Effects of oral and intravenous rehydration on ratings of perceived exertion and thirst.

The purpose of this investigation was to compare the effects of oral and intravenous saline rehydration on differentiated ratings of perceived exertion (RPE) and thirst. Eight men underwent three randomly assigned rehydration treatments following a 2- to 4-h exercise-induced dehydration bout to reduce body weight by 4%. Treatments included 0.45% saline infusion (i.v.), 0.45% saline oral ingestion (ORAL), and no fluid (NF). Following rehydration and rest (2 h total), subjects walked at 50% VO2max for 90 min at 36 degrees C (EX). Central RPE during ORAL was lower (P < 0.05) than i.v. and NF throughout EX. Local RPE during NF was higher (P < 0.05) than i.v. and ORAL at minutes 20 and 40 of EX and overall RPE during NF was higher (P < 0.05) than ORAL at minutes 20 and 40 of EX. Significant correlations were found between overall RPE and mean skin temperature for i.v. (r = 0.72) and NF (r = 0.75), and between overall RPE and thirst ratings for i.v. (r = 0.70). Thirst ratings were not different among trials at postdehydration. Following rehydration, thirst was higher (P < 0.05) during NF than i.v. and ORAL and lower (P < 0.05) during ORAL than i.v. at all subsequent time points. Results suggest that oral rehydration is likely to elicit lower RPE and thirst ratings compared with intravenous rehydration.