Effect of a 4-week extreme heat (100±2°C) sauna baths program in combination with resistance training on lower limb strength and body composition
| ISRCTN | ISRCTN48038929 |
|---|---|
| DOI | https://doi.org/10.1186/ISRCTN48038929 |
- Submission date
- 22/07/2025
- Registration date
- 22/09/2025
- Last edited
- 02/09/2025
- Recruitment status
- No longer recruiting
- Overall study status
- Completed
- Condition category
- Other
Plain English summary of protocol
Background and study aims
This study aims to evaluate whether four weeks of exposure to extreme heat (approximately 100°C) through passive sauna bathing can enhance the effects of resistance training on maximal muscular strength and body composition.
Who can participate?
Healthy adult male volunteers aged 18 to 25 years
What does the study involve?
Participants will be randomly assigned to one of two groups: a training-only control group, and a group that, following each resistance training session, undergoes sauna exposure at approximately 100°C for 10 minutes, twice weekly over four weeks. The intervention includes assessments at baseline, during, and after the training period to measure muscle strength, body composition, and other relevant health variables.
What are the possible benefits and risks of participating?
Participants may experience gains in muscular strength and improvements in body composition. Risks are minimal but could include discomfort or dehydration related to heat exposure; therefore, the study will be supervised by healthcare professionals to ensure participant safety throughout the protocol.
Where is the study run from?
The University of Extremadura in Cáceres, Spain
When is the study starting and how long is it expected to run for?
January 2020 to July 2022
Who is funding the study?
The Regional Government of Extremadura, Spain
Who is the main contact?
Ignacio Bartolomé, ibartolomesa@upsa.es, ignbs.1991@gmail.com
Jesús Siquier-Coll, jsiquier.research@gmail.com
Contact information
Scientific
Av. de las Universidades, 2
Dos Hermanas, Sevilla
41704
Spain
 ORCID ID |
0000-0003-3185-3615 |
|---|---|
| Phone | +34 645593427 |
| jsiquier.reserch@gmail.com |
Public, Scientific, Principal Investigator
Campus Universitario, Av. de la Universidad, S/N
Cáceres
10003
Spain
| Phone | +34 654368503 |
|---|---|
| ibartolomesa@upsa.es |
Study information
| Study design | Randomized controlled study |
|---|---|
| Primary study design | Interventional |
| Secondary study design | Randomised controlled trial |
| Study setting(s) | University/medical school/dental school |
| Study type | Other |
| Participant information sheet | Not available in web formar, please use contact details to request a participant information sheet |
| Scientific title | Effect of a 4-week extreme heat (100±2°C) sauna baths program in combination with resistance training on lower limb strength and body composition |
| Study objectives | The study objective is to evaluate the effect of a 4-week passive sauna bathing program to extreme heat (100±2°C) as a support for resistance strength training program on the development of maximum strength and body composition in young physically active subjects. Considering current evidence, it can be hypothesized that the use of extreme heat sauna baths, in combination with resistance training, may be a beneficial strategy to improve body composition and strength. |
| Ethics approval(s) |
Approved 16/03/2020, Bioethics and Biosecurity Commission of The University of Extremadura (Comisión de Bioética y Bioseguridad de la Universidad de Extremadura) (Avenida de Elvas s/n, Badajoz, 06071, Spain; +34 924289305; vrinvestigacion@unex.es), ref: 32//20 |
| Health condition(s) or problem(s) studied | No diseases |
| Intervention | The study was conducted over 13 weeks. The first week involved a familiarization phase, during which all participants visited the facilities where the research would take place. In the laboratory, they were introduced to the sauna and assessment instruments, while in the weight training room, they performed a warm-up similar to that of the experimental phase and familiarized themselves with the machines used for assessments and training. Subsequently, participants were randomly assigned to either the Hyperthermia Group (HG) or the Normothermia Group (NG). Group randomization was performed using a specialized online tool (https://www.randomizer.org). To maintain blinding conditions, participants received a specific informed consent form tailored to their assigned group and their participation status in the sauna program. During the study, participants from different groups were scheduled on separate days to prevent overlap at the facilities and minimize the risk of participants becoming aware of the activities performed by other groups. Following a one-week break, the initial assessment was conducted, consisting of an evaluation of the level of physical activity, anthropometric parameters, body composition, and assessment of lower limb strength in both isometric and counter-resistance conditions. In the third week of the study, after another week of rest, both the counter-resistance strength training and the sauna bathing program