Time Course of Adaptive Responses in Humans During a 16-day Hot and Cold Acclimation Program, and Its Effect on Health-related Indicators

Change in body mass index (kg/m^2)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

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

Change in ventilation (l/min)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Ventilation (in l/min) will be measured using Cortex METALYZR® 3B, Leipcig, Germany).

Change in heart rate variability (ms)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

R-R intervals (in ms) in supine resting will be recorded using a Polar heart ratesensor (Finland) and simultaneously transferred to Polar Pro Trainer 5 software (Finland)

Change in body mass and body composition (kg)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Body mass and composition (in kg) will be evaluated using Tanita Body Composition Analyzer (Japan).

Change in skinfold thickness (mm)

时间窗: Before acclimation (1st day), 2 days and 2 weeks after the end of acclimation (44 th and 51st day)

Skinfolds thickness (in mm) will be measured using a skinfold caliper (Saehan, Korea) at 10 sites and the mean subcutaneous fat thickness will be calculated.

Change in body surface area (m^2)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

The participant's body surface area (BSA) (in m\^2) will be estimated using the following equations: BSA = 128.1 ×weight\^0.44 × height\^0.60 for males and BSA = 147.4 ×weight\^0.47 × height\^0.55 for females.

Change in substrate oxidation

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Oxygen consumption (VO2) and carbon dioxide (VCO2) output will be measured using Cortex METALYZR® 3B, Leipcig, Germany), and the respiratory quotient (RQ = VCO2 / VO2) will be computed to determine substrate utilisation. The RQ values for fat is assumed as 0.7, for protein is assumed as 0.8 and for carbohydrate isassumed as 1.0.

Change in substrate oxidation (g/day)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Carbohydrate and fat oxidation (in g/day) will be measured using Cortex METALYZR® 3B, Leipcig, Germany).

Change in breathing frequency (t/min)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Breathing frequency (in t/min) will be measured using Cortex METALYZR® 3B, Leipcig, Germany).

Change in resting energy expenditure (kcal/day)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

The resting energy expenditure (REE; in kcal/day) will be computed using the following equation: REE = \[3.941 × (VO2) + 1.106 × (VCO2)\] × 1440

Change in heart rate variability (time domain) (ms)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Heart rate variability data will be analyzed using Kubios heart rate variability analysis software (Finland). In the time domain that reflects general heart rate variability (HRV), the standard deviation of normal-to-normal intervals (SDNN; estimate of overall HRV) and the root mean square of successive differences (RMSSD; estimate of short-term components of HRV will be assessed (in ms).

Change in heart rate (bpm)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Heart rate (in bpm) will be recorded using a heart rate sensor with a chest strap (Polar, Finland) or Physioflow hemodynamic monitor (France).

Change in stroke volume (ml)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Stroke volume (in ml) will be recorded using Physioflow hemodynamic monitor (France).

Change in cardiac output index (l/min//m^2)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Cardiac output (in l/min/m\^2) will be recorded using Physioflow hemodynamic monitor (France).

Change in metabolic heat production (W)

时间窗: during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days)

The metabolic heat production (MHP; in W) will be computed using the equation: MHP = (281.65 + 80.65 × RQ) × VO2.

Change in blood pressure (mmHg)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Systolic and diastolic blood pressure (in mmHg) will be measured using PROVIEW 10 Compact Patient Monitor (Germany).

Change in heart rate variability (time domain) (Ln)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Heart rate variability data will be analyzed using Kubios heart rate variability analysis software (Finland). In the time domain that reflects general heart rate variability (HRV), the standard deviation of normal-to-normal intervals (SDNN; estimate of overall HRV) and the root mean square of successive differences (RMSSD; estimate of short-term components of HRV) will be assessed and logarithmically transformed (Ln) to correct the skewness of distribution.

Change in mean arterial pressure (mmHg)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

The mean arterial pressure (MAP; in mmHg) will be estimated using the formula: MAP = DP + 1/3(SP - DP) or MAP = DP + 1/3(SP - DP), where SP is systolic bood pressure and DP is diastolic blood pressure.

