This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
The physiological claim most often made for the Wim Hof Method rests on one controlled trial, led by Matthijs Kox and Peter Pickkers at Radboud University Medical Center in the Netherlands and published in the Proceedings of the National Academy of Sciences in 2014. Twelve men trained for ten days in the method were injected with bacterial endotoxin alongside a group of untrained controls; the trained group produced more adrenaline, ran milder flu-like symptoms and showed lower levels of certain inflammatory markers, results the authors read as evidence that the autonomic nervous system and innate immune response, both usually considered involuntary, can be influenced through trained voluntary technique.
What the trial does not show is as important as what it does. Twelve trained subjects is a small sample for a claim this striking, and the design tested the method as a whole rather than separating out which of its three elements, breathing, cold exposure or the stated mental commitment, produced the measured effect, a limitation the authors themselves noted. It also measured a specific, narrow physiological response to one experimental stressor, not the much broader set of health claims that circulate in the method's marketing, disease prevention, athletic performance gains, general immune enhancement, none of which this or any other published trial has tested. The finding is real and has been treated seriously by other researchers since; the gap between what it demonstrates and what is popularly claimed on its strength is the part most retellings leave out.