Comparing the Effects of Water, Sodium-Potassium, and Potassium-Rich Solutions on Fluid Balance and Thermal Strain Following Exercise in the Heat: A Randomized Triple-Blind Crossover Study.

Exercise in the heat perturbs human physiology through elevated core temperature, fluid loss, and cardiovascular strain. While fluid intake can mitigate these effects, the electrolyte composition of hydration solutions may improve rehydration efficacy. This study evaluated whether hydration strategy modulates thermal strain, inflammation, and performance during and after exercise in a hot environment, comparing three different fluid solutions: water, sodium-potassium drink, and coconut water. Twelve participants (seven males) completed a randomized, triple-blind crossover trial. Measures included handgrip strength, countermovement jump, tympanic temperature, thermal sensation, discomfort, body mass, body water percentage, heart rate, and total leukocyte count. Participants were randomly assigned 300 ml of one of three solutions before cycling for 60 min at 1.5 W/kg in ∼33 °C conditions. Additional 300-ml doses were consumed postexercise at 0, 30, and 60 min; measures were taken at each time point before solution consumption and at 90-min postexercise. Following exercise in the heat, a significant main effect for time was observed for all outcomes: thermal responses, heart rate, body mass and body water (p < .001); fatigue (p < .001); and leukocyte count (p = .016), indicating a strong physiological response to heat stress. However, no significant differences were observed between hydration strategies (p ≥ .152) for all measures. In conclusion, exercise in the heat elicited significant thermal strain, fatigue, and inflammation, independent of hydration strategy. Electrolyte composition did not significantly alter responses when fluid intake was controlled, highlighting the need for further research.