Abstract/Details

Mild preexercise hyperhydration with electrolyte -containing beverages: Effect on thirst, water intake, and physiologic function


2007 2007

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Abstract (summary)

The American College of Sports Medicine's (ACSM) position stand on appropriate fluid intake for long duration exercise states that individuals should drink fluids containing sodium (0.5 - 0.7 g/l), potassium (0.08 - 0.2 g/l), and carbohydrate (5 - 10%) at a rate of 400 - 800 ml/h, depending on the individual's sweat rate and body size, in order to keep body water losses < 2%. The ACSM guidelines for preexercise hydration are unclear. Beverages containing significant amounts of sodium increase water intake and retention, subsequently improving fluid balance during and after exercise. However, whether sodium containing beverages ingested before exercise influence water intake and urine production during endurance exercise has not been studied. Two primary studies were conducted in order to test the efficacy of chicken noodle soup (167 mmol Na+/l) to improve fluid balance by increasing water intake and retention during exercise in thermoneutral (WBGT = 16°C) and hot, dry (WBGT = 26°C) environments. In both studies, fluid balance was improved during 90 min of moderate intensity exercise (∼55% VO2peak) 45 min after ingesting 355 ml of chicken noodle soup (CNS) compared with a similar quantity of water (WATER). The improvement in fluid balance was mainly because of an increase in ad libitum water intake that persisted throughout the 90 min of exercise. The increase in water intake was apparent in both the thermoneutral (801 ± 415 vs. 594 ± 391; CNS vs. WATER) and hot, dry (1434 ± 592 vs. 1163 ± 427; CNS vs. WATER) environments. Water retention was also improved after CNS in the thermoneutral environment, but not the hot, dry environment despite decreased calculated free water clearance in both studies. Although fluid balance was greater in both studies, no cardiovascular, temperature regulatory, or performance benefits were observed. Perceived thirst was also similar in all trials when water intake was allowed ad libitum. When water ingested at a similar rate to the CNS trial during a second water hyperhydration trial (WATER/R) in the hot, dry environment, ratings of perceived thirst decreased. Interestingly, when participants were forced to drink more water than normal in the hot, dry environment (WATER/R) without the additional preexercise sodium load (CNS), plasma sodium concentrations were consistently lower during exercise. From these studies we conclude that preexercise beverage composition can affect both dipsogenic drive and kidney function resulting in improved body water status during exercise. Also, these results indicate that it may not be necessary to replace sodium losses during exercise if anticipated losses are ingested before exercise.

Indexing (details)


Subject
Sports medicine;
Anatomy & physiology
Classification
0575: Sports medicine
0719: Anatomy & physiology
Identifier / keyword
Health and environmental sciences; Biological sciences; Electrolyte-containing beverages; Exercise; Hydration; Hyperhydration; Preexercise; Thirst; Water intake
Title
Mild preexercise hyperhydration with electrolyte -containing beverages: Effect on thirst, water intake, and physiologic function
Author
Johannsen, Neil Michael
Number of pages
149
Publication year
2007
Degree date
2007
School code
0097
Source
DAI-B 68/07, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
9780549154297
Advisor
Sharp, Rick L.
University/institution
Iowa State University
Department
Health and Human Performance
University location
United States -- Iowa
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3274856
ProQuest document ID
304854902
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/304854902
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