HIIT has been with us for over 100 years now. During that period, it has been sporadically repackaged or given a few harmless cosmetic modifications and paraded as a new style of training with almost every fitness fad or craze that pops up. Recently it has been promoted as a good (if not better alternative) to conventional steady state cardiovascular training. So what exactly is HIIT, what are the claimed benefits and should we really be swapping all our regular cardio sessions for these fast paced alternatives?

What is HIIT?

HIIT stands for High Intensity Interval Training. It describes a cardio session that alternates between maximal exertions lasting around 10-90 seconds, followed by lower intensity phases which could range from 20 seconds all the way up to two or three minutes. There are no hard or fast rules but an example of this type of session could be:

Warm up for five minutes followed by:

Sprint 30 seconds

Gentle jog 2 minutes

Repeat for six intervals in total

Cool down five minutes

A family of related training approaches exist that would fall under the HIIT label. They are known as metabolic conditioning or Metcons and include Swedish Fartlek training or ‘speed play’ which is a little less structured where you maybe use trees, hills or lampposts as markers for when to switch between different paces. 

HIIT should not be muddled with ‘HIT’ or High Intensity Training. This is a method of weight training where the intensity refers to the physical effort rather than the load used relative to your maximum. It involves you training to muscular failure. They are two different methods and people would usually know which of the two methods you are referring to from the context. However, to avoid confusion some people like to say HIT very abruptly and conversely exaggerate the double i in HIIT, pronouncing as HIIIIIIIIT.

HIIIIIIIIT usually suggests some type of cardio is being used. I’m not a fan of incorporating weights into these as the technique usually gets so bad it would make an onion cry. In theory, any kind of exercise would work, but in practice some allow you to change pace more easily than others. Something like the treadmill or stair master doesn’t work so well. The bikes, rowers, ellipticals and road or track running are better.

What are the benefits?

As it is a form of cardio, the health benefits are vast. Usually when discussing HIIT, the question is not what are the benefits of cardio, but how does it compare to regular cardio? 

I have set out below the claims you’ll hear made by HIIT proponents.

It is more enjoyable

Many will tell you that cardio is a miserable affair, but a short blast of HIIT isn’t only bearable but actually fun. 

What’s the catch? Opinions here are split. Some enjoy it more than steady state but training at ‘all out’ effort is uncomfortable, painful and enough to suck the enjoyment out of the session. In other words, this is just down to preference. I would say that initially HIIT may seem more fun, but the novelty wears off and you can’t really train harder than maximal. Cheap intense thrills soon grow stale and in my experience long term adherence  can only be maintained by the intellectual challenge of constant improvement. I also oppose giving people the impression that the harder you work, the better it must be.

It saves time

In the short term, the health benefits and training effects from a moderate, steady paced cardio session can be achieved equally well in less than half the training time by following a HIIT protocol. This makes HIIT extremely time efficient. 

What’s the catch? The headline is that a 40 minute cardio session has been halved to a 20 minute session. The reality is that the travel time, getting changed, the shower after, the warm up are all identical, so the gain is actually marginal. In my experience, if you don’t have 40 minutes to get in a session, you probably don’t have 20 minutes you can spare either. This is not always bad time management; I appreciate some people simply cannot justify spending any time working out. Trying to add in a half-assed session here and there isn’t ‘better than nothing’. It will have minimal effect, which then really does makes the exertion a waste of time and effort. 

Improved sporting performance 

Exclusive benefits to HIIT include: Improved neuromuscular status, improved anaerobic power and improved heart rate reserve (the difference between resting and maximum heart rate). Some prefer HIIT as they think it allows cardio without an adverse impact on weight training. Really, so long as the cardio is moderate (i.e. no more than an hour two to three times a week), it will probably not negatively affect your strength or muscle in the slightest.

What’s the catch? These only really apply to well-trained endurance athletes. Anyone else would see almost no change in these markers. Especially if you are already incorporating weights into your sessions.

It burns more calories 

HIIT burns more calories per unit time than normal cardio in the same way sprinting uses more energy than jogging. That bit is obvious, but some claim HIIT has an ‘afterburn’ effect. This is the additional calories burnt after the workout ends, and is known as EPOC (excess post-exercise oxygen consumption).

Following something like steady state cardio, this might be 7% of the calories burned during the session. For a HIIT session or a weights session, this could be as high as 15% extra – more than double!

What’s the catch? The EPOC is quite significant in relative terms, but a 20 minute burst of HIIT can’t burn the calories of a normal cardio session as it is too short, irrespective of the EPOC boost. 

This is not the end of the world. The calories you can burn during exercise is immaterial compared to what you eat and there are more important reasons to be doing cardio than just burning calories!

HIIT or Steady state

Firstly, please understand that to have any effect, cardio must be of a minimum level of intensity. Dragging your feet on a treadmill whilst you play on your phone for an hour will not have any benefit (unless you weigh a lean 150kg and are particularly unfit like an off-season pro bodybuilder!). If it is between that or a decent HIIT session, then there is no comparison – the one with real training involved will win hands down.

Assuming we are comparing real cardio with HIIT, initially either method will increase insulin sensitivity, reduce blood lipids, help reduce body-fat and improve cardiovascular fitness. The real difference comes later; continued progress is going to be ‘dose dependent’. You simply can’t sustain or recover from HIIT sessions alone if you want to keep improving. Recovery from a HIIT session can exceed five days – using them more than twice a week would just be too strenuous. You couldn’t train enough to get fitter and if you tried, you’d wind up exhausted or injured.

But wait – the tortoise may not again beat the hare! You can of course use both. Keeping most of your sessions as steady state will give you the conditioning and the chance to recover. Save the HIIT sessions for when you are a little short on time or intersperse them once a week or so.

Another option is to use them exclusively for a two to three week block and then switch to regular cardio for four to six weeks.

In either case, HIIT is a great addition to your cardio workouts, but you have to build up to them. If you can’t sustain twenty minutes of moderate cardio then you wouldn’t be ready for a HIIT session. Once you can use them, they really do blow away the cobwebs and allow you to feel what an all-out effort really is. I’m a big advocate in varying intensities from session to session and week to week to maintain interest and facilitate long-term adherence. By design, spicing up your routines with some HIIT jalapenos allows that to happen so you can get the best of both worlds.


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