Three additional environmental factors can interact to alter performance further. They are relative humidity, air movement, and radiation. High humidity, because it inhibits evaporation, has the same effect as increasing the ambient temperature. This effect is worse for higher temperatures where it can increase the effective ambient temperature by as much as 10 degrees. Air movement over the body enhances the ability to lose heat by convection and evaporation.
Movement is generated both by the runners speed and by any prevailing wind.
These can combine to lower the effective temperature by as much as 8 or 9 degrees while increasing evaporation and fluid loss. Running downwind cancels out this cooling effect. Direct sunlight adds heat to the body by radiation. The effective temperature increase can be as much as 8 or 9 degrees. Running unwisely under environmental heat stress may lead to a variety of heat illnesses which can be life threatening.