Fluid Balance, Hydration, and Athletic Performance

Flavia Meyer, Zbigniew Szygula, Boguslaw Wilk, Flavia Meyer, Zbigniew Szygula, Boguslaw Wilk

• Publisher: CRC Press
• Year: 2016
• Print ISBN: 9781032098159
• eBook ISBN: 9781000218961
• Edition: 1
• Topic: Medicina
• Subtopic: Nutrición, dietética y bariatría

Athletes and nonathletes frequently consume too little water or fluids, affecting exercise performance as well as overall health. This book comprehensively reviews the aspects relating to body fluid balance, rehydration, and physical exercise. It provides background on body water balance and turnover, topics related to electrolyte balance, and sweating as the basis for thermoregulatory and fluid homeostasis during exercise. In addition, chapters cover body water balance evaluation and regulation; cardiovascular and metabolic responses to fluid imbalance; effects of dehydration on aerobic power, muscle strength, and cognitive function; fluid intake timing; and optimal beverage selection.

Section III
Special Populations

10 Dehydration and the Young Athlete

Effects on Health and Performance

Anita M. Rivera-Brown

CONTENTS

10.1 Introduction

10.2 Sweat Loss and Involuntary Dehydration during Training and Competition

10.2.1 Maturity and Sex-Related Differences in Sweat Loss

10.2.2 Effects of Environmental Conditions and Heat Acclimatization

10.2.3 Sports-Related Differences in Sweat Loss and Drinking Patterns

10.2.4 Sweat Loss in the Young Female Athlete in the Playing Field

10.2.5 Electrolyte Loss in Sweat

10.2.6 Involuntary Dehydration during Exercise

10.3 Prevalence and Effects of Pre-Training Fluid Deficit

10.3.1 Pre-Training Fluid Deficit and Thermal Strain

10.3.2 Pre-Training Fluid Deficit and Deterioration in Sports Skills

10.3.3 Persistent Fluid Deficit in Athletes Competing in Weight Category Sports

10.4 Effects of Dehydration during Exercise on Health and Athletic Performance

10.4.1 Dehydration and the Risk of Heat Illness during Exercise in Hot Weather

10.4.2 Impairment of Endurance Performance

10.4.3 Impairment of Sports Skills

10.5 Fluid Intake Patterns during Training and Competition

10.5.1 Ad Libitum Intake of Water and Carbohydrate–Electrolyte Drinks

10.5.2 Performance-Enhancing Benefits of Carbohydrate–Electrolyte Drinks

10.6 Fluid Intake Guidelines for Young Athletes

10.6.1 General Guidelines

10.6.2 Sweat Test for Individualized Fluid Intake Recommendations in Children and Adolescents

10.6.3 Prevention of Dehydration during Exercise

10.7 Hydration Knowledge, Attitudes, and Behaviors

10.7.1 Effects of Educational Interventions

10.7.2 Impediments to Adequate Hydration Practices

10.7.3 Strategies to Improve Hydration Practices

10.8 Challenges for Future Research

References

10.1 INTRODUCTION

An optimal state of body hydration is necessary for adequate cardiovascular, thermoregulatory, and mental function during exercise. Young athletes may lose copious amounts of body fluid in sweat during training and competition in sports, especially in hot and humid environments. In addition to starting exercise in a state of fluid deficit, young athletes do not replace enough of the fluid lost through sweat when drinking water ad libitum. The mismatch between the sweat produced and the fluid ingested leads to dehydration which may result in decrements in sports performance and heat illness. The risk is exacerbated during exercise in the heat and by sports uniforms and protective gear that increases the metabolic load and impedes adequate heat dissipation. Of great concern is that dehydration has been implicated in deaths due to heat stroke in adolescent athletes.

Until recently, most of the studies about fluid balance in children and adolescents were performed in the laboratory with untrained subjects. During the last few years, more data have been collected in the field of play in team sports like basketball, soccer, American football, and ice hockey and in long-duration sports like tennis, triathlon, and swimming. This chapter will review data related to fluid and electrolyte deficits during exercise in young female and male athletes and its effects on thermal strain and decrements in endurance performance and sports skills. The benefits of carbohydrate–electrolyte drinks to promote a greater fluid intake and minimize dehydration will be discussed as well as impediments that young athletes face when trying to rehydrate, and ways to facilitate fluid intake before, during, and after exercise. General guidelines provided by leading sports and medical organizations will be presented and a description of the sweat test for the development of individual fluid intake recommendations according to the sweat rate and sweat sodium loss. For the purpose of the chapter, young athletes refers to children and adolescents between the ages of 9 and 18 who train and compete in sports at recreational and elite level.

