Ventilatory and perceptual habituation achieved with twice-daily, six total brief 12 °C head-out water immersions

Repetitive cold exposure can evoke habituation capable of reducing physiological stress, energy expenditure and improving comfort in the cold. This study sought to evaluate physiological responses to repeated 10-min 12 °C head-out cold immersions to determine whether metabolic habituation with lower temporal burden could be achieved. Fourteen males (25 ± 7 years, 23.8 ± 5.8% body fat) completed two water immersion sequences consisting of twice daily, six total 10-min head-out immersions, one in cold water (CWI, 12.0 ± 0.1 °C) and the other in thermoneutral water (TN, 35.0 ± 0.2 °C). Water immersion was completed twice per day, separated by at least 4 h, for three consecutive days wearing only compression shorts. CWI was unable to induce metabolic habituation evidenced by unchanged oxygen consumption (p = 0.281) across immersions. Six 12 °C CWIs were sufficient to reduce average 10-min V_E after just three immersions (IMM4: 22.12 ± 4.68 vs. IMM1: 30.90 ± 14.15 L min⁻¹, p < 0.001), via reduced tidal volume (−0.252 [-0.446 to −0.058] L). Perceptual habituation was achieved, with cold exposure inducing shivering sensation habituation after 2 immersions (p = 0.002), thermal comfort improvement after 4 (p = 0.017), and thermal sensation elevation (p = 0.029) after the completion of 5 head-out immersions. Heart rate, mean arterial blood pressure, change in core temperature, and mean weighted skin temperature did not demonstrate evidence of cold-water habituation. In summary, a total of six 12 °C water head-out immersions provided an adaptive stimulus capable of inducing both ventilatory and perceptual habituation but unable to habituate cardiovascular, metabolic, or thermoregulatory cold response.