Title

Intravenous versus oral rehydration: Physiological and performance considerations for exercise in the heat

Date of Completion

January 2010

Keywords

Health Sciences, Recreation|Biology, Physiology

Degree

Ph.D.

Abstract

Intravenous rehydration (IV) is a widely accepted practice in athletic settings. It is believed rapid plasma volume restoration enhances cardiovascular, thermoregulatory, and performance benefits by stimulating recovery rates. Limited research has not demonstrated a clear advantage of IV over oral rehydration (ORAL). To date no study has incorporated ad libitum or half-IV and half-ORAL (I+O). The purpose of this study was to study the effects of mode of rehydration on performance, and perceptual and stress-hormone response to a subsequent maximal-intensity exercise-heat challenge (EHC). Ten healthy, non-smoking, active men (age 23.3 ± 1.1 y; height, 177.8 ± 2.8 cm; body mass, 81.4 ± 1.3 kg; body fat, 11.0 ± 1.0%; V˙O 2max, 58.8 ± 1.3 ml·kg−1·min −1) completed four trials consisting of dehydration by −4% body mass, rehydration to −2% body mass (via ADL, ORAL, IV or I+O), and EHC [25 minute run at 60% V˙O2max, maximal effort 0.5 mile run, five minutes rest and five minutes self-paced repetitive box lifting (RBL)]. Ratings of perceived exertion, thirst, thermal and muscle pain sensation were obtained immediately before EHC, immediately post 0.5 mile run (RUN), and immediately post RBL (IP). Catecholamines and cortisol (CORT) were analyzed at baseline, post-exercise dehydration, RUN, IP, and 15 minutes post RBL (+15). Half-mile run time was not significantly different among trials (213 ± 12.4 s), but I+O resulted in significantly more boxes lifted (52 ± 3.5) compared to ADL (47 ± 3) and ORAL (46 ± 3.7). Perceptual responses were not different among trials. RPE peaked at RUN (17.8 ± 0.5). Thirst and pain peaked at IP (8.1 ± 0.3, and 4.7 ± 0.7, respectively). Catecholamine response was not significantly different among modes of rehydration, but significantly increased during EHC (RUN, 21.648 ± 2.346 nmol·L−1; IP, 15.451 ± 2.010 nmol·L−1). CORT response was significantly lower during I+O compared to all other trials. Although prolonged heat exposure diminshed any differences in perceptual response due to mode of rehydration during subsequent EHC. These results suggest a synergistic effect of I+O on later stages of EHC, and CORT response. These benefits may be increased if athletes are euhydrated prior to exercise. ^