began. These programs spanned 4 weeks, with a frequency of 2 sessions per week, allowing 48 hours of recovery between sessions. Both groups followed the same training program. Additionally, the HG engaged in a passive sauna bath immediately after each training session. One week after completing the training and sauna programs, the assessments carried out in the initial evaluation were repeated, adhering completely to the same protocol, test order, and assessment schedules, which remained consistent for each participant in both assessments. To avoid negative interaction effects derived from circadian chronobiology, the hours of evaluation did not vary along the survey. Each training session began with a warm-up, similar to that performed in the assessments. Subsequently, 4 sets of 8-10 repetitions were performed in the guided half squat exercise on the multipower station, followed by 4 sets of 8-10 repetitions on the leg press. Recoveries were passive, with a duration of 1.5 minutes between sets and 3 minutes between exercises. The load was initially set at 75% of the initial 1RM and increased by 5% weekly, finishing the last week with 90% of the initial 1RM. To reduce contamination from technique, each participant maintained the same position and configuration for both the machine positions and joint angles used in the initial assessment, remaining constant throughout the entire study. The training sessions were conducted at room temperature of 23±1°C and 24±1% relative humidity (RH). Sauna bathing program: Participants in the HG completed a sauna session immediately after each workout, totaling 2 sessions per week. Sauna sessions were passive, with participants sitting inside the sauna. The sauna was set to 100±2°C with normal ambient relative humidity, and participants completed 4 sets of 10 minutes each, with passive breaks of 5 minutes at room temperature (23±1°C). The RH of both laboratory and sauna was 24±1%. The sauna was preheated in advance to ensure that participants completed the entire exposure time at the desired temperature. |
| Intervention type | Behavioural |
| Primary outcome measure | Muscle strength measured using the 1RM test in squat and leg press exercises, and isometric strength measured using an isokinetic dynamometer, at baseline and after 8 and 13 weeks |
| Secondary outcome measures | Body composition measured using bioelectrical impedance and anthropometric methods at baseline and after 8 and 13 weeks |
| Overall study start date | 01/01/2020 |
| Completion date | 31/07/2022 |
Eligibility
| Participant type(s) | Learner/student |
|---|---|
| Age group | Adult |
| Lower age limit | 18 Years |
| Upper age limit | 25 Years |
| Sex | Male |
| Target number of participants | 29 |
| Total final enrolment | 30 |
| Key inclusion criteria | 1. Male participants aged between 18 and 25 years 2. No diseases or contraindications for resistance training 3. No pharmacological and/or nutritional treatment in the 12 months before the study 4. No engagement in any strength or resistance training program in the 12 months before the study 5. No consumption of coffee, tea, or caffeine during assessments and training 6. No intake of sports nutritional supplements or dietary changes during the study |
| Key exclusion criteria | 1. Suffering from a musculoskeletal injury at the beginning or during the research phase 2. Consuming any doping substances or anabolic supplements 3. Initiating any pharmacological or nutritional treatment during the study 4. Changing the type of diet or dietary regimen during the study 5. Not attending any of the training or acclimatization sessions 6. Experienced experimental dropout |
| Date of first enrolment | 15/09/2021 |
| Date of final enrolment | 16/07/2022 |
Locations
Countries of recruitment
- Spain
Study participating centre
Cáceres
10003
Spain
Sponsor information
University/education
Av. de Elvas, s/n
Badajoz
06006
Spain
| Phone | +34 924289305 |
|---|---|
| vrinvestigacion@unex.es | |
| Website | https://www.unex.es |
"ROR" |
https://ror.org/0174shg90 |
Funders
Funder type
Government
Government organisation / Local government
- Alternative name(s)
- Regional Government of Extremadura
- Location
- Spain
Results and Publications
| Intention to publish date | 07/08/2025 |
|---|---|
| Individual participant data (IPD) Intention to share | Yes |
| IPD sharing plan summary | Available on request |
| Publication and dissemination plan | Planned publication in a peer-reviewed journal |
| IPD sharing plan | The datasets generated during and/or analysed during the current study will be available upon request from Dr. Ignacio Bartolomé, ibartolomesa@upsa.es, ignbs.1992@gmail.com. · The data to be shared will be the data published in the article (anthropometric characteristics, age, sex, performance variables, and strength). · Data will be available starting August 1, 2025. · Consent was requested and obtained from all participants. · The data were anonymized at all times. · There are no legal or ethical restrictions. · There are no additional comments. |
Editorial Notes
02/09/2025: Study's existence confirmed by the Bioethics and Biosecurity Commission of the University of Extremadura.
