The Effect of Different Rehydration Drinks on Post-Exercise Electrolyte Excretion in Trained Athletes

Eight well-trained cyclists were dehydrated (median [P₂₅-P₇₅ percentiles]) 3.21 [2.97-3.56] % of body mass by cycling in the heat (28 C). During the first 2 h of recovery, the subjects randomly ingested ad libitum either a caffeinated soft drink (CC), a low Na⁺ mineral water (MW), or an isotonic carbohydrate-electrolyte solution (CES). Fluid intake and urine loss amounted respectively to 2.77 [2.34 - 2.85] kg, 1.00 [0.82-1.20] kg for CC, 2.15 [1.86 - 2.79] kg, 0.96 [0.40 - 1.49] kg for MW, and 2.86 [2.15 - 3.58] kg, 1.10 [0.86 -1.50] kg for CES. Electrolyte retention was calculated from electrolyte intake with the drink and loss with the urine. Consumption of CC and MW which were low in electrolytes resulted in marked loss of Na⁺, K⁺, Cl^-, Mg²⁺ and Ca²⁺ Consumption of CES resulted in Na⁺, Mg²⁺ and Ca²⁺ retention while K⁺ and Cl^- loss were not influenced. The significantly lower Na+, Mg²⁺ and Ca²⁺ loss with CES compared to both CC and MW may be explained by its higher electrolyte content in CES, compared to CC and MW, which only had minor amounts of these electrolytes. Furthermore, it was shown that CC potentiated urinary Mg²⁺ and Ca²⁺ excretion. It is concluded that: 1) Post-exercise MW or CC ingestion results in a negative electrolyte balance, 2) Caffeine containing beverages potentiate Mg²⁺ and Ca²⁺ excretion; 3) Consumption of CES containing moderate amounts of Na⁺, Mg²⁺ and) Ca²⁺ results in sufficient replacement to compensate for urinary losses.

Key words

Exercise-induced dehydration - rehydration - fluid replacement - electrolyte excretion - electrolyte balance