How heat and humidity affect running performance and how to acclimatize to hot conditions.
Changes In Blood Flow And Sweating
The human body has the ability to cool itself in hot conditions by sweating. Actually, it’s the evaporation of sweat that causes cooling, not sweating itself. (This is important with regards to humidity.)
For sweating and cooling to occur, the body must increase blood flow to the surface of the skin. Why blood? Blood is the major carrier of heat, and sweat is composed of plasma, which comes from blood. So when we sweat at high rates, we’re actually losing blood volume, not to mention electrolytes. This is why proper hydration is vital.
Increased skin blood flow is problematic for an endurance athlete because less blood is available to working muscles and vital organs such as the heart, making exercise more difficult.