Considerations for ultra-endurance activities: Part 2 - hydration It is not unusual that those participating in extreme duration events develop a different degree of hypohydration or hyperhydration. For extreme athletes, however, it is important to avoid the performance limiting and potentially fatal consequences of these conditions. During short load times, low impact on the relationship between body mass change and hydration status resulted from the body mass loss due to the oxidation of endogenous fuel storage and water, which supports the intravascular volume generated and released by endogenous fuel oxidation in the oxidation of glycogen. However, these effects have significant impact on longer stresses. In fact, the body mass loses significantly more than 2% in some endurance activities in order to avoid hyperhydration.Therefore, the typical hydration guidelines for avoiding more than 2% body mass loss do not apply to extreme duration activities and may possibly lead to hyperhydration.
Fortunately, achieving balanced hydration must not be complicated during extreme endurance activities, and it has been well demonstrated that this is generally achieved by simply drinking and avoiding excessive sodium supply with the intention of replacing all sodium losses during the load. The whole work can be found under https://pubmed.ncbi.nlm.nih.gov/30056755/