|Temperature, humidity and air pressure illustration by Mr. Mulroy’s Earth Science|
Humidity makes running more difficult on warm days in that high moisture content in the air will make it feel hotter . It is important to recognize that feeling sluggish on a day with high humidity doesn't indicate a lack of fitness or a lapse in mental toughness. Body temperature naturally rises when one runs and sweat glands produce sweat to carry excess heat to the surface of the skin, where it evaporates and produce a cooling effect on the body. But with higher humidity in the air, sweat is prevented from evaporating.
When the body continues to heat up and get dehydrated, it goes into survival mode of trying to maintain blood flow only to your essential organs and to your skin. If you continue pushing hard despite the early warnings, your brain temperature may even rise as a result and make matters worse as your ability to assess your own body temperature will be compromised. You may start to lose control over your body movements and your mental abilities may end up disoriented.
Some of the factors that affect your susceptibility to humidity include your body size. The more body mass you have the more insulation and load you carry and the more heat your body will generate, which will make it easier for you to overheat. Health condition, age and place of origin may also affect how your body adapts to humidity. That is why it pays to train in almost the same weather conditions ahead of racing in hot and humidity conditions.
It is always important to give your health priority over your race goals. Make sure to hydrate properly and to adjust your pace to adapt to the racing conditions. Pay close attention to the early warning signs of heat exhaustion and heat stroke: fatigue, nausea, dizziness, headaches, tingly skin, and confusion. It might be time to pull out of the race and live to run another next time.