The vasculature plays a key role in metabolic changes in skeletal muscle during endurance exercise. Increased metabolic demand during endurance exercise induces angiogenesis, evidenced by an increase in capillary density (small arrows) followed temporally by a shift from glycolytic type IIb/IId/x fibers (white, or fast twitch) to more oxidative (red, or slow twitch) fibers (large arrow).

The role of different angiogenic signaling proteins in this process and in the cross-talk between blood vessels and myocytes is poorly understood.  more