Abstract
Background: When suddenly immersed in cold water, humans typically exhibit the cold shock response, although training can attenuate hyperventilation. This study extends previous findings by considering the influence of physical activity to maintain buoyancy and subsequent swimming performance. Methods: Six inexperienced swimmers (three men and three women; mean age 22.8) received 1 wk of cold-water head-out immersions (10 x 3 min at 15 degrees C) alongside mental skills training to improve their treading water technique and to control hyperventilation upon immersion. Six inexperienced control swimmers (four men and two women; mean age 21.8) received immersions in temperate water (27 degrees C). Ventilation, brain blood flow velocity, and blood oxygenation were measured during a physiological test in which participants trod water for 150 s. In a subsequent simulated survival test, performance (swimming duration and distance) and perception of effort were recorded. All the tests were in 10 degrees C water with the head out. Results: There were significant improvements in the intervention group's ability to suppress rapid increases in respiratory frequency; 62 +/- 24 breaths . min(-1) to 33 +/- 12. The drop in brain blood flow was smaller and more transient than that previously reported due to the hypertensive response associated with treading water. Discussion: Inexperienced swimmers could benefit from cold-water habituation combined with mental skills training in order to improve voluntary control over the respiratory portion of the cold shock response as part of learning to tread water. This may improve survival prospects in a real-life emergency scenario such as an overturned boat.