10.2 SWEAT LOSS AND INVOLUNTARY DEHYDRATION DURING TRAINING AND COMPETITION

The need to cool the body by sweating can lead to a significant loss of body fluid during exercise. Dehydration, the reduction in body water due to the delay in restoring the fluid lost in sweat by drinking, is a common occurrence in young athletes of all ages who train and compete at recreational and elite levels. The risk is higher for those participating in prolonged duration sports in hot climate. In warm and humid environment, there is a greater need to dissipate internal heat and therefore higher sweat production and fluid loss (Yeargin et al. 2010). Sweat rates also vary depending on exercise intensity, level of heat acclimatization, maturity level of the athletes, and the type of clothing and protective equipment worn.

There is typically a mismatch between the sweat produced and the amount of fluid intake that leads to varying levels of body fluid deficit in young athletes in different sports and environmental conditions. Table 10.1 illustrates sweating rates and dehydration levels in young athletes studied in laboratory settings both indoors and outdoors, and in field conditions during training and competition in cool and hot weather. As seen in the table, the majority of these studies have examined non- acclimatized adolescent males ranging in age from 9 to 18 years and scant information is available for young female athletes. Soccer, the most played sport in the world, is where most data have been collected in the playing field in the past 10 years.

Reported sweat rate values are in the range of 0.5–2.0 L/h in young male athletes and 0.4–1.0 L/h in young female athletes. As evidenced by data in Table 10.1, even the youngest athletes may sweat as much as adults and may need as much fluid during training and competition to avoid dehydration. Furthermore, similar to adults dehydration levels may reach 2.5% during training and 3% during competition in hot and humid conditions.

10.2.1 MATURITY AND SEX-RELATED DIFFERENCES IN SWEAT LOSS

The lowest sweating rates have been reported in the youngest athletes (9–14 years old) both in laboratory settings (Bergeron 2009; Iuliano et al. 1998; Rivera-Brown et al. 1999) and during training in the playing field (McDermott et al. 2009; Perrone et al. 2011). Typical values in this age group range from 0.4 to 1.3 L/h, and no negative outcomes related to diminished heat dissipation because of low sweat production have been reported. There is variability in drinking patterns, and dehydration levels among the youngest athletes average about 1%. Differences between genders in this age group are minimal and may be explained, in part, by differences in fitness levels (Wilk et al. 2007). The highest sweating rates are observed in older male adolescents with reported values ranging from 0.7 to 1.7 L/h. The values for female adolescents range from 0.4 to 1.0 L/h. The available data indicate slightly higher sweat rates for male athletes before the age of 15 years and a larger difference between the genders as they mature.

10.2.2 EFFECTS OF ENVIRONMENTAL CONDITIONS AND HEAT ACCLIMATIZATION

In tropical countries, exercise in hot weather cannot be avoided. It is common to see young athletes training at any time of the day. Continued exposure to a hot environment induces physiological adaptations that cause an increased capacity and sensitivity of sweat glands to thermal stimuli that lead to a greater sweat production (Inoue et al. 1999) and a need to drink more fluid to avoid dehydration. Two investigations in the tropical island of Puerto Rico have documented sweat rate values during prolonged intermittent cycling in hot and humid environment in 11- to 14-year-old male (Rivera-Brown et al. 1999) and 9- to 12-year-old female, heat-acclimatized athletes (Rivera-Brown et al. 2008) that are almost twice as high compared to those reported for non-acclimatized, untrained children studied with similar protocols (Bar-Or et al. 1980; Falk et al. 1992; Wilk and Bar-Or 1996; Wilk et al. 2007). A higher sweat production is beneficial since it helps cool the body during exercise, but there is also a greater need for fluid replenishment to avoid the adverse effects of dehydration.

TABLE 10.1
Studies Reporting Sweat Loss and % Dehydration in Young Athletes during Testing in the Laboratory, and While Training and Competing in Different Sports in the Field

M, males; F, females; RH, relative humidity; WBGT, wet bulb globe temperature; PP, pre-pubertal; P, pubertal; W, water; FW, flavored water; CED, carbohydrate–electrolyte drink; JM, junior males; SM, senior males; JF, junior females; SF, senior females.

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10.2.3 SPORTS-RELATED DIFFERENCES IN SWEAT LOSS AND DRINKING PATTERNS

Intermittent intensity sports such as tennis and team sports like basketball, soccer, American football, and ice hockey are stop and go in nature with high intensity exercise bouts and periods of low intensity or no activity. Young athletes participating in these sports show higher sweat rates and dehydration levels during competition than during training, due to the higher intensities of exercise and less focus on hydration (Broad et al. 1996; McDermott et al. 2009). In soccer, for example, adolescent players may spend most of the game running at high intensity and sweat rates of 1.7 L/h have been reported during games in hot weath...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• Preface
• Acknowledgments
• Editors
• Contributors
• Section I The Fundamentals
• Section II Effects of Fluid imbalance on Body Functions and Performance
• Section III Special Populations
• Section IV Recommendations
• Index