title: Effects of exercise intensity and altered substrate availability on cardiovascular and metabolic responses to exercise after oral carnitine supplementation in athletes.
abstract: The effects of 15 d of supplementation with L-carnitine L-tartrate (LC) on metabolic responses to graded-intensity exercise under conditions of altered substrate availability were examined. Fifteen endurance-trained male athletes undertook exercise trials after a 2-d high-carbohydrate diet (60% CHO, 25% fat) at baseline (D0), on Day 14 (D14), and after a single day of high fat intake (15% CHO, 70% fat) on Day 15 (D15) in a double-blind, placebo-controlled, pair-matched design. Treatment consisted of 3 g LC (2 g L-carnitine/d; n = 8) or placebo (P, n = 7) for 15 d. Exercise trials consisted of 80 min of continuous cycling comprising 20-min periods at each of 20%, 40%, 60%, and 80% VO2peak. There was no significant difference between whole-body rates of CHO and fat oxidation at any workload between D0 and D14 trials for either the P or LC group. Both groups displayed increased fat and reduced carbohydrate oxidation between the D14 and D15 trials (p < .05). During the D15 trial, heart rate (p < .05 for 20%, 40%, and 60% workloads) and blood glucose concentration (p < .05 for 40% and 60% workloads) were lower during exercise in the LC group than in P. These responses suggest that LC may induce subtle changes in substrate handling in metabolically active tissues when fatty-acid availability is increased, but it does not affect whole-body substrate utilization during short-duration exercise at the intensities studied.
authors.affiliation: Sports Nutrition, Australian Institute of Sport, Canberra, Australia.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Broad
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Maughan
authors.forename: D R
authors.initials: DR
authors.lastname: Galloway S
mesh_terms: D000284:Administration, Oral; D000328:Adult; D001642:Bicycling / Q000502:physiology; D001786:Blood Glucose / Q000378:metabolism; D050260:Carbohydrate Metabolism / Q000187:drug effects*; D002331:Carnitine / Q000494:pharmacology*; D004032:Diet; D059305:Diet, High-Fat; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000378:metabolism; D004041:Dietary Fats / Q000008:administration & dosage; D019587:Dietary Supplements; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D050356:Lipid Metabolism / Q000187:drug effects*; D008297:Male; D010807:Physical Endurance / Q000502:physiology; D013644:Tartrates / Q000494:pharmacology; D014803:Vitamin B Complex / Q000494:pharmacology; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D013644:Tartrates; D014803:Vitamin B Complex; D002331:Carnitine; C029768:tartaric acid