Effect of regular winter swimming on the activity of the sympathoadrenal system before and after a single cold water immersion.

This study deals with the adaptation of the sympathoadrenal responses to an acute cold water immersion in ordinary winter swimmers. Hormonal responses were determined at the beginning of the winter swimming period in the autumn and after regular swimming for one and three months. Water temperature in the river was 10 degrees C at the beginning and 4 degrees C after one and three months. The mean duration of the test immersion was 36 s. Plasma catecholamine levels determined before the test immersion decreased with the winter swimming period for one month (NA, p < 0.001, A, p < 0.01). The test immersion significantly increased noradrenaline levels (p < 0.001). Plasma adrenaline and serum cortisol levels were increased or decreased by the immersion. After 1 month's swimming the test immersion to 4 degrees C increased noradrenaline to a similar level than the immersion to 10 degrees C at the beginning. Regularly practiced winter swimming for three months led to diminished catecholamine levels measured immediately after the test immersion (p < 0.01). The results suggest that cold adaptation induced by winter swimming attenuates the catecholamine responses to cold water. Adrenaline responses are also affected by its level prior to the immersion.