In the ongoing debate on the optimal training intensity, it seemed that the advocates of shorter high intensity training and/or high intensity interval training were close to gaining the overhand. A new study in the J Endocrinol Invest. (Lazza. 2010), on the other hand, confirmed conventional wisdom that percentual fat-loss is higher with low intensity exercise, i.e. 40% VO2Max (LI), than with training at high intensities, i.e. 70% of the VO2max (HI) threshold.
The scientists had a group of twenty obese adolescents, aged 15-17 years (BMI: 37.5 kg/m2 ; 38.2 % fat mass) participate in a custom made exercise regime:
Before starting (week 0, W0) and at the end of the weight-management period (week 3, W3), body composition was assessed by a multifrequency tetrapolar impedancemeter (BIA); basal metabolic rate (BMR), energy expenditure and substrate oxidation rate during exercise and post exercise recovery by indirect calorimetry. At W3, body mass and fat mass decreased significantly (p<0.005) in all groups, and the decreases were significantly greater in the LI than in the HI group (-8.1+/-1.6 vs -5.9+/-1.6 kg and -4.2+/-1.9 vs -2.3+/-1.7 kg, p< 0.05, respectively).On the other hand, improvements in VO2Max, i.e. in exercise performance, were only observed in the high intensity group. At least, if you are already obese and have a relatively low exercise capacity, you obviously have to choose, whether you want to lose fat by exercising at a low intensity or whether you want to increase your performance by exercising at a high intensity.
My personal opinion is that the study results could have been completely different if the subjects had been athletes or recreational athletes. So, while the advice "low intensity training for fat loss" is certainly still valid for the obese, people who struggle with those last pounds and problem areas might well be better off by throwing in three high intensity interval training sessions per week.