8 Jun 2017

Is high-intensity exercise too much of a good thing?

From Healthy or Hoax, 8:00 am on 8 June 2017

Anyone who belongs to a gym has probably done it. Even those who don't have probably heard of it.

High Intensity Interval Training (HIIT) has had a lot of media coverage in recent years for being a quick fitness fix for anyone short of time; which is pretty much everyone, right?

Even RNZ has discussed its benefits.

HIIT is essentially short, intense bouts of exercise interspersed with periods of rest. It's the antithesis of long steady cardio training. Some of the more well-known studies involve participants sprinting on stationary bikes for one minute intervals at a maximum pace versus slow continuous pedaling. 

Carol Hirschfeld takes part in a group HIIT class.

Photo: RNZ

As the Healthy or Hoax podcast team, led by host Carol Hirschfeld, found out HIIT definitely has some benefits. The most obvious is that you can finish a workout in 20 minutes instead of an hour... or more.

Performance physiologist and AUT adjunct professor Paul Laursen said studies showed participants achieved as much, if not more, in the shorter time.

"You wind up being able to accumulate a greater amount of hard work than if you were just going to perform that same amount of work continuous. 

"So by breaking it up you get a longer period total of high intensity work."

But, Dr Laursen warned HIIT is not necessarily as good as it sounds.

"Sometimes it's just interpreted as 'all I need to do is go out and kill myself', and of course we've all got pretty busy lives, we're under a lot of stress, sometimes we're not always on the healthiest diet, so there's loads of different stressors."

In that case, adding further stress in the form of high intensity exercise is asking for trouble, he said.

"You can really speed your way to over training... ultimately you can make yourself sick, or feel run down, and you can injure yourself as well."

One to three HIIT workouts a week should be the maximum, Dr Laursen said.

Carol Hirschfeld takes part in a HIIT class/

Photo: RNZ

Les Mills head of research Bryce Hastings said the gym's HIIT classes were for people who already exercise consistently.

"You might be up to five days a week.. and when you've got that going and you're pretty comfortable there and people are wanting that next level of improvement - that's where we see HIIT as being really really useful."

The most important thing was to be moving consistently, he added.

Fitness instructor Chris Richardson is a HIIT convert.

He said he feels energised after an intense workout.

"Being a little bit time poor, being a little bit more mature in years, it was good to get into a shorter form of training."

The key thing here, like so much in life, is moderation.

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Healthy or Hoax is a RNZ podcast series looking into the latest exercise, nutrition, and well-being fads to see whether there's any evidence to back up their claims. Hosted by Carol Hirschfeld.