Interest of quantification of muscle mass for interpreting exercise calorimetry

摘要

Aims. -We investigated whether expressing fat oxidation by kilogram of muscle mass improves the interpretation of results of exercise calorimetry. Methods. -In 40patients with diabetes or obesity (26women and 14men, age 46.2+-2.5, BMI: 32.7+- 1.04), we studied, before and after exercise training targeted at the level of maximal lipid oxidation (LIPOXmax), the balance of substrates. Total body bioelectrical impedance (according to Janssen) was used for calculating muscle mass. Results. - Pre-training maximal fat oxidation rate (MFOR) is more directly related to muscle mass (r = 0.583, P<0.001) than to lean mass (r = 0.419, P<0.01), showing that muscle is the main anthropometric determinant of MFOR. Post-training increase in total MFOR was not correlated with changes in muscle mass, but MFOR expressed in mg/min/kg muscle mass increased very significantly from 4.09 +-0.61 to 7.01 +-0.45 mg/min/kg, i.e. +71 % (P< 0.001) in the whole sample. The increase in MFOR expressed by lean body mass or weight is less clearly evidenced and is significant only in the group of women (P<0.03). Physical training also causes weight loss of -2.14+-0.89 kg (P<0.02), waist circumference of -1.61 +-0.82cm (P<0.05) and shifts to the right the LIPOXmax by 8.85 +-4.08watts (P< 0.03). There was a correlation between pre-training MFOR and the changes in both weight (r =-0.320, P<0.05) and waist circumference (r = - 0.320, P<0.05) and between MFOR expressed by kg of muscle mass and the change in waist to hip ratio (r = -0.390, P<0.05). Above a MFOR in 5 mg/min/kg muscle, exercise induced a loss of 3cm in waist circumference (P<0.05) and reduced waist to hip ratio by -0.15 (P< 0.05), while below this threshold it was ineffective. Conclusion. -These results indicate that: (1) muscle mass calculated by bioimpedance is more closely related to MFOR that the overall lean body mass; (2) that exercise training increases the maximal ability to oxidize lipids independently of quantitative variations of ...