Reidratação durante exercício no calor reduz o índice de esforço fisiológico em adultos saudáveis

Marcelo Gava Pompermayer,Rodrigo Rodrigues,Flávia Meyer,Bruno Manfredini Baroni,Raquel De Oliveira Lupion,Marco Aurélio Vaz

doi:10.5007/1980-0037.2014v16n6p629

Abstract

Exercise in the heat leads to physiological alterations that reflect mainly on the cardiovascular system. The physiological strain index (PSI) uses heart rate (HR) and rectal temperature (Tre) to evaluate the cardiovascular strain and lately it has been brought up on the literature. However, few studies used the PSI to evaluate its response following dehydration and rehydration protocols. Thus, the aim of the present study was to verify the effect of rehydration proportional to fluid losses during prolonged exercise in the heat on hydration status, PSI and rating of perceived exertion (RPE) in healthy subjects. Ten volunteers performed two sessions of exercise in heat. The first with fluid restriction until subjects reach 2% of body mass (BM) reduction. The second with rehydration proportional to fluid losses of the first. HR and Tre were monitored during the entire exercise protocol in order to calculate PSI. Subjects also reported their RPE. BM, urine specific gravity (USG) and urine color (UC) were measured to evaluate hydration status. Results demonstrated greater PSI in the fluid restricted trial compared to the rehydration trial from 45 minutes of exercise (p<0,05), and that differences remain significant until the end of the protocol. RPE also presented significant differences between trials (p<0,001). Rehydration strategy was effective to maintain hydration status and attenuate the increase on PSI and RPE, which has important implications for sports, especially those with more than 45 minutes

Highlights

Exercise in the heat causes physiological changes that can affect the functioning of the neuromuscular[1] and cardiovascular[2] systems and impair exercise performance[3]
Loss of body water through sweating can lead to dehydration, which is another aggravating factor in lowered performance, considering that the main form of heat dissipation during exercise is through sweat evaporation[4]
Since it is common that athletes finish and even start a training session or competition already dehydrated, the identification of the hydration status is essential to develop appropriate rehydration strategies

Summary

Introduction

Exercise in the heat causes physiological changes that can affect the functioning of the neuromuscular[1] and cardiovascular[2] systems and impair exercise performance[3]. Loss of body water through sweating can lead to dehydration, which is another aggravating factor in lowered performance, considering that the main form of heat dissipation during exercise is through sweat evaporation[4]. The effects of dehydration can occur even under light to moderate body mass reductions (1-3%)[5]. According to the guidelines of the Brazilian Society of Sports Medicine[6], severe reductions (4-6%) are even more deleterious to performance and can lead to thermal fatigue, while dehydration levels of 7% show risk of thermal shock, coma and death. There are several markers to assess hydration status, non-invasive methods such as change in body mass (BM), urine specific gravity (USG) and urine color (UC) are commonly used in laboratory and field situations due to their low cost and good reproducibility[7]

Objectives

Results

Conclusion