Healthy ParticipantsNCT07198334
The Effect of Daily Brief Heat Exposures on Heat Acclimation
A study testing Heat acclimation in people with Healthy Participants, run by Lithuanian Sports University at 1 site in Lithuania.
Trial summary
This study is the first to examine the effects of short passive heat exposure on heat acclimation (HA). Unlike traditional protocols requiring prolonged heat exposure, this study tests whether a daily 5-minute whole-body immersions at 45°C water repeated over two weeks can trigger adaptive responses, offering a… Read more about this study
- Who is it for?
- Ages 18 to 35 yearsHealthy volunteers can take part
- Conditions the study is for
- Healthy Participants
- What is being tested?
- Heat acclimation
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 26 participants
- Where
- 1 siteLithuania
- Study dates
- 1 Oct 2020to 31 May 2024
- Phase
- Interventional
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 35 years
- All sexes
- Healthy volunteers accepted
- Adult
Who may be able to join
- Healthy, non-obese males and females aged 18 to 35 years with a body mass index between 18.5 and 29.9 kg/m².
- No participation in temperature manipulation programs (e.g., cold or heat acclimation) within the past three months.
- No engagement in excessive formal exercise.
- Female participants must have a regular menstrual cycle.
Who cannot join
- Current smokers.
- Fear of needles or blood.
- Use of medications or supplements that could affect study outcomes.
- History of neurological, cardiovascular, metabolic, or inflammatory diseases that could be aggravated by hot water exposure.
Trial locations and contacts
1 site in 1 country.
About this study
Official title: The Effect of Daily Brief Whole-body Heat Exposures on Heat Acclimation and Its Decay
This study is the first to examine the effects of short passive heat exposure on heat acclimation (HA). Unlike traditional protocols requiring prolonged heat exposure, this study tests whether a daily 5-minute whole-body immersions at 45°C water repeated over two weeks can trigger adaptive responses, offering a potentially more accessible and time-efficient method for heat acclimation. This study aims to investigate whether brief, repeated passive heat exposure can induce HA in both female and male participants. It evaluates changes across physiological, biological, and psychological markers to determine the efficacy of this minimal-exposure protocol. It is hypothesized that such short, repeated immersions may be sufficient to elicit significant adaptive responses across key HA indicators.
- Conditions
- Healthy Participants
- Being tested
- Heat acclimation
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Heat acclimationOther
Passive heat acclimation was designed to induce adaptation in participants through 14 consecutive days of controlled 5-minute whole-body immersion in water at 45°C.
| Study group | Role | What they receive |
|---|---|---|
| Heat acclimation | Experimental | Not described Receives: Other: Heat acclimation |
What is being measured
The primary outcome is the main question the study is designed to answer.
Dehydration (kg)
Dehydration (in kg) was assessed by calculating body mass loss (Tanita Body Composition Analyzer; USA) during heat exposure.
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Heart rate (bpm)
Heart rate (in bpm) was recorded using a heart rate sensor with a chest strap (Polar, Finland).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Blood pressure (mmHg)
Systolic and diastolic blood pressure (in mmHg) was measured using with an automatic cuff monitor (Gentle+, Microlife, Switzerland).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Pulse pressure (mmHg)
Pulse pressure (in mmHg) was calculated by subtracting diastolic blood pressure from systolic blood pressure.
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Rate of pressure production (AU)
Rate of pressure production (in AU) was calculated by multiplying heart rate , by systolic blood pressure.
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Shivering/sweating (points)
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.
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Thermal comfort (points)
Thermal comfort will be evaluated using 4-point scale. The rating of thermal comfort range from 0 (neutral) to 3 (very uncomfortable).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Body temperature (°C)
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).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Physiological strain index
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.
