High intensity intermittent exercise helps shift fat and brings many other benefits

A few weeks back I wrote about a study regarding what is often termed ‘high intensity intermittent exercise’ (HIIE). As it names suggests, this form of activity involves blasts of explosive exercise (such as sprinting or cycling) interspersed with periods of much less intense effort. The study I wrote about revealed HIIE to improve running speed in relatively fit individuals, though I used the blog post to share other evidence which suggests that this form of exercise can bring considerable improvements in terms of fat loss and insulin functioning (improved insulin sensitivity). What is more, the benefits of this form of exercise seem to generally exceed those of ‘steady state’ exercise such as running at a continuous speed.

Since I wrote that blog post, another study on HIIE has been published [1]. The target participants here were young (average age 25), overweight (average body mass index 28/29) men. The men were divided randomly into two groups. One group were not instructed on exercise (sedentary) and served as the ‘control’ or comparison group. The other group undertook a HIIE regime over 12 weeks.

Each session was made up of the following exercise:

5 minutes warm up on a stationary bicycle
20 repetitions of 8 seconds sprinting followed by 12 seconds of easy peddling (overall intensity was about 90 of maximal output)
5 minutes warm down on the bicycle

The sessions were performed 3 times a week.

The HIIE induced a number of significant changes including:

  • weight loss (average loss 1.5 kg)
  • fat loss (average loss 2.0 kg)
  • a reduction in ‘visceral’ fat (fat found in and around the organs that is particularly strongly linked with chronic diseases such as heart disease and type 2 diabetes)
  • a reduction in waist circumference
  • an increase in fat-free mass (mainly muscle)
  • increased fitness
  • increased power output
  • reduced carbohydrate metabolism
  • increased fat metabolism (average increase of 13 per cent)

No significant changes were seem in terms of measurements such as blood glucose levels, blood fat levels, measure of insulin sensitivity and resting metabolic rate.

Overall, it appears that HIIE in this group of young men brought significant benefits in a range of parameters that one would expect would translate into better health and relative protection from chronic disease. I find the fact that there seemed to be a shift from carbohydrate to fat oxidation interesting, but there is a commonly-held belief that lower intensity activity is better for fat burning while more intense activity burns just carbohydrate. This could lead some to conclude that high intensity exercise might not be so good for ‘fat burning’. Actually, this study suggests that this is not true, and adds to other evidence we have which has found HIIE to be generally superior to steady state, less intense activity in terms of fat loss.


1. M. Heydari, et al. The Effect of High-Intensity Intermittent Exercise on Body Composition of Overweight Young Males. Journal of Obesity Volume 2012;1-8 doi:10.1155/2012/48046

11 Responses to High intensity intermittent exercise helps shift fat and brings many other benefits

  1. Robin Dowswell 20 July 2012 at 4:48 pm #

    I find it very interesting that the high intensity exercise increased fat burning. That goes against a lot of coaching theories from the 1990’s for endurance athletes. However it does not surprise me, as my experience has always been (especially with running) that I get fitter using the fast intense workouts and that long slow workouts seem to slow me down.
    I guess it all boils down to what ways there are to change the levels of key hormones in the blood, e.g. epinephrine, cortisol etc. Some people definitely seem to benefit from these high intensity protocols.
    I have known a number of people who do seem to improve their fat burning ability when they perform a lot of steady state training, however in my experience these have been people training for more than 12 hours per week.
    Thanks for unearthing this study John. I’ve downloaded the pdf now so can examine it in more detail!

  2. Alan Carson 20 July 2012 at 6:10 pm #

    Great news! No long boring cardio sessions!

  3. kem 21 July 2012 at 5:12 am #

    People confuse chronic cardio with long aerobic sessions in specific athletic training. Runners, cyclists, swimmers, skiers… whoever are perfecting technique, honing specific muscle movements and keeping an edge on fitness for racing, not health.

    I would think elite athletes have been doing high intensity training for a long time. Sort of started with Lydiard, lots of long slow distance and then dragging tyres uphill for short burts, or whatever. Whatever the sport, there’s a good way to do it.

    What isn’t often said is that the sprint part of HIIT is hard to manage, as it must be at a level that screams “quit now!” by the third sprint, if you want to get those benefits.

  4. Ally 22 July 2012 at 9:21 pm #

    This workout was highlighted in a Horizon programme a couple of months ago. This was a trial with young volunteers however. Is this high intensity workout, short as it may be, recommended for anyone?

  5. Jim Healthy 23 July 2012 at 12:33 am #

    Its easy to understand why the reserachers saw no benefit in glucose reduction or insulin sensitivity from this experiment. (Eights seconds of exertion?) It would have been more interesting to monitor the results when the metabolism went from aerobic to aneobolic (when glycogen stores are tapped and untimately exhausted). This is what Kem is referring to when your body screams “Quit now!” (Eight seconds of “exertion” isn’t going to cut it.) I find that, not only does intense interval training produce better results (calorie burn, glucose reduction, cardiovascular training), but its a more effiecient use of my time. Beginners should start with 15 seconds of exertion, followed by 30 seconds of recovery — increasing to 30/60 in the same session. A typical 30-minute workout for newbies (if they are cleared by their physcian) would be: 5-minute warm-up followed by 15/30 intervals, followed by 20/40 intervals, and then 30/60s. Allow 5 minutes for cool-down and 5 minutes for stretching. An interval timer is helpful, but a slow silent count will suffice. Successful training of your heart (cardiovascular fitness) can be noted by how quickly you recover your composure and your heart rate slows. Progress is made by increasing the duration of your intervals. Listening to up-tempo music while exercising definitely helps. Personally, I’d much rather do 30 minutes of intense interval training than 60 minutes or more of jogging or moderate cycling. I’m 64. Jim H

  6. Chris 23 July 2012 at 6:59 pm #

    Dr Briffa, Where do position this in relation to your own training programme as outlined in your books? Would you recommend this over the aerobic element?

    I did this workout and now think that 20 reps is a daft number as it equates to 6 mins 40 secs. 18 or 21 is a lot easier to remember during the workout as it rounds to a minute. I had to do some serious thinking when I was on my bike!

  7. Ralph, Cleethorpes, UK 25 July 2012 at 8:21 pm #

    Anaerobic exercise necessitates glucose; fat can’t be burned in the absence of oxygen.

    Could it be then, that this type of training benefits fat loss by its effect on glucose metabolism in a similar manner to a controlled carbohydrate diet?

    Some aerobic exercise is still beneficial for improving/maintaining cardiovascular function.

  8. Jim Healthy 27 July 2012 at 1:32 am #

    Could it be that, once glucose and insulin levels have been diminished, fat stores are more readily converted to essential fatty acids — provided that the post-workout meals isn’t high in carbs? Jim H

  9. Bill 13 August 2012 at 7:15 pm #

    Great article. I’m going through a few of these issues as well..

  10. Carolyn 4 February 2013 at 2:09 am #

    Dr. Briffa, it’s “pedaling,” not “peddling.” “Peddling” is what one does when selling wares door-to-door–not sure how much fat that burns!


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