Balance des substrats à l'exercice déterminée par calorimétrie d'effort chez des patientes entreprenant un réentraînement après traitement d'un cancer mammaire

Physical activity (PA) is a very important component of breast cancer management in complement of the purely carcinologic approach, since it decreases mortality from all causes in these patients. Endurance PA targeted at low to moderate intensity has proved its efficacy and usefulness in this context. Since the efficacy of low intensity PA is explained by its lipid-oxidizing effect, we thus aimed at determining the balance of lipids and carbohydrate oxidation during exercise in these patients. Fifteen patients (age 56.8 + 1.8; BMI 32.7 + 1.3 kg/m2) realize an exercise calorimetry test and are compared to 182 women matched by age and anthropometry. The patients have a lower aerobic capacity (−12%; P = 0.01), their level of maximal lipid oxidation (LIPOXmax) occurs at a lower power intensity (P = 0.01) as well as their crossover point (P = 0.01) and the level where carbohydrates become the exclusive substrate (P = 0.009). The carbohydrate cost of the watt, which quantifies the linear relation between carbohydrates oxidation and power, is also higher in patients (0.32 ± 0.03 vs. 0.26 ± 0.02 mg/min/kg/watt; P = 0.02). These data show that patients, for reasons probably related to their clinical background (sedentary lifestyle, obesity) as well as therapeutic procedure (low-grade inflammation, muscular weakness, deconditioning), exhibit a calorimetric profile at exercise characterized by a higher use of carbohydrates and a lower use of lipids, even more than matched women who have the same adiposity and the same age and are also to some extent 'glucodependent'. This provides a rationale for targeting more closely on lipid oxidation (LIPOXmax) low endurance training, which has already been found on the average to improve life expectancy and quality of life in these patients.