A sodium drink enhances fluid retention during 3 hours of post-exercise recovery when ingested with a standard meal

The purpose of this study was to examine the efficacy of water and a 50 mmol/L NaCl solution on post-exercise rehydration when a standard meal was consumed during rehydration. Eight healthy participants took part in two experimental trials during which they lost 1.5 ± 0.4 % of initial body mass via intermittent exercise in the heat. Participants then rehydrated over a 60 minute period with water or a 50 mmol/L NaCl solution in a volume equivalent to 150% of their body mass loss during exercise. In addition, a standard meal was ingested during this time which was equivalent to 30% of participants predicted daily energy expenditure. Urine samples were collected before and after exercise and for three hours after rehydration. Cumulative urine volume (981 ± 458 mL and 577 ± 345 mL; P = 0.035) was greater, whilst percentage fluid retained (50 ± 20% and 70 ± 21 %; P = 0.017) was lower during the water compared to the NaCl trial respectively. A high degree of variability in results was observed with one participant producing 28% more urine and others ranging from 18 – 83% reduction in urine output during the NaCl trial. The results of this study suggest that after exercise induced dehydration, the ingestion of a 50 mmol/L NaCl solution leads to greater fluid retention compared with water, even when a meal is consumed post-exercise. Furthermore, ingestion of plain water may be effective for maintenance of fluid balance when food is consumed in the rehydration period