Weight loss workouts – High intensity interval training

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Raising the Barre

Fat loss in a flash

No time to burn serious fat this festive season? High intensity interval training could slash your gym time and supercharge your fat loss, writes PT Jay Bonaretti


No time to burn serious fat this festive season? High intensity interval training could slash your gym time and supercharge your fat loss, writes PT Jay Bonaretti


What if there was a way to minimise your training time while actually maximising your fat burning results?

The good news is, there is a way to shorten your workouts and maximise your kilojoule burn.

And unlike most things that sound too good to be true, this actually isn’t, because we’re not talking about the latest fitness fad, but a method of training that has been proven over decades to be far more effective than normal steady-state cardio (where you maintain the same pace for an extended period of time).

The magic bullet is called high intensity interval training (HIIT), a method of training where you perform short bouts of high intensity exercise (or sprints) intermittently, accompanied by short periods of recovery.

Why is high intensity so effective?

If you’ve ever used an exercise machine, chances are you’ve seen a graph showing the  ‘fat burning zone’. The theory is that by maintaining a low to medium level of intensity at a steady pace, you will maximise your fat burn. Unfortunately, though, this concept is somewhat misunderstood.

At a lower level of intensity, you will in fact utilise a greater percentage of adipose tissue (or body fat) relative to carbohydrates. Meanwhile, at a higher level of intensity, more carbohydrate will be utilised relative to fat, as carbohydrates are an easier source of energy for your body to tap into.

But let’s keep in mind that this is only relative to one another. What this outdated theory does not consider is that at a higher intensity, a greater amount of energy is expended. Hence, at a higher level of effort, even though carbohydrate utilisation may be higher compared to fat usage, the actual amount of fat used will still be higher. Confused?

The below table demonstrates findings by Laforge and Kosich back in 1995: While the in-workout burn results are fairly impressive – 29.3g versus 26.6g of fat burned, for a start – the true benefit of high intensity exercise is in the kilojoule burn after your workout. If you’ve ever trained at a higher intensity and really pushed through a workout, you’ll know that exhausted feeling well.

LaForge and Kosich (1995)            Lower intensity     Higher intensity
Cardio Duration                              60 minutes            60 minutes
VO2max (A measure of intensity)   50%                      70%
Total calories                                   480                       660
Percentage FAT                              50%                      40%
Percentage CARBOHYDRATE       50%                      60%
Absolute FAT                                   26.6g                    29.3g
Absolute CARBOHYDRATE            60g                       99g

Tabata et al (1996)                            70% VO2max     170% VO2max
Cardio Duration                                 60 minutes          4 minutes
VO2max INCREASE                         10%                    14%
Anaerobic Capacity INCREASE        NONE                 28%

When you are this exhausted, your body is furiously burning energy in order to recover from the physical stress (exercise) that you just placed on your body. More technically speaking, following a bout of high intensity exercise, you’ll create a heighted degree of excess post-exercise oxygen consumption (EPOC), which revs up your metabolism for many hours afterwards.

A famous study that considered the effects of the post-workout burn was by Tremblay et al in 1994. Two groups of exercisers were compared. Group A performed 30 to 45 minutes of steady state cardio (this was known as the ‘endurance group’). Group B performed short interval training workouts lasting less than half the duration.


The wash-up?
“[Metabolic adaptations resulting from HIIT] may lead to a better lipid utilisation in the post-exercise state and thus contribute to a greater energy and lipid deficit.” In other words, significantly more fat was burned after the conclusion of the bout of exercise. Researchers estimated this to be nine times more when performing interval training than in steady state.

So what does this mean for you? Not only will you maximise your fat burning results by incorporating HIIT, you will also significantly increase your level of fitness compared to if you stuck with steady state cardio. A study conducted in 1996, where one group of participants exercised at a moderate level of intensity and another undertook a four minute HIIT session, clearly demonstrated this efficacy.

In the study, the anaerobic capacity in the high intensity group improved significantly more than that of the moderate intensity group. Meanwhile, the high intensity group exercised for only a 15th of the time!

Jay Bonaretti is the owner of Amino Z, a leading online personal training and supplement