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
in 1994, a study was published in the scientific journal metabolism by angelo tremblay and his team from the physical activity sciences laboratory at laval university in quebec, canada. Based on the results of this study, you hear personal trainers across the globe claiming that “hiit burns 9 times more fat than steady state cardio.”
this claim has often been interpreted by the not so scientifically literate public as meaning something like this: If you burned 3 pounds of fat in 15 weeks on steady state cardio, you would now burn 27 pounds of fat in 15 weeks (3 lbs x 9 times better = 27 lbs).
Although it’s usually not stated as such, frankly, i think this is what some trainers want you to believe, because the programs that some trainers promote are based on convincing you of the vast superiority of hiit and the “uselessness” of low intensity exercise.
Indeed, higher intensity exercise is more effective and time efficient than lower intensity exercise. The question is, how much more effective? There’s no evidence that the “9 times more fat loss” claim is true outside the specific context in which it was mentioned in this study.
In order to get to the bottom of this, you have to read the full text of the research paper and you have to look very closely at the results.
13 men and 14 women age 18 to 32 started the study. They were broken into two groups, a high intensity intermittent training program (hiit) and a steady state training program which they referred to as endurance training (et).
The et group completed a 20 week steady state aerobic training program on a cycle ergometer 4 times a week for 30 minutes, later progressing to 5 times per week for 45 minutes. The initial intensity was 60% of maximal heart rate reserve, later increasing to 85%.
The hiit group performed 25-30 minutes of continuous exercise at 70% of maximal heart rate reserve and they also progressively added 35 long and short interval training sessions over a period of 15 weeks. Short work intervals started at 10 then 15 bouts of 15 seconds, increasing to 30 seconds. Long intervals started at 5 bouts of 60 seconds, increasing to 90 seconds. Intensity and duration were progressively increased over the 15 week period.
The results: 3 times greater fat loss in the hiit group
even though the energy cost of the exercise performed in the et group was twice as high as the hiit group, the sum of the skinfolds (which reflects subcutaneous body fat) in the hiit group was three times lower than the et group.
So where did the “9 times greater fat loss” claim come from?
Well, there was a difference in energy cost between groups, so in order to show a comparison of fat loss relative to energy cost, tremblay wrote,
“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.”
translation: The subjects did not lose 9 times more body fat, in absolute terms. But hey, 3 times more fat loss? You’ll gladly take that, right?
Well hold on, because there’s more.
Did you know that in this oft-quoted study, neither group lost much weight? In fact, if you look at the charts, you can see that the hiit group lost 0.1 kg (63.9 kg before, 63.8 kg after). Yes, the hiit group lost a whopping 100 grams of weight in 15 weeks!
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.
Based on these results, if i wanted to manipulate statistics to promote steady state cardio, i could go around telling people, “research study says steady state cardio (endurance training) results in 5 times more weight loss than high intensity interval training!” or the reverse, “clinical trial proves that high intensity interval training is 5 times less effective than steady state cardio!”
mind you, this is the same study that is most often quoted to support hiit!
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, because it doesn’t distinguish between weight loss and body composition 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.
For example, advertisements for a popular fat burner claim that use of their supplement resulted in twice as much fat loss, based on scientific research. The claim was true. Of course, in the ad, they forget to tell you that after six months, the control group lost no weight, while the supplement group lost only 1.0 kilo. Whoop de doo! One kilo of weight loss after going through a six month supply of this “miracle fat burner!”
but i digress…
back to the hiit story – there’s even more to it.
