High intensity interval training (HIIT) has gained popularity in recent decades.
It refers to any form of activity that alternates high intensity activity with periods of lower to moderate intensity activity (eg, 20-second sprint intervals with 60 seconds of walking, jogging or even complete rest.
By contrast, aerobic or steady state training (eg, jogging) is where a reasonably steady intensity is maintained for an extended period (say, 20 minutes or more).
For some, HIIT is revered as the single best way to burn calories in a time efficient manner.
With numerous variations under the broad umbrella of HIIT methods (e.g. Tabata, a short interval training protocol), HIIT can indeed be a time-efficient way to improve conditioning and overall fitness.
Perhaps because it also shares a couple of metabolic traits with resistance training (short bursts of intense effort followed by a period of rest, and an ‘afterburn’ effect), it’s often sold as a way to burn fat with minimal loss of lean mass.
But actually, HIIT does not always translate to an improvement in body composition or fat-loss efforts.
For a given amount of work, you will burn more calories with HIIT compared to aerobic or steady state training. There is also a greater ‘afterburn’ effect, meaning you will continue to burn more calories after you’ve finished the exercise.
In most instances, however, the amount of energy burned afterwards, known as excess post-exercise energy expenditure (EPEE) and related to post-exercise oxygen consumption (EPOC), is considerably overplayed.
When comparing a 20-minute high intensity interval session versus a 30-minute continuous running session at a lower intensity, the interval session resulted in 57 more calories burned. This figure included both the calories burned during the exercise session as well as those burned afterwards (EPEE) and concluded that the major contribution to weight loss from both steady-state jogging and HIIT was from the energy expended during the actual exercise. The afterburn effect was “of negligible physiological significance as far as weight loss is concerned.”
It’s well worth noting that the researchers in this study made sure that the total amount of work done was equal between the two sessions.
The main benefit of interval training (HIIT) for fat loss is not, then, the calories burned per se but rather the time efficiency. For those with busy lifestyles, HIIT may be a preferable method to expend more calories in less time but a true HIIT session (repeated all-out sprints for 30 seconds-plus) is not for everyone.
The problem with regular HIIT is that it is taxing on the body and may interfere with strength and muscle gain by causing too much fatigue. Higher intensity means higher recovery and thus may prevent effective, progressive resistance training over time.
Given the fact that steady state training involves far less recovery, a reduction in injury risk and a lower requirement for cardiovascular fitness compared to HIIT, it may be a more feasible approach for beginners or people who are overweight or obese. Similarly, for those looking to optimise muscle building, it may be prudent to steer clear of regular engagement in true HIIT sessions.
Both HIIT and steady state training are effective methods for increasing overall fitness and can be used as a fat-loss tool to complement your nutrition. In the context of fat loss, adherence is the primary predictor of success, so choose a training protocol that you know you can stick to rather than worry about what type of ‘afterburn’ it might give you.
Nutritionist and Bodyscan Consultant
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