A semi-randomised control trial assessing psychophysiological effects of breathwork and cold immersion.

The paradoxical nature of stress lies in its ability to both enhance and hinder psychological, physiological, and cognitive functioning. While chronic stress impairs functioning, acute stress can enhance resilience, cognition, and performance. We examined whether intentional short-term stress induced by cyclic hyperventilation and cold exposure (the Wim Hof Method (WHM)) improves psychophysiological and cognitive outcomes compared to an active control (mindfulness meditation). In this semi-randomised controlled trial, healthy adults (N = 404; 226 females, 177 males, 1 other; mean age = 37) completed one of three 29-day interventions: WHM in-person, WHM-remote, or meditation. Measures included physiological and sleep biometrics, executive function tests, and psychometric event sampling surveys (state and trait change). WHM conditions showed greater momentary improvements in self-reported energy, mental clarity, and ability to handle stress following daily protocol compared with meditation. Although WHM protocols initially resulted in smaller reductions in self-reported state stress, their impact increased across days on protocol, while the impact of meditation decreased. A similar time-condition interaction was also observed for energy, mental clarity, and ability to handle stress, suggesting cumulative, dose-dependent benefits. While minimal significant between-condition trait changes emerged over 29-days, state interaction patterns suggest potential for longer-term state-trait shifts. Executive function, physiological, and sleep results showed nuanced between-condition differences.