Title

Effects of hypohydration on running economy and excess post-exercise oxygen consumption in a mild (23$\sp\circ$C) environment

Date of Completion

January 1997

Keywords

Biology, Animal Physiology|Health Sciences, Recreation

Degree

Ph.D.

Abstract

The purpose of this study was to determine if hydration level had an effect on either running economy at 70% and 85% VO$\sb2$max or recovery from exercise. Ten collegiate distance runners (age 20 $\pm$ 1yr, VO$\sb2$max 66.5 $\pm$ 1ml$\sp\cdot$kg$\sp{-1}$min$\sp{-1}$ and 9.6% body fat) participated in the study. Subjects performed two 10 min euhydrated (EU) and hypohydrated (HY) runs, at both 70% (3.7 $\pm$ 0.1m$\sp\cdot$min$\sp{-1}$) and 85%VO$\sb2$max (4.6 $\pm$ 0.1m$\sp\cdot$min$\sp{-1}$) (EU70%, EU85% and HY70%, HY85%). Pre-exercise hydration indices of urine specific gravity and osmolality, and body weight loss of $-$5.7 and $-$5.5 (HY70% and HY85%, respectively) verified that subjects were dehydrated due to fluid restriction. T$\sb{\rm re}$ was significantly greater during the HY compared to EU sessions. However, the change in $\rm T\sb{re}\ (\Delta T\sb{re}$) was significantly less during the HY compared to EU sessions at 70%VO$\sb2$. Cardiac output (Q) measured via CO$\sb2$ rebreathing technique, stroke volume (SV) and HR were significantly (p $<$ 0.05) smaller during HY, compared to respective EU sessions. However, plasma norepinephrine (NE) was significantly greater during the HY trials. There was no significant difference in either absolute or relative oxygen consumption with respect to hydration level. Post-exercise HR, rectal temperature (T$\sb{\rm re}$), and excess post-exercise oxygen consumption (EPOC) were all significantly (p $<$ 0.05) greater during recovery in the 85%VO$\sb2$ sessions versus the 70%VO$\sb2$ conditions. T$\sb{\rm re}$ at all time points during recovery was significantly (p $<$ 0.05) greater during both HY trials, compared to their respective EU trials. The time of recovery for both EPOC and T$\sb{\rm re}$ was greater for HY (25 min and 35 min for HY70% and HY85%, respectively) sessions compared to EU (10 min and 25 min for EU70% and EU85%, respectively). This delay in EPOC may be in response to the elevated T$\sb{\rm re}$ during the HY conditions. Both T$\sb{\rm re}$ and $\rm\Delta T\sb{re}$ of HY tests during recovery were significantly (p $<$ 0.05) higher than EU at both 70%VO$\sb2$ and 85%VO$\sb2$, indicating that hydration influenced rectal temperature during recovery. In conclusion, hypohydration of more than 5% significantly altered cardiovascular measures but had no affect on anaerobic metabolism or running economy. Similarly, this hypohydration did not influence the magnitude of EPOC, but did prolong the recovery of T$\sb{\rm re}$ and EPOC at both 70%VO$\sb2$ and 85%VO$\sb2$. ^