title: Heat exposure increases circulating fatty acids but not lipid oxidation at rest and during exercise.
abstract: Alterations in lipid oxidation during exercise have been well studied, but limited data exists on the effects of passive heat exposure and exercise in the heat on changes in lipid oxidation. This study was designed to examine: (1) the effects of heat exposure on lipid metabolism during passive heating and subsequent exercise in the heat by focusing on changes in whole-body lipid oxidation and plasma lipid concentrations, and (2) the effects of extended passive pre-heating on exercise performance in the heat. Male participants (n=8) were passively heated for 120 min at 42 °C, then exercised on a treadmill in the same temperature at 50% V̇O2 max for 30 min (HEAT). This same procedure was followed on a separate occasion at 23 °C (CON). Results showed that lipid oxidation rates were not different between HEAT and CON during passive heating or exercise. However, non-esterified fatty acid (NEFA) concentrations were significantly higher following passive heating (618 µM, 95% CI: 479-757) compared to CON (391 µM, 95% CI: 270-511). The same trend was observed following exercise (2036 µM, 95% CI: 1604-2469 for HEAT and 1351 µM, 95% CI: 1002-1699). Triacylglycerol, phospholipid and cholesterol levels were not different between HEAT and CON at any point. Four of 8 participants could not complete 30 min of exercise in HEAT, resulting in a 14% decline in total external work. Rate of perceived exertion over the final 5 min of exercise was higher in HEAT (9.5) than CON (5). We conclude that: (1) heat exposure results in increased circulating NEFA at rest and during exercise without changes in whole-body lipid utilization, and (2) passive pre-heating reduces work capacity during exercise in the heat and increases the perceived intensity of a given workload.
authors.affiliation: School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5.
authors.forename: Katharine
authors.initials: K
authors.lastname: O'Hearn
authors.affiliation: School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5.
authors.forename: Hans Christian
authors.initials: HC
authors.lastname: Tingelstad
authors.affiliation: Department of Medicine, Centre de Recherche du Centre Hospitalier Universitaire de Sherbrooke, Universite de Sherbrooke, Quebec, Canada J1H 5N4.
authors.forename: Denis
authors.initials: D
authors.lastname: Blondin
authors.affiliation: University of Ottawa, Flow Cytometry Core Facility, Canada.
authors.forename: Vera
authors.initials: V
authors.lastname: Tang
authors.affiliation: Department of Biochemistry Microbiology and Immunology, Faculty of Medicine, University of Ottawa, Ottawa Ontario, Canada K1H 8M5.
authors.forename: Lionel G
authors.initials: LG
authors.lastname: Filion
authors.affiliation: School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5. Electronic address: fhaman@uottawa.ca.
authors.forename: François
authors.initials: F
authors.lastname: Haman
mesh_terms: D000328:Adult; D001831:Body Temperature; D001835:Body Weight; D002245:Carbon Dioxide / Q000378:metabolism; D015444:Exercise; D005080:Exercise Test; D005227:Fatty Acids / Q000378:metabolism*; D006339:Heart Rate; D006358:Hot Temperature; D006801:Humans; D050356:Lipid Metabolism; D008055:Lipids / Q000097:blood; D008297:Male; D010101:Oxygen Consumption; D012123:Pulmonary Ventilation; D012881:Skin Temperature; D013312:Stress, Physiological; D022722:Thermogenesis; D055815:Young Adult
chemical_list: D005227:Fatty Acids; D008055:Lipids; D002245:Carbon Dioxide
keywords: Exercise performance; Fuel selection; Hyperthermia; Non-esterified fatty acids