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The effects of substrate and fluid provision on thermoregulatory and metabolic responses to prolonged exercise in a hot environment.
J Sports Sci. 2000 May; 18(5):339-51.JS

Abstract

A high ambient temperature reduces the capacity to perform prolonged exercise. Total carbohydrate oxidation is less, and thus glycogen depletion is not limiting. Fluid ingestion in the heat should, therefore, focus on maintenance of hydration status rather than on substrate provision. Six healthy males cycled to exhaustion at 60% of maximum oxygen consumption (VO2max) with no drink, ingestion of a 15% carbohydrate-electrolyte drink (1.45+/-0.29 litres) or ingestion of a 2% carbohydrate-electrolyte drink (3.12+/-0.47 litres). The ambient temperature was 30.2+/-0.6 degrees C (mean +/- s), with a relative humidity of 71+/-1% and an air speed of approximately 0.7 m x s(-1) on all trials. Weighted mean skin temperature, rectal temperature and heart rate were recorded and venous samples drawn for determination of plasma volume changes, blood metabolites, serum electrolytes and osmolality. Expired gas was collected to estimate rates of fuel oxidation. Exercise capacity was significantly (P < 0.05) different in all trials. The median (range) time to exhaustion was 70.9 min (39.4-97.4 min) in the no-drink trial, 84.0 min (62.7-145 min) in the 15% carbohydrate trial and 118 min (82.6-168 min) in the 2% carbohydrate trial. The 15% carbohydrate drink resulted in significantly (P < 0.05) elevated blood glucose and total carbohydrate oxidation compared with the no-drink trial. The 2% carbohydrate drink restored plasma volume to pre-exercise values by the end of exercise. No differences were observed in other thermoregulatory or cardiorespiratory responses between trials. These results suggest that fluid replacement with a large volume of a dilute carbohydrate drink is beneficial during exercise in the heat, but the precise mechanisms for the improved exercise capacity are unclear.

Authors+Show Affiliations

Department of Biomedical Sciences, University of Aberdeen Medical School, Foresterhill, UK. s.d.r.galloway@stir.ac.ukNo affiliation info available

Pub Type(s)

Clinical Trial
Journal Article
Randomized Controlled Trial
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

10855680

Citation

Galloway, S D., and R J. Maughan. "The Effects of Substrate and Fluid Provision On Thermoregulatory and Metabolic Responses to Prolonged Exercise in a Hot Environment." Journal of Sports Sciences, vol. 18, no. 5, 2000, pp. 339-51.
Galloway SD, Maughan RJ. The effects of substrate and fluid provision on thermoregulatory and metabolic responses to prolonged exercise in a hot environment. J Sports Sci. 2000;18(5):339-51.
Galloway, S. D., & Maughan, R. J. (2000). The effects of substrate and fluid provision on thermoregulatory and metabolic responses to prolonged exercise in a hot environment. Journal of Sports Sciences, 18(5), 339-51.
Galloway SD, Maughan RJ. The Effects of Substrate and Fluid Provision On Thermoregulatory and Metabolic Responses to Prolonged Exercise in a Hot Environment. J Sports Sci. 2000;18(5):339-51. PubMed PMID: 10855680.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - The effects of substrate and fluid provision on thermoregulatory and metabolic responses to prolonged exercise in a hot environment. AU - Galloway,S D, AU - Maughan,R J, PY - 2000/6/16/pubmed PY - 2000/9/23/medline PY - 2000/6/16/entrez SP - 339 EP - 51 JF - Journal of sports sciences JO - J Sports Sci VL - 18 IS - 5 N2 - A high ambient temperature reduces the capacity to perform prolonged exercise. Total carbohydrate oxidation is less, and thus glycogen depletion is not limiting. Fluid ingestion in the heat should, therefore, focus on maintenance of hydration status rather than on substrate provision. Six healthy males cycled to exhaustion at 60% of maximum oxygen consumption (VO2max) with no drink, ingestion of a 15% carbohydrate-electrolyte drink (1.45+/-0.29 litres) or ingestion of a 2% carbohydrate-electrolyte drink (3.12+/-0.47 litres). The ambient temperature was 30.2+/-0.6 degrees C (mean +/- s), with a relative humidity of 71+/-1% and an air speed of approximately 0.7 m x s(-1) on all trials. Weighted mean skin temperature, rectal temperature and heart rate were recorded and venous samples drawn for determination of plasma volume changes, blood metabolites, serum electrolytes and osmolality. Expired gas was collected to estimate rates of fuel oxidation. Exercise capacity was significantly (P < 0.05) different in all trials. The median (range) time to exhaustion was 70.9 min (39.4-97.4 min) in the no-drink trial, 84.0 min (62.7-145 min) in the 15% carbohydrate trial and 118 min (82.6-168 min) in the 2% carbohydrate trial. The 15% carbohydrate drink resulted in significantly (P < 0.05) elevated blood glucose and total carbohydrate oxidation compared with the no-drink trial. The 2% carbohydrate drink restored plasma volume to pre-exercise values by the end of exercise. No differences were observed in other thermoregulatory or cardiorespiratory responses between trials. These results suggest that fluid replacement with a large volume of a dilute carbohydrate drink is beneficial during exercise in the heat, but the precise mechanisms for the improved exercise capacity are unclear. SN - 0264-0414 UR - https://www.unboundmedicine.com/medline/citation/10855680/The_effects_of_substrate_and_fluid_provision_on_thermoregulatory_and_metabolic_responses_to_prolonged_exercise_in_a_hot_environment_ L2 - https://www.tandfonline.com/doi/full/10.1080/026404100402403 DB - PRIME DP - Unbound Medicine ER -