Research has shown that both dehydration and overhydration can impact endurance exercise performance. Studies suggest that voluntary dehydration may not significantly affect adaptation for team sports or endurance events. However, limiting dehydration to 2% body mass loss can help maintain physiological and perceptual functions in high-performance athletes. Endurance performance may not be significantly affected by dehydration in exercises lasting less than 1 hour, but athletes are recommended to mouth-rinse with sports drinks during such exercises. A 2% body mass loss due to dehydration can impair endurance performance across various types and durations of exercise. Without proper fluid replacement during exercise, both physiological function and endurance capacity can be significantly decreased. Scientific research has shown that dehydrated endurance athletes, such as triathletes and marathoners, can experience a performance drop of 7% to 60%. Hydration plays a crucial role in affecting physical performance, as it can compromise cardiovascular and thermoregulatory systems. The latest research in this field suggests that a better understanding of the connection between dehydration and endurance performance is necessary.