Body water observes storage and shifting between different sites within the body, which complicates the hydration assessment. Despite much research, there still needs to be better best-practice guidelines for assessing hydration in athletes. The present review highlights the unique strengths and limitations of various hydration assessment methods described in the literature and provides best practice guidelines.

There are numerous methods with different validity and reliability. These include complicated and invasive methods like neutron activation analysis and stable isotope dilution; moderately invasive blood, urine, and salivary variables; and non-invasive metrics such as tear osmolality, body mass, bioimpedance analysis, and sensation of thirst. Any single assessment of hydration status needs to be revised. Rather, the recommendation exists to use a combination that has complementary strengths and increases accuracy and validity. Using methods such as salivary variables, urine color, vital signs, and sensation of thirst in isolation demands great care due to their lack of sensitivity, reliability, and/or accuracy. Furthermore, detailed evaluations like neutron activation and stable isotope dilution analysis give highly accurate results but are expensive, with significant time delays due to data analysis, thus having little potential for immediate action. At the same time, alternative variables such as hormonal and electrolyte concentration, bioimpedance, and tear osmolality demand further research to confirm their validity and reliability before inclusion into any test battery.

Hence best practice improvement demands additional, comprehensive research to clear the scientific understanding of evaluating hydration status.

Barley OR, Chapman DW, Abbiss CR. Reviewing the current methods of assessing hydration in athletes. Journal of the International Society of Sports Nutrition. 2020;17:1. DOI: 10.1186/s12970-020-00381-6