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This Article Full Text Full Text (PDF) All Versions of this Article: 292/6/E1715    most recent 00678.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via ISI Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by Stellingwerff, T. Articles by van Loon, L. J. C. Search for Related Content PubMed PubMed Citation Articles by Stellingwerff, T. Articles by van Loon, L. J. C.

Significant intramyocellular lipid use during prolonged cycling in endurance-trained males as assessed by three different methodologies

Departments of ¹Movement Sciences and ²Human Biology, Nutrition Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands; and ³Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Canada

Submitted 12 December 2006 ; accepted in final form 7 February 2007

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% O_{2 max}) in eight well-trained male cyclists. Continuous infusions with [U-¹³C]palmitate and [6,6-²H₂]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.

fat metabolism; intramyocellular triacylglycerol; skeletal muscle; cycling; substrate utilization