Influencia de la ingesta de bebidas con diferente osmolaridad, sobre el tipo de deshidratación y las concentraciones de electrolitos, plasmáticos y urinarios, durante una actividad física de alta intensidad y larga duración

objetive: to establish the effects on plasma osmolality and serum and urine electrolyte composition of the intake of three beverages with different osmolarities after a high intensity, long duration run in endurance athletes. methodology: nine long-distance runners performed 88 minutes of running on a treadmill (1% of inclination at a speed equivalent to 80% of the reserve heart rate), followed by 90 minutes of recovery; at the beginning there was no fluid replacement -dehydrated treatment- (dh); later on three sequential and randomized procedures were used, drinking equal volumes of one of three beverages, namely: hyperosmolar (hyper), hyposmolar (hypo) and isosmolar (iso). plasmatic osmolality and urinary osmolarity were measured by means of standard laboratory techniques, before and after the running period. results: in dh, at the end of the exercise period, a hypernatremic and hyperchloremic dehydration was observed (p < 0.05); throughout the procedure there was hyperkaliemia (p < 0.011); at the end of the recovery period there were an urinary volume reduction (p< 0.05) and hyperkaliuria (p < 0.001). partial replacement of the water loss, with beverages of different osmolarity, attenuated dehydration and the plasmatic changes of sodium and chloride, but not those of potassium at the end of the exercise period, or those of urinary potassium at the end of the recovery period. all studied variables, except for the urinary concentration of chlorine, were associated with the duration of the physical activity (p < 0.03); only the weight loss showed time-treatment association (p < 0.001). there were correlations with all treatments and during all procedures between plasmatic sodium and chloride (r: 0.85-0.96) and between urinary osmolarity and sodium (r: 0.50-0.83). conclusions: at the end of the physical activity there was, in the dh group, a hypernatremic, hyperchloremic and hyperkaliemic type of dehydration; partial replacement of the water loss, although in the low