We know little about high-performance adolescent athletes′ fluid balance characteristics and fluid replenishment behaviors. The heterogeneity of hydration status and practices of adolescent athletes deserve efficient approaches to individualize hydration strategies. The present study evaluated and characterized the hydration status and fluid balance characteristics of high-performance adolescent athletes and examined the differences in fluid consumption behaviors during training. 

It included 105 high-performance adolescent athletes (male: 66, female: 39; age 14.1 ± 1.0 y) across 11 sports and assessed their hydration status on three separate occasions—upon rising and before a low and a high-intensity training session (pre-training). 

The study observed-

• 20–44% of athletes were hypohydrated, with 21–44% and 15–34% of athletes commencing low- and high-intensity training in a hypohydrated state, respectively.
• More fluid consumption by hypohydrated athletes.
• K-means cluster analyses showed three clusters: "Heavy sweaters with sufficient compensatory hydration habits," "Heavy sweaters with insufficient compensatory hydration habits," and "Light sweaters with sufficient compensatory hydration habits." 

This study shows that High-performance adolescent athletes who drink ad libitum have compensatory mechanisms to replenish fluid lost during training. The strategy to differentiate athletes by hydration characteristics could aid practitioners in prioritizing future hydration intervention protocols.

Suppiah HT, Ng EL, Wee J, Taim BC, Huynh M, Gastin PB, Chia M, Low CY, Lee JKW. Hydration Status and Fluid Replacement Strategies of High-Performance Adolescent Athletes: An Application of Machine Learning to Distinguish Hydration Characteristics. Nutrients. 2021; 13(11):4073. https://doi.org/10.3390/nu13114073