HIIT workouts are everywhere – in high street gym chains, in boutique studios, on apps and in fitness magazines. But what actually are they? This guide will break everything down for you, from what HIIT is to the benefits of it, how to do a HIIT workout, what you should wear and what the risks involved are.
What is HIIT?
HIIT stands for high intensity interval training. Interval training in itself has been around for years – think speedwork on a running track or higher and lower intensity cardio songs in an aerobics class. HIIT differs in that during the working intervals, you push yourself to the max for a short period of time, rest for a short period of time and then repeat.
A true high intensity interval training session shouldn't last longer than 20 minutes – if it does, the likelihood is you're not going all out during your working intervals. It's a form of anaerobic workout, meaning that you should be working at 80% or more of your maximum heart rate and recruiting fast twitch muscle fibres. This forces your body to work without enough oxygen to supply the muscles, making it rely on the energy sources within the muscles instead.
You can structure a HIIT workout in endless ways, but these are a few popular ones:
Tabata: Created by Japanese sports scientist Dr Izumi Tabata, this type of HIIT involves 20 seconds of maximal effort followed by 10 seconds of rest, repeated eight times for an intense four-minute workout.
Timed Work/Rest: A similar structure to Tabata, but with varying timings. These could be equal periods (such as 30 seconds work, 30 seconds rest), longer intervals (40 seconds work, 20 seconds rest) or longer rest (25 seconds work, 35 seconds rest).
EMOM: Every minute on the minute. This involves a move (or series of moves) which you have a minute to complete. The sooner you complete it, the more time you have to rest. An example would be 10 burpees, 10 jump squats and 10 jumping jacks for a three-minute EMOM.
AMRAP: As many rounds/reps as possible. In a set period of time, you'll be given a series of exercises that you'll have to repeat for as many rounds or reps as you can. For example, in a 20-minute session, you'll repeat a 200m row, 20 kettlebell swings and 10 V-ups as many times as you can.
You Go, I Go: A popular method for training in pairs, one person will complete the exercise while the other rests, then they'll switch. For example, one person does 20 plyometric lunges and when they complete it the other person takes over. This is repeated for a set period of time, generally three to five minutes.
Whichever way you frame it, you'll be mixing hard efforts with total rest repeated over and over for a solid heart-pumping workout.
What are the benefits of HIIT?
"HIIT is versatile, so it can be done with little or no equipment, and potentially all you need is a small space like your living room," says personal trainer and three-time Olympian Sarah Lindsay, founder of Roar Fitness. "It is designed to elevate your heart rate which can help increase your Vo2 max."
Essentially, it's an all-round cardio win that can give you both an anaerobic and aerobic boost.
Dr Tabata's original HIIT study, which was published in 1996, saw one group of participants tasked with completing eight sets of 20 seconds hard, 10 second rest on a stationary bike, while the other group did one hour of cycling at a steady pace. After doing this five times a week for six weeks, the HIIT participants were found to have an average increase of 28% in their anaerobic capacity (their ability to work out for short, intense periods of time) as well as improvements in their aerobic (endurance) fitness, while the steady state group only saw aerobic improvements.
So, if you are an endurance junkie, HIIT is still for you. "Combining both steady state and HIIT training will result in brilliant all-round fitness," says Dan Little, head of fitness at indoor cycling and HIIT studio Digme. "Steady state training will increase endurance tolerances and essentially build a strong fitness level, whilst HIIT will increase your power and efficiency." So, if you're a long distance runner, cyclist or triathlete, blending HIIT into your training programme with speedwork or threshold intervals is ideal for pushing your fitness to the next level.
If you're focusing on aesthetics or generally want to lose fat, HIIT can also help. A study published in the European Journal of Nutrition reported that combining anaerobic training such as HIIT with aerobic training (gentler, steady state exercise like cycling) led to better fat metabolism than aerobic training alone.
In this study, they had participants do a 25-minute aerobic workout followed by five minutes of anaerobic training – something you can replicate in the gym by mixing 25 minutes of steady state running, cycling or rowing with five minutes of hard efforts or plyometric moves.
What equipment do you need to do HIIT training?
