Dehydration, the process of losing body water through thermoregulatory sweating, can lead to marked alterations in physiological function and decrements in endurance performance during training and competition in temperate and hot environments.

Impaired endurance capacity in the dehydrated and hyperthermic athlete is associated with physiological strain in multiple systems, organs and tissues involving the brain, heart and skeletal muscles.

Ingesting fluids during prolonged exercise in temperate and hot environments attenuates or even prevents the deleterious effects of dehydration on physiological function and endurance performance.