The aim of the present study was to examine the acute effects of middle-distance competitive
swimming in cold water on selected physiological and biochemical variables.
Fourteen male marathon swimmers competed in a 1-km race in the sea at 9°C water temperature and 14°C air
temperature. Their average swim time was 23 min. Blood lactate and blood glucose, oral temperature, heart rate, blood
pressure, were measured before and after the race. Lactate and glucose were measured by spectrophotometric methods.
The oral temperature dropped by 0.7°C (p < 0.001, 95% CI 0.5-1.0) with swimming without any incidents of hypothermia.
The heart rate increased (p < 0.001) but the blood pressure did not change. Significant elevations were found
in the blood lactate concentration, which reached an average of 9.0 mmol/l (p < 0.001), and blood glucose concentration,
which reached an average of 6.8 mmol/l (p < 0.01).
In conclusion, swimming 1 km in cold water caused no hypothermia or other untoward reactions and no
change in blood pressure, although it increased the heart rate, blood lactate and blood glucose. Based on the increases in
lactate and glucose, exercise had a high impact on carbohydrate metabolism in muscle and liver.