Free-living, continuous hypo-hydration, and cardiovascular response to exercise in a heated environment

Abstract

Chronic dehydration (DEH) and heat stress combined with poor cardiovascular (CV) health may influence physiological responses to exercise. We examined the effects of free-living induced hypo-hydration on physiological responses to exercise in a heated environment and whether resting CV health is related to these changes. Participants (N = 16, 20.6 ± 1.2 years) were randomized to 3 days of voluntary fluid restriction (DEH) or intake (hydration [HYD]) followed by an exercise bout. CV health was assessed by flow-mediated dilation (FMD), pulse wave analysis, and heart rate variability (HRV). HYD was assessed by weight, urine color, and specific gravity (USG). Exercise trials were conducted in a heated environment (30.3 ± 0.8°C, 27.4 ± 7.4% RH) on a cycle ergometer for 30 min. Heart rate (HR), weighted skin (T_sk ) and mean body temperature (T_b ) and skin blood flow (SBF) were assessed during exercise. Pre-exercise weight (P < 0.005), urine color, and USG (P < 0.001) were different in between trials. HR was greater in DEH (153 ± 26 bpm) versus HYD (144 ± 23 bpm, P = 0.02) after exercise. No group differences were found, but a time interaction P < 0.001) for all temperature responses and time-by-trial interaction for T_re (P < 0.01) and T_sk (P < 0.001) was observed. Greater changes in T_re (P = 0.02) and T_sk (P < 0.01) were associated with increased FMD. Free-living, continuous DEH alters weight, blood, and urine markers of HYD as well as HR response during exercise. Resting CV health was related to increased change in T_re and T_sk , suggesting CV health plays a role in the mechanism of heat dissipation when DEH even in college-age men and women.

Keywords: Cardiovascular; heat stress; hydration; thermoregulation.

Figure 1

Crossover study design and randomization scheme following baseline testing. Participants were randomly assigned to dehydration (DEH) or hydration (HYD) protocols. Measurements were taken at pre‐intervention, pre‐exercise and post‐exercise.

Figure 2

Mean temperature changes (°C) for a 30‐min exercise bout. T _re rectal temperature, T _sk weighted skin temperature, and T _b total body temperature. Main effect time for all temperatures (P < 0.001) and T _re (P < 0.001) and T _sk (P < 0.01) time and trial interaction.

Figure 3

Relationship of brachial artery flow mediated dilation (FMD) to change in rectal (T _re) and mean body (T _b) after a 30‐min exercise bout. Significant correlation was found between FMD and T _re (P = 0.04) and T _b (P < 0.01).