Sodium Enhances Rehydration, but Not Post-Recovery Performance

Researchers from Loughborough University, England, recently investigated the effects of sports drinks with various sodium concentrations on rehydration after exercise in the heat and on exercise capacity in a subsequent workout. Eight subjects exercised in the heat until they had lost 2 percent of their body mass. They then drank a sports drink contain either no sodium, 31 ml/l sodium, 40 ml/l sodium or 50 ml/l sodium. Urine output was measured to assess fluid retention. After four hours, all of the subjects cycled at 95 percent VO2max to exhaustion. The researchers found that the sports drinks containing 40 and 50 ml/l sodium reduced urine output (hence enhanced rehydration) relative to the other two formulations. However, there were no differences in time to exhaustion.