Title

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

Date of Completion

January 1997

Keywords

Biology, Animal Physiology|Education, Physical|Health Sciences, Medicine and Surgery|Health Sciences, Recreation

Degree

Ph.D.

Abstract

The purpose of this study was to assess if intravenous (IV) fluid rehydration, versus oral rehydration, during a brief period (20 min) differentially effects cardiovascular, thermoregulatory, endocrine, and performance factors during exhaustive exercise in the heat. Following dehydration ($-$4% of body weight), eight heat-nonacclimated men (Age - 23.5 $\pm$ 1.2 years, VO$\sb2$max - 61.4 $\pm$ 0.8 ml$\cdot$kg$\cdot$min$\sp{-1}$, % body fat- 13.5 $\pm$ 0.6%) cycled at 70% VO$\sb2$max to exhaustion in 36$\sp\circ$C. Testing (random, cross-over design) included: (1) CONTROL (C), no fluid during the rehydration period, (2) DRINK (D), oral rehydration (0.45% NaCl) equal to 50% of prior dehydration, and (3) IV (0.45% NaCl) equal to 50% of prior dehydration. Thus, in the D and IV treatments subjects began exercise at $-$2% of body weight. Exercise time to exhaustion was not different (p $>$.05) between D (34.86 $\pm$ 4.01 min) and IV (29.48 $\pm$ 3.50 min), but both were significantly (p $<$.05) longer than C (18.95 $\pm$ 2.73 min). Plasma lactate during D was lower (p $<$.05) than C and IV at min 15 and post-exercise, and was greater (p $<$.05) during C than IV at min 5. Percent plasma volume changes during IV were better (p $<$.05) restored than C and D at pre-exercise and 5 min, and different (p $<$.05) from C at min 15. Heart rate during C was greater (p $<$.05) than D and IV values from min 0 through 8, and greater (p $<$.05) than D from min 10 through 14. Rectal temperatures (T$\sb{\rm re}$) during C were greater (p $<$.05) than D and IV measures from min 0 through 12, and T$\sb{\rm re}$ during D was less (p $<$.05) than IV from min 0 through 24. Mean weighted skin temperatures (MWST) during D were less (p $<$.05) than C from min 0 through 12 and less (p $<$.05) than IV from min 4 through 12. No differences (p $>$.05) were found for plasma norepinephrine, ACTH, and cortisol among trials, but all post-exercise values were higher than corresponding pre-exercise values. Thus, no significant performance advantage was found between D and IV, but it appears that certain physiological parameters were better maintained in the D trial. Both D and IV methods of rehydration offered clear performance and physiological advantages over C. ^