How Much High Intensity Interval Training Should You Do?

WH investigates whether just one minute of exercise could be all you need.

Perhaps this isn’t the right place to admit I’m not mad about cardio. Weight training? Fine. I like the max-effort, minimum-sweat ratio. And I’d do my weekly ashtanga yoga every day if life didn’t get in the way. But cardio? I hate every sweaty, undignified, clock-watching minute, so I dodge it.

The problem is, this has left me with the nagging doubt that I’m not as fit as I’d like to believe. A doubt that’s confirmed when I have my cardio fitness scrutinised by a ‘VO2 max’ test. After 15 minutes of agonising treadmill intervals, I’m given the results. I just scrape into the ‘healthy’ bracket, but it’s clear that my lungs and heart aren’t working the way they could be.

So what’s the answer for a busy, cardio-loathing woman? Potentially, it’s this research finding from Martin Gibala, a world expert in high-intensity interval training (HIIT): just 60 seconds of intense exercise, three times a week, could be all we need to keep fit.

How low can you go?

Before we go on – here’s the small print: The workout is actually three 20-second hits of all-out, hard-as-you-can cardio, followed by two minutes of active rest during which you
try to reclaim your breath, composure and will to live. Add in a warm-up and obligatory cool-down and you’re looking at a 10-minute workout. So it’s actually 600 seconds of time, 60 seconds of sweat.

But still doable. And effective. Gibala says that one minute is enough to improve cardio fitness by 12 per cent in six weeks and metabolic fitness (the ability of muscle to burn fuel). “That kind of significant improvement translates to a 12-15 per cent reduction in your risk of developing cardiovascular and other diseases,” Gibala says.

So why the big change with such a small amount of exercise? Gibala and his team think the success of the 60-second workout lies in the fact that you only have to hammer at it for 20 seconds, so you’re more able to hit that high intensity (90-100 per cent of your maximum capacity) and sustain it for the whole duration. This causes your muscles to produce more mitochondria – and the more mitochondria you generate, the more efficient your muscles become at using oxygen to burn fuel for energy.

Alright, sign me up

So here I am, climbing on an exercise bike under the watchful eye of personal trainer Anna Reich, who’s helping me put Gibala’s theory into practice. Having just been witness to my average VO2 max test, she’s buoying me with a fairly convincing HIIT sales pitch: “You’ll feel the difference within weeks,” she promises. “You’ll start to utilise energy more efficiently and you’ll be burning kilojoules post workout.”

After a two-minute warm-up, it’s sprint time. Anna ramps up the resistance to eight, which is as high as I can go and maintain maximum speed throughout. She yells at me not to drop my pace for a nanosecond and by the time I’ve completed my final 20-second sprint, I’m purple-faced, too breathless to tell her that in another 10 seconds I would have started to cry. Then after a three-minute cool-down (essential to ensure your blood pressure doesn’t drop dangerously low and you faint), I towel down and walk out.

Net gains, more pain

I commit to three weekly sessions, keeping up with my weight training and yoga in between. Anna wasn’t overstating it – by the end of week two, there are noticeable improvements. I’m pedalling faster in my workouts, but I’m now able to talk comfortably between sprints. Friends begin to comment that my eyes and complexion look brighter. On week three, I go away on a family holiday, eat like two fat men, but maintain my high-speed workouts (the hotel has a gym with bikes) and I don’t put on a kilo.

And so, after six weeks, I’m back on the treadmill to test my VO2 max. The results? It’s no less painful, but I’ve gone from teetering towards ‘below average’ to ‘excellent’. I’ve also had a 4 per cent drop in body fat which takes me from ‘average’ to ‘ideal’ and my blood pressure, which had been slightly higher than my GP liked to see, is no longer a cause for concern. I’ve lost 3cm from my waist, nearly 2cm from my hips and 1cm from my upper arms. But, I also wonder, could the workout be even shorter still? Gibala thinks not. “We’re scraping the bottom now and clearly there’s a minimal amount of work you have to do to stimulate some benefits,” he says.

I think my cardio-dodging excuses have just run out.

This article originally appeared in the June issue of Women’s Health.

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