THE EFFECT OF DIFFERENT REHYDRATION DRINKS ON POSTEXERCISE ELECTROLYTE EXCRETION IN TRAINED ATHLETES

Eight well-trained cyclists were dehydrated (median [P-25-P-75 percent iles]) 3.21 [2.97-3.56]% of body mass by cycling in the heat (28 degre es C). During the first 2 h of recovery, the subjects randomly ingeste d od libitum either a caffeinated soft drink (CC), a low Na+ mineral w ater (MW), or an isotonic carbohydrate-electrolyte solution (CES). Flu id 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. Electrol yte retention was calculated from electrolyte intake with the drink an d loss with the urine. Consumption of CC and MW which were low in elec trolytes resulted in marked loss of Na+, K+, Cl-, Mg2+ and Ca2+. Consu mption 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 high er electrolyte content in CES, compared to CC and MW, which only had m inor 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 bal ance, 2) Caffeine containing beverages potentiate Mg2+ and Ca2+ excret ion; 3) Consumption of CES containing moderate amounts of Na+, Mg2+ an d Ca2+ results in sufficient replacement to compensate for urinary los ses.