Influence of lipolysis and fatty acid availability on fuel selection during exercise
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The aim of the present study was to investigate the influence of substrate availability on fuel selection during exercise. Eight endurance-trained male cyclists performed 90-min exercise at 70 % of their maximal oxygen uptake in a cross-over design, either in rested condition (CON) or the day after 2-h exercise practised at 70 % of maximal oxygen uptake (EX). Subjects were given a sucrose load (0.75 g kg−1 body weight) 45 min after the beginning of the 90-min exercise test. Lipolysis was measured in subcutaneous abdominal adipose tissue (SCAT) by microdialysis and substrate oxidation by indirect calorimetry. Lipid oxidation increased during exercise and tended to decrease during sucrose ingestion in both conditions. Lipid oxidation was higher during the whole experimental period in the EX group (p = 0.004). Interestingly, fuel selection, assessed by the change in respiratory exchange ratio (RER), was increased in the EX session (p = 0.002). This was paralleled by a higher rate of SCAT lipolysis reflected by dialysate glycerol, plasma glycerol, and fatty acids (FA) levels (p < 0.001). Of note, we observed a significant relationship between whole-body fat oxidation and dialysate glycerol in both sessions (r 2 = 0.33, p = 0.02). In conclusion, this study highlights the limiting role of lipolysis and plasma FA availability to whole-body fat oxidation during exercise in endurance-trained subjects. This study shows that adipose tissue lipolysis is a determinant of fuel selection during exercise in healthy subjects.
KeywordsLipolysis Fat oxidation Fuel selection Exercise
Atrial natriuretic peptide
Adipose tissue blood flow
Area under the curve
Non-esterified fatty acid
Respiratory exchange ratio
Subcutaneous abdominal adipose tissue
Maximal oxygen uptake
The authors are very grateful to Marie-Adeline Marques for outstanding technical assistance, to the staff of the Clinical Investigation Center, and to the study participants. We thank Drs. François Crampes, Michel Berlan, and Pr. Max Lafontan for pivotal advice and fruitful discussions.
This work was supported by a grant of the Toulouse hospital “PHRC #0508202”.
Conflict of interest
The authors have no conflict of interest to disclose.
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