Skeletal muscle capillarization and fiber types in urban and homing pigeons (Columba livia).

1. Fiber types, capillary supply and other morphometrical parameters were analysed in pectoral, gastrocnemius and pronator muscles of homing and urban pigeons. 2. The two kinds of birds were analysed before and after a restrainment period of at least 5 months. 3. Only slight differences in fiber type frequencies were noted between urban and homing pigeons in control conditions. 4. The effect of restrainment on the different parameters studied was unclear in gastrocnemius and pronator muscles and negligible in M. pectoralis. 5. Mean diffusion distances for oxygen from capillaries were smaller in oxidative fibers; also, vascularization indexes were higher for these fiber types. 6. The contribution of each fiber type to total sectional ara of muscle remains stable in spite of fiber type frequencies heterogeneity.