Hypohydration does not Exacerbate Age‐related Impairments in Whole‐body Heat Loss during Exercise in the Heat.
Notice bibliographique
Résumé
In young adults, hypohydration elicits impairments in whole‐body heat loss that are greater during moderate vs. high exercise‐heat loads. However, it is unknown if the effect of hypohydration on heat dissipation is exacerbated in older adults who demonstrate reduced heat loss capacity compared to their younger counterparts, even when euhydrated. On two separate occasions, six young (25 years [SD 3]) and six older (58 years [SD 4]) males performed a dehydration protocol consisting of light‐to‐moderate intensity intermittent treadmill walking (~150 min) in the heat (40°C) while wearing impermeable clothing. Thereafter, participants rested in a thermoneutral environment (~21°C) for ~240 min during which time they received either 1) a volume of intravenous saline (0.9%) equal to the fluid lost (euhydrated condition; EUH) or 2) no infusion (hypohydrated condition; HYP). Participants then performed a heat stress test (semi‐nude) consisting of two 30‐min bouts of cycling at moderate (175 W·m 2 ) and higher (275 W·m 2 ) rates of metabolic heat production, each followed by a 15‐min recovery, in hot, dry conditions (40°C, ~15% relative humidity). Fluid loss was estimated from changes in body mass and plasma volume from pre‐trial values. Metabolic heat production and whole‐body heat loss were measured during each heat stress test via indirect and direct calorimetry, respectively. Body heat storage was calculated as the temporal summation of heat production and loss. In both age groups, body mass was reduced (mean ± 95% confidence interval) from pre‐trial values prior to the start of the the heat stress test in HYP (young: −5.0 ± 0.5%; older: −4.1 ± 0.8%; both P≤0.03) but not EUH (young: −0.3 ± 0.6%; older: 0.1 ± 0.3%; both P≥0.38). Likewise, plasma volume was attenuated from pre‐trial values prior to the heat stress test in both groups in HYP (young: −11 ± 3%; older: −9 ± 6%; both P≤0.03), whereas no changes in plasma volume were seen in EUH (young: 3 ± 5%; older: 2 ± 4%; both P≥0.23). The alterations in body mass and plasma volume were not different between age groups in either condition (all P≥0.59). In the young, whole‐body heat loss was similar between hydration conditions during the moderate exercise bout (EUH: 352 ± 22 W vs. HYP: 324 ± 33 W; P=0.36) but diminished in HYP (461 ± 34 W) relative to EUH (516 ± 37 W) at the higher work rate (P=0.04). In the older adults however, no influence of hydration on heat loss was noted during either the moderate (EUH: 346 ± 27 W vs. HYP: 331 ± 26 W; P=0.54) or higher (EUH: 445 ± 33 W vs. HYP: 440 ± 32 W; P=0.98) work rates. When participants were EUH, heat loss was comparable between age‐groups during the moderate work bout (P=0.32) but reduced in the older relative to young adults during exercise at the higher work rate (P=0.03). By contrast, similar rates of heat loss were observed in the young and older adults during both exercise bouts when participants were HYP (P=0.40). In the moderate exercise bout, there were no differences in body heat storage as a function of age or hydration status (all P≥0.22). However, during the higher work rate, body heat storage in the young was elevated in HYP (174 ± 17 kJ) relative to EUH (117 ± 30 kJ; P=0.04) to a level comparable to that observed in the older adults during both EUH (188 ± 57; P=0.68) and HYP (184 ± 51 kJ; P=0.40). In summary , we demonstrate impairments in whole‐body heat loss at higher work rates in young but not older adults matched for fluid loss, indicating that hypohydration does not exacerbate the age‐related impairments in heat dissipation. Support or Funding Information The Ministry of Labour (Ontario) and Natural Sciences and Engineering Research Council of Canada. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .
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Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».