摘要
Background: It remains unclear if ad libitum water drinking, as a hydration strategy, prevents exercise-associated hyponatremia(EAH) during prolonged exercise. The aim of this study was to determine the incidence of EAH within the broader context of fluid regulation among soldiers performing a 40-km route-march ingesting water ad libitum.Methods: Twenty-eight healthy male soldiers participated in this observational trial. Pre-and post-exercise body mass, blood and urine samples were collected. Blood samples were assessed for serum sodium([Na+]), glucose, creatinine, urea nitrogen(BUN), plasma osmolality, creatine kinase(CK), and plasma arginine vasopressin(AVP) concentrations. Plasma volume(PV) was calculated using hematocrit and hemoglobin. Urine samples were analyzed for osmolality and (Na+)Water intake was assessed by weighing bottles before, during and after the march. The mean relative humidity was 55.7%(21.9–94.3%) and the mean dry bulb temperature was 27.1°C(19.5°C-37.0°C) during the exercise.Results: Twenty-five soldiers(72±10 kg)(Mean±SD) completed the march in 09:11±00:43(hr:min). Participants consumed 736±259 ml/h of water and lost 2.8±0.9 kg(4.0%±1.4%, P<0.05) of body mass. Significant(pre-march vs. post-march;P<0.05) decreases in serum [Na+](141 mmol/L vs. 136 mmol/L), plasma osmolality(303 m Osmol/kg H2O vs. 298 m Osmol/kg H2O), and serum creatinine(111 μmol/L vs. 101 μmol/L) and urine [Na+](168 mmol/L vs. 142 mmol/L), as well as significant increases in plasma AVP(2 pg/ml vs. 11 pg/ml), plasma CK(1423 U/L vs. 3894 U/L) and urine osmolality(1035 m Osmol/kg H2O vs. 1097 m Osmol/kg H2O) were found. The soldier(72 kg) with the lowest postexercise sodium level completed the march in 08:38. He drank 800 ml/h, lost 2% body mass, and demonstrated(prepost) increases in plasma osmolality(294–314 m Osmol/kg H2O), BUN(20–30 mg/dl), AVP(2–16 pg/ml) and PV(41%). His urine osmolality decreased from 1114 m Osmol/kg H2O to 1110 m Osmol/kg H2O. No participants finished the route-march with a serum [Na+] indicating hypernatremia(range, 134–143 mmol/L).Conclusions: Ad libitum drinking resulted in 4% body mass loss with a 2 mmol/L serum [Na+] reduction in conjunction with high urine osmolality(>1000 m Osmol/kg H2O) and plasma AVP. No single hydration strategy likely prevents EAH, but hypernatremia(cellular dehydration) was not seen despite >2% body mass losses and high urine osmolality.
Background: It remains unclear if ad libitum water drinking, as a hydration strategy, prevents exercise-associated hyponatremia（EAH） during prolonged exercise. The aim of this study was to determine the incidence of EAH within the broader context of fluid regulation among soldiers performing a 40-km route-march ingesting water ad libitum.Methods: Twenty-eight healthy male soldiers participated in this observational trial. Pre-and post-exercise body mass, blood and urine samples were collected. Blood samples were assessed for serum sodium（[Na+]）, glucose, creatinine, urea nitrogen（BUN）, plasma osmolality, creatine kinase（CK）, and plasma arginine vasopressin（AVP） concentrations. Plasma volume（PV） was calculated using hematocrit and hemoglobin. Urine samples were analyzed for osmolality and [Na+]. Water intake was assessed by weighing bottles before, during and after the march. The mean relative humidity was 55.7%（21.9–94.3%） and the mean dry bulb temperature was 27.1°C（19.5°C-37.0°C） during the exercise.Results: Twenty-five soldiers（72±10 kg）（Mean±SD） completed the march in 09:11±00:43（hr:min）. Participants consumed 736±259 ml/h of water and lost 2.8±0.9 kg（4.0%±1.4%, P<0.05） of body mass. Significant（pre-march vs. post-march; P<0.05） decreases in serum [Na+]（141 mmol/L vs. 136 mmol/L）, plasma osmolality（303 m Osmol/kg H2O vs. 298 m Osmol/kg H2O）, and serum creatinine（111 μmol/L vs. 101 μmol/L） and urine [Na+]（168 mmol/L vs. 142 mmol/L）, as well as significant increases in plasma AVP（2 pg/ml vs. 11 pg/ml）, plasma CK（1423 U/L vs. 3894 U/L） and urine osmolality（1035 m Osmol/kg H2O vs. 1097 m Osmol/kg H2O） were found. The soldier（72 kg） with the lowest postexercise sodium level completed the march in 08:38. He drank 800 ml/h, lost 2% body mass, and demonstrated（prepost） increases in plasma osmolality（294–314 m Osmol/kg H2O）, BUN（20–30 mg/dl）, AVP（2–16 pg/ml） and PV（41%）. His urine osmolality decreased from 1114 m Osmol/kg H2O to 1110 m Osmol/kg H2O. No participants finished the route-march with a serum [Na+] indicating hypernatremia（range, 134–143 mmol/L）.Conclusions: Ad libitum drinking resulted in 4% body mass loss with a 2 mmol/L serum [Na+] reduction in conjunction with high urine osmolality（>1000 m Osmol/kg H2O） and plasma AVP. No single hydration strategy likely prevents EAH, but hypernatremia（cellular dehydration） was not seen despite >2% body mass losses and high urine osmolality.
基金
funded by the Director Technology Development,Department of Defence,South Africa
