Haematological and plasma electrolyte changes after long distance running in high heat and humidity

To investigate the acute effects of an 18 km run on the haematological and plasma electrolyte parameters, in recreational runners under conditions of high temperatures and humidity.

Haematological and electrolyte parameters changes were measured in 21 acclimatised recreational runners before and after an 18 km run in environmental temperatures and relative humidity of 27.1 +/- 0.3 degrees C and 85.0 +/- 1.7% respectively, which was measured using the wet bulb globe monitor.

There was a loss of weight which averaged 2.5 +/- 0.2% (p < 0.001) of initial body weight. Rectal temperature increased by an average of 2.7 +/- 0.2 degrees C (an increase of 7.2 +/- 0.7%; p < 0.001). Immediately after the race, there was a significant (p < 0.01) increase in haemoglobin, haemotocrit and plasma osmolality. Mean plasma volume decreased by 4.1 +/- 1.1%. Plasma sodium and potassium significantly (p < 0.01) increased by 4.5 +/- 0.5% and 20.3 +/- 3.5% respectively, while magnesium significantly (p < 0.01) decreased by 9.0 +/- 1.8%. Peripheral blood profile showed significant increases in the post-race white blood cell counts (p < 0.001) and platelets (p < 0.01).

The acute changes in haematological variables and plasma electrolytes reported in this study at relatively high ambient temperature and humidity were found to be similar to that seen after long-distance running under cooler climatic conditions. However, it is recommended that long-distance runners should be hyperhydrated just before the race and also be encouraged to consume 150 mL to 300 mL every 15 minutes while running to prevent the effects of dehydration.