title: Fluid homoeostasis during prolonged low-intensity walking on consecutive days.
abstract: 1. The effect on fluid homoeostasis of walking 37 km on each of 4 consecutive relatively cool days was studied in six male subjects. The daily exercise intensity was consistent and was equivalent to 17(1)% [mean (SE)] of maximum oxygen uptake for these subjects. 2. The diet during the study consisted of a mainly carbohydrate breakfast, consumed immediately before each day's exercise, and unrestricted access to a normal mixed diet after completion of each day's exercise. Water was allowed ad libitum during the walk. Food and fluid intake were recorded. 3. Body weight remained constant over the 4-day walk. The difference between total daily fluid intake and the corresponding 24 h urine output was 1684 (250) ml, 1621 (522) ml, 1107 (252) ml and 1406 (208) ml, respectively, on each of the 4 exercise days. 4. There was a calculated increase of 21.3(6.6)% in plasma volume over the 4-day walk; the largest daily change [11.3(2.9)%] occurred during the walk on day 1. The increase in plasma volume was maintained for at least 4 days after completion of the walk. 5. From day 2, serum sodium concentration tended to increase during the exercise period and fell to the pre-exercise concentration during the overnight rest periods. The concentration of the other measured serum constituents remained relatively constant, and serum osmolality did not alter over the study period.
authors.affiliation: Department of Environmental and Occupational Medicine, University Medical School, Foresterhill, Aberdeen, U.K.
authors.forename: J B
authors.initials: JB
authors.lastname: Leiper
authors.forename: K
authors.initials: K
authors.lastname: McCormick
authors.forename: J D
authors.initials: JD
authors.lastname: Robertson
authors.forename: P H
authors.initials: PH
authors.lastname: Whiting
authors.forename: R J
authors.initials: RJ
authors.lastname: Maughan
mesh_terms: D001798:Blood Proteins / Q000378:metabolism; D001835:Body Weight; D003404:Creatinine / Q000097:blood; D004573:Electrolytes / Q000097:blood; D006400:Hematocrit; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D008297:Male; D009994:Osmolar Concentration; D005082:Physical Exertion; D010953:Plasma Volume; D014508:Urea / Q000097:blood; D014882:Water-Electrolyte Balance
chemical_list: D001798:Blood Proteins; D004573:Electrolytes; D006454:Hemoglobins; D014508:Urea; D003404:Creatinine