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- Title
THE METHOD OF DEHYDRATION IS RELEVANT WHEN CONSIDERING THE EFFECTS OF DEHYDRATION.
- Authors
Davies, Ali E. N.; Rehrer, Nancy J.; Akerman, Ashley P.; Lucas, Samuel J. E.; Thornton, Simon N.; Cotter, James D.
- Abstract
Background: Passive dehydration has a relatively high reliance on sourcing extracellular fluid, whereas exercise-induced dehydration releases and also produces endogenous water from glycogen stores. Thus physiological and behavioural effects are likely to differ between exercise- vs heat- or fluidrestriction- induced dehydration. Aim: To investigate physiological and behaviour-mediating effects of heat versus exercise-induced dehydration. Design: Controlled-trial, fully repeated measures design; laboratory setting. Methods: Twelve participants completed four trials; they dehydrated to mild extent (3% ΔBM) or rehydrated to prevent ΔBM under passive heat stress (~40°C, 60% RH) or exercise heat stress (cycling intervals at ~90% V⊠O2max in 29°C, 50% RH). Plasma osmolality (Posm), change in plasma volume (ΔPV), and thirst were measured at baseline and 3% gross ΔBM. Respired gas was also measured at 3% gross ΔBM. Results: PV decreased 2.3% more per % ΔBM in passive than exercising dehydration, and was 7.7% lower at 3% ΔBM (13.2 vs 4.4%; p=0.003). But, after subtracting ΔPV across the corresponding rehydration trials, PV reductions were not clearly different between passive and exercise dehydration (1.2 vs 0.4% per % ΔBM; p=0.550). Posm rose by 6 ±5 vs 3 ±7 mOsmol/L during passive vs exercise dehydration (p=0.087). Again, subtracting the corresponding value in the rehydration trial produced unclear differences (4 vs 5 mOsmol/L per % ΔBM; p=0.880). However, 'full rehydration' decreased Posm to 8 ±5 and 11 ±5 mOsmol/L below baseline in passive and active trials, respectively (main effect: p<0.001). Thirst averaged an unclear 1.1 (/9) points higher in active than passive dehydration at 3% ΔBM (p=0.084). Conclusions: PV and perhaps Posm are impacted more by mild (3%) body mass deficit incurred by heat than by exercise. But, such effects may be due primarily to the stressors per se (heat or exercise) than to the mass deficit. Full replacement causes substantial hypotonicity, and thus seems inappropriate.
- Subjects
DEHYDRATION; EXTRACELLULAR fluid; EXERCISE physiology
- Publication
New Zealand Journal of Sports Medicine, 2017, Vol 44, Issue 1, p42
- ISSN
0110-6384
- Publication type
Abstract