Table 3. Summary of WHM description, key findings, and quality assessment.

Study	Description of meditation component of WHM	Description of breathing technique of WHM	Description of cold exposure of WHM	Key findings
Kox et al., 2014	Third eye meditation is a type of meditation that includes visualisations aimed at complete relaxation.	Two breathing exercises. The first exercise is the same as Bahenský et al., 2020. The second exercise consisted of deep inhalations and exhalations. After each inhalation and exhalation breath was held for 10s, during which the individual tightened all the muscles. The breathing techniques were also implemented during endotoxemia. Strength workouts were also included in the training programme (e.g., yoga balance techniques and push-ups).	Standing in the snow barefoot for up to 30 minutes. Lying bare chested in the snow for 20 minutes. Daily swimming or dipping in ice-cold water for several minutes. Hiking a snowy mountain (5–12°C) bare chested, wearing nothing but shoes and shorts.	Intermittent hypoxia and respiratory alkalosis brought on by WHM markedly raised epinephrine levels. After endotoxin treatment, IL-10 levels increased more quickly and were higher. They also showed a substantial correlation with baseline epinephrine levels. TNF-α, IL-6, and IL-8 levels were lower in WHM-trained group and correlated negatively with IL-10 levels. Flu-like symptoms were lower in the WHM-trained group.
Middendorp et al., 2016	Same as Kox et al., 2014.	Same as Kox et al., 2014.	Same as Kox et al., 2014.	Generalised outcome expectancy optimism is a potential predictor of the immune and autonomic response to induced inflammation following training, while more specific expectations regarding the training’s effects might be especially relevant for the clinical symptom report.
Buijze et al., 2019	Same as Kox et al., 2014.	Same as Kox et al., 2014.	Patients submerged their entire body for several minutes in ice-cold water (0–1°C) incrementally up to a maximum of 5 minutes. Cold showers were taken incrementally up to 5 minutes (10–14°C) daily at home.	No significant differences in adverse events between groups, with one serious adverse event occurring 8 weeks after finishing the intervention and judged ‘unrelated’. During the 8-week intervention period, there was a significant decline of erythrocyte sedimentation rate (ESR), Ankylosing Spondylitis Disease Activity Score C-reactive protein (ASDAS-CRP), and serum calprotectin, whereas no effect was found in the control group. ESR, ASDAS-CRP, and high-sensitive CRP (hs-CRP) are endpoints that measure inflammation. High ESR, ASDAS-CRP, or hs-CRP means there is inflammation. The decline in ESR, ASDAS-CRP, and serum calprotectin suggest that there is a decrease in inflammation. No significant decline was found for hs-CRP.
Zwaag et al., 2020	Same as Kox et al., 2014	Same as Kox et al., 2014.	Same as Kox et al., 2014.	The training program’s effects were most noticeable soon after WHBM started but before LPS was administered, and they point to greater activation of the Cori cycle. Increased levels of IL-10 were associated with elevated lactate and pyruvate concentrations in trained individuals. Co-incubation with lactate and pyruvate increases IL-10 production while decreasing the release of pro-inflammatory IL-1 and IL-6 by LPS-stimulated leukocytes, according to in vitro validation trials.
Bahenský et al., 2020	N/A	Participants were instructed to take 30–50 complete breaths at a pace of 20 breaths/min. Exhale completely when tingling in the fingers is noticed. The participants were told to hold their breath until they felt a strong urge to breathe or until the diaphragm spontaneously contracted. Each breath hold was followed immediately by a complete breath then a secondary 15-sec breath hold. Three similar rounds were performed without rest, lasting between 17–22 min.	N/A	During the testing stages, preceded by the breathing techniques, O2 consumption was significantly higher (2.4–4.9%; p<0.05). Following breathing exercises, perceived effort was reduced throughout the exercise session (18.5±1.2 vs. 17.4±1.1; p<0.01). Prior to an acute exercise bout, breathing techniques including deep breathing and breath holds appear to enhance VO2 kinetics and minimise subjective strain in participants.
Citherlet et al., 2021	N/A	Participants followed the audio guide on the WHM application. WHBM was repeated for three cycles. One cycle consisted of 30 breaths of hyperventilation, defined as maximal amplitude respiratory movements at the frequency specified by the audio guidance (0.32 Hz). This process lasted for approximately 1 minute and 30 seconds. The participants then exhaled completely to residual volume and kept their breath for as long as they could. Afterwards, the participants inhaled to total lung capacity and held their breath for 15 seconds before beginning the next cycle.	N/A	No significant negative or positive condition effects were discovered on Repeated Ability Sprint Test (RAST) peak power, average power, or fatigue index despite considerable physiological effects on the finger pulse oxygen saturation (SpO2) and expired carbon dioxide (VCO2) levels of both WHBM and hyperventilation (HV). Finger SpO2 was reduced at the end of the voluntary breath-holds (BH). End-tidal CO2 partial pressure measurements during the final HV in the WHBM and HV conditions were suggestive of respiratory alkalosis with an elevation in arterial pH. After RAST, the 8min cumulated VCO2 volumes in the HV and WHBM were higher than in the spontaneous breathing (SB), indicating the depletion of residual CO2 stores. 33% of individuals in the WHBM reported deafness and heaviness. For the HV condition, 73% of the individuals reported benefits including decreased fatigue and better breathing. For the WHBM condition, 87% of the participants reported benefits like less fatigue, better breathing, and more energy. In contrast to 53% who said they would not use the WHM in the future, 47% said they intended to employ the WHBM in their future personal training and competition practise. Participants conducting the trial in the WHBM condition felt the most advantaged, followed by the HV condition. WHBM condition resulted in feeling significantly more advantaged than SB condition.
Zwaag et al., 2022	N/A	The first exercise is the same as Bahenský et al., 2020. In the exercise without retention of breath, participants hyperventilated 30 times using powerful and deep breaths. Participants held their breath for only 10 seconds, during which all muscles were tightened. Afterwards, a new cycle of hyperventilation was started.	Same as Kox et al., 2014. Participants were told to take a 1 minute cold water rinse at the end of each day’s shower.	Epinephrine levels increased after performing both breathing exercises, and this effect was independent of training duration or instructor. The breathing exercise raised epinephrine levels in the endotoxemia trial. The LPS-induced inflammatory response was not modulated by cold exposure training alone. The breathing exercise resulted in significantly increased levels of anti-inflammatory and decreased levels of pro-inflammatory cytokines. Training in cold exposure considerably improved the breathing exercise’s immunomodulatory effects. In healthy young males, the in vivo inflammatory response is most effectively attenuated by the combination of cold exposure training and breathing exercise.
Petraskova Touskova et al., 2022	Participants were told to focus on‚ body awareness, comprising enhancement of self-awareness and will-power.	Same as Bahenský et al., 2020.	Cold exposures were carried out on an individual basis by submersion in the water of Prince Gustav Channel or in the shower. Prior to entering the cold water, participants took five to ten long, deep breaths while contracting particular abdominal and pelvic muscles. Participants were asked to carry out the exercises once per day on their own after the first three supervised sessions. One session was around 20 minutes.	Depressive symptoms decreased over an 8-week training programme. There was a significant reduction in stress response. Cortisol reduction was also observed to be non-significant.
Marko et al., 2022	N/A	Same as Bahenský et al., 2020.	N/A	There were no significant variations in minute ventilation, tidal volume, or breathing frequency before or after the intervention between the experimental and control groups. Following the 4 week intervention period, there was a non-significant small-to-large effect for an increase in BF and VE in both groups, probably as a result of a decrease in training volume and intensity brought on by the break between competing seasons.