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Oxygen consumption (mL/min/kg)
Oxygen consumption (in mL/min/kg) was measured using Cortex METALYZR® 3B, Leipcig, Germany).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Carbon dioxide output (mL/min/kg)
Carbon dioxide output (in mL/min/kg) was measured using Cortex METALYZR® 3B, Leipcig, Germany).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Carbon dioxide output (mL/min)
Carbon dioxide output (in mL/min) was measured using Cortex METALYZR® 3B, Leipcig, Germany).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Oxygen consumption (mL/min)
Oxygen consumption (in mL/min) was measured using Cortex METALYZR® 3B, Leipcig, Germany).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Respiratory quotient
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.
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Ventilation (L/min)
Ventilation (in L/min) was measured using Cortex METALYZR® 3B, Germany).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Tidal volume (L)
Tidal volume (in L) was measured using Cortex METALYZR® 3B, Germany).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Breathing frequency (t/min)
Breathing frequency (t/min) was measured using Cortex METALYZR® 3B, Germany).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Secondary outcomes (8)
Height (cm)
Height (in cm) was measured using a Harpenden anthropometer set (Holtain Ltd, UK).
Measured: During enrollment
Body mass and body composition (kg)
Body mass and composition (in kg) was evaluated using Tanita Body Composition Analyzer (USA).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Body mass index (kg/m^2)
Body mass index (in kg/m^2) will be defined as the body mass divided by the square of the body height.
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Body composition (%)
Body composition (in %) was evaluated using Tanita Body Composition Analyzer (USA).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Maximal oxygen consumption (in mL/min/kg)
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).
Measured: During enrollment
Prolactin (ng/mL)
Serum prolactin (in ng/mL) was measured using enzyme-linked immunosorbent assay kits and a Spark multimode microplate reader (Tecan, Austria).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
17beta-estradiol (pg/mL)
Serum 17beta-estradiol (in pg/mL) was measured using enzyme-linked immunosorbent assay kits and a Spark multimode microplate reader (Tecan, Austria).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Progesterone (ng/mL)
Serum progesterone (in ng/mL) was measured using enzyme-linked immunosorbent assay kits and a Spark multimode microplate reader (Tecan, Austria).
Measured: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted30 Sep 2025
- Study start1 Oct 2020
- Primary completion31 May 2024
- Study completion31 May 2024
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Healthy ParticipantsStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Basic science
- Allocation
- Not applicable
- Intervention model
- Single group
- Masking
- None (open label)
- Enrolment
- 26 participants (actual)
Sponsor and investigators
- Lead sponsor
- Lithuanian Sports University
- Sponsor type
- University, hospital or other
- Responsible party
- Sponsor
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07198334
- Sponsor's protocol ID
- LithuanianSportsU-26
- Status last verified
- Dec 2025
- First submitted
- 25 Sep 2025
- Last updated
- 24 Dec 2025
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Undecided
Study at a glance
From the registry record, last updated by the sponsor on 24 Dec 2025. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- The Effect of Daily Brief Whole-body Heat Exposures on Heat Acclimation and Its Decay
- ClinicalTrials.gov ID
- NCT07198334
- Acronym / sponsor ID
- LithuanianSportsU-26
- Conditions
- Healthy Participants
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 26 participants (actual)
- Lead sponsor
- Lithuanian Sports UniversityUniversity, hospital or other
- Study start
- 1 Oct 2020 (actual)
- Primary completion
- 31 May 2024 (actual)
- Study completion
- 31 May 2024 (actual)
- First posted
- 30 Sep 2025 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
This study is the first to examine the effects of short passive heat exposure on heat acclimation (HA). Unlike traditional protocols requiring prolonged heat exposure, this study tests whether a daily 5-minute whole-body immersions at 45°C water repeated over two weeks can trigger adaptive responses, offering a potentially more accessible and time-efficient method for heat acclimation. This study aims to investigate whether brief, repeated passive heat exposure can induce HA in both female and male participants. It evaluates changes across physiological, biological, and psychological markers to determine the efficacy of this minimal-exposure protocol. It is hypothesized that such short, repeated immersions may be sufficient to elicit significant adaptive responses across key HA indicators.
