title: The effect of glycogen availability on power output and the metabolic response to repeated bouts of maximal, isokinetic exercise in man.
abstract: The relationship of glycogen availability to performance and blood metabolite accumulation during repeated bouts of maximal exercise was examined in 11 healthy males. Subjects performed four bouts of 30 s maximal, isokinetic cycling exercise at 100 rev.min-1, each bout being separated by 4 min of recovery. Four days later, all subjects cycled intermittently to exhaustion [mean (SEM) 106 (6) min] at 75% maximum oxygen uptake (VO2max). Subjects were then randomly assigned to an isoenergetic low-carbohydrate (CHO) diet [7.8 (0.6)% total energy intake, n = 6] or an isoenergetic high-CHO diet [81.5 (0.4)%, n = 5], for 3 days. On the following day, all subjects performed 30 min cycling at 75% VO2max and, after an interval of 2 h, repeated the four bouts of 30 s maximal exercise. No difference was seen when comparing total work production during each bout of exercise before and after a high-CHO diet. After a low-CHO diet, total work decreased from 449 (20) to 408 (31) J.kg-1 body mass in bout 1 (P < 0.05), from 372 (15) to 340 (18) J.kg-1 body mass in bout 2 (P < 0.05), and from 319 (12) to 306 (16) J.kg-1 body mass in bout 3 (P < 0.05), but was unchanged in bout 4. Blood lactate and plasma ammonia accumulation during maximal exercise was lower after a low-CHO diet (P < 0.001), but unchanged after a high-CHO diet. In conclusion, muscle glycogen depletion impaired performance during the initial three, but not a fourth bout of maximal, isokinetic cycling exercise. Irrespective of glycogen availability, prolonged submaximal exercise appeared to have no direct effect on subsequent maximal exercise performance.
authors.affiliation: Department of Physiology and Pharmacology, University of Nottingham Medical School, UK.
authors.forename: A
authors.initials: A
authors.lastname: Casey
authors.forename: A H
authors.initials: AH
authors.lastname: Short
authors.forename: S
authors.initials: S
authors.lastname: Curtis
authors.forename: P L
authors.initials: PL
authors.lastname: Greenhaff
mesh_terms: D000328:Adult; D000641:Ammonia / Q000097:blood; D001642:Bicycling; D004032:Diet; D004040:Dietary Carbohydrates / Q000494:pharmacology; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006003:Glycogen / Q000378:metabolism*; D006801:Humans; D007773:Lactates / Q000097:blood; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology
chemical_list: D004040:Dietary Carbohydrates; D007773:Lactates; D000641:Ammonia; D006003:Glycogen