New Insights Into the Impact of Dehydration on Blood Flow and Metabolism During Exercise

Steven J. Trangmar; José González-Alonso

Disclosures

Exerc Sport Sci Rev. 2017;45(3):146-153. 

In This Article

Abstract and Introduction

Abstract

Exercise-induced dehydration can lead to impaired perfusion to multiple regional tissues and organs. We propose that the impact of dehydration on regional blood flow and metabolism is dependent on the extent of the cardiovascular demand imposed by exercise, with the greatest physiological strain seen when approaching cardiovascular and aerobic capacities.

Introduction

Whole-body dehydration, associated with reductions in plasma, interstitial, and intracellular volume, generally occurs when people exercise for prolonged periods without fluid replacement. The progressive fall in total body fluid poses a marked challenge to thermoregulation and cardiovascular control. This is because dehydration attenuates sweat rate and skin blood flow[25,42] and reduces active muscle and systemic blood flow and mean arterial pressure,[11,14,15,23] which result in significant increases in rate of body heat storage, core hyperthermia, and physiological strain. A compromised active muscle perfusion when dehydrated or hyperthermic has been implicated as an important factor in the chain of events leading to eventual fatigue because of its negative impact on oxygen supply.[11,12] Based on an earlier series of investigations,[11,14,15] previously discussed in this journal,[7] our related findings from recent work indicate that the detrimental effects of dehydration and hyperthermia are not necessarily uniform among the tissues of the human body and across a range of exercise intensities and modalities.[36,44,47,48] Our current hypothesis is that the cardiovascular challenge of dehydration, evident during strenuous whole-body exercise, does not occur at rest, during isolated muscle group exercise, or low-intensity whole-body exercise. Moreover, essential tissues of the human body (e.g., the brain) are still susceptible to the combined cardiovascular challenge of dehydration and exhaustive exercise but seem to be better able to defend their metabolism in the face of compromised oxygen delivery than active skeletal muscle.

Throughout this article, and unless otherwise stated, the term "dehydration" is referred to as a loss of body fluids (e.g., equivalent to a body mass loss of ~3%–5%) in combination with elevations in body core temperature (hyperthermia). This is because many of the studies in the literature induced dehydration through prolonged exercise in the heat. For reference, studies invoking hyperthermia without dehydration are presented and distinguished from those combining body hyperthermia and dehydration, respectively. The primary data presented in this review are from studies investigating the impact of dehydration and concomitant hyperthermia on physiological function in young, healthy, trained men undertaking knee-extensor and cycling exercise. Comparable cardiovascular data currently are limited for other population groups (e.g., young untrained, older trained and untrained, and women); however, it is reasonable to suggest that the physiological principles, explored subsequently, also would be applicable to those populations.

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