Work capacity and cardiopulmonary performance were studied in a group of 11 young obese subjects (BMI 39.9 kg/m²) and a group of 10 young normal subjects (BMI 22 kg/m²). First of all they underwent an incremental cycle ergometer test up to exhaustion. Subsequently, every subject of the two groups performed a constant work rate test at different work loads to estimate cardiac output (q̇) below anaerobic threshold (AT) by a 20-second CO₂ rebreathing method. Obese subjects had a significantly lower AT (79 vs. 109 W). The ratio between oxygen uptake and heart rate (v̇O₂/HR) (O₂ pulse) was higher in the obese group; nevertheless, this variable became significantly lower if we took into consideration the ratio between O₂ pulse and kilogram fat-free body mass or kilogram body weight. Both these observations suggest that their reduced work tolerance is linked with a reduced oxygen supply to the muscles in activity. q̇ increased in similar ways in obese and normal subjects at the preset work rates. The ratio q̇/body surface (cardiac index; CI) that we considered in order to try to minimize the differences in body sizes between the two groups, increased less in response to increasing work rates in our obese subjects than in normal subjects. As a whole, these data appear to be in line with a relatively less efficient cardiac performance during progressive work rates in obese subjects.

This study aimed to compare fat oxidation, hormonal and plasma metabolite kinetics during exercise in lean (L) and obese (O) men. Sixteen L and 16 O men [Body Mass Index (BMI): 22.9±0.3 and 39.0±1.4 kg.m−2] performed a submaximal incremental test (Incr) on a cycle-ergometer. Fat oxidation rates (FORs) were determined using indirect calorimetry. A sinusoidal model, including 3 independent variables (dilatation, symmetry, translation), was used to describe fat oxidation kinetics and determine the intensity (Fatmax) eliciting maximal fat oxidation. Blood samples were drawn for the hormonal and plasma metabolite determination at each step of Incr. FORs (mg.FFM−1.min−1) were significantly higher from 20 to 30% of peak oxygen uptake () in O than in L and from 65 to 85% in L than in O (p≤0.05). FORs were similar in O and in L from 35 to 60% . Fatmax was 17% significantly lower in O than in L (p<0.01). Fat oxidation kinetics were characterized by similar translation, significantly lower dilatation and left-shift symmetry in O compared with L (p<0.05). During whole exercise, a blunted lipolysis was found in O [lower glycerol/fat mass (FM) in O than in L (p≤0.001)], likely associated with higher insulin concentrations in O than in L (p<0.01). Non-esterified fatty acids (NEFA) were significantly higher in O compared with L (p<0.05). Despite the blunted lipolysis, O presented higher NEFA availability, likely due to larger amounts of FM. Therefore, a lower Fatmax, a left-shifted and less dilated curve and a lower reliance on fat oxidation at high exercise intensities suggest that the difference in the fat oxidation kinetics is likely linked to impaired muscular capacity to oxidize NEFA in O. These results may have important implications for the appropriate exercise intensity prescription in training programs designed to optimize fat oxidation in O.

Objective: To compare the effects of two different 2-week-long training modalities [continuous at the intensity eliciting the maximal fat oxidation (Fat max ) versus high-intensity interval training (HIIT)] in men with class II and III obesity. ) were assigned to Fat max group (G Fatmax ) or to HIIT group (G HIIT ). Both groups performed eight cycling sessions matched for mechanical work. Aerobic fitness and fat oxidation rates (FORs) during exercise were assessed prior and following the training. Blood samples were drawn to determine hormones and plasma metabolites levels. Insulin resistance was assessed by the homeostasis model assessment of insulin resistance (HOMA2-IR). Results: Aerobic fitness and FORs during exercise were significantly increased in both groups after training (P 0.001). HOMA2-IR was significantly reduced only for G Fatmax (P 0.001). Resting non-esterified fatty acids (NEFA) and insulin decreased significantly only in G Fatmax (P 0.002). Conclusions: Two weeks of HIIT and Fat max training are effective for the improvement of aerobic fitness and FORs during exercise in these classes of obesity. The decreased levels of resting NEFA only in G Fatmax may be involved in the decreased insulin resistance only in this group.