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High Intensity Interval Training: So why all the hype?

Workout trends come and go, and one of these that is getting a lot of attention is High Intensity Training (HIT). The attention, such as that in television shows like Catalyst and Michael Mosely’s ‘The truth about exercise’ (claiming that 6 minutes of exercise per week is all that we need) is largely well deserved, but as with anything, there are always two sides to the story. Let’s start with some definitions and then make sure we end up with a balanced and informed perspective!

A senior woman and a mature man riding stationary bikes

HIT (High Intensity Training)

High Intensity Training (HIT) is the umbrella term given to a number of different high intensity training modalities. The measures used to determine the level of intensity are typically Heart Rate, or a Rating of Perceived Exertion (RPE). To qualify as high intensity, Heart Rate needs to be be over 70% of maximum heart rate (if you don’t know what yours is from personally testing it, it can be calculated by substracting your age (in yrs) from 220); and the exercise needs to be considered to be ‘hard’, or around 5-6 on an RPE scale, where 1 is “very, very easy”, and 10 is “maximal”.

HIIT (High Intensity Interval Training)

HIIT involves alternating short periods (Intervals) of work and rest over the duration of a session. The intervals can be programmed in different ways, with their length and actual intensities varying to meet the desired demands. For example, the lengths and intensities of the ‘work’ intervals can range very widely, to address either the anaerobic threshold, or maximal anaerobic power. Similarly, the rest period can be performed as active or passive rest.

HIRT (High Intensity Resistance Training)

A close member of the family, HIRT is based on the well researched varieties of cardiovascular based HIT training, but is performed largely with ‘weights’. So the work intervals may be made up of exercises that you may be more used to seeing in a gym floor, such as squats, lunges, presses, kettlebell swings, etc.

So, why would we bother with these types of training, and how do they compare to more traditional training methods?

Studies consistently show that HIIT improves metabolic health markers and fitness measures. For example Irving et al. (2008, Med Sci Sport Exerc) found that after 16 weeks of exercise, women with Metabolic Syndrome lost twice the amount of weight and fat mass, and four times the amount of fat around the abdomen when compared to those who did the same amount (isocaloric) of low intensity training. These type of studies strongly show that when it comes to energy in, or out, the amount of calories (or kilojoules) themselves are less important than the hormonal response that is created; with suggested mechanisms to explain this difference including improved insulin sensitivity and cortisol levels. More on the hormonal effect on energy in and out on weight management on a blog coming out soon!

High intensity training has been shown to reduce the risk of dying prematurely by up to 17% compared to those who do no HIT (Tanasescu et al, 2002, J Am Med Assoc), and after only one training session a week! Other often cited benefits include: reduce subcutaneous fat; improved insulin sensitivity; total body mass; aerobic fitness; blood pressure and glucose regulation; improved lipid profiles; and greater tolerance to stress! phew, great list!!

In addition, different varieties of HIT may be seen as more attractive exercise options, due to the opportunity to gain greater health benefits in less time. For those who lack motivation it may be a more enticing option than the prospect of continuously exercising for an extended period of time.

Bartlett (et al. 2011) found that the ratings of perceived enjoyment (yes, “enjoyment”) after HIIT were higher when compared to moderate intensity training. Considering that ‘lack of time’ remains the most commonly cited barrier to regular exercise participation, this seems too good to be real, right?! Well, perhaps.

There’s certainly some things that we need to be aware of:
While the physiological  effects are evident, the duration of most studies is very short, with very short follow-ups, and largely in unhealthy populations. The long-term effect of has not been well established and if I was to take a guess I would say that eventually there would be a decreased return on investment.  A yet to be published (large scale) study looking at physical activity trends in Australia shows that more Australians are performing vigorous physical activity; but less low-moderate physical activity; and the amount of sedentary time continues to increase. It appears that while HIIT is certainly more time efficient, the less time we spend moving the more opportunity we allow for sedentary time. This might help explain the increasing rates of Type II diabetes and Cardiovascular Disease, as it is well accepted that the negative physiological effects of sedentary time can cancel out and even outweigh the physiological benefits of exercise.

In addition, by its very nature, high intensity exercise carries a greater risk of injury, particularly for those new to exercise, so careful and guided progressions are recommended!

To conclude, other than the imbalance that is created between active and sedentary time, by shortening exercise time, I believe there is another significant issue with the way that research on HIT training is communicated to the public. The type of reporting seen in the media only reinforces the mindset that exercise is like some nasty medicine that we need to take, so we are best off pinching our nose and getting it over and done with as fast as possible! Surely the message should rather be one of promoting an active lifestyle, and that HIIT training can be a fantastic adjunct to that?  Our body is the machinery that we have to go out and experience the world in and with, and the broader and deeper our physical capabilities, the wider the range of experiences  we can potentially have. While High Intensity Training can certainly help us improve some specific health measures, does it help us live our lives more fully?

Written By Max Martin

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