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Fluid and electrolyte loss and replacement in exercise.
J Sports Sci 1991; 9 Spec No:117-42JS

Abstract

Prolonged exercise leads to a progressive water and electrolyte loss from the body as sweat is secreted to promote heat loss. The rate of sweating depends on many factors and is increased in proportion to the work rate and the environmental temperature and humidity. Sweat rate is highly variable between individuals, and can exceed 21 h-1 for prolonged periods. Since it is established that dehydration will impair exercise capacity and can pose a risk to health, the intake of fluid during exercise to offset sweat loss is important. Fluid intake is also aimed at providing a source of substrate, usually in the form of carbohydrate. The availability of ingested fluids may be limited by gastric emptying or by intestinal absorption. Gastric emptying of liquids is slowed by the addition of carbohydrate in proportion to the carbohydrate concentration and osmolality of the solution. With increasing glucose concentration, the rate of fluid delivery to the small intestine is decreased, but the rate of glucose delivery is increased. Water absorption in the small intestine is a passive process and is stimulated by the active absorption of glucose and sodium. The optimum fluid for rehydration during exercise depends on many factors, particularly the intensity and duration of the exercise, the environmental conditions, and the individual physiology of the athlete. There is no advantage to fluid intake during exercise of less than 30 min duration. The composition of fluids to be used will depend on the relative needs to replace water and to provide substrate. Where rehydration is a priority the solution should contain some glucose and sodium and should not exceed isotonicity: this will require the glucose concentration to be low (20-309 g l-1) or the substitution of glucose polymers, and the sodium content to be high (perhaps as much as 60 mmol l-1). Where substrate provision is more important, a more concentrated solution, incorporating large amounts of glucose polymers in concentrations of 150-200 g l-1, is to be preferred. To minimize the limitation imposed by the rate of gastric emptying, the volume of fluid in the stomach should be kept as high as is comfortable by frequent ingestion of small amounts of fluid. Addition of sodium, and perhaps also of potassium, may be important for rehydration after exercise.

Authors+Show Affiliations

Department of Environment and Occupational Medicine, University Medical School, Foresterhill, Aberdeen, Scotland.

Pub Type(s)

Journal Article
Review

Language

eng

PubMed ID

1895359

Citation

Maughan, R J.. "Fluid and Electrolyte Loss and Replacement in Exercise." Journal of Sports Sciences, vol. 9 Spec No, 1991, pp. 117-42.
Maughan RJ. Fluid and electrolyte loss and replacement in exercise. J Sports Sci. 1991;9 Spec No:117-42.
Maughan, R. J. (1991). Fluid and electrolyte loss and replacement in exercise. Journal of Sports Sciences, 9 Spec No, pp. 117-42.
Maughan RJ. Fluid and Electrolyte Loss and Replacement in Exercise. J Sports Sci. 1991;9 Spec No:117-42. PubMed PMID: 1895359.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Fluid and electrolyte loss and replacement in exercise. A1 - Maughan,R J, PY - 1991/1/1/pubmed PY - 1991/1/1/medline PY - 1991/1/1/entrez SP - 117 EP - 42 JF - Journal of sports sciences JO - J Sports Sci VL - 9 Spec No N2 - Prolonged exercise leads to a progressive water and electrolyte loss from the body as sweat is secreted to promote heat loss. The rate of sweating depends on many factors and is increased in proportion to the work rate and the environmental temperature and humidity. Sweat rate is highly variable between individuals, and can exceed 21 h-1 for prolonged periods. Since it is established that dehydration will impair exercise capacity and can pose a risk to health, the intake of fluid during exercise to offset sweat loss is important. Fluid intake is also aimed at providing a source of substrate, usually in the form of carbohydrate. The availability of ingested fluids may be limited by gastric emptying or by intestinal absorption. Gastric emptying of liquids is slowed by the addition of carbohydrate in proportion to the carbohydrate concentration and osmolality of the solution. With increasing glucose concentration, the rate of fluid delivery to the small intestine is decreased, but the rate of glucose delivery is increased. Water absorption in the small intestine is a passive process and is stimulated by the active absorption of glucose and sodium. The optimum fluid for rehydration during exercise depends on many factors, particularly the intensity and duration of the exercise, the environmental conditions, and the individual physiology of the athlete. There is no advantage to fluid intake during exercise of less than 30 min duration. The composition of fluids to be used will depend on the relative needs to replace water and to provide substrate. Where rehydration is a priority the solution should contain some glucose and sodium and should not exceed isotonicity: this will require the glucose concentration to be low (20-309 g l-1) or the substitution of glucose polymers, and the sodium content to be high (perhaps as much as 60 mmol l-1). Where substrate provision is more important, a more concentrated solution, incorporating large amounts of glucose polymers in concentrations of 150-200 g l-1, is to be preferred. To minimize the limitation imposed by the rate of gastric emptying, the volume of fluid in the stomach should be kept as high as is comfortable by frequent ingestion of small amounts of fluid. Addition of sodium, and perhaps also of potassium, may be important for rehydration after exercise. SN - 0264-0414 UR - https://www.unboundmedicine.com/medline/citation/1895359/Fluid_and_electrolyte_loss_and_replacement_in_exercise_ L2 - http://www.tandfonline.com/doi/full/10.1080/02640419108729870 DB - PRIME DP - Unbound Medicine ER -