Abstract.To evaluate the relationships between changes in muscle morphology and metabolic adaptation to physical training in obesity, twenty obese women were subjected to a physical training pro‐gramme with three sessions a week for 3 months. Physical training resulted in lowering of plasma insulin and improved glucose tolerance. Neither body weight nor body fat changed. With physical training the percentage distribution of fast twitch oxidative (FTa) muscle fibres (m vastus lateralis) increased (from 30.3±5.1% to 35.2±4.8%,P<0.05) and that of fast twitch glycolytic fibres decreased (from 18.3±6.6 to 5.8±4.8%,P<0.05). The number of capillaries increased, mainly around slow twitch (ST) fibres (from 4.5±0.6 to 5.8±0.8,P<0.01) and fast twitch oxidative (FTa) fibres (from 3.9±0.7 to 4.7±0.8,P<0.01). The activities of oxidative enzymes (cytochrome‐c‐oxidase and citrate synthase) increased (P<0.05) while those of glycolytic enzymes (phosphofructokinase and hexokinase) decreased after physical training (P<0.01).Significant negative correlations between plasma insulin and number of capillaries in contact with ST fibres (r=0.80,P<0.001) and FTafibres (r= 0.62,P<0.001) were found before training. The capillary density around those fibres could predict 80% of the explained variance of plasma insulin levels (P<0.001). The changes of glucose concentration after training could be predicted by observed changes in enzyme activities. The strong associations between muscle morphology and capillarization and enzyme activities and glucose and insulin concentrations and their changes after training suggest an important regulatory role of muscle which warrants fu