Perceived Dehydration Impairs Endurance Cycling Performance in the Heat in Active Males
Participants
n=9 active males (age 25 ± 2 yr, VO2peak 52.5 ± 9.1 mL/kg/min)
Protocol
Two randomized trials at 34°C: intermittent preload (8 × 10 min cycling / 5 min rest), then a 15-min all-out cycling performance test
Both trials: water orally every 10 min (0.3 mL/kg) plus intragastric infusion producing ~1.5% body-mass dehydration before the performance test — actual hydration identical
Deception: participants were told the infusion produced euhydration (0%; Perceived-EUH) or 2% dehydration (Perceived-DEH), told before the preload and "confirmed" after a body-mass measurement
Key Results
| Condition | Actual body-mass loss | Work in 15-min test |
|---|---|---|
| Perceived euhydrated | 1.6 ± 0.2% | 187.4 ± 37.0 kJ |
| Perceived dehydrated | 1.7 ± 0.2% (p=0.459 vs EUH) | 176.9 ± 36.0 kJ (−5.6 ± 6.1%, p=0.038) |
Heart rate, gastrointestinal temperature and RPE did not differ (p≥0.110); thirst was greater at the end of the preload and of the performance test in Perceived-DEH (p≤0.040).
Key Findings
Belief about hydration status impaired performance with physiology held constant (~1.5% dehydration in both trials)
Thirst rose with the belief, not with the fluid deficit
Context from the same group: at >3% body-mass dehydration performance falls regardless of knowledge (the abstract's opening statement); this study asks about the <2% range, where perception could matter
Practical Application
In 9 active males with identical ~1.5% dehydration, being told they were 2% dehydrated cut work in a 15-min all-out cycling test by 5.6 ± 6.1% (187.4 → 176.9 kJ, p=0.038) and raised thirst, with HR, gut temperature and RPE unchanged. At mild deficits (<2% body mass), what an athlete believes about their hydration can cost as much as the deficit itself.
Combined with James 2017 REF-226 (blinded, ~2.4% deficit → about 8% less work): real and perceived dehydration both harm performance in the heat.
Not from this paper; the base's own practice: settle the hydration plan before the race so it is not a live worry; avoid "I'm dehydrated" self-talk mid-effort; keep monitoring to the plan (bottles per hour), not to sensations.
Limitations
Small sample (n=9); single dehydration level (~1.5%); active males, not trained cyclists; hot environment only; the SD of the effect (6.1%) is larger than the mean (5.6%) — individual responses varied widely.
How this entry was checked and changed
Why this level
regraded 2026-09-27 from A-: crossover, n=9 (rubric: crossover <15)
Content correction 2026-09-27
Level A- -> B: crossover with n=9. Tier 2-3 "trained cyclists" -> Tier 1-2: the abstract says "active males", VO2peak 52.5.
Journal line "281, 114571" -> article number per DOI is 114462; volume not verified, removed.
Practical lead was house psychology advice -> replaced by the study's finding with its numbers; house advice labelled. Added the abstract's protocol, deception details, HR/Tgi/RPE null results and the ±6.1% SD.