High Intensity Interval Training – What is HIIT?

High Intensity Interval Training – What is HIIT?

You may have seen articles about High Intensity Interval Training or HIIT and heard people talking about it as the latest thing in fitness, helping people achieve great results in terms of weight loss toning up and fitness improvements. As the American College of Sports Medicine (ACSM) has just announced HIIT as the number one fitness trend for 2018 it’s not a trend that is going to fade anytime soon.  Head over to the ACSM’s journal if you want to see their Top 20 fitness trends for 2018 in full.

But if you’ve not heard of HIIT, what is it? Is it any good? If so why? And how do you do it?


What is HIIT?

Traditional aerobic (cardio) training that is done at constant steady pace – a steady, run, cycle or whatever is your preference.  Interval training is any training where is a ‘work’ phase and ‘rest’ phase.  As the name suggests, in a HIIT workout you go as hard as you can in the work interval!  While that sounds quite brutal, the work intervals are short allowing you to work at a much harder than you could do over a longer period. The ‘rest’ phase doesn’t necessary mean complete rest – you may well continue very light activity (e.g. walking, gentle jog).


Why is it good?

There is now a significant amount of scientific research highlighting the benefits of HIIT workouts as well as the practical benefits. These include:

  • Time efficient – a session is short,  often no more than 25-30mins including warm up and cool down. So it is much quicker than a long run or gym session, so easier to fit into our busy lives! Yet the research highlights that a HIIT session is more beneficial. There is even some evidence that a very short HIIT workouts can be effective.
  • Improved fat burning capacity and weight loss:
    • Firstly, HIIT is better at increasing the number and size of Mitochondria in your cells. They are the part of the cell that burns calories. So increasing these means more calories are being burnt by your body.
    • Secondly, with HIIT you work much harder. As calorie expenditure increases exponentially the harder you work, you burn more energy overall in a shorter workout.
    • Thirdly –  Excess Post-exercise Oxygen Consumption. With traditional aerobic training you work at a level where you burn energy at the rate your body can replenish it at. So you only burn calories during the activity. In a HIIT session your body goes into oxygen debt and has to keep burning energy for up to 24hrs to replenish stores in your muscles after the activity.
  • Increased Endorphins – Endorphins are a natural response to pain, so working harder means more ‘feel-good’ chemicals are released into the body.
  • Motivation – As you are changing pace or even activity, it’s not monotonous as traditional aerobic training where you are plodding along at a steady pace.
  • Portability – as you’ll see a HIIT session can use almost any activity. So it can be adapted to where you are and what you have a available. Ideal for when you are away from your normal environment.
  • Improved VO2Max – or how well we can use oxygen in the body. Simply our heart and lungs become more efficient at using and transporting oxygen around the body to the muscles that also use it more efficiently.
  • Improved Anaerobic Threshold – basically as this improves it means you’ll be better at working harder and keeping this going for longer before lactic acid build up kick in.
  • Athletic performance – for those involved in sports HIIT training better replicates the physical demands of the activity they do. (e.g. netball or football players need to do lots of short bursts in a game rather than running steadily throughout).


Man with a kettlebell

So what is involved in a HIIT workout?

The great thing about HIIT is that there are various formats you can use for the workout. You can also adapt it to pretty much any activity – running, rowing machine, cycling, body weight exercise, as well as indoors or outdoors. (I do HIIT sessions in my kayak and in my spare room!)

Which activities: Chose the activity you prefer or what fits with the equipment, space, location you have. Activities and exercises that use the whole body or major muscle groups will be more intense than those using isolated muscle groups. Some variety is good too. Your body adapts to what you do in workouts, so mixing it up brings and new challenge and helps you progress

Formats: There are various ‘intervals’ you could use. Two common workout formats include:

  • 30 sec work and 30 rest repeated say 15 times (e.g. 5 different exercises, repeated 3 times through)
  • Tabata format – 20 sec work and 10 sec rest repeated (e.g. 5 or 6 exercises, doing 8 sets of each exercise before a minutes rest and repeating with the next exercise).

