Drinking for Long or Hot Sessions
Preventing a water deficit beyond about 2% of body mass in long or hot sessions: one way to carry out what the review summary this entry was written from reports: that dehydration beyond 2% impairs endurance and thermoregulation, clearly in the heat and little in the cool.
- Confusion, headache or nausea during prolonged exercise in the heat: stop and seek medical help
How to do it
What the evidence says
This practice is one way to carry out what the sources on the concept entry (phys.nutrition.dehydration-threshold-endurance) studied: keeping water deficits during long or hot sessions below about 2% of body mass. Cheuvront 2003 (narrative review) reports that dehydration exceeding 2% of body weight degrades endurance performance, accentuated by heat stress, and that fluid intake should keep dehydration under 2%, usually achievable with intakes under 1 L/h; Shirreffs 2008 reports the 2% threshold impairing endurance in hot environments but with a lesser or inconsequential effect in temperate conditions; Kałwa 2026 (systematic review) reports that a 2% fluid loss can result in an 8% decrease in endurance performance; McCartney 2017 (meta-analysis) reports that fluid intake improved continuous exercise performance (g = 0.46), especially under heat stress, and concludes that fluid after dehydration may improve performance under heat stress even when rehydration is incomplete. The full account, source by source, is on the concept entry this practice links to (phys.nutrition.dehydration-threshold-endurance).
- Does not prescribe individual fluid volumes
- Does not diagnose or treat heat illness or dehydration
- Agreement
- Direction recorded for 0 of 9 sources; not yet recorded for the rest.
- The claim's outcome
- Outcome not yet recorded
- Certainty
- No source states a certainty rating.
- Authors
- Sources share authors: S. Shirreffs (senior author of 2 sources).
- How the sources were read
- Some sources are based on abstracts, not full texts.
What each source measured and concluded (9)
- What it measured
- Rating of perceived exertion (RPE, Borg scale) during endurance exercise
- How it was read
- based on the abstract, not the full text
- What the review says it includes
- Systematic review with meta-analysis (of controlled crossover studies)
- Studies and participants, as stated
- 16 studies, 147 individuals
- What it measured
- Continuous exercise performance.
- How it measured it
- Objective indicators (validated).
- How it was read
- read in full text
- What the review says it includes
- Systematic review and meta-analysis of 64 trials from 42 publications
- Studies and participants, as stated
- N=643 participants across 42 studies
- What it measured
- Physical performance.
- How it measured it
- Objective measures (implied).
- How it was read
- read in full text
- What it measured
- Effect of hydration state on physical and mental performance
- How it was read
- screened only, not extracted
- What it measured
- Water, carbohydrate and salt intake effects on fatigue and illness
- How it was read
- screened only, not extracted
- What it measured
- Effect of fluid balance/dehydration on endurance exercise performance
- How it was read
- screened only, not extracted
- What it measured
- Water needs and consequences of failing to meet them
- How it was read
- screened only, not extracted
- What it measured
- Neuromuscular function (muscle performance, central and peripheral mechanisms)
- How it was read
- based on the abstract, not the full text
- What the review says it includes
- Systematic review
- Studies and participants, as stated
- 23 articles
- What it measured
- Heart rate (HR), heart rate variability (HRV), systolic blood pressure (SBP), diastolic blood pressure (DBP).
- How it measured it
- Objective measurements using mean and standard deviations.
- How it was read
- read in full text
Each source below is shown with its study design and a link to the original study, or, where it is not a completed research paper, with what kind of record it is; those are not counted. This is the audit trail.
Why do some records show a record type instead of a study design?
A study design is shown for a completed, peer-reviewed paper. A registered protocol, a preprint, a conference abstract, a referee report or a book chapter has not been through peer review as a finished paper, so it is labelled for what it is, and it is counted in no source count. Where a record could not be confirmed as a completed paper at all, it says so rather than guessing. They all stay in the list, and their DOI still resolves, because the count of what was screened is part of the audit trail.
- Protocol / registration A registered plan for a review or trial, not its results.
- Preprint Posted by its authors before peer review.
- Conference abstract A conference summary rather than a peer-reviewed paper.
- Peer-review report A referee's report on a paper, not the paper itself.
- Guideline / position stand A recommendation derived from evidence, which is a step further from the data than the evidence itself.
- Book chapter A chapter in a scholarly book rather than a journal paper.
- Type not recorded Our record does not say what kind of publication this is, so it is counted in no source count. That is a gap in our data, not a judgement about the research.
“Abstract only” means the review read that paper’s abstract, not its full text; “screened only” means it was included at re-screening and not extracted. Both stay in the trail with their DOI, because how a source was read is part of the audit.