Limited Effect of Dehydrating via Active vs. Passive Heat Stress on Plasma Volume or Osmolality, Relative to the Effect of These Stressors per Se
The physiological, perceptual, and functional effects of dehydration may depend on how it is incurred (e.g., intense exercise releases endogenous water via glycogenolysis) but this basic notion has rarely been examined. We investigated the effects of active (exercise) heat- vs. passive heat-induced...
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| Format: | Article |
| Language: | English |
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MDPI AG
2023-02-01
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| Series: | Nutrients |
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| Online Access: | https://www.mdpi.com/2072-6643/15/4/904 |
| _version_ | 1797618898127814656 |
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| author | Alexandria Davies Ashley Paul Akerman Nancy Jane Rehrer Simon N. Thornton James David Cotter |
| author_facet | Alexandria Davies Ashley Paul Akerman Nancy Jane Rehrer Simon N. Thornton James David Cotter |
| author_sort | Alexandria Davies |
| collection | DOAJ |
| description | The physiological, perceptual, and functional effects of dehydration may depend on how it is incurred (e.g., intense exercise releases endogenous water via glycogenolysis) but this basic notion has rarely been examined. We investigated the effects of active (exercise) heat- vs. passive heat-induced dehydration, and the kinetics of ad libitum rehydration following each method. Twelve fit participants (five females and seven males) completed four trials in randomised order: DEHydration to −3% change in body mass (∆BM) under passive or active heat stress, and EUHydration to prevent ∆BM under passive or active heat stress. In all trials, participants then sat in a temperate-controlled environment, ate a standard snack and had free access to water and sports drink during their two-hour recovery. During mild dehydration (≤2% ∆BM), active and passive heating caused comparable increases in plasma osmolality (P<sub>osm</sub>: ~4 mOsmol/kg, interaction: <i>p</i> = 0.138) and reductions in plasma volume (PV: ~10%, interaction: <i>p</i> = 0.718), but heat stress per se was the main driver of hypovolaemia. Thirst in DEHydration was comparably stimulated by active than passive heat stress (<i>p</i> < 0.161) and shared the same relation to P<sub>osm</sub> (r ≥ 0.744) and ∆BM (r ≥ 0.882). Following heat exposures, at 3% gross ∆BM, PV reduction was approximately twice as large from passive versus active heating (<i>p</i> = 0.003), whereas P<sub>osm</sub> perturbations were approximately twice as large from EUHydration versus DEHydration (<i>p</i> < 0.001). Rehydrating ad libitum resulted in a similar net fluid balance between passive versus active heat stress and restored PV despite the incomplete replacement of ∆BM. In conclusion, dehydrating by 2% ∆BM via passive heat stress generally did not cause larger changes to PV or P<sub>osm</sub> than via active heat stress. The heat stressors themselves caused a greater reduction in PV than dehydration did, whereas ingesting water to maintain euhydration produced large reductions in P<sub>osm</sub> in recovery and therefore appears to be of more physiological significance. |
| first_indexed | 2024-03-11T08:20:05Z |
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| id | doaj.art-9f6f82f26bf04cc799354f1a6b8bb6b3 |
| institution | Directory Open Access Journal |
| issn | 2072-6643 |
| language | English |
| last_indexed | 2024-03-11T08:20:05Z |
| publishDate | 2023-02-01 |
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| spelling | doaj.art-9f6f82f26bf04cc799354f1a6b8bb6b32023-11-16T22:30:33ZengMDPI AGNutrients2072-66432023-02-0115490410.3390/nu15040904Limited Effect of Dehydrating via Active vs. Passive Heat Stress on Plasma Volume or Osmolality, Relative to the Effect of These Stressors per SeAlexandria Davies0Ashley Paul Akerman1Nancy Jane Rehrer2Simon N. Thornton3James David Cotter4School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin 9016, New ZealandSchool of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin 9016, New ZealandSchool of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin 9016, New ZealandFaculty of Medicine, Université de Lorraine, Inserm, DCAC, F-54000 Nancy, FranceSchool of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin 9016, New ZealandThe physiological, perceptual, and functional effects of dehydration may depend on how it is incurred (e.g., intense exercise releases endogenous water via glycogenolysis) but this basic notion has rarely been examined. We investigated the effects of active (exercise) heat- vs. passive heat-induced dehydration, and the kinetics of ad libitum rehydration following each method. Twelve fit participants (five females and seven males) completed four trials in randomised order: DEHydration to −3% change in body mass (∆BM) under passive or active heat stress, and EUHydration to prevent ∆BM under passive or active heat stress. In all trials, participants then sat in a temperate-controlled environment, ate a standard snack and had free access to water and sports drink during their two-hour recovery. During mild dehydration (≤2% ∆BM), active and passive heating caused comparable increases in plasma osmolality (P<sub>osm</sub>: ~4 mOsmol/kg, interaction: <i>p</i> = 0.138) and reductions in plasma volume (PV: ~10%, interaction: <i>p</i> = 0.718), but heat stress per se was the main driver of hypovolaemia. Thirst in DEHydration was comparably stimulated by active than passive heat stress (<i>p</i> < 0.161) and shared the same relation to P<sub>osm</sub> (r ≥ 0.744) and ∆BM (r ≥ 0.882). Following heat exposures, at 3% gross ∆BM, PV reduction was approximately twice as large from passive versus active heating (<i>p</i> = 0.003), whereas P<sub>osm</sub> perturbations were approximately twice as large from EUHydration versus DEHydration (<i>p</i> < 0.001). Rehydrating ad libitum resulted in a similar net fluid balance between passive versus active heat stress and restored PV despite the incomplete replacement of ∆BM. In conclusion, dehydrating by 2% ∆BM via passive heat stress generally did not cause larger changes to PV or P<sub>osm</sub> than via active heat stress. The heat stressors themselves caused a greater reduction in PV than dehydration did, whereas ingesting water to maintain euhydration produced large reductions in P<sub>osm</sub> in recovery and therefore appears to be of more physiological significance.https://www.mdpi.com/2072-6643/15/4/904hypohydrationheat stressplasma volumeexercisethirst |
| spellingShingle | Alexandria Davies Ashley Paul Akerman Nancy Jane Rehrer Simon N. Thornton James David Cotter Limited Effect of Dehydrating via Active vs. Passive Heat Stress on Plasma Volume or Osmolality, Relative to the Effect of These Stressors per Se Nutrients hypohydration heat stress plasma volume exercise thirst |
| title | Limited Effect of Dehydrating via Active vs. Passive Heat Stress on Plasma Volume or Osmolality, Relative to the Effect of These Stressors per Se |
| title_full | Limited Effect of Dehydrating via Active vs. Passive Heat Stress on Plasma Volume or Osmolality, Relative to the Effect of These Stressors per Se |
| title_fullStr | Limited Effect of Dehydrating via Active vs. Passive Heat Stress on Plasma Volume or Osmolality, Relative to the Effect of These Stressors per Se |
| title_full_unstemmed | Limited Effect of Dehydrating via Active vs. Passive Heat Stress on Plasma Volume or Osmolality, Relative to the Effect of These Stressors per Se |
| title_short | Limited Effect of Dehydrating via Active vs. Passive Heat Stress on Plasma Volume or Osmolality, Relative to the Effect of These Stressors per Se |
| title_sort | limited effect of dehydrating via active vs passive heat stress on plasma volume or osmolality relative to the effect of these stressors per se |
| topic | hypohydration heat stress plasma volume exercise thirst |
| url | https://www.mdpi.com/2072-6643/15/4/904 |
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