Fluid ingestion does not influence intense 1-h exercise performance in a mild environment

Purpose: It is generally recommended that fluid be ingested during exercise at a rate that prevents body mass loss and prevents dehydration. It is, ho wever, not known whether these recommendations are Valid during intense end urance exercise in a mild environment. The purpose of this study was to exa mine the effect of fluid ingestion volume on heart rate (HR), rectal temper ature, plasma electrolytes, and performance during intense endurance exerci se at 21 degrees C. Methods: Eight well-trained men (26 +/- 1 yr; 79.6 +/- 3.5 kg; (V) over dot O-2peak = 5.05 +/- 0.17 L.min(-1); mean +/- SEM) cycle d for 45 min at 80 +/- 1% (V) over dot O-2peak while receiving either no fl uid replacement (NF), a volume of water that prevented body mass loss (FR-1 00 = 1.47 +/- 0.05 L), or 50% of this volume (FR-50 = 0.72 +/- 0.03 L). The 45-min exercise bout was followed immediately by a 15-min "all-out" perfor mance ride. Results: NF was associated with a 1.9 +/- 0.0% body mass loss, while FR-50 and FR-100 resulted in losses of 1.0 +/- 0.1% and 0.0 +/- 0.1%, respectively. Although values tended to be higher in NF, fluid ingestion h ad no significant effect on HR or rectal temperature during exercise. Reduc tions in plasma volume and increases in plasma sodium and potassium concent rations during exercise were largely unaffected by fluid ingestion. RPE inc reased to a similar extent during exercise in the three trials while a mild increase in the degree of stomach bloating/fullness was evident in FR-100. Work completed during the 15-min performance ride was similar in the three trials (NF: 233 +/- 8, FR-50: 267 +/- 8, FR-100: 269 +/- 9 kJ). Conclusion s: There appears to be little benefit from ingesting water during intense 1 -h cycling exercise in mild environmental conditions since such ingestion h as no significant effect on IIR, body temperature, plasma volume, plasma el ectrolytes, or performance.