title: NADH content in type I and type II human muscle fibres after dynamic exercise.
abstract: The effect of dynamic exercise on the NADH content of human type I (slow-twitch) and II (fast-twitch) muscle fibres was investigated. Muscle biopsy samples were obtained from the quadriceps femoris of seven healthy subjects at rest and after bicycle exercise at 40, 75 and 100% of the maximal oxygen uptake [VO2(max.)]. At rest and after exercise at 100% VO2(max.), muscle NADH content was significantly higher (P less than 0.05) in type I than in type II fibres. After exercise at 40% VO2(max.), muscle NADH decreased in type I fibres (P less than 0.01), but was not significantly changed in type II fibres. After exercise at 75 and 100% VO2(max.), muscle NADH increased above the value at rest in both type I and II fibres (P less than 0.05). Muscle lactate was unchanged at 40% VO2(max.), but increased 20- and 60-fold after exercise at 75 and 100% VO2(max.) respectively. The finding that NADH decreased only in type I fibres at 40% VO2(max.) supports the idea that type I is the fibre type predominantly recruited during low-intensity exercise. The increase of NADH in both fibre types after exercise at 75% and 100% VO2(max.) suggests that the availability of oxygen relative to the demand is decreased in both fibre types at high exercise intensities.
authors.affiliation: Department of Clinical Physiology, Karolinska Institute, Huddinge University Hospital, Sweden.
authors.forename: J M
authors.initials: JM
authors.lastname: Ren
authors.forename: J
authors.initials: J
authors.lastname: Henriksson
authors.forename: A
authors.initials: A
authors.lastname: Katz
authors.forename: K
authors.initials: K
authors.lastname: Sahlin
mesh_terms: D006801:Humans; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D008297:Male; D009132:Muscles / Q000378:metabolism*; D009243:NAD / Q000378:metabolism*; D005082:Physical Exertion
chemical_list: D007773:Lactates; D009243:NAD; D019344:Lactic Acid