type IIb muscle fiber quantity 2008-11-11T04:15:56Z caripark type IIb myofiber abundance VT:1000612 ATOL:0001669 type IIb muscle fiber number white myofiber abundance The proportion or number of type IIb, fast glycolytic fibers in skeletal muscle; these white fibers are greater in diameter than red fibers, have less myoglobin, sarcoplasm, and mitochondria, and contract more quickly. Trait.ontology skeletal muscle fiber quantity