Effect of an electrolyte beverage on blood hydration markers following 45 minutes of high-intensity exercise

The replacement of sodium during and after high-intensity exercise is necessary for effective restoration of fluid balance. Body water and electrolyte balance are critical for normal cellular function and maintaining adequate blood and plasma osmolality (PO). PURPOSE: To examine the effect of a beverage containing sodium on blood parameters for hydration following 45 minutes of high-intensity exercise. METHODS: 8 healthy, recreationally active males (mean ± SD: age 24.5 ± 3.3 y, height 1.8 ± 0.06 m, BM 78.1 ± 9.4 kg) took part in two main trials, in a randomised crossover design, each separated by 7 days. Following a preliminary heart-rate loading trial, the exercise protocol consisted of exercising for 45 minutes on a cycle ergometer at 75% of heart rate max. Heart-rate monitors were used to assess exercise intensity. Participants ingested beverages containing either 0 (CON) or 22 mmol∙L of sodium (Na+). Beverage consumption was prescribed at 2.5 ml∙Kg of body weight, which was ingested immediately before and every 15 minutes during the main trials. This served to replace 100% of sweat loss during exercise and maintain a state of euhydration. Finger prick blood samples were collected to assess measures of blood lactate (BLac), hematocrit (Hct), hemoglobin (Hb) and plasma osmolality (PO) throughout each trial. Self-perceived measures for exertion, thirst and gut fullness were recorded throughout the main trials. RESULTS: No significant difference was observed in PO following 45 minutes exercise (CON: 297.5 ± 12.0, Na+: 296.5 ± 10.7, p: 0.869). Similarly, there were no differences observed in Values for Hb (CON: 14.8 ± 1.2, Na+:15.3 ± 0.7, p: 0.110) or haematocrit (CON: 44.6 ± 4.1, Na+: 44.8 ± 4.2, p: 0.888) following the completion of the main trial. CONCLUSION: When fluid ingestion maintains a state of euhydration during 45 minutes of high-intensity exercise, the addition of 22 mmol∙L of (Na+) to the beverage has no significant effect on subsequent measures of selected blood hydration parameters, when compared to a Na+ free beverage.