Introduction: Winter swimming represents an intensive short-term exposure to cold, and thus it is considered a strong physical stress. Cold-based treatments, i.e. immersions in cold water, are spreading in sport medicine for improving recovery following muscle traumas, although a universal acceptance of that method is not still achieved.
Materials and methods: Fifteen healthy subjects (13 males and 2 females) were recruited among the participants to a 150 meters long swimming race in cold water (6 degrees C). Blood samples were collected the day before and immediately after the race and a panel of haematological parameters was evaluated.
Results: Swimming in cold water induced a significant variation in the blood cell fraction composition compared to the rest condition, as measured the day before the competition. Red blood cells, white blood cells and platelets count increased significantly (4.7%, P = 0.005; 40.6%, P < 0.001 and 25.0%, P < 0.001, respectively). While the relative number of leukocytes did not change significantly, apart from a strong decrease of the eosinophils population (-48.6%; P < 0.001), a strong increase in the total number of neutrophil granulocytes, lymphocytes and monocytes was recorded (42.6%, P = 0.002, 58.2%, P = 0.001 and 27.5%, P = 0.021, respectively). Following normalization on plasma volume change (-2.54%) the results were unchanged, demonstrating that the variations were not due to a mere haemoconcentration.
Conclusions: When represented by brief exposure to cold water, winter swimming induces strong non-pathological modifications of haematological homeostasis.