ABSTRACT
To fully understand the regulation of body fluid balance and the importance of fluid and electrolyte replacement during and after exercise, an understanding of the fluid compartments and forces that affect the movement between these compartments is necessary. This chapter focuses on the factors that maintain fluid within the separate compartments of the body and how physiologic changes during heat stress and exercise alter these compartments. It explores the principles that govern fluid homeostasis and provides the basic concepts necessary to decipher information from the volumes of research papers on fluid replacement. Fluid and electrolyte replacement should occur throughout exercise in an attempt to match water losses from sweating. Without adequate fluid replacement during exercise, progressive fluid losses will undermine thermoregulation and result in increasing loss of performance. Replacement of fluid and electrolytes in preparation for, during, and after exercise is of paramount concern to the athlete.
