Limitations
hyperventilation
COLD
Several limitations of this study must be addressed. First, the study only included healthy young male adults, which may limit the generalizability of the results to other populations, such as individuals with a higher risk profile or female participants. Second, the home-based intervention did not allow for standardization of water temperature. Even though the participants were instructed to set the water temperature as low as possible, there were considerable differences in the water temperature throughout the intervention period and in the different regions where the participants lived. According to the local water provider (Wasserverbund Region Bern AG), the mean water temperature throughout the intervention period was 14.1 ± 3.2 °C.Third, although participants received clear instructions on the duration and the body parts to be exposed to the cold water, compliance with these instructions was only documented using a daily log. Fourth, the intervention duration was relatively short. Even though Wim Hof claims that changes will occur after 10 days, it is expected that more extended intervention periods lead to more pronounced effects. Fifth, it would be interesting to investigate the individual effects of different combinations of the intervention components (hyperventilation, meditation, cold exposure) before exploring their combined effects. Sixth, we only included individuals with no prior experience with the various components of the intervention. It could be argued that, especially for the meditation component, some prior experience and a specific mindset might be beneficial.Finally, it is unclear whether it is necessary to be trained by the creator of the intervention or a trained instructor with regard to the so-called guru effect