title: Intramyocellular lipid stores increase markedly in athletes after 1.5 days lipid supplementation and are utilized during exercise in proportion to their content.
abstract: Intramyocellular lipids (IMCL) and muscle glycogen provide local energy during exercise (EX). The objective of this study was to clarify the role of high versus low IMCL levels at equal initial muscle glycogen on fuel selection during EX. After 3 h of depleting exercise, 11 endurance-trained males consumed in a crossover design a high-carbohydrate (7 g kg(-1) day(-1)) low-fat (0.5 g kg(-1) day(-1)) diet (HC) for 2.5 days or the same diet with 3 g kg(-1) day(-1) more fat provided during the last 1.5 days of diet (four meals; HCF). Respiratory exchange, thigh muscle substrate breakdown by magnetic resonance spectroscopy, and plasma FFA oxidation ([1-(13)C]palmitate) were measured during EX (3 h, 50% W (max)). Pre-EX IMCL concentrations were 55% higher after HCF. IMCL utilization during EX in HCF was threefold greater compared with HC (P < 0.001) and was correlated with aerobic power and highly correlated (P < 0.001) with initial content. Glycogen values and decrements during EX were similar. Whole-body fat oxidation (Fat(ox)) was similar overall and plasma FFA oxidation smaller (P < 0.05) during the first EX hour after HCF. Myocellular fuels contributed 8% more to whole-body energy demands after HCF (P < 0.05) due to IMCL breakdown (27% Fat(ox)). After EX, when both IMCL and glycogen concentrations were again similar across trials, a simulated 20-km time-trial showed no difference in performance between diets. In conclusion, IMCL concentrations can be increased during a glycogen loading diet by consuming additional fat for the last 1.5 days. During subsequent exercise, IMCL decrease in proportion to their initial content, partly in exchange for peripheral fatty acids.
authors.affiliation: Department of Clinical Research, University and Inselspital, 3010, Bern, Switzerland.
authors.forename: Monica
authors.initials: M
authors.lastname: Zehnder
authors.forename: Emanuel R
authors.initials: ER
authors.lastname: Christ
authors.forename: Michael
authors.initials: M
authors.lastname: Ith
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Acheson
authors.forename: Etienne
authors.initials: E
authors.lastname: Pouteau
authors.forename: Roland
authors.initials: R
authors.lastname: Kreis
authors.forename: Roman
authors.initials: R
authors.lastname: Trepp
authors.forename: Peter
authors.initials: P
authors.lastname: Diem
authors.forename: Chris
authors.initials: C
authors.lastname: Boesch
authors.forename: Jacques
authors.initials: J
authors.lastname: Décombaz
mesh_terms: D000328:Adult; D015308:Anaerobic Threshold / Q000502:physiology; D001642:Bicycling / Q000502:physiology; D001823:Body Composition / Q000502:physiology; D018592:Cross-Over Studies; D004032:Diet; D004040:Dietary Carbohydrates / Q000378:metabolism; D004041:Dietary Fats / Q000378:metabolism / Q000494:pharmacology*; D004044:Dietary Proteins / Q000378:metabolism; D004311:Double-Blind Method; D004734:Energy Metabolism / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D050356:Lipid Metabolism / Q000502:physiology*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000097:blood; D010168:Palmitates / Q000097:blood; D010807:Physical Endurance / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology
chemical_list: D004040:Dietary Carbohydrates; D004041:Dietary Fats; D004044:Dietary Proteins; D010168:Palmitates; D006003:Glycogen; D010100:Oxygen