Is HIIT legit? A comprehensive guide to high-intensity interval training

As we grow older, it’s easy to become trapped in the safe place of our regular exercise regimes and fail to innovate how we exercise.

I hope to challenge this mindset by exploring the increasingly popular high-intensity interval training (HIIT) and shed some light on why we should all consider incorporating it into our weekly routine.

What on earth is HIIT?

In recent years, the water has been muddied with popular brands like F45 being mistakenly called HIIT. One of these things is not like the others!

HIIT describes a form of exercise completed in repeated efforts (1-4 minutes in duration) at near-maximal to maximal intensities interspersed with recovery. A typical workout can be completed in less than 40 minutes!

Effort phases of the workout should feel “hard to very hard” and we should only be able to speak single words or grunt.

F45 and similar classes involve multiple exercise stations and importantly, aren’t typically completed at the same high level of intensity compared to HIIT. This makes the growing amount of evidence to support HIIT inapplicable to F45 and similar circuit training gyms.

Note: If you hope to improve your cardiorespiratory fitness (aka VO2 max), studies suggest that HIIT is more effective than circuit training with less time involved! [1]

Benefits of HIIT

HIIT is great “bang for your buck” for those stretched with busy schedules given the numerous benefits that can be drawn in almost half the time compared to moderate-intensity continuous aerobic training (MICT).

These include:

• Significant improvements to cardiorespiratory conditioning [2]

• Fat loss mediated through metabolic afterburn and appetite suppression [3]. This includes potentially greater visceral fat loss compared to MICT mediated through increased growth hormone levels [4]

• Increased lean body mass and muscular strength supported by acute surges in testosterone post-workout [5][6]

• Improved mental well-being, executive function and perceived stress [7]

• Improvements in cholesterol markers, insulin sensitivity, fasting blood sugar, HBA1c and blood pressure [8][9]

How can HIIT be so time-efficient?

HIIT strongly stimulates a process known as excess post-exercise oxygen consumption (EPOC), or otherwise nicknamed “the afterburn effect”.

EPOC occurs when increased amounts of oxygen are utilised whilst restoring muscle glycogen and repairing damaged muscle tissue. Your metabolism is effectively “kickstarted” after a HIIT workout and continues burning calories at a greater rate throughout the day.

The afterburn effect results in a similar amount of energy burnt between HIIT and continuous exercise (at submaximal intensity) despite less time involved in the HIIT workout (see graph below).

Sinking less time into your workout and adding variety through HIIT can increase your motivation and decrease the toll a 1-hour+ MICT session puts on your body physically and mentally.

Getting started with HIIT

HIIT isn’t a “one size fits all” approach. It can vary in time, intensity and exercise mode, which allows you to add variety and tailor the workout to your requirements.

The HIIT workout can be split into warm-up, protocol and exercise mode. 

We recently discussed this topic on Compound's podcast, How To Get Good, and Benny made a good recommendation for HIIT beginners and that's to start with using a bike or rower. Why? Well, when you're giving maximal effort, your form will usually suffer and if you're running, the injury risk can get very high.

Warm-up

An effective warm-up is essential to getting in the right mindset and reducing the risk of injury.

Start with a 10-minute dynamic warm-up that takes the major joints through their full range of motion and activates major muscle groups.

Pick your protocol

Beginner: Establish base fitness

At Compound, we complete a battery of baseline fitness testing focused on cardiorespiratory conditioning and muscular strength to help establish a safe and effective workout regime from day 1.

As such, we recommend the following when beginning your HIIT journey.

• Don’t bite off more than you can chew!

• Spend consistent time in zone 2 aerobic exercise for roughly 40 min x1-4/week for several weeks before diving into HIIT

• Develop exercise form and muscular strength to reduce the risk of injury

• When starting HIIT we recommend just one workout per week in conjunction with resistance training and zone 2 cardio to reduce the risk of overtraining syndrome

Intermediate: 4x4 (The Norwegian Method)

• Four intervals, each lasting 4 minutes at 85-95% maximum heart rate with 3-minute recoveries interspersed

• It takes some trial and error to find a consistent pace to maintain this heart rate for 4 minutes 

• There’s a balance between going too hard too early vs. too slow too late in each interval

Elite: Tabata

• 7-8 intervals, each lasting 20 seconds at high intensity with 10 seconds recovery interspersed

• Tabata originated from this 1996 study by Izumi Tabata whereby he determined “high intensity” to be 170% of the subjects' V̇O2 max intensity [10]

• Tabata is much more intuitive to find your pace compared to 4x4… full throttle for 20 seconds

• Keep this in mind! Higher intensity = potentially increased risk of injury

Pick your exercise mode

Running

• Both concentric and eccentric muscle activation

• Include variations in the running location (flat, uphill, treadmill) to suit your requirements

• Flat: a longer stride at higher speeds demands increased flexibility and increased acceleration and deceleration. Those undertrained or unaccustomed may face increased risk of injury starting here

• Uphill offers the ability to maintain intensity at reduced speeds and work different muscle groups, finding the right hill can be a challenge

• Treadmill offers all-weather training… no excuses!  The slow change in the pace of treadmills makes interval changes difficult

• Running can have a higher impact exercise on joints (eg. knees and ankles) compared to modes like cycling and swimming

Exercise bike

• Commonly studied and used in practice

• Precise control over resistance to increase intensity

• All-weather option

• Can monitor power output to maintain intensity

• Low impact on the body

• No upper body involvement

Swimming

• Less commonly studied but highly accessible to many people

• Utilises all major muscle groups

• Lower impact on the body

• A great option during summer to avoid the heat

Rowing erg

• Near full-body workout engaging muscles in arms, legs, back and core

• Able to monitor power output to maintain intensity

• Requires specialised equipment

Other Common Methods

• Ski erg
• Assault Bike
• Cycling

Hot tip for commuters

Have a crack at “Renegade HIIT” during your next trip! Whilst imperfect, you can try incorporating high-intensity efforts into your commute.

Cycling to work? When the traffic light goes green your next 10 seconds should be at an all-out intensity — repeat these efforts at each light until you get to work.

Jogging to work? Take a detour to an open field and complete 7 bouts of maximal intensity sprints for 20 seconds with 10 seconds recovery interspersed.

Alternatively, try incorporating 4 minutes of high-intensity running followed by 3 minutes of walking until you arrive at work.

The ins and outs of HIIT

If you're interested in learning more about all things HIIT, listen to our episode on Hot To Get Good. The Compound team dives into:

• The science behind HIIT and how it enhances cardiovascular health and boosts metabolism
• Key differences between HIIT and other popular training methods like F45
• Detailed breakdown of various HIIT protocols including Tabata, Wingate, and the Norwegian method

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Longer, stronger living

For those looking to take their health optimisation a step further, you've come to the right place. At Compound, we take a multi-disciplinary approach to preventative care to help men unlock barriers to everyday performance. 

Compound’s program is executed in 3 stages — starting with a suite of diagnostics to get the clearest picture of health you’ve ever had, using tools like DEXA scans, a VO2 max test and HbA1c blood testing. This is followed by a complete diet, health and training program, all guided by an expert health coach.

The final piece of the puzzle is medical treatment, supplements and hardware, like a CGM device, that you need to boost performance and meet your goals. 

Once you commit, our team is dedicated to ensuring you see returns. Your part won’t be easy but we’ll equip you for success like never before.

This post contains general information about health and wellness practices. It is not intended as medical advice and should not be treated as such. Please consult with a healthcare professional before starting any new health regimen. This information is provided without any representations or warranties, express or implied.