What is HIIT training?

PhD Ambassadors workout

What is HIIT training?


You’ve heard of HIIT training, but what is it and should you be incorporating it in your week? We’ve rounded up everything you need to know about HIIT so you can use it as a smart training technique to build your fitness – and your physique.


 HIIT – high intensity interval training


HIIT stands for high intensity interval training. As the name suggests, HIIT is defined by short periods of intense exercise (followed by active recovery or rest periods). But what exactly is HIIT and how should you do it? HIIT has become so popular in recent years that its true meaning can get a bit blurred. So let’s take things back to basics and explore what HIIT is – and what it definitely is not – so you can make good use of this amazing training tool.


The history of HIIT in sports training


These days, you’ll see HIIT mentioned everywhere from Instagram workouts to studio classes. HIIT can be done with cardio training, bodyweight exercises, resistance kit, or no equipment at all. Confusing? It can be. This is why we’ll start by going right back to the beginning with the origins of HIIT.

The earliest mention of HIIT as we know it is at the 1924 Olympic Games where runner Paavo Nurmi used interval training in his successful Olympics prep. After that, the development of HIIT as a training tool stepped up a gear with coach Gosta Holmer creating “fartlek” (speed play) interval training. Sebastian Coe (now Lord Coe) used interval training in the 1970s when it was still a pretty rate form of training. And when Professor Izumi Tabata developed the Tabata form of HIIT in 1996, this type of training went mainstream.


What exactly is HIIT training?


We’ve already mentioned Tabata training, which is 20 seconds of high intensity work followed by 10 seconds rests, repeated 8 times for 4 minutes of work. But there are lots of ways to use HIIT as a training protocol.


HIIT always involves alternating periods of very high and low intensity work, so you get your heart rate up high and then recover just enough to go again. The reason for this is increasing the total amount of high intensity training you do in a session. The low intensity or rest periods simply allow you to get ready to do another bout of work at a really intense effort.


What sets HIIT apart is the intensity of the efforts and the short duration of the recovery periods. Any workout labelled as HIIT should leave you feeling like you absolutely can’t do another round. If it feels easier than that, it’s not HIIT!


How does HIIT work?


HIIT combines very intense work periods with rest so you can actually put in more repeated bouts of high intensity than if you were doing one continuous push. This means you get benefits of endurance training, fat burning, cardiovascular training and “after burn” effects – all in a relatively short period of time.


HIIT is hugely efficient, allowing you to get a lot of quality work done in a short amount of time (think about sprint workouts or Crossfit WODs – both good examples of how HIIT can empty the tank in minutes!) Studies have shown that HIIT has numerous health benefits, with one 2019 paper suggesting that HIIT is the best form of exercise to improve skeletal muscle, respiration, cardiac function, blood pressure, exercise capacity, VO2 max, and even quality of life (

Pele Zac On Rower

HIIT training vs steady state cardio


Whilst heading out for an hour of steady exercise might seem like the easier option, there are lots of compelling reasons to swap some LISS cardio with HIIT.


HIIT makes better use of lipids as a fuel source making it superior for fat loss (


HIIT promotes more growth hormone which is amazing for weight loss, muscle building, and body recomposition


HIIT has been shown to have a positive impact on insulin sensitivity and glucose metabolism (


HIIT has a large EPOC (excel post oxygen consumption) benefit, meaning you’ll keep burning calories – particularly from the body’s fat stores – after the workout finishes


When to use HIIT in your training


By now you’re probably thinking “sign me up!” Who wouldn’t want to burn more fat, build lean muscle, get healthier, and bullet-proof your future self in a short sharp workout? But hold on. HIIT isn’t an every day thing. Here’s when you should – and when you shouldn’t – use HIIT sessions.


HIIT for fat loss


If your main goal is fat loss or body recomposition, HIIT is definitely your friend. Add 1-3 short HIIT workouts into your week (perfect for after your main session) or replace 1-3 of your longer cardio workouts.


