Why was this study done?

The timing of fluid replacement is of great interest to competitive athletes. This study was designed to understand how starting fluid replacement immediately upon exercising compared to starting fluid later and how these strategies would affect time to fatigue in competitive cyclists.

What did the study find?

A fluid replacement (including glucose and electrolytes) strategy that started later (90 minutes into exercise) was more successful at forestalling fatigue than one that started immediately.

Glucose-Electrolyte Ingestion: Influence on Endurance Factors in Highly Trained Female Cyclist
Sirotniak AC, Foster VL. Med Sci Sports Exerc, 1992. 24(5):S121.
PDF Abstract: Med Sci Sports Exerc, 1992.