Decreased skeletal muscle mass and proportion of fast-twitch glycolytic fibers are well-documented correlates of aging; however, data on concomitant changes on capillary-to-fiber ratio (C:F) are inconsistent. We simultaneously examined fiber-type composition and arteriolar and venular portions of capillaries in the distal hind-limb muscles of 12-, 24-, and 35-month old F1 hybrid F344 Brown Norway rats. Aging significantly increased C:F of venular capillaries in muscles, which also presented significant age-related increase in slow-(type I) and fast-(type IIa) oxidative fibers (plantaris, tibialis anterior, medial gastrocnemius; p