Influence of self-induced hypnosis on thermal responses during immersion in 25 degrees C water

The efficacy of self-induced post-hypnotic suggestion to improve thermogenic responses to head-out immersion in 25 degrees C water was evaluated in 12 males. An on-line computerized system permitted the change in body heat storage to be used as the independent variable and immersion time as the dependent variable. Test-retest reliability was good, exhibiting a coefficient of variation of less than 5% for exposure time. Immersion profiles consisted of the following: rest until 200 kJ of heat were lost, leg exercise at VO2 approximately 1.5 L.min-1 to regain 200 kJ, rest until 100 kJ were lost, and repeat the exercise to regain 100 kJ. A control immersion was done prior to two 1-h hypnotic training sessions. A second immersion (hypnotic) occurred within 24 h after training. There were no differences in rates of heat production, heat loss, mean skin temperature, or rectal temperature between control and hypnotic immersions. Individual hypnotic susceptibility scores did not correlate with changes in thermal status. Ratings of perceived exertion during exercise were similar for both immersions, but perceived sensation of cold was lower during the second rest period of the hypnotic immersion. Three subjects used images of warm environments during their hypnotic immersion and lost heat at a faster rate than during control immersions. These results indicate that brief hypnotic training did not enhance the thermogenic response to cool water immersion.