Intravenous versus oral rehydration during a brief period: responses to subsequent exercise in the heat

Purpose: The purpose of this study was to assess whether a brief period (20 min) of intravenous (IV) fluid rehydration versus oral rehydration differe ntially affects cardiovascular, thermoregulatory, and performance factors d uring exhaustive exercise in the heat. Methods: Following dehydration (-4% of body weight), eight nonacclimated highly trained cyclists (age = 23.5 +/ - 1.2 yr; (V) over dot O-2peak = 61.4 +/- 0.8 mL.kg.min(-1): body fat = 13. 5 +/- 0.6%) rehydrated and then cycled at 70% (V) over dot O-2peak to exhau stion in 37 degrees C. Rehydration (randomized, cross-over design) included : 1) CONTROL (no fluid), 2) DRINK (oral rehydration, 0.45% NaCl) equal to 5 0% of prior dehydration, and 3) IV (intravenous rehydration, 0.45% NaCl), e qual to 50% of prior dehydration. Thus, in the DRINK and IV treatments subj ects began exercise (EX) at -2% of body weight. Results: Exercise time to e xhaustion was not different (P = 0.07) between DRINK (34.9 +/- 4 min) and I V (29.5 +/- 3.5 min), but both were significantly (P < 0.05) longer than CO NTROL (18.9 +/- 2.7 min). Plasma volume was better (P +/- 0.05) restored du ring IV than CONTROL and DRINK at pre-exercise and 5 min EX, but different (P < 0.05) from only CONTROL at 15 min EX. Plasma lactate during DRINK was lower (P < 0.05) than TV at 15 min EX and postexercise. Heart rare during C ONTROL was greater (P < 0.05) than DRINK and IV from 0-8 min EX, and greate r (P < 0.05) than DRINK from 10-14 min EX. Rectal temperature during DRINK was less (P < 0.05) than IV from 0-24 min EX. Mean weighted skin temperatur e during DRINK was less: (P < 0.05) than IV from 4-12 min EX. Conclusions: Thus, despite no statistically significant performance differences between DRINK and IV, it appears that certain physiological parameters were better maintained in the DRINK trial, and the trend toward performance differences may be important to elite athletes.