Experimental trials
RPE, thirst, fluid loss
FLUID LOSS
Each participant consumed a diet of his choice before the first trial but was required to eat this same diet before the second trial. The last meal was consumed 2 h before each trial. Participants were also instructed to drink 1 L of a commercial sports drink (6 g LThe trials were planned to consist of cycling for three hours at 55% Participants arrived approximately ~ 1 h before exercise was to start. They first voided their bladders and collected a urine sample, for urine specific gravity (USG) measurement to assess hydration status, and then were weighed. Thereafter, a rectal thermistor was inserted (11 cm past the anal sphincter), cycling clothes were put on and a heart rate monitor was attached. A venous catheter was placed in an antecubital vein and, after sitting for 10 min, the first baseline blood sample and other baseline physiological and subjective measures were taken. Participants then moved into the climate-controlled chamber and began cycling.The beverage was consumed every 15 min (from 15–165 min) at a rate equal to the fluid loss, determined in the pre-trial.Core temperature and heart rate (Polar Electro, Finland) were monitored continuously and recorded at 15 min intervals along with ratings of perceived exertion (RPE) (Borg scale 6–20) (3), body temperature sensation (scale 1–13) and thirst (scale 1–9). Subjective ratings were collected prior to beverage consumption and any blood draw.Nude body mass (after voiding and drying) was also recorded before and after any trips to the toilet and at the end of each trial. Urine was collected, volume and USG of the post-exercise micturition were measured. Some urine samples were not collected. Criteria for terminating a trial before the planned three hours were: (1) a plasma sodium ≤ 130 mmol L