How Much HIIT Is Beneficial?

Picture by Irving Henson from The PIT

A young lady I spoke to in the clinic today told me she has been attending HIIT (or high intensity interval training) sessions recently and gotten injured. (HIIT involves alternating very intense bouts of exercise with low intensity recovery exercise. It can be done in the gym with weights or on the bike or running set times or distances).

Being on the slightly plump side, she was tempted by the many benefits promised by the trainer conducting the HIIT sessions and the fact that she could lose weight and become stronger quickly whilst spending little time training.

Sounds too good to be true?

Considerable evidence definitely exists to support a role for low volume HIIT as a potent and super time efficient training method for inducing both central (cardiovascular) and peripheral (skeletal muscle) adaptations that are linked to improved health outcomes (see references below).

HIIT is designed to briefly strain your body to its limits. And these short bursts of very intense exercise lead to beneficial physiological changes similar to those much longer duration workouts. How much or how little do you need is still debated.

Leading interval training researcher Professor Martin Gibala found that 30 seconds worth of sprint intervals (four to six repeats of all out efforts three times a week) in young active but trained males produced just as good results as endurance training (subjects rode continuously for 40-60 mins five times a week). This is also known as the Wingate Test. The subjects generally hated the process though.

I clearly remember doing this while I was a young physiotherapy student in our Exercise Physiology lessons. It's extremely demanding and may not be safe, tolerable or appealing for some individuals. Definitely not for the faint-hearted.

With a less taxing program in which subjects did 60 seconds interval (or HIIT) training at 90 % effort (10 reps), the subjects found it more bearable although they had to do more repetitions (10x) to get the same benefits as the 30 seconds all out effort (Gibala et al, 2012).

Here's another workout that may be more palatable. Dr Gibala studied a group of obese/ overweight group of men and women on a program of 20 seconds of all out intervals followed by a recovery of two minutes.

They started with a 2 minute warm up on a stationary bike, followed by 3 x 20 seconds of all out sprints with two minutes recovery followed by a three minute cool down. A grand total of three minutes of intense work per week within a total training time of 30 minutes. Results were very encouraging as he subjects become fitter and improved their health (their VO2 max increased by 12%).

And if you find even 20 seconds of all out effort too difficult, there's the 30-20-10 workout which "only" requires 10 seconds of sprinting.

My take? Clearly, despite its many benefits, HIIT is not suitable for everyone, especially if you're just starting on an exercise program. As I've written before, we live in an instantaneous society now where we want results at the snap of a finger. Train don't strain is still important, or you risk a visit to your physiotherapist or doctor soon.


References

Burgomaster KA, Howarth KR et al (2008). Similar Metabolic Adaptations During Exercise After Low Volume Sprint Interval And Traditional Endurance Training in Humans. J Physiol. 586(1): 151-160.

Gibala MJ, Little JP et al (2012). Physiological adaptations To Low-volume, High-intensity Interval Training In Health And Disease. J Physiol. 590(5): 1077-1084. DOI: 10.1113/physiol.2011.224725

Gillen JB, Percival ME et al (2014). Three Minutes of All-out Intermittent Exercise Per Week Increases Skeletal Muscle Oxidative Capacity And Improves Cardiometabolic Health. PlosONe. DOI: 10.1371/journal.pone.0111489.