2.5. Experimental Protocol
dehydration, dry
DEHYDRATION, HEAT
Upon arrival at the laboratory for each trial, participants voided their bladders before a baseline BM was recorded (±0.02 kg, Wedderburn Scales Ltd., Dunedin, New Zealand), either nude or wearing underwear. The ∆BM from the baseline was used to estimate the level of dehydration after correcting for fluid intake. Following the insertion of a rectal thermistor, a baseline blood sample was collected after being seated for at least 10 min in an upright posture [Passive heat stress entailed sitting sedentary in 40 °C and 60% RH for the first 20–30 min in a hot water bath (~43 °C) to expedite the rise in TAt each % ∆BM during DEHydration trials (Once a −3% gross ΔBM was achieved, participants returned to the adjacent laboratory (25–27 °C, 33–40% RH) for recording of their corrected ΔBM relative to baseline, i.e., once toweled dry and skin thermistors removed. A capillary blood sample was collected after being seated for ~15–20 min to ensure their posture and physiological state at −3% ∆BM were comparable with baseline conditions and between experimental trials. Participants were provided with a standard meal (250 g) of lasagna (protein: 37 g, fat: 40, CHO: 98 g, sodium: ~500 mg) or macaroni and cheese (protein: 37 g, fat: 40, CHO: 105 g; sodium: ~500 mg) before having ad libitum access to 2500 mL of fluid (~5 °C; water or sports drink, in different bottles: sports drink sodium 540 mg/L, osmolality: ~285 mOsmol/kg), which were weighed before and after to determine the volume of fluid ingested (±0.001 kg, Type 1574, Sartorius, Gottingen, Germany) over the 2-h rehydration period. Participants were then given a post-trial food and urine diary to record food and fluid intake along with urine output (volume, time, and colour). Participants returned 24 h after the start time of their trial for follow up measurements (