title: Significant intramyocellular lipid use during prolonged cycling in endurance-trained males as assessed by three different methodologies.
abstract: Intramyocellular triacylglycerol (IMTG) has been suggested to represent an important substrate source during exercise. In the present study, IMTG utilization during exercise is assessed through the use of various methodologies. In addition, we identified differences in the use of intramyocellular lipids deposited in the immediate subsarcolemmal (SS) area and those stored in the more central region of the fiber. Contemporary stable isotope technology was applied in combination with muscle tissue sampling before and immediately after 3 h of moderate-intensity cycling exercise (62 +/- 2% Vo(2 max)) in eight well-trained male cyclists. Continuous infusions with [U-13C]palmitate and [6,6-(2)H2]glucose were applied to quantify plasma free fatty acid (FFA) and glucose oxidation rates and to estimate whole body IMTG and glycogen use. Both immunohistochemical analyses of oil red O (ORO)-stained muscle cross sections and biochemical triacylglycerol (TG) extraction were performed to assess muscle lipid content. During exercise, plasma FFA, muscle (and/or lipoprotein)-derived TG, plasma glucose, and muscle glycogen oxidation contributed 24 +/- 2, 22 +/- 3, 11 +/- 1, and 43 +/- 3% to total energy expenditure, respectively. In accordance, a significant net decline in muscle lipid content was observed following exercise as assessed by ORO staining (67 +/- 8%) and biochemical TG extraction (49 +/- 8%), and a positive correlation was observed between methods (r = 0.56; P < 0.05). Lipid depots located in the SS area were utilized to a greater extent than the more centrally located depots. This is the first study to show significant use of IMTG as a substrate source during exercise in healthy males via the concurrent implementation of three major methodologies. In addition, this study shows differences in resting subcellular intramyocellular lipid deposit distribution and in the subsequent net use of these deposits during exercise.
authors.affiliation: Department of Movement Science, Maastricht University, Maastricht, The Netherlands. trent.stellingwerff@rdls.nestle.com
authors.forename: Trent
authors.initials: T
authors.lastname: Stellingwerff
authors.forename: Hanneke
authors.initials: H
authors.lastname: Boon
authors.forename: Richard A M
authors.initials: RA
authors.lastname: Jonkers
authors.forename: Joan M
authors.initials: JM
authors.lastname: Senden
authors.forename: Lawrence L
authors.initials: LL
authors.lastname: Spriet
authors.forename: René
authors.initials: R
authors.lastname: Koopman
authors.forename: Luc J C
authors.initials: LJ
authors.lastname: van Loon
mesh_terms: D000328:Adult; D001391:Azo Compounds; D001642:Bicycling; D001671:Biochemistry / Q000379:methods; D001786:Blood Glucose / Q000378:metabolism; D002247:Carbon Isotopes / Q000493:pharmacokinetics; D004396:Coloring Agents; D003903:Deuterium / Q000493:pharmacokinetics; D004734:Energy Metabolism; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006003:Glycogen / Q000378:metabolism; D006728:Hormones / Q000097:blood; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D050356:Lipid Metabolism; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D010806:Physical Education and Training; D010807:Physical Endurance; D012508:Sarcolemma / Q000378:metabolism; D013194:Staining and Labeling; D013997:Time Factors; D014018:Tissue Distribution; D014280:Triglycerides / Q000378:metabolism
chemical_list: D001391:Azo Compounds; D001786:Blood Glucose; D002247:Carbon Isotopes; D004396:Coloring Agents; D005230:Fatty Acids, Nonesterified; D006728:Hormones; D014280:Triglycerides; D006003:Glycogen; D003903:Deuterium; C011049:oil red O