Influence of ingested fluid volume on physiological responses during prolonged exercise

The effect of different rates of fluid ingestion on heart rate, rectal temperature, plasma electrolytes, hormones and performance was examined during prolonged strenuous exercise conducted at 21 degree C. Seven well-trained males (24 plus or minus 1 yr; 68.6 plus or minus 2.9kg; Vo2 peak=4.69 plus or minus 0.17Lmin-1; mean plus or minus SEM) cycled for 2h at 69 plus or minus 1% Vo2 peak while receiving either no fluid replacement (NF), a volume of water estimated to prevent body weight loss (FR-100=2.32 plus or minus 0.10L2 h-1) or 50% ofthis volume (FR-50=1.16 plus or minus 0.05L2 h-1). The 2-h exercise bout was followed by a ride to exhaustion at a workload estimated to be 90% Vo2 peak. After 2h of exercise, NF was associated with a 3.2 plus or minus 0.1% weight loss, while FR-50 and FR-100 resulted in losses of 1.8 plus or minus 0.1 and 0.1 plus or minus 0.1%, respectively. Compared with FR-100, heart rate and rectal temperature were elevated (P