Change in heart rate variability (frequency domain) (Ln)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

In the frequency domain that measures the more specific contribution of the autonomic nervous system branch, low-frequency (LF; estimates sympathetic and parasympathetic activity) and high-frequency (HF; estimates parasympathetic activity) powers will be assessed and logarithmically transformed (Ln) to correct the skewness of distribution.

Change in heart rate variability (frequency domain) (ms^2)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Heart rate variability data will be analyzed using Kubios heart rate variability analysis software (Finland). In the frequency domain that measures the more specific contribution of the autonomic nervous system branch, low-frequency (LF; estimates sympathetic and parasympathetic activity) and high-frequency (HF; estimates parasympathetic activity) powers in absolute units (in m\^2) will be assessed.

Change in ventricular ejection fraction (percent)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Ejection fraction (in percent) will be recorded using Physioflow hemodynamic monitor (France).

Change in end diastolic volume (ml)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

End diastolic volume (in ml) will be recorded using Physioflow hemodynamic monitor (France).

Change in salivary cortisol concentration (µg/dl)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

The saliva samples will be collected to measure cortisol level (in µg/dl) using an ELISA kits and a Spark multimode microplate reader (Tecan, Austria)..

Change in stroke volume index (ml/m^2)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Stroke volume index (in ml/m\^2) will be recorded using Physioflow hemodynamic monitor (France).

Change in cardiac output index (l/min)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Cardiac output (in l/min) will be recorded using Physioflow hemodynamic monitor (France).

Change in contractility index

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Contractility index will be recorded using Physioflow hemodynamic monitor (France).

Change in testosterone concentration (µg/dl)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

The saliva samples will be collected to measure testosterone level (in µg/dl) using an ELISA kits and a Spark multimode microplate reader (Tecan, Austria).

Change in early diastolic filling ratio (percent)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Early diastolic filling ratio (in percent) will be recorded using Physioflow hemodynamic monitor (France).

Change in female sex hormones concentration (pg/mL)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

The venous 17beta-estradiol and progesterone (in pg/mL), follicle stimulating hormone and luteinizing hormone will be measured using an ELISA kits and a Spark multimode microplate reader (Tecan, Austria).

Change in anxiety and depression (points)

时间窗: Before acclimation (1st day), 2nd day and 2 weeks after the end of acclimation (44th and 51st days)

The level of anxiety and depression (in points) will be defined using Hospital Anxiety and Depression scale. Scale scores range from 0 to 21, with higher scores indicating more severe symptoms.

Change in cytokines concentrations (pg/ml)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

The venous tumor necrosis factor alpha, interleukin-6 and IL-1 beta (in pg/ml) will be measured using an ELISA kits and a Spark multimode microplate reader (Tecan, Austria).

Change in complete blood count (10^9/L)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Complete blood count with 5 different white blood count components (absolute neutrophils, lymphocytes, monocytes, eosinophils, basophils) analysis (in 10\^9/L) will be performed using an automated Mythic 60 hematology analyzer (Switzerland).

Change in complete blood count (percent)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Complete blood count with 5 different white blood count components (absolute neutrophils, lymphocytes, monocytes, eosinophils, basophils) analysis (in percent) will be performed using an automated Mythic 60 hematology analyzer (Switzerland).

Change in glucose tolerance (mmol/l)

时间窗: Before acclimation (1st day), 2nd day and 2 weeks after the end of acclimation (44th and 51st days)

The glucose concentration (in mmol/l) will be measured using a On-call GK dual meter (Acon Laboratories, USA).

Change in catecholamines concentration (ng/ml)

时间窗: Before acclimation (1st day),during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

The venous adrenaline and noradrenaline concentrations (in ng/ ml) will be measured using enzyme-linked immunosorbent assay kits and a Spark multimode microplate reader (Tecan, Austria).

