Which individuals become fatter when they practice exercise?

Abstract

Summary Introduction It is well established that high volumes (15–20 h/week) of physical activity at intensities > 60% VO 2max , as well as low volumes (2–3 hrs/wk) of low intensity exercise targeted in the zone of the LIPOXmax (around 40% VO 2max ) allow a significant and prolonged loss of fat mass. By contrast it is not uncommon to observe patients whose fat mass increases when they practice low volumes of activity at intensity around or above 60% VO 2max . This paradoxical situation has surprisingly retained little attention. This study aimed at characterizing these patients. Methods Over 2 years we observed and investigated 26 patients (5 men and 13 women) aged 21 to 69 who gained weight when they began to engage in physical activity. They weighed 62 to 144 kg. These patients achieved an exercise calorimetry and segmental impedance and we compared to 15 matched subjects (2 men and 13 women) who gradually lose weight with a protocol of physical activity at low to moderate intensity. Results There are no differences in body composition. Exercise calorimetry evidences that the ability of these subjects to oxidize lipid was both significantly lower (8.10 ± 0.49 vs 10.8 ± 1.04 mg/min/kg of muscle, P P = 0.05). The level where there is no longer lipid oxidation and an exclusive use of carbohydrates also occurs in these subjects at a lower intensity (61.7 ± 3.1% vs 75.18 ± 5.90% VO 2max , P Conclusion Therefore, paradoxical weight gain due to low volume of exercise at > 60% VO 2max is not uncommon, although it seems a priori illogical and is thus largely ignored. It seems to be primarily determined by a targeting above the area of lipid oxidation, resulting into orexigenic falls in blood glucose, mostly in subjects that are low fat oxidizers. The glucose lowering effect of exercise performed in water may also favor this mechanism.