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Review
. 2025 Apr 7:16:31-50.
doi: 10.2147/OAJSM.S508656. eCollection 2025.

Reference Values for Hydration Biomarkers: Optimizing Athletic Performance and Recovery

Lawrence E Armstrong  1 , Rebecca L Stearns  1 , Robert A Huggins  1 , Yasuki Sekiguchi  2 , April J Mershon  3 , Douglas J Casa  1
Affiliations
Review

Reference Values for Hydration Biomarkers: Optimizing Athletic Performance and Recovery

Lawrence E Armstrong et al. Open Access J Sports Med. .

Abstract

The negative effects of dehydration or overhydration on exercise performance and health are widely recognized. However, the interindividual variability of fluid imbalances among athletes and across various sports is large, due to the complex interactions of physiological, environmental, and sport-specific factors. Such complexity not only makes it difficult to predict fluid needs prior to competition or training sessions, but also supports the creation of an individualized hydration plan (IHP) for each athlete. Measurements of valid, field-expedient biomarkers such as body mass change, urine concentration, and thirst enable ongoing monitoring of an athlete's hydration state and are integral components of an IHP. Unfortunately, no extensive repository of sport-relevant hydration biomarker data exists. Therefore, this narrative review presents a novel inventory of pre- and post-exercise reference values for body mass change, urine specific gravity, and subjective rating of thirst. These reference values were identified via electronic database searches that discovered field studies of competitive events, weight category sports, training sessions, and routine daily activities. We propose that comparing an athlete's real-time body mass change, urine specific gravity, and thirst rating to previously published reference values will clarify the extent of dehydration or overhydration, guide rehydration efforts, and optimize subsequent exercise performance, recovery, and health.

Keywords: cyclist; runner; swimmer; thirst; triathlete; urine specific gravity.

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Conflict of interest statement

Professor Rebecca Stearns reports Royalties for Editing book from Jones & Bartlett LLC, as well as serving on the USA Football Medical Advisory Panel. Professor Robert Huggins works for the Korey Stringer Institute (KSI) which is a 501.3c not for profit housed in the Department of Kinesiology at the University of Connecticut. KSI has corporate partners who support the mission of KSI. Those partners are the National Football League, Gatorade, National Athletic Trainers’ Association, Kestrel, Camelbak, MISSION, DeFibtech, and MAGID. None of the partners indicated influenced, supported, or reviewed this manuscript. All authors declare no other conflicts of interest in this work.

Figures

Figure 1
Figure 1
Selection process for the 16 field research studies which appear in the present review.
Figure 2
Figure 2
A visual summary of body mass, thirst rating, and urine specific gravity changes due to net body water loss during various activities. The 10 color-coded symbols represent the athletic competitions and training sessions described in Table 1. White symbols denote the 24-h period of water restriction during routine daily activities (n = 14) with no exercise, as described in Table 5 (columns 2 to 4). All symbols represent group averages (range, n = 6–57). Abbreviation: VAS, visual analog scale.
Figure 3
Figure 3
Relationships among the three hydration-relevant variables of this review: thirst, body mass loss, and urine specific gravity. Data points are mean values from the studies cited in Tables 1–5. Test participants rated thirst using either a 100-mm visual analog scale (left vertical axis) or a 9-point category scale (right vertical axis) in panels (A) and (B). Percent female sex: panel (A), 21%, panel (B), 8%, panel (C), 8%.
See this image and copyright information in PMC

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