Change in insulin concentration (μIU/ml)

时间窗: Before acclimation (1st day), 2nd day and 2 weeks after the end of acclimation (44th and 51st days)

The venous insulin concentrations (in μIU/ml) will be measured using enzyme-linked immunosorbent assay kits and a Spark multimode microplate reader (Tecan, Austria)

Change in cold strain index

时间窗: During baseline provocative cold test (8th or 15th day), during acclimation (from 22 to 37th days), during repeated provocative cold test (41st or 42nd days)

A cold strain index (CSI) will be used to indicate cold strain. CSI = 6.67 x (Tre t - Tre 0) x (35 - Tre 0)\^-1 + 3.33 x (Tsk t - Tsk 0) x (20 - Tsk 0)\^-1, where rectal temperature (Tre) 0 and skin temperature (Tsk) 0 are initial measurements and Tre t and Tsk t are simultaneous measurements taken at the end of the cold exposure.

Change in pain sensations

时间窗: During baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st or 42nd day)

The pain sensation will be evaluated using numeric pain scale ranging from 0 (no pain) to 10 (worst possible pain).

Change in thermal sensations (points)

时间窗: During baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st or 42nd day)

The thermal sensation will be evaluated using 9-point scale. The rating of thermal sensation range from 1 (very cold) to 9 (very hot), with 5 being neutral.

Change in plasma metabolites of the kynurenine pathway (μm)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

An ultra-performance liquid chromatography-tandem mass spectrometry system (UPLC-MS/MS) will be used to measure venous plasma levels of tryptophan, kynurenine, kynurenic acid, 3-hydroxy-kynurenine, quinolinic acid, nicotinamide and picolinic acid (in μm). The UPLC-MS/MS system uses a Xevo TQ-XS triple quadrupole mass spectrometer (Waters) with a Z-spray electrospray interface, and the system operates in electrospray positive multiple reaction monitoring mode.

Change in root mean square (RMS) amplitude (mV)

时间窗: During baseline provocative cold test (8th or 15th day), during acclimation (from 22 to 37th days), during repeated provocative cold test (41st or 42nd day)

Root mean square (RMS) amplitude (in mV) of pectoralis major muscle indicating shivering intensity will be measured using a surface EMG (Biometrics, UK).

Change in shivering/sweating (points)

时间窗: During baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st or 42nd day)

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.

Change in ventricular ejection time (ms)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Ventricular ejection time (in ms) will be recorded using Physioflow hemodynamic monitor (France).

Change in systemic vascular resistance (dyn.s/cm5.m^2)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Systemic vascular resistance (in dyn.s/cm5.m\^2) will be recorded using Physioflow hemodynamic monitor (France).

Change in cardiac work index (kg.m/m^2)

时间窗: Before acclimation (1st day), during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Cardiac work index (in kg.m/m\^2) will be recorded using Physioflow hemodynamic monitor (France).

Change in lipid profile (mmol/l)

时间窗: Before acclimation (1st day),during baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Blood samples will be collected to measure lipid profile (in mmol/l) (total cholesterol, high density and low density cholesterol, triglycerides) using a CardioChek PA analyzer (USA).

Change in body temperature (°C)

时间窗: During baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st and 42nd days), and 2 weeks after the end of acclimation (51st day)

Rectal temperature (in °C) will be measured using a thermocouple (Rectal Probe, Ellab, Denmark) inserted to a depth of 12 cm past the anal sphincter, skin temperature (in °C) will be measured with thermistors (Skin/Surface Probe, DM852, Ellab) at four sites: supraclavicular, back, thigh, and forearm, and right lateral gastrocnemius muscle temperature (in °C) will be measured using a needle microprobe (MKA; Ellab).

Change in physiological strain index

时间窗: During baseline provocative heat test (8th or 15th day), during acclimation (from 22 to 37th days), during repeated provocative heat test (41st or 42nd days)

A physiological strain index (PSI) will be 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.

Change in thermal comfort (points)

时间窗: During baseline provocative tests (8th and 15th day), during acclimation (from 22 to 37th days), during repeated provocative tests (41st or 42nd day)

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