HIIT for efficiency


Who isn’t busy these days? One of the big benefits of HIIT is how short the sessions are. Forgot 30 minutes of boring cardio. You literally can’t do HIIT for more than 20 minutes (if you can, you’re not doing true HIIT). 10 minutes to burn calories, boost fat loss, and increase your fitness? Yes please.


HIIT for health


Fitness goes beyond how we look, and HIIT has some amazing benefits for short term and long term health. Adding just one HIIT session into your week will reduce your risk of numerous common health issues.


HIIT for motivation


We all know how it feels to lose your training mojo. HIIT is a great way to add some oomph to your training week – you certainly won’t be bored with HIIT in your programme!


How to create a HIIT workout


  • The three key variables of a HIIT workout are intensity, duration, and rest periods. Be smart about using these to support your goal.
  • Choose simple full body exercises that use multiple joints and large muscle groups. Avoid high skill movements and needing to move between lots of different bits of kit.
  • Start with one HIIT session a week, building to HIIT 3-4 times a week as part of a progressive programme

Faisal Swings Kettlebell

Pros and cons of HIIT




Efficiency – HIIT is short, sharp, and amazingly efficient, perfect if you’ve got a busy schedule with little time for training

Variety – there are dozens of forms of exercise you can use for HIIT, from running hill sprints to using gym cardio machines, dumbbells, kettlebells, and functional fitness

Flexibility – you can do HIIT anywhere, no gym required, making it one of the most adaptable workout styles around

Health – HIIT is great for fat loss and lean muscle gains, but it also has important long-term health benefits




Energy demands – HIIT puts a lot of stress on your physical and mental energy, so it may not be the best option if you’re feeling sub-par

Injury risk – HIIT is fast and furious, which puts you at higher risk of injury as you move quickly and switch between exercises

DOMS – there’s a risk that the soreness from HIIT workouts may impact your readiness to train the next day

Consistency – HIIT is hard work, so be sure you set a HIIT goal you can stick to


15 ways to do a HIIT workout


Use any combination of these simple pieces of fitness equipment to create your own fat-burning HIIT session.


A flat stretch of playing field or pavement

A steep hill

Boxing bag or pads (and a partner)

A kettlebell

Rowing machine

A speed rope or skipping rope

One or two dumbbells

Air bike or assault bike


Battle ropes




Light barbell

Bodyweight – no equipment

Sample HIIT workouts for gym and outdoors


Try these HIIT sessions then get creative and design your own. Remember to warm up to get blood into your muscles, and always cool down completely before grabbing a post-workout drink.


Try this HIIT workout (just 10 minutes!)


40 seconds effort + 20 seconds rest of all 3 exercises

Repeat 3 times

Plus bonus 60 seconds work


1 Max calories on a rowing machine or air bike

2 Double dumbbell squat to overhead press (thruster)

3 Press ups

Finish with 60 seconds skipping

ambassadors out on run

Outdoor HIIT workout


This HIIT session combines running and bodyweight exercises – perfect for a no-equipment blast of endorphins and fresh air! The running should be at 8-9/10 effort.


Run 200m


20 air squats

10 press ups


Run 400m


20 walking lunges

10 down ups (modified burpee)


Run 200m


20 air squats

10 press ups


Run 400m


20 walking lunges

10 down ups (modified burpee)


Run 200m


HIIT is demanding on your body so remember to stay hydrated and energised. Try PhD Hydro to stay on top of your body’s hydration needs so you can give your HIIT workout everything you’ve got and recover faster for the next training session!


Want to get some more training tips and tricks? Check them out here.

Don’t forget to fuel yourself Pre, Intra and Post-workout – You can grab yourself all your workout must-haves here.  Make sure to let us know how you get on with your training program and tag us in your workouts on Instagram, Facebook, and Twitter – @phdnutrition

Nicola is a specialist freelance copywriter for the fitness industry @thefitwriter