The Lowdown on HIIT
High-intensity interval training (HIIT) is like the Hugh Jackman of exercise systems – it can do everything, it seems just so perfect, but if you’re not careful, you can get too much of it – and that can be a little bit painful. HIIT describes a range of activities with bouts of ‘all-out’ maximal effort or intensities of 85–95% of maximum heart rate alternated with periods of low activity or rest. High intensity intervals can range from 10 seconds to four minutes, and the rests can between 30 seconds and four minutes. Your ‘conventional’ style of cardio exercises, known as moderate intensity continuous training (MICT) is a continuous activity where you maintain 60–80% of your maximum heart rate. Like Hugh, HIIT is still hip and happening and can create a stir, but it’s been around a long time.
HIIT has a long history, even when it comes to steady endurance events such as distance running. ‘The Flying Finn’ Paavo Nurmi shocked the world when his unconventional training methods made him unbeatable in 121 races, ranging from 800m up to 20km (plus nine Olympic gold medals!) through the 1920s. Then in the late 1940s and ’50s, Czech runner Emil Zapotek, who won Olympic gold in the 5000m, 10,000m and marathon, laid the foundation for modern distance runners with sessions of repeat intervals, typically ranging from 150m-400m. HIIT has also proved a popular training format for many sports, including combat sports, and field and court sports, as it imitates the requirement for short, sharp bursts of effort and recovering efficiently in between them.
For general health and fitness, HIIT has three big advantages, especially compared to MICT. First, it allows more scope for variety, so people often find it more interesting and enjoyable. It’s also time-saver, with the shorter sessions burning the same or even more calories per session as an MICT session that might be twice as long. Add these two points together and you have a training schedule that people are often more inclined to stick to.
Is it really HIIT?
First up, you need to be able to tell the difference between moderate-intensity exercise and high-intensity exercise. It’s not all about heart rate numbers – these can vary from person to person. An easy way to distinguish between the two is with the talk test. You can talk during moderate-intensity exercise, even if you’re gasping a bit – but you can’t sing. During high-intensity exercise, you can only say a few words (usually swear words) before your need to suck in the big ones makes speaking futile. Your exercise output at high intensity is relative – but no matter what your level, ‘high intensity’ is something you can only hold for a very limited time before you have rest or lower your intensity considerably (active rest).
Many of the health benefits of HIIT come from reactions triggered within the body. These reactions rely on a large amount of muscle being stimulated, so true HIIT is done with whole-body actions or activities that stimulate large groups of muscles. So doing biceps curls or bench press (i.e. you are not even supporting your whole body because you’re lying on a bench) is less likely to trigger all the benefits of HIIT than doing kettlebell swings, running or using an elliptical trainer.
Why it works
According to the British Journal of Sports Medicine, HIIT can produce similar if not greater improvements in cardiorespiratory fitness than MICT. The mechanics are fairly straightforward. You condition your cardiovascular and respiratory systems by pushing them beyond your comfort zone, while also training yourself to recover from the physical stress more efficiently. However, HIIT goes far beyond this, because while HIIT causes physiological changes that can also come from traditional endurance training, the reactions and processes it causes inside the body are significantly different.
Let’s look at fat loss. HIIT has a higher calorie-burning rate than MICT – but then, you also do it for less time. However, comparing straight calories burned per session with HIIT and MICT doesn’t work because of EPOC – excess post-exercise oxygen consumption (or “afterburn”). This means that after your session, you will continue to expend calories at a higher rate for hours, even if you are sitting around on your… But are you burning fat, carbs or muscle? Many studies have confirmed that HIIT makes you use more fat as fuel under a variety of conditions (whether you’re a beginner or reasonably well conditioned). This occurs because this type of activity is like lighting up the bat signal for two super fat-fighters, adiponectin and catecholamines such as adrenaline and noradrenaline. The first is a is a protein that is involved in regulating glucose levels as well as fatty acid breakdown, and the second act as hormones or neurotransmitters to mobilise fatty acids (i.e. take them off the shelf to use as fuel) so that more fat can be burned from under the skin and within the exercising muscles. This flies in the face of many years of almost anyone with enough scientific education to explain gravity ruling out the wishful idea of “spot reducing” troublesome fatty bits on our bodies. Now several studies on HIIT suggest that this exercise type might be unique in this way. For example, a landmark 2006 study at the University of NSW on 45 overweight women, which noted an “unusual but consistent” outcome that saw the women lose the most weight off the legs and buttocks.
