The Effect of Daily Brief Heat Exposures on Heat Acclimation

Dehydration (in kg) was assessed by calculating body mass loss (Tanita Body Composition Analyzer; USA) during heat exposure.

Heart rate (in bpm) was recorded using a heart rate sensor with a chest strap (Polar, Finland).

Systolic and diastolic blood pressure (in mmHg) was measured using with an automatic cuff monitor (Gentle+, Microlife, Switzerland).

Pulse pressure (in mmHg) was calculated by subtracting diastolic blood pressure from systolic blood pressure.

Rate of pressure production (in AU) was calculated by multiplying heart rate , by systolic blood pressure.

The shivering/sweating rate will be evaluated using 7-point scale. The rating of shivering/sweating range from 1 (heavily sweating) to 7 (vigorously shivering), with 4 being neutral.

Thermal comfort will be evaluated using 4-point scale. The rating of thermal comfort range from 0 (neutral) to 3 (very uncomfortable).

Rectal temperature (in °C) was measured using a thermocouple (Rectal Probe, Ellab, Denmark) inserted to a depth of 12 cm past the anal sphincter, skin temperature (in °C) was measured with thermistors (Skin/Surface Probe, DM852, Ellab), and muscle temperature (in °C) was measured using a needle microprobe (MKA; Ellab).

Physiological strain index (PSI) was used to indicate heat strain. PSI = 5 x (Tret - Tre0) x (39.5 - Tre0)^-1+ 5 x (HRt - HR0) x (180 - HR0)^-1, where rectal temperature (Tre) t and heart rate (HR) t are simultaneous measurements taken at the end of the heat exposure and Tre0 and HR0 are the initial measurements.

Oxygen consumption (in mL/min/kg) was measured using Cortex METALYZR® 3B, Leipcig, Germany).

Carbon dioxide output (in mL/min/kg) was measured using Cortex METALYZR® 3B, Leipcig, Germany).

Carbon dioxide output (in mL/min) was measured using Cortex METALYZR® 3B, Leipcig, Germany).

Oxygen consumption (in mL/min) was measured using Cortex METALYZR® 3B, Leipcig, Germany).

The respiratory quotient was calculated by dividing the carbon dioxide output by the oxygen consumption. This ratio was used to assess substrate utilization. The values for fat is assumed as 0.7, for protein is assumed as 0.8 and for carbohydrate is assumed as 1.0.

Ventilation (in L/min) was measured using Cortex METALYZR® 3B, Germany).

Tidal volume (in L) was measured using Cortex METALYZR® 3B, Germany).

Breathing frequency (t/min) was measured using Cortex METALYZR® 3B, Germany).

Height (in cm) was measured using a Harpenden anthropometer set (Holtain Ltd, UK).

Body mass and composition (in kg) was evaluated using Tanita Body Composition Analyzer (USA).

Body mass index (in kg/m^2) will be defined as the body mass divided by the square of the body height.

Body composition (in %) was evaluated using Tanita Body Composition Analyzer (USA).

Maximal oxygen consumption (VO2max) (in mL/min/kg) was defined through a maximal incremental exercise test conducted on an electromechanically braked cycling ergometer (Ergometrics-800S; Ergoline Medical Measurement Systems, Germany) and was measured on a breath-by-breath basis using a stationary MetaLyzer® 3B spiroergometry system (Cortex Biophysik GmbH, Germany).

Serum prolactin (in ng/mL) was measured using enzyme-linked immunosorbent assay kits and a Spark multimode microplate reader (Tecan, Austria).

Serum 17beta-estradiol (in pg/mL) was measured using enzyme-linked immunosorbent assay kits and a Spark multimode microplate reader (Tecan, Austria).

Serum progesterone (in ng/mL) was measured using enzyme-linked immunosorbent assay kits and a Spark multimode microplate reader (Tecan, Austria).