Dehydration Impairs Cycling Performance, Independently of Thirst: A Blinded Study

Adams, Jennifer; Sekiguchi, Yasuki; Suh, HyunGyu; Seal, Adam D.; Sprong, Cameron; Kirkland, Tracie; Kavouras, Stavros A.

doi:10.1249/mss.0000000000001597

Cited by 52 publications

(64 citation statements)

References 27 publications

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“…To address this issue, more recent research has blinded subjects from their hydration status (2,12,28,50). These studies have used two different methods to manipulate hydration status; 1) intravenous delivery of isotonic fluids (12,50) and 2) intragastric delivery of water via a gastric feeding tube (2,28). Interestingly, the different methods appear to induce divergent physiological and performance responses.…”

Section: Introductionmentioning

confidence: 99%

“…Interestingly, the different methods appear to induce divergent physiological and performance responses. Studies using intragastric rehydration with water, combined with standardised oral rehydration, report blinded hypohydration to impair performance (2,28), whilst those using intravenous rehydration with isotonic saline do not (12,50). Importantly, manipulating hydration status via intravenous rehydration with isotonic saline meant serum osmolality (12,50) and thirst sensation (50) remained elevated at levels equivalent to hypohydration, irrespective of hydration status.…”

Section: Introductionmentioning

confidence: 99%

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Blinded and unblinded hypohydration similarly impair cycling time trial performance in the heat in trained cyclists

Funnell

Mears

Bergin-Taylor

et al. 2019

Journal of Applied Physiology

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Knowledge of hydration status may contribute to hypohydration-induced exercise performance decrements; therefore, this study compared blinded and unblinded hypohydration on cycling performance. Fourteen trained, nonheat-acclimated cyclists (age: 25 ± 5 yr; V̇o2peak: 63.3 ± 4.7 ml·kg−1·min−1; cycling experience: 6 ± 3 yr) were pair matched to blinded (B) or unblinded (UB) groups. After familiarization, subjects completed euhydrated (B-EUH; UB-EUH) and hypohydrated (B-HYP; UB-HYP) trials in the heat (31°C); 120-min cycling preload (50% Wpeak) and a time trial (~15 min). During the preload of all trials, 0.2 ml water·kg body mass−1 was ingested every 10 min, with additional water provided during EUH trials to match sweat losses. To blind the B group, a nasogastric tube was inserted in both trials and used to provide water in B-EUH. The preload induced similar ( P = 0.895) changes in body mass between groups (B-EUH: −0.6 ± 0.5%; B-HYP: −3.0 ± 0.5%; UB-EUH: −0.5 ± 0.3%; UB-HYP −3.0 ± 0.3%). All variables responded similarly between B and UB groups ( P ≥ 0.558), except thirst ( P = 0.004). Changes typical of hypohydration (increased heart rate, rating of perceived exertion, gastrointestinal temperature, serum osmolality and thirst, and decreased plasma volume; P ≤ 0.017) were apparent in HYP by 120 min. Time trial performance was similar between groups ( P = 0.710) and slower ( P ≤ 0.013) with HYP for B (B-EUH: 903 ± 89 s; B-HYP: 1,008 ± 121 s; −11.4%) and UB (UB-EUH: 874 ± 108 s; UB-HYP: 967 ± 170 s; −10.1%). Hypohydration of ~3% body mass impairs time trial performance in the heat, regardless of knowledge of hydration status. NEW & NOTEWORTHY This study demonstrates, for the first time, that knowledge of hydration status does not exacerbate the negative performance consequences of hypohydration when hypohydration is equivalent to ~3% body mass. This is pivotal for the interpretation of the many previous studies that have not blinded subjects to their hydration status and suggests that these previous studies are not likely to be confounded by the overtness of the methods used to induce hypohydration.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Blinded and unblinded hypohydration similarly impair cycling time trial performance in the heat in trained cyclists

