Tuesday, October 13, 2009

intervals or low intensity to burn fat

This debate seems to keep going. One minute everyone is talking about EPOC and Afterburn and the advantages of interval training....then it is back to the advantages of long low intensity cardio to burn fat.....

Lyle McDonald had a good series on this recently....Anyway, here is another study...which seems to point towards the advantages of low intensity exercise. Then again...it is not as straightforward as that....

Fat oxidation rate during and after a low- or high-intensity exercise in severely obese Caucasian adolescents

Abstract The objective is to study the effects of low-intensity (LI) or high-intensity (HI) equicaloric exercises on energy expenditure (EE) and substrate oxidation rate during and after the exercises in severely obese Caucasian adolescents.

Twenty obese boys (BMI-SDS 3.04 ± 0.52, %Fat Mass 38.2 ± 2.1%) aged 14–16 years (pubertal stage >3) participated in this study. Maximal oxygen uptake (V′O2max) and maximal fat oxidation rate were determined with indirect calorimetry using a graded exercise test on a treadmill. EE and substrate oxidation rate during equicaloric low-intensity (LI, 42% V′O2max for 45 min) and high-intensity (HI, 67% V′O2max for 30 min) exercises on a treadmill and during post-exercise recovery period (60 min) were determined with indirect calorimetry. Maximal fat oxidation rate was observed at 42 ± 6% V′O2max (62 ± 5% HRmax) and fat oxidation rate was 0.45 ± 0.07 g/min.

The total amounts of EE, during the LI and HI exercises, and the post-exercise recovery periods were not significantly different (1,884 ± 250 vs. 1,973 ± 201 kJ, p = 0.453), but the total amount of fat oxidised was significantly higher (+9.9 g, +55.7%, p < 0.001) during the LI exercise than during the HI exercise. However, fat oxidation rates during the post-exercise recovery periods were not significantly different following LI and HI exercises.

Total fat oxidised was significantly higher during the LI than during the HI exercise in obese adolescents. However, the equicaloric exercise intensity did not influence EE, fat and carbohydrate oxidation rate during the recovery period.


Ogg the Caveman said...

Another study published in the Journal of Sports Sciences (LaForgia, 2006) suggests that the earlier research optimism regarding EPOC (after burn) in weight loss is generally unfounded. Also, the exercise intensity required to promote a prolonged (and thus appreciable) EPOC is not likely attainable by the general exercising population.

Of course, it goes without saying that high-intensity interval-based exercises provide other health benefits, like increased VO2 uptake, lactate threshold improvement, lactic acid buffering efficiency, etc. But, just how high must a person push these physical factors in order to simply enjoy general health, fitness, and body composition?

Ian said...

Well, the jury is still out whether High Intensity intervals are better or Low Intensity cardio is, but this study isn't showing anything of the kind. The way I'm reading the abstract, what was compared were a low intensity and a medium intensity steady-state workout. All it is showing is that performing a low intensity workout burns more fat than a high(er) intensity workout does, which was already pretty well known because fat is a preferred source of energy at low intensity with carbohydrate coming in as intensity increases. I doubt that either of these workouts was intense enough to produce EPOC of any substantial amount. In the end though...this study has nothing to do with intervals or high intensity.


btw, been reading your blog a while but never posted. Good stuff!