Study design
- Primary purpose
- Basic science
- Allocation
- Not applicable
- Intervention model
- Single group
- Masking
- None (open label)
- Number of arms
- 1
| Arm | Type | Receives |
|---|---|---|
| Heat acclimation | Experimental | Other: Heat acclimation |
Who may qualify
- Ages
- 18 to 35 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult
Key inclusion criteria (4 listed)
- Healthy, non-obese males and females aged 18 to 35 years with a body mass index between 18.5 and 29.9 kg/m².
- No participation in temperature manipulation programs (e.g., cold or heat acclimation) within the past three months.
- No engagement in excessive formal exercise.
- Female participants must have a regular menstrual cycle.
Key exclusion criteria (4 listed)
- Current smokers.
- Fear of needles or blood.
- Use of medications or supplements that could affect study outcomes.
- History of neurological, cardiovascular, metabolic, or inflammatory diseases that could be aggravated by hot water exposure.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Heat acclimationPassive heat acclimation was designed to induce adaptation in participants through 14 consecutive days of controlled 5-minute whole-body immersion in water at 45°C. | Other | Heat acclimation |
Primary outcome
Dehydration (kg)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Dehydration (in kg) was assessed by calculating body mass loss (Tanita Body Composition Analyzer; USA) during heat exposure.
Heart rate (bpm)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Heart rate (in bpm) was recorded using a heart rate sensor with a chest strap (Polar, Finland).
Blood pressure (mmHg)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Systolic and diastolic blood pressure (in mmHg) was measured using with an automatic cuff monitor (Gentle+, Microlife, Switzerland).
Pulse pressure (mmHg)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Pulse pressure (in mmHg) was calculated by subtracting diastolic blood pressure from systolic blood pressure.
Rate of pressure production (AU)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Rate of pressure production (in AU) was calculated by multiplying heart rate , by systolic blood pressure.
Shivering/sweating (points)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
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 (points)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Thermal comfort will be evaluated using 4-point scale. The rating of thermal comfort range from 0 (neutral) to 3 (very uncomfortable).
Body temperature (°C)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
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
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
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 (mL/min/kg)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Oxygen consumption (in mL/min/kg) was measured using Cortex METALYZR® 3B, Leipcig, Germany).
Carbon dioxide output (mL/min/kg)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Carbon dioxide output (in mL/min/kg) was measured using Cortex METALYZR® 3B, Leipcig, Germany).
Carbon dioxide output (mL/min)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Carbon dioxide output (in mL/min) was measured using Cortex METALYZR® 3B, Leipcig, Germany).
Oxygen consumption (mL/min)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Oxygen consumption (in mL/min) was measured using Cortex METALYZR® 3B, Leipcig, Germany).
Respiratory quotient
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
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 (L/min)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Ventilation (in L/min) was measured using Cortex METALYZR® 3B, Germany).
Tidal volume (L)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Tidal volume (in L) was measured using Cortex METALYZR® 3B, Germany).
Breathing frequency (t/min)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Breathing frequency (t/min) was measured using Cortex METALYZR® 3B, Germany).
8 secondary outcomes
Height (cm)
Time frame: During enrollment
Body mass and body composition (kg)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Body mass index (kg/m^2)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Body composition (%)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Maximal oxygen consumption (in mL/min/kg)
Time frame: During enrollment
Prolactin (ng/mL)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
17beta-estradiol (pg/mL)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Progesterone (ng/mL)
Time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 24 Dec 2025.
- Individual participant dataSharing planned: Undecided
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
The record lists no contact. Use the official record to reach the sponsor.
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Heat acclimation in people with Healthy Participants, run by Lithuanian Sports University at 1 site in Lithuania.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 4 inclusion and 4 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 24 Dec 2025. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Lithuania. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Dehydration (kg) (time frame: From enrollment to the end of deacclimation (one month after the 14-day heat acclimation period).). The study lists 17 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 24 Dec 2025.