title: Effect of low glycogen on glycogen synthase in human muscle during and after exercise.
abstract: Subjects cycled at a work load calculated to elicit 75% of maximal oxygen uptake on two occasions: the first to fatigue (34.5 +/- 5.3 min; mean +/- SE), and the second at the same workload and for the same duration as the first. Biopsies were obtained from the quadriceps femoris muscle before and immediately after exercise, and 5 min post-exercise. Before the first experiment, muscle glycogen was lowered by a combination of exercise and diet, and before the second, experiment muscle glycogen was elevated. In the low glycogen condition (LG), muscle glycogen decreased from 169 +/- 15 mmol glucosyl units kg-1 dry wt at to rest to 13 +/- 6 after exercise. In the high glycogen condition (HG) glycogen decreased from 706 +/- 52 at rest to 405 +/- 68 after exercise. Glycogen synthase fractional activity (GSF) was always higher during the LG treatment. During exercise in the HG condition, those subjects who cycled for less than 35 min (n = 3) had GSF values in muscle which were lower than at rest, whereas those subjects who cycled for greater than 35 min (n = 4) had values which were similar to or higher than at rest. Thus the change in GSF in muscle during HG was positively related to the exercise duration (r = 0.94; y = 254-17x + 0.3x2; P less than 0.001) and negatively related to the glycogen content at the end of exercise (r = -0.82; y = 516-2x + 0.001x2; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Kinesiology, University of Illinois, Urbana-Champaign 61801.
authors.forename: Z
authors.initials: Z
authors.lastname: Yan
authors.forename: M K
authors.initials: MK
authors.lastname: Spencer
authors.forename: A
authors.initials: A
authors.lastname: Katz
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000494:pharmacology; D015444:Exercise / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006003:Glycogen / Q000502:physiology*; D006006:Glycogen Synthase / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D007328:Insulin / Q000097:blood; D007773:Lactates / Q000097:blood; D008297:Male; D009132:Muscles / Q000201:enzymology / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D012119:Respiration / Q000502:physiology
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D007773:Lactates; D006003:Glycogen; D006006:Glycogen Synthase