simultaneously. A really good circuit will also train agility, balance and coordination. Commonly, individuals work for around 40-45 seconds and then have 15-20 seconds to transition to the next exercise.
HIIT and circuit training are both excellent (as are the infinite variations between the two), and these training styles have their respective advantages and disadvantages.
There are very good reasons why circuit training has been so popular with sports teams, athletes, martial artists, the armed forces and the general public for so much of the last century. It is an excellent style of training that can be used to deliver very balanced, comprehensive and easily scalable workouts. I’ve delivered thousands of circuit training sessions in the past 11 years to individuals ranging from the clinically obese (barely able to walk) to international sportspeople. It is a style of workout that can be performed multiple times per week for long periods. Circuit training is also not too daunting, so individuals can motivate themselves to follow an online workout in their living room.
HIIT, as I define it, is a great way to challenge individuals who already have a good level of fitness. It delivers excellent results in a short time but can be very exhausting, so individuals may struggle to perform multiple HIIT sessions per week. I would also recommend occasionally taking a few weeks off from HIIT workouts. It can be difficult to motivate yourself to do HIIT independently. Subsequently, it’s a style of training that lends itself to personal training sessions or group fitness classes, where an instructor is ensuring the intensities are high and the recoveries are not being stretched.
Many fitness classes advertised as HIIT are more accurately described as circuit training, which is a great form of training that I recommend. However, if you fancy incorporating HIIT into your exercise routine, look for the signs that a workout is distinctly HIIT, namely long periods of recovery, tough exercises and an expectation that you push yourself hard.
