Response of mitochondrial respiration in adipose tissue and muscle to 8 weeks of endurance exercise in obese subjects.

CONTEXT: Exercise training improves glycemic control and increases mitochondrial content and respiration capacity in skeletal muscle. Rodent studies suggest that training increases mitochondrial respiration in adipose tissue. OBJECTIVE: To assess the effects of endurance training on respiratory capacities of human skeletal muscle and abdominal subcutaneous adipose tissue and to study the correlation with improvement in insulin sensitivity. DESIGN: Using high-resolution respirometry, we analyzed biopsies from 25 sedentary (VO2 peak 25.1 ± 4.0 VO2 mL/[kg*min]) subjects (16 female, 9 male; 29.8 ± 8.4 years) with obesity (body mass index [BMI] 31.5 ± 4.3 kg/m2), who did not have diabetes. They performed a supervised endurance training over 8 weeks (3 × 1 hour/week at 80% VO2 peak). RESULTS: Based on change in insulin sensitivity after intervention (using the Matsuda insulin sensitivity index [ISIMats]), subjects were grouped in subgroups as responders (>15% increase in ISIMats) and low-responders. The response in ISIMats was correlated to a reduction of subcutaneous and visceral adipose tissue volume. Both groups exhibited similar increases in fitness, respiratory capacity, and abundance of mitochondrial enzymes in skeletal muscle fibers. Respiratory capacities in subcutaneous adipose tissue were not altered by the intervention. Compared with muscle fibers, adipose tissue respiration showed a preference for β-oxidation and complex II substrates. Respiratory capacities were higher in adipose tissue from female participants. CONCLUSION: Our data show that the improvement of peripheral insulin sensitivity after endurance training is not directly related to an increase in mitochondrial respiratory capacities in skeletal muscle and occurs without an increase in the respiratory capacity of subcutaneous adipose tissue