HIIT, SIT and LISS: Why should I care about cardio?

Running track

Some people live for running; others love nothing more than working up a sweat on a bike. For some individuals, endless lengths of a 50 metre pool are enjoyable. I feel it is time for me to admit that I am not one of those people. Sure, there are times when I enjoy and have enjoyed running – but it’s mainly the bit when the run comes to an end.

For a year of my life, I was an avid cyclist, swimmer and runner. I would ride twice a week, swim twice a week and run three times a week – all in the pursuit of a good marathon time. I enjoyed the buzz I felt at the end of each session, despite the fact that it took me, on average, about a hour to get out of the door.

I know a lot of people who feel the same way. These are people who would happily spend half a day in the gym lifting weights; but who balk at the idea of spending 10 minutes on a treadmill. Cardio is awkward. It’s energy sapping, it’s sweaty, it eats into valuable weight training time and can make you feel completely awful. This could be why, according to certain stats, some 31 per cent of the world’s adult population fail to meet minimum physical activity guidelines.

The World Health Organisation (WHO) recommends at least 150 minutes of moderate-intensity physical activity per week, or 75 min of vigorous physical activity

This is a tall order for most people. When you only have a limited amount of free time each week, why on earth would you want to fill it with something that you don’t enjoy?

What it boils down to, though, is that cardio training is vitally important to maintaining the health of your heart. At its most basic level, the harder you exercise, the harder your heart has to work to pump more oxygen around your body – this causes the heart muscle (known as the myocardium) to get bigger, thus making your heart stronger and more able to deal with the exertions of everyday life.

So, the big question is: is there any way to cut down the amount of cardio you do to get the same health benefits as longer sessions? According to some research, the answer is a resounding ‘yes’.

Interval training: HIIT and SIT

Interval training is one of the core principles of SPLIT (in fact, it’s the ‘IT’ at the end). At its most basic level, interval training refers to set periods of heightened activity, followed by periods of rest, repeated over a set period of time.

This high intensity interval training, more commonly known as HIIT – is currently taking the fitness world by storm, and it’s easy to see why. Numerous studies have demonstrated the benefits of HIIT compared with moderate continuous training on cardiovascular health; however, few studies have reviewed any other potential effects of HIIT, like its ability (or inability) to help you shed fat.

According to a systematic review of 65 studies, published in the British Journal of Sports Medicine, short term adherence to HIIT (less than 12 weeks) “revealed no significant effect on body composition in normal weight populations”, which basically means, if you’re a healthy weight, HIIT isn’t going to help you quickly lose weight. Unfortunately, there have also been too few studies to review the long term effects.

However, body composition aside, the research did reveal that short term HIIT “significantly improved VO2 max by medium effects to large effects” – which means, in layman’s terms, HIIT can help you get fitter. Fast!

A separate study, conducted by researchers at Manchester Metropolitan University, partly supports this review. The study looked at the effects of sprint interval training (SIT) on fitness levels and body composition in men and women separately.

During the study, 24 men and 17 women (admittedly, a pretty small sample) performed four 20 second sprints on a cycling machine, three times a week, for 12 weeks. According to this study, just 80 seconds of sprinting, three times a week, “resulted in statistically significant reductions to body fat mass” – although this was far more pronounced in men and negligible in women. The study also showed that fitness levels increased by 9 per cent overall; conversely, this was far more pronounced in women.

Interestingly, according to the researchers, the improvement in cardiovascular fitness was on a par with “conventional endurance training programmes” lasting around an hour. Pretty impressive, really.

So, what can we take away from this? Clearly a comparison of HIIT and continous training would be useful. Much has been written about the benefits of low intensity steady state cardio – or LISS – for fat loss, and maybe there is something to be said for getting on the treadmill and jogging for 30 minutes. However, for quick cardio fitness gains, HIIT – or in fact SIT – is one way to go. While the effects on body composition vary, evidence does suggest that, if you are overweight, HIIT can have a beneficial effect on fat loss.

What’s more, some research has found that resting metabolic rate (the number of calories you burn while doing nothing) remained around 15 per cent higher for those performing SIT than for those undertaking endurance training – and it also acts as an appetite suppressant.

What does this mean for me?

What it boils down to is this; if you love running, by all means, keep doing it. But if, like a lot of people, you hate cardio, you can still make fairly significant gains to your fitness by performing sprints three times a week. Perform 20 seconds of SIT, followed by 1 minute of rest, then repeat three times. You may not notice much difference in your body composition, but hey, that’s what diet and weights are there for: resistance training for weight loss and toning up, and HIIT for keeping your heart healthy. Strength, performance, life and interval training. SPLIT.


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