title: Determinants of the variability in respiratory exchange ratio at rest and during exercise in trained athletes.
abstract: We examined the variability and determinants of the respiratory exchange ratio (RER) at rest and during exercise in 61 trained cyclists. Fasting (10-12 h) RER was measured at rest and during exercise at 25, 50, and 70% of peak power output (W(peak)), during which blood samples were drawn for [lactate] and [free fatty acid] ([FFA]). Before these measurements, training volume, dietary intake and muscle fiber composition, [substrate], and enzyme activities were determined. There was large interindividual variability in resting RER (0.718-0.927) that persisted during exercise of increasing intensity. The major determinants of resting RER included muscle glycogen content, training volume, proportion of type 1 fibers, [FFA] and [lactate], and %dietary fat intake (adjusted r(2) = 0.59, P < 0.001). Except for muscle fiber composition, these variables also predicted RER at 25, 50, and 70% W(peak) to different extents. The key determinant at 25% W(peak) was blood-borne [substrate], at 50% was muscle [substrate] and glycolytic enzyme activities, and at 70% was [lactate]. Resting RER was also a significant determinant of RER at 25 (r = 0.60) and 50% (r = 0.44) W(peak).
authors.affiliation: University of Cape Town Bioenergetics of Exercise Research Unit, University of Cape Town Medical School, Newlands 7725, South Africa. juliag@sports.uct.ac.za
authors.forename: J H
authors.initials: JH
authors.lastname: Goedecke
authors.forename: A
authors.initials: A
authors.lastname: St Clair Gibson
authors.forename: L
authors.initials: L
authors.lastname: Grobler
authors.forename: M
authors.initials: M
authors.lastname: Collins
authors.forename: T D
authors.initials: TD
authors.lastname: Noakes
authors.forename: E V
authors.initials: EV
authors.lastname: Lambert
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D001823:Body Composition; D004040:Dietary Carbohydrates / Q000493:pharmacokinetics; D004041:Dietary Fats / Q000493:pharmacokinetics; D005080:Exercise Test; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D015999:Multivariate Analysis; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012146:Rest / Q000502:physiology*; D012737:Sex Factors; D014280:Triglycerides / Q000378:metabolism
chemical_list: D004040:Dietary Carbohydrates; D004041:Dietary Fats; D005230:Fatty Acids, Nonesterified; D014280:Triglycerides; D019344:Lactic Acid; D006003:Glycogen