Normal mitochondrial function and increased fat oxidation capacity in leg and arm muscles in obese humans

The aim of this study was to investigate mitochondrial function, fibre-type distribution and substrate oxidation during exercise in arm and leg muscles in male postobese (PO), obese (O) and age- and body mass index (BMI)-matched control (C) subjects. The hypothesis of the study was that fat oxidation during exercise might be differentially preserved in leg and arm muscles after weight loss.

Indirect calorimetry was used to calculate fat and carbohydrate oxidation during both progressive arm-cranking and leg-cycling exercises. Muscle biopsy samples were obtained from musculus deltoideus (m. deltoideus) and m. vastus lateralis muscles. Fibre-type composition, enzyme activity and O(2) flux capacity of saponin-permeabilized muscle fibres were measured, the latter by high-resolution respirometry.

During the graded exercise tests, peak fat oxidation during leg cycling and the relative workload at which it occurred (FatMax) were higher in PO and O than in C. During arm cranking, peak fat oxidation was higher in O than in C, and FatMax was higher in O than in PO and C. Similar fibre-type composition was found between groups. Plasma adiponectin was higher in PO than in C and O, and plasma leptin was higher in O than in PO and C.

In O subjects, maximal fat oxidation during exercise and the eliciting relative exercise intensity are increased. This is associated with higher intramuscular triglyceride levels and higher resting non esterified fatty acid (NEFA) concentrations, but not with differences in fibre-type composition, mitochondrial function or muscle enzyme levels compared with Cs. In PO subjects, the changes in fat oxidation are preserved during leg, but not during arm, exercise.