High Intensity Interval Training, or HIIT for short, has been promoted as one of the most effective training methods ever to come down the pike, both for fat loss and for cardiovascular fitness. One of the most popular claims for HIIT is that it burns "9 times more fat" than conventional (steady state) cardio. This figure was extracted from a study performed by Angelo Tremblay at Laval University in 1994. But what if I told you that HIIT has never been proven to be 9 times more effective than regular cardio… What if I told you that the same study actually shows that HIIT is 5 times less effective than steady state cardio??? Read on and see the proof for yourself.
"There are lies, damned lies, and then there are statistics."
- Mark Twain
The results: 3 times greater fat loss in the HIIT group
"It appeared reasonable to correct changes in subcutaneous fat for the total cost of training. This was performed by expressing changes in subcutaneous skinfolds per megajoule of energy expended in each program."
The ET group lost 0.5 kilograms (60.6 kg before, 60.1 kg after).
Naturally, lack of weight loss while skinfolds decrease could simply mean that body composition improved (lean mass increased), but I think it's important to highlight the fact that the research study from which the "9 times more fat" claim was derived did not result in ANY significant weight loss after 15 weeks.
If I said 5 X greater weight loss with steady state, I would be telling the truth, wouldn't I? (100 grams of weight loss vs 500 grams?) Of course, that would be misleading because the weight loss was hardly significant in either group and because interval training IS highly effective. I'm simply being a little facetious in order to make a point: Be careful with statistics. I have seen statistical manipulation used many times in other contexts to deceive unsuspecting consumers.
Back to the HIIT story – there's even more to it.
In the ET group, there were some funky skinfold and circumference measurements. ALL of the skinfold measurements in the ET group either stayed the same or went down except the calf measurement, which went up.
The girths and skinfold measurements in the limbs went down in the HIIT group, but there wasn't much difference between HIIT and ET in the trunk skinfolds. These facts are all very easy to miss. I didn't even notice it myself until exercise physiologist Christian Finn pointed it out to me. Christian said,
"When you look at the changes in the three skinfold measurements taken from the trunk, there wasn't that much difference between the steady state group (-6.3mm) and the HIIT group (-8.7 mm). So, much of the difference in subcutaneous fat loss between the groups wasn't because the HIIT group lost more fat, but because the steady state group actually gained fat around the calf muscles. We shouldn't discount simple measurement error as an explanation for these rather odd results."
"So while this study is interesting, weaknesses in the methods used to track changes in body composition mean that we should treat the results and conclusions with some caution."
"For a given level of energy expenditure, a high intensity training program induces a greater loss of subcutaneous fat compared with a training program of moderate intensity."
My intentions for writing this article were four-fold:
1. To encourage you to question where claims come from, especially if they sound too good to be true.
2. To alert you to how advertisers might use research such as this to exaggerate with statistics.
3. To encourage the fitness community to swing the pendulum back to center a bit, by not over-selling the benefits of HIIT beyond what can be supported by the scientific research.
4. To encourage the fitness community, that even as they praise HIIT, not to condemn lower and moderate intensity forms of cardio.