Hydration in exercise: is it necessary to replace all lost body mass?

RODRIGUES, A. P. S.; CASTRO, M. S.; SHIGUEMOTO, G. E.; LINO, A. D. S.; PRESTES, J. Hydration in exercise: is it necessary to replace all lost body mass? Brazilian Journal of Biomotricity, v. 3, n. 4, p. 302-314, 2009. Currently, there is a debate about which percentage of body mass loss can compromise performance and lead to complications to athletes’ health. Most of the drinking guidelines for exercise recommend replacing all the body mass lost during exercise and drinking as much as tolerable to avoid body mass loss over 2%. A greater dehydration can compromise aerobic exercise and cognitive/mentalperformance in warm-hot environments and increase the risk for heat stroke, heat exhaustion and cramps. A“cardiovascular model of thermoregulation” is used to explain the thermal regulation during exercise, whichproposes that sweating reduces body water content, reducing blood flow and increasing the cardiovascularstrain. However, this model has been criticized by many authors, who state that sweating response isregulated by neural mechanisms that are not dependant of the cardiovascular response to the exercise. Theaim of this study was to review the recommendations for fluid replacement during exercise and detail the realnecessity to replace all body mass lost during exercise for better performance. We searched the followingelectronic databases with no data limitation: national and international articles related to the subject, in thescientific portals of Capes, Scielo, PubMed, Science Direct, Highwire and randomized control trails, in English and Portuguese. The inclusion criteria was considered human studies, papers on dehydration and performance, recommendations on hydration and exercise, ingestion of electrolytic beverages in exercise and the effects of hydration status and thermoregulation. The exclusion criteria were: experimental articles and general recommendation for non athletes.