Too much high-intensity exercise may be bad for your health


Interval training or (HIIT) has been a buzzword in the fitness industry for years, but is it really what’s best for our health?

We can’t escape the lure of ‘abs in 45 minutes’ compared to slugging it out for hours on the treadmill. Let’s face it, HIIT is the busy-person’s hack to fitness.

But is there such a thing as too much high-intensity exercise? Researchers in Sweden have set out to answer just that, and found that yes, we really can overdo it on the training.

The study, published recently in Cell Metabolism and reported on by the Sydney Morning Herald, had 11 healthy men and women complete varying levels of HIIT training over a four week timeframe.

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In week one, they performed just two HIIT sessions at four minute intervals and during week two they completed three sessions with some intervals as long as eight minutes.

Post-workout muscle tests revealed that the participants were improving their physical condition and their cells showed better glucose regulation and more efficient energy-producing mitochondria.

While all was looking good, a gruelling third week of five days HIIT (intervals at four and eight minutes) saw the numbers take a surprising decline.

Researchers discovered a striking reduction in mitochondrial function and a disturbance in glucose tolerance and insulin secretion causing big ‘ups and downs’ in glucose across the day.

In the fourth recovery week, where exercise was halved, participants began to improve but were still sitting at 25% less energy than they had in week two.

The results of this study suggest that HIIT workouts are best completed in a balanced way, two to three times a week to avoid what researchers call the ‘excessive training load’ where overall health declines.

Acclaimed trainer, Tiff Hall agrees. She told Body+Soul’s podcast Healthy-ish that despite loving HIIT, she wouldn’t advise practicing it too often in your week.

“I think you should do it twice a week,” she tells host Felicity Harley. “With HIIT you want to do it 100% to get the results…so you want to give it your all and you want to be really well rested.”

“HIIT’s going to be really energizing and good for the endorphin hit, but you’ll also want to compliment that training with some strength training, recovery, stretching or yoga.”

She also suggested that we not think about our exercise in a day mindframe, but with the whole week in mind.

“Look not at your day, in terms of a workout, but look at your week. What does your week look like and how you can have these different kinds of workouts throughout the week? Not every day is going to be a HIIT day.”

This sits in line with a recent New York Times story, which covered a study comparing HIIT to more regular medium intensity workouts.

Published in Medicine & Science in Sports & Exercise, it was found that normal half-hour mid-intensity workouts on a regular basis had better results on blood pressure, body fat and overall metabolism that interval training.

That’s not to say that HIIT is bad.

In fact, the study found that both types of exercise were beneficial. The overarching message though is to keep your HIIT workouts to a minimum (2-3 days per week) and supplement the rest of your week with beautiful walks, yoga, and other types of exercise.

Sounds like it’s time to get going on that coastal hike.



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