The glory of HIIT is that you can do it with virtually any equipment or with your own bodyweight. "Anything that raises your heart rate quickly will do," says Lindsay.
Simply choose your interval timings or workout structure, as explained above, then go hard and rest when necessary.
Popular pieces of gym equipment for HIIT include:
- Stationary bike
- Rowing machine
- Punch bag
- Ski erg
- Battle ropes
- Skipping rope
- Box (for box jumps)
- Elliptical trainer
- Assault bike
Going equipment free? Try running fast or challenging intervals to the timings set out above or use a selection of these bodyweight exercises:
- Squat jumps
- Plyometric lunges
- Lateral skaters
- Mountain climbers
- Tuck jumps
- Jumping jacks
- Squat thrusts
- Fast feet
- Broad jumps
- Plank ups/Commandos
- Inch worms
- V ups
Where can you do HIIT?
Most high street gym chains offer HIIT classes as part of their schedules. DW Fitness First offer 30:30 or 40:20 HIIT sessions (the numbers describing the work:rest ratio), Virgin Active have their signature Grid classes which include Tabata training principles and decreasing rest periods, and Pure Gym's Burn It class is a tough HIIT session using only your bodyweight.
If you like to splash out, there are tons of boutique studios around the globe that offer HIIT training. In the UK the majority of the big names are London-based. Digme's Matrix class mixes treadmills, TRX, kettlebells and bodyweight exercises for a heart-racing full body workout, while Frame's HIIT and Chill uses explosive cardio and strength movements followed by fascia release techniques to give you a workout and kickstart your recovery.
More into solo workouts? There are tons of online HIIT programmes and fitness apps you can try out, without committing to a gym membership. The appropriately named FIIT is a mobile app with plenty of cardio interval sessions that come free with the basic package. Alternatively, the infamously tough Insanity workout is available by subscription from Beachbody – but be warned, it's definitely for advanced HIITers.
On top of all those options, you can do HIIT without even leaving the room you're in. "The best thing about HIIT is that you can do it anywhere, be it at home, in a hotel or on holiday. All you need is one square metre of space," says Ben Davies, Matrix lead trainer at Digme.
What to wear?
To keep comfortable throughout a massive range of movements, you'll need activewear that will offer flexibility and sweat-wicking properties in equal measure. Think tops, tights and shorts made with technical material, and nothing too tight or restrictive. Equally, if you're that way inclined, make sure you wear a high impact sports bra to avoid discomfort and bouncing during running and plyometric moves.
- Check out: The best sports bras for every workout
Another handy piece of kit is a heart rate monitor. Data nerds will love being able to review the zones they hit and how long they spent at their max. Many fitness trackers and running watches have built-in optical heart rate monitors, but for optimum accuracy pair them with a chest strap.
What are the risks of HIIT?
While HIIT is enormously popular and has plenty of benefits associated with it, it's not a magical solution to all your workout needs. "HIIT is the current industry buzzword, and really something that’s being overdone and incorrectly performed more often than not," says human movement and elite performance specialist Luke Worthington.
One main issue is that the high pace of HIIT means form can often fall by the wayside, especially in group classes where the focus is on getting as sweaty as possible rather than performing exercises well. "The people most at risk of damage from HIIT group classes are those new to exercise – the very population at which these classes are marketed," says Worthington. "Someone new to exercise would be better suited to spending some time with a trainer to learn technique and build a base level of strength and conditioning, before moving on to a group exercise setting.
"The onus on correcting this is actually on the fitness industry, not on the client. The industry is in the position of expertise and has a responsibility to correctly advise its customers, and also ensure the technical standards of its instructors."
Plus, while HIIT can boost your anaerobic fitness, it's not the be all and end all when it comes to cardio. If you're looking to generally improve your aerobic fitness, work on endurance or lose fat, there's nothing wrong with classic steady state cardio. "HIIT's upsides are it is a very time efficient way of burning fuel, however it is nothing more effective at this than low intensity training which does the same thing, but requires longer training sessions!" says Worthington.
Essentially, HIIT can be a great addition to your workout arsenal, but make sure your form is spot on and if you're not absolutely certain it is then seek help from a qualified personal trainer.
Main image credit: Unsplash