Risk Factors and Predictors of Hypothermia and Dropouts During Open-Water Swimming Competitions.

Purpose: To measure core temperature (T_core) in open-water (OW) swimmers during a 25-km competition and identify the predictors of T_core drop and hypothermia-related dropouts. Methods: Twenty-four national- and international-level OW swimmers participated in the study. Participants completed a personal questionnaire and a body fat/muscle mass assessment before the race. The average speed was calculated on each lap over a 2500-m course. T_core was continuously recorded via an ingestible temperature sensor (e-Celsius, BodyCap). Hypothermia-related dropouts (H group) were compared with finishers (nH group). Results: Average prerace T_core was 37.5°C (0.3°C) (N = 21). 7 participants dropped out due to hypothermia (H, n = 7) with a mean T_core at dropout of 35.3°C (1.5°C). Multiple logistic regression analysis found that body fat percentage and initial T_core were associated with hypothermia (G² = 17.26, P <.001). Early T_core drop ≤37.1°C at 2500 m was associated with a greater rate of hypothermia-related dropouts (71.4% vs 14.3%, P =.017). Multiple linear regression found that body fat percentage and previous participation were associated with T_core drop (F = 4.95, P =.019). There was a positive correlation between the decrease in speed and T_core drop (r =.462, P <.001). Conclusions: During an OW 25-km competition at 20°C to 21°C, lower initial T_core and lower body fat, as well as premature T_core drop, were associated with an increased risk of hypothermia-related dropout. Lower body fat and no previous participation, as well as decrease in swimming speed, were associated with T_core drop. [ABSTRACT FROM AUTHOR]