To determine the effects of a moderate amount of amino acids on the rate of water absorption and availability as a precursor fluid for sweat. Young and healthy (male or female) volunteers will take part in three experimental trials. In each trial, volunteers will be given one of two commercially available sports drinks or a commercially available sport drink with added amino acids in a double-blinded, randomised, crossover design. Each drink will be a single 550 mL bolus. All beverages will be labelled with deuterium (D2O). Trials will be compared for temporal accumulation of deuterium in plasma over the course of 60 minutes. Whole blood measurements of haemoglobin and haematocrit will also be made and plasma volume changes calculated. It is hypothesised that the amino acid trial will increase the rate of fluid absorption.

Inclusion Criteria:

• Generally fit and healthy (determined by health screen questionnaire)
• Recreationally active (minimum 3 hours of physical activity per week including walking)

Exclusion Criteria:

• Any cardiovascular, gastrointestinal, renal or acute/chronic health conditions that may influence the outcomes
• Smoking (including vaping)
• BMI of greater than 30 (combined with a body fat percentage greater than 20%) or BMI lower than 17.5

Double-blind