Other healthy reactions HIIT triggers include helping with increased insulin sensitivity through improved regulation of glucose, and an increase in mitochondrial protein synthesis, which doesn’t just help you preserve and rebuild your muscles, it fights the ageing process by preventing some of the deterioration processes that occur in our cells to make the magic happen (respiration, energy release, etc.)
Is HIIT the answer?
The good news is that ‘high intensity’ is a relative measure and HIIT works with a wide range of intervals, even as short as 10 seconds – which means that can work well with almost anyone, even older people, the overweight, deconditioned people, and even cardiac patients (although supervision and/or training prescription is recommended for these groups).
However, while HIIT hits a lot of buttons, it is best to consider it only part of the solution. For a start, HIIT isn’t something you can do every day – if you’re doing more than three HIIT sessions in a week, then it’s probably not HIIT at all. The intensity is so high that if you do it correctly, you’ll need a day or two to recover (with rest or lower-intensity activity). For most people, 2-3 days per week will work best. While not all HIIT has to be high-impact (low-impact HIIT training options include water running, cycling or elliptical trainer), an allowance has to be made for impact on joints and soft tissue and muscle recovery. Lower intensity continuous cardio activity has less stress on the body and allows you to do exercise more frequently (e.g. in between HIIT sessions), while still providing many health benefits, such as offering protection against heart disease, hypertension and diabetes.
Another factor is – and I apologise for getting so technical – is that HIIT is very hard. Some people might need a trainer or a group or a session leader to push them to the intensity required. Others who have been ill (especially those with heart or respiratory issues, or those who are at risk of these) injured or deconditioned may need to consult a trainer, exercise physiologist or doctor for guidance on what level to start at.
HIIT the spot
Here are some ways that you can best make HIIT work for you.
- Always take time to warm-up and cool down for high intensity work. We know – you’re trying to save time, but it’s being injured that the big waste of time, not the warming up.
- HIIT is not something you should do when you’re sick or recovering from illness or injury (unless you can take the injured body part completely out of play). By contrast, you can do low to moderate intensity exercise when you have a minor ‘above the neck’ illness (e.g. a cold, headache) and when recovering from injury
- If you’re a beginner or deconditioned, then you need longer recovery periods. Try a training-to-recovery ratio of 1:3 initially, e.g. you could use intervals as short as 10 seconds followed by 30 seconds of rest or lower intensity.
- If you are deconditioned, it is suggested that you work up to a level where you can exercise continuously at moderate intensity only for at least 20 minutes and do this for several sessions before progressing to HIIT
- There is no ideal interval length – in the many studies of HIIT over the last decade, researchers have proven results with different interval types. In fact, varying your interval and rest lengths and exercise type periodically may challenge your body so that reactions in the body continue to occur as your body fights to adapt to what you are throwing at it.
- HIIT can be used to build strength-endurance by hitting large groups of muscles with exercises such as burpees, kettlebell swings, dumbbell snatches, clean and presses, rowing exercises, box jumps and medicine ball throws.
- Remember, intensity is the key, not duration. As you get fitter, you can simply push yourself harder and do more in the same interval time – it’s not about extending the interval time. However, with better fitness, you may be able to bring down the interval to rest times closer, e.g. a 1:2 ratio of work time to rest, or more advanced endurance athletes might do an interval of two minutes followed by an active rest period of three minutes.
- A sweet spot for long endurance athletes is intervals of 2 minutes or a little more, with an active rest, e.g. run hard, then slow jog or walk – you’re getting your breath back to a point where you can hold a conversation.
- A typical HIIT workout, minus warm-up and cooldown, is 15-30 minutes.
By Dom Cadden
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