I’ve been trying to stay away from addressing the populist exercise fads but there is one I can’t escape: H.I.I.T.
You probably know it stands for High Intensity Interval Training. If you want some definitions – look it up here. Exercise fads can be like religions and their followers can range from the nominal follower to the fervent fundamentalist. HIIT certainly has its share of evangelicals.
Firstly, let me say that arguing about forms of exercise is as pointless and as common as arguing over the best diets. While scientists can’t universally agree on which is more evil: fats or sugars, they can agree that its safest to moderate both and to keep portion sizes low. The same goes for exercise: comparing exercise religions misses the point that anything done regularly is exponentially better than anything done sporadically or not at all.
So, that brings me to the first good point about HIIT;
1. It is something
Not a groundbreaking statement but true none-the-less. And something is vastly better than nothing.
2. It is efficient.
Not having the time to exercise is the most common excuse for not exercising in Australians under the age of 55. HIIT is certainly time efficient. It generally burns more calories in a given time than any other form of exercise. Also, if we compare it to aerobic exercise that burns the same number of calories DURING exercise, HIIT results in a higher basal metabolic rate which burns more total calories in the 24hr period that follows. Efficiency is not everything though. You will still burn far more calories on a 6hr slow bike ride than any HIIT workout as you will be eventually limited by muscular exhaustion.
3. It is proven to build both anaerobic and aerobic capacity
Explaining the difference between anaerobic and aerobic capacity is beyond the scope of this blog but think of your aerobic capacity as the type of exercise you could do for an hour without getting completely unable to talk or feeling jelly-legged. Think of anaerobic capacity as your ability to run quickly up a steep hill for about 500m (not a 50m sprint – that is something different again). Despite HIIT only accessing your anaerobic systems, it has been proven to improve your aerobic abilities as well.
4. It is the fastest way to increase mitochondrial density
Mitochondria are the powerhouses of our cells that produce units of energy from fatty acids. Mitochondrial density in cells has been shown to increase within 24hrs of HIIT – far quicker than we previously thought was possible.
What about the downsides?
1. It often leads to nothing
This is by far the biggest and most important downside. The best exercise is something you can stay compliant with. HIIT has been shown repeatedly to have the poorest levels of compliance of almost any other form of activity. Very few people can sustain it. It is really hard getting yourself out the door, even if it is for just a short workout, if you know you have to push yourself to extreme levels again and again. Doing that for a few motivated weeks is one thing. Doing it for years on end is near-impossible.
2. High injury rates.
High intensity almost always involves high forces. High forces of joint impact. High forces of muscle contraction. High forces of tendon loading. The risk of injury is extreme. And, if consistency is key, avoiding injury is essential.
3. Not for sufferers of chronic disease
HIIT has far more risk of precipitating acute events in cardiac, respiratory and vascular disease. As morbid as it sounds, there are many conditions like cardiomyopathies and aneurysms that increase one risk during exercise but are only ever discovered at autopsy.
4. World Class Athletes train differently.
Different sports and events require different training methods and whilst elite athletes may incorporate some HIIT, almost all world class athletes do it very sparingly. The huge advances in athletic performances over the last few decades have been almost entirely due to improved training methods. Most elite athletes doing events requiring both aerobic and anaerobic capacity (think any running event over 1500m) do an extraordinary amount of very low intensity aerobic training with small amounts of very high quality, high intensity work. HIIT is not going to get you to your fastest possible marathon.
The verdict.
Do what you enjoy and you can sustain. Personally, I’m not a follower of this religion because it falls short on the most important factor of any exercise program: compliance and consistency. Even if you can maintain motivation, it is more likely to result in injuries that limit your ability to stay consistent.
Fitness also has many different components and systems. It is optimized when we work all those systems independently. This means alternating between strength training, aerobic training, anaerobic training, balance, agility, upper body, lower body, core……. The list goes on. Someone who has done exclusively low intensity training for years may certainly find it useful to add some blocks of HIIT work.
