Respiratory gas-exchange ratios during graded exercise in fed and fasted trained and untrained men

• Published in: Journal of applied physiology (1985) 1999-02, Vol.86 (2), p.479-487
• Main Authors: Bergman, Bryan C, Brooks, George A
• Format: Article
• Language: English
• Subjects: Adult; Biological and medical sciences; Blood gas. Hemoglobin. Myoglobin. Hemotissulary gas exchange. Acid-base balance; Carbohydrate Metabolism; Carbohydrates; Energy Metabolism - physiology; Exercise; Exercise Test; Fasting; Fundamental and applied biological sciences. Psychology; Humans; Kinetics; Lactic Acid - blood; Lipids; Male; Nutrition; Nutritional Status; Oxidation; Oxidation-Reduction; Oxygen Consumption - physiology; Physical Endurance - physiology; Physical Fitness - physiology; Postprandial Period; Pulmonary Gas Exchange - physiology; Respiratory system; Space life sciences; Vertebrates: respiratory system
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.1999.86.2.479

Exercise Physiology Laboratory, Department of Integrative Biology, University of California, Berkeley, California 94720-3140 We evaluated the hypotheses that endurance training increases relative lipid oxidation over a wide range of relative exercise intensities in fed and fasted states and that carbohydrate nutrition causes carbohydrate-derived fuels to predominate as energy sources during exercise. Pulmonary respiratory gas-exchange ratios [(RER)   = CO 2 production/O 2 consumption ( O 2 )] were determined during four relative, graded exercise intensities in both fed and fasted states. Seven untrained (UT) men and seven category 2 and 3 US Cycling Federation cyclists (T) exercised in the morning in random order, with target power outputs of 20 and 40% peak O 2 ( O 2 peak ) for 2 h, 60% O 2 peak for 1.5 h, and 80% O 2 peak for a minimum of 30 min after either a 12-h overnight fast or 3 h after a standardized breakfast. Actual metabolic responses were 22 ± 0.33, 40 ± 0.31,   59 ± 0.32, and 75 ± 0.39% O 2 peak . T subjects showed significantly ( P