Funnell

Mears

Bergin-Taylor

et al. 2019

Journal of Applied Physiology

View full text Add to dashboard Cite

show abstract

“…16,17 In contrast, few investigations have observed performance differences even when thirst was matched by mouth rinsing or water ingestion. 3,15,18 In the present study, subjects during the HYP had lower power output and cycling speed in the second time trial, even when hypohydration was just 1% of bodyweight. However, thirst was not higher during the first two exercise bouts, since subjects were drinking 25 mL of water every 5 minutes and 1 km of the steady-state and time trial, respectively.…”

Section: Discussionmentioning

confidence: 42%

“…The present study is not without limitations. Regarding the methodology of blinding, the intravenous fluid induced plasma volume expansion in the EUH trial that we would probably not see if the subjects were receiving the same fluid volume orally (Table 1) as shown in a previous study by the same authors 15 and elsewhere. 26 The authors found that infusion of 0.9% NaCl as a blinding method expanded PV (~3%) and found differences in performance compared to HYP trial under a mild degree of dehydration.…”

Section: Discussionmentioning

confidence: 93%

“…Studies that manipulate hydration status through fluid ingestion are limited by nature of drinking and its effects on subject bias. [12][13][14] Recently, few studies have attempted to blind subjects to their fluid replacement and overall hydration state via nasal/ oral-gastric tubes 15,16 or intravenous saline infusion. 17,18 The former studies administered fluids via gastric infusion and reported that dehydration of 2%-2.5% body mass resulted in impaired performance.…”

Section: Introductionmentioning

confidence: 99%

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Mild hypohydration impairs cycle ergometry performance in the heat: A blinded study

Adams

Scott

Brand

et al. 2019

Scandinavian Med Sci Sports

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The aim of the present study was to observe the effect of mild hypohydration on exercise performance with subjects blinded to their hydration status. Eleven male cyclists (weight 75.8 ± 6.4 kg, VO 2peak : 64.9 ± 5.6 mL/kg/min, body fat: 12.0 ± 5.8%, Power max : 409 ± 40 W) performed three sets of criterium-like cycling, consisting of 20-minute steady-state cycling (50% peak power output), each followed by a 5-km time trial at 3% grade. Following a familiarization trial, subjects completed the experimental trials, in counter-balanced fashion, on two separate occasions in dry heat (30°C, 30% rh) either hypohydrated (HYP) or euhydrated (EUH).In both trials, subjects ingested 25 mL of water every 5 minutes during the steadystate and every 1 km of the 5-km time trials. In the EUH trial, sweat losses were fully replaced via intravenous infusion of isotonic saline, while in the HYP trial, a sham IV was instrumented. Following the exercise protocol, the subjects' bodyweight was changed by −0.1 ± 0.1% and −1.8 ± 0.2% for the EUH and HYP trial, respectively (P < 0.05). During the second and third time trials, subjects averaged higher power output (309 ± 5 and 306 ± 5 W) and faster cycling speed (27.5 ± 3.0 and 27.2 ± 3.1 km/h) in the EUH trial compared to the HYP trial (Power: 287 ± 4 and 276 ± 5 W, Speed: 26.2 ± 2.9 and 25.5 ± 3.3 km/h, all P < 0.05). Core temperature (T re ) was higher in the HYP trial throughout the third steady-state and 5-km time trial (P < 0.05). These data suggest that mild hypohydration, even when subjects were unaware of their hydration state, impaired cycle ergometry performance in the heat probably due to greater thermoregulatory strain. K E Y W O R D Scycling, heat stress, time trial, water intake

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Dehydration Impairs Cycling Performance, Independently of Thirst: A Blinded Study

Abstract: These data indicated that hypohydration decreased cycling performance and impaired thermoregulation independently of thirst, while the subjects were unaware of their hydration status.

Cited by 52 publications

References 27 publications

Blinded and unblinded hypohydration similarly impair cycling time trial performance in the heat in trained cyclists

Blinded and unblinded hypohydration similarly impair cycling time trial performance in the heat in trained cyclists

Mild hypohydration impairs cycle ergometry performance in the heat: A blinded study

Hydration, dehydration, underhydration, optimal hydration: are we barking up the wrong tree?

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