The effect of hypohydration severity on the physiological, psychological and renal hormonal responses to hypoxic exercise.

Evidence of the effect of dehydration on physiological responses to hypoxia is limited. The purpose of this study was to determine the effect of hypohydration severity on physiological, renal hormonal and psychological responses to acute hypoxia. Eight males completed intermittent walking tests under normobaric hypoxic conditions (FI O(2) = 0.13) after completing four separate hypohydration protocols, causing change in body mass of approximately 0% (EU), -1% (H1), -2% (H2) and -3% (H3). Physiological and psychological markers were monitored throughout the 125 min test. Fluid controlling hormones were measured pre and post exposure. Heart rate, core temperature, peripheral arterial oxygen saturation (SpO(2)), minute ventilation and urine osmolality were found to be significantly different between hydration conditions and correlated with Lake Louise Questionnaire score (LLQ) (P < 0.05). LLQ score increased with hypohydration severity above H2 (EU 1.3 +/- 1; H1 1.2 +/- 1; H2 2.7 +/- 2; H3 3.9 +/- 2) (P < 0.001). Antidiuretic hormone and aldosterone increased over the test, but were not different between hydration conditions (P < 0.05). Atrial natriuretic peptide showed no change over time, or with conditions. Therefore, renal hormones are not influenced by hypohydration severity during moderate intensity hypoxic exercise. Hypohydration less than -2% induces greater physiological strain during hypoxic exercise and may cause rise in symptoms such as, fatigue, headache, nausea and lightheadedness.