title: Human skeletal muscle fiber type adaptability to various workloads.
abstract: Muscle biopsy specimens were removed from the vastus lateralis muscles of three groups of human subjects: controls, weight lifters, and distance runners. The runners proved to be a unique group with respect to the variables measured (low body weight and percentage body fat, and high VO2 max). Additionally, a histochemical analysis of the biopsy specimens revealed that the runners had a significantly higher percentage of fiber types I and IIC than either the controls or the weight lifters. Using a cryostatic retrieval method, each of the fibers identified histochemically was then analyzed morphometrically using electron microscopy. The results of volume-percent mitochondria demonstrated a strong relationship between the ATPase activity and oxidative potential of the fiber types for all three groups such that the oxidative activity would be ranked I greater than IIA greater than IIB. Irrespective of fiber type, there were significant differences between the groups with regard to muscle-fiber mitochondrial (runners greater than lifters greater than controls) and lipid content (runners greater than controls greater than lifters). The lifters had a significantly greater content of mitochondria than the controls, which may suggest that inactivity rather than the lifting exercise contributes to a low volume-percent mitochondria and a high percentage of type IIB fibers.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D006651:Histocytochemistry; D006801:Humans; D008931:Mitochondria, Muscle / Q000201:enzymology / Q000378:metabolism; D009132:Muscles / Q000378:metabolism* / Q000648:ultrastructure; D010101:Oxygen Consumption; D005082:Physical Exertion; D012420:Running; D014891:Weight Lifting
chemical_list: D000251:Adenosine Triphosphatases