Purpose To investigate the incidence of hyponatremia and its relationship to plasma copeptin, a surrogate marker for arginine vasopressin (AVP) during 28 days of high-volume rowing training. Methods Thirty rowers from the German junior national team (21 male) were studied during a training camp. Serum sodium ([Na+]), osmolality, and copeptin were measured before the beginning of the camp (day 0), and at days 7, 13, 18, 24, and 28. Daily fluid intake, body weight, urine parameters, and training volume were recorded. Results Seventy percent of the rowers developed hyponatremia at least once. At day 18, training volume and incidence of hyponatremia (43%) were highest. [Na+] decreased from 143 ± 9 mmol/L (day 0) to 135 ± 5 mmol/L (day 18, P < .01). Hyponatremia was correlated significantly with weight gain compared with the previous day (P < .01). Copeptin decreased from day 0 to 28 (male: 6.7 ± 2.8 to 3.6 ± 1.7 pmol/L; P < .05; female: 4.8 ± 1.1 to 3.2 ± 1.5 pmol/L; P < .05), being only partially suppressed. Relative fluid intake per body surface area increased from day 7 (male: 2.79 ± 0.78 L·m-2; female: 2.20 ± 0.70 L·m-2) to day 28 (3.88 ± 0.69 L·m2 and 2.65 ± 0.93 L/m2; P < .05). No athlete developed symptomatic hyponatremia. Conclusion Prolonged high-volume rowing training can lead to a high incidence of hyponatremia. Overdrinking and inadequate suppression of AVP contribute to its development.
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