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Does hypohydration really impair endurance performance? Methodological considerations for interpreting hydration research

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journal contribution
posted on 2019-11-29, 09:46 authored by Lewis JamesLewis James, Mark Funnell, Ruth M James, Stephen MearsStephen Mears
The impact of alterations in hydration status on human physiology and performance responses during exercise is one of the oldest research topics in sport and exercise nutrition. This body of work has mainly focussed on the impact of reduced body water stores (i.e. hypohydration) on these outcomes, on the whole demonstrating that hypohydration impairs endurance performance, likely via detrimental effects on a number of physiological functions. However, an important consideration, that has received little attention, is the methods that have traditionally been used to investigate how hypohydration affects exercise outcomes, as those used may confound the results of many studies. There are two main methodological limitations in much of the published literature that perhaps make the results of studies investigating performance outcomes difficult to interpret. First, subjects involved in studies are generally not blinded to the intervention taking place (i.e. they know what their hydration status is), which may introduce expectancy effects. Second, most of the methods used to induce hypohydration are both uncomfortable and unfamiliar to the subjects, meaning that alterations in performance may be caused by this discomfort, rather than hypohydration per se. This review discusses these methodological considerations and provides an overview of the small body of recent work that has attempted to correct some of these methodological issues. On balance, these recent blinded hydration studies suggest hypohydration equivalent to 2–3% body mass decreases endurance cycling performance in the heat, at least when no/little fluid is ingested.

Funding

This article is based on a presentation by Lewis J. James to the GSSI Expert Panel in March 2019. Funding for attendance at that meeting together with an honorarium for preparation of this article were provided by the GSSI, with this honorarium being paid to Lewis J. James’s institution, not him personally

History

School

  • Sport, Exercise and Health Sciences

Published in

Sports Medicine

Volume

49

Issue

Supp 2

Pages

S103–S114

Publisher

Springer International Publishing

Version

  • VoR (Version of Record)

Rights holder

© The Authors

Publisher statement

This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Publication date

2019-11-06

Copyright date

2019

ISSN

0112-1642

eISSN

1179-2035

Language

  • en

Depositor

Dr Lewis James. Deposit date: 28 November 2019