Whatever activity and format you opt for, make sure you do a good warm up before a HIIT workout, and cool down afterward (as you would for any workout).


What does ‘High Intensity’ mean?  

As mentioned in a HIIT session you need to go as hard as you can for in the work phase which may be putting you off. Remember these are relatively short so you can work at that very high level (at or close to maximal). Importantly bear in mind that :

  • Everyone is different – so your ‘as hard as you can’ will be different to another person, depending on each person’s fitness, the exercise or activity.
  • As you get fitter, you still push yourself to be working ‘as hard as you can’, so over time you will notice you are getting fitter as you do more in each work phase.

But am I fit enough for HIIT?  This a common worry for those starting out with HIIT workouts. Firstly, remember ‘High Intensity’ is individual, and relative to your personal level of fitness. So go as hard as YOU can. That may mean taking it a bit easier initially. But you are looking to build up to that ‘as hard as you can’ level – whatever that is for YOU- as soon as you can. Secondly the evidence shows that risk from a bout of vigorous exercise is very low and that habitual vigorous exercise reduces the risk from the exercise itself.

As with any exercise programme if you are sedentary or don’t exercise regularly it is recommended you check with a doctor that you are fit enough to take part.  If you are ok to start, then build up steadily.


How often should you do a HIIT workout?

It depends on what you want to achieve and what other training you are doing. Don’t forget you need some rest/easy days in a programme too. So if you exercise regularly you might only slot one HIIT session a week into your training. Or you might substitute a HIIT session when you can’t do your usual training.

If you are looking to lose weight, because on the benefits and effectiveness of HIIT we looked at before, I’d suggest 3 sessions per week.


Starting out and moving on

Depending on your fitness you may start with a small number of work intervals (say 5 or 10). Increase the number of intervals as your fitness improves. Similarly if you can’t sustain 20 or 30 seconds exercising at high intensity start with 10 seconds and work up from there.

However, if you are starting to find it getting easier I wouldn’t advise working longer than 30 secs in an interval. Any exercise you can sustain for 40-60 secs you should be able to at a much higher intensity for 20-30 secs. And it is the high intensity that brings the benefits to this format. A much better option is to make the activity harder to increase the intensity. Run up hill, crank up the resistance, add weights (or more weight) to exercises etc. Also remember that your body adapts to the exercise, changing the exercise can make a big difference.


Some example workouts to try:

The first two of these using simple body weight exercises could easily be done in your home.

Remember to warm up before and cool down after!

Body weight HIIT:  Do each exercise for 30sec at high / max intensity, followed by a 30 sec rest before moving to the next exercise.  Work through the 5 different exercises 3 times.  Total time 15mins (plus warm up & cool down).

Exercises: Star jumps, Mountain climbers, Push ups, Plank, Squats.

Tataba workout:  Do 8 sets of the first exercise comprised of 20sec activity and 10sec rest. Then take a 1min rest before repeating this format on each exercise.  All exercises to be performed at high / max intensity. Total time 30mins (plus warm up & cool down).

Exercises: Step ups, Tricep dips, Squats, Wipers, Lunges, Push ups.

Running HIIT:  Find somewhere that you can run at top speed for 15-20 secs and then slow to a walk or gentle jog for 40-45secs – i.e. a total of 1minute. Repeat this 10-15.  Total time 15mins (plus warm up & cool down).

To do away with the watch, find a circuit or route where there are markers such as trees or lampposts. Then sprint from one tree to the other and loop back to the beginning and go again.


Top tips

  • It is hard – it’s supposed to be! But you will start adapting to it after a few sessions! So bare with it for a few weeks.
  • You need to use a timer. A stopwatch or your phone’s timer will work if they have a timer with a repeat function you can programme it for the desired work and rest phase. There are also various free and paid for app that will do this for you. I use the ‘Tabata Stopwatch’ (Pro version) as it can save different work outs.
  • Try to record how far or how many of each exercise you do in each work phase. This helps you track both whether you are working as hard in each interval, and highlights when you are making progress.
  • When it begins to feel easy change things up (different exercises, make the exercise more difficult, change work and rest times).