Running in hot weather is not easy, but running in high humidity, regardless of the temperature, is always challenging. It’s not just the temperature that matters, it’s the humidity. Humidity is the biggest factor, the higher the moisture content of the air, the hotter it feels.
Why Humidity Matters
When you run, your core temperature naturally rises, and your sweat glands produce droplets that carry excess heat to the surface of the skin, where it evaporates. Humidity prevents sweat from evaporating, so the heat stays in. On hot, humid days with no breeze, there is no way to get rid of your building body heat, which can make running very challenging, even dangerous.
When our body heats up and gets more and more dehydrated, it goes into survival mode, maintaining blood flow to our essential organs (to keep us alive) and to our skin (to regulate temperature). In high humidity, less blood will flow to the GI tract, which will make the digestion of sports drinks and gels difficult, we may even feel nauseous as a result. Some runners might be more prone to side stiches once they get overheated, especially if their breathing becomes shallow and uneven. The heart rate will escalate, as the heart and lungs work overtime trying to deliver oxygen throughout the body.
If we keep running, our brain temperature will rise, which makes matters worse. The ability to assess our own body temperature will become difficult (runners often report feeling chilled or goose bumpy when they’re overheating). With high humidity, we can also start to lose control over body mechanics (form and footing will get sloppy), and mental abilities may start to break down (feeling of dizziness and disorientation).
As humidity increases, thermal strain and premature fatigue increase exponentially, so running at our normal pace will be very difficult. It is also important to recognize that feeling sluggish on a very humid day doesn’t indicate a lack of fitness or a lapse of mental toughness- it’s our body’s physical response to a stressful environment. Some runners can handle heat more than others. Body size is one factor, the more body mass, the more insulation and load the body carries, the more heat the body generates, which makes it easier to overheat.
Age is another factor affecting humidity tolerance. As we get older, our body becomes less adaptable to heat, age related changes in sweat glands can decrease sweat production and reduce the body’s ability to cool itself effectively. According to our body type, sweat content varies; some people lose more sodium in their sweating than others, which can impact performance and increase the risk of cramping if not enough electrolytes are consumed. Once the high humidity starts it can take 10-14 days to acclimatize to hot and humid conditions. People who train in countries with high humidity, their body gets accustomed to these intense conditions.
When and Where to Run in High Heat and Humidity
It is easier to run early morning or evening, or cloudy and rainy days. But for runners who according to their available training schedule can only run during the day, it is safer to run on a shaded course, run close to water (breezier conditions), and run slower.
It is essential to hydrate properly with high humidity, even in cooler temperature. In countries with yearly high humidity, to drink electrolytes even in winter runs is essential. Include electrolytes with sodium, potassium, magnesium, calcium, and vitamin C.
Once the humidity rises, let go of any time-based goals, run by feel instead of pace. Once the temperature rises from 24C to 32C, the heart rate can increase 10-20 beats/minute. With high humidity, the effect will be even more significant. Be mindful of the early warning signs of heat exhaustion and heat stroke; fatigue, nausea, dizziness, headache, tingly skin and confusion. If you feel any of these symptoms, call it quits.
Wear the Proper Gear
When choosing your running gear for high humidity runs, make sure you wear light, lose clothing made of breathable fabric that is light in color, not dark. Sunglasses and visor are also helpful, especially when running in the sun.
Heart Rate Side Effects of High Humidity and Heat
The heat alone rises the heart rate, but with added high humidity, the body can’t cool down because the sweat never evaporates.
- HR increases up to 10 beats/minute in humidity range from 50% to 90%.
- HR increases by 2 to 4 beats/minute in temperature from 15C to 24C.
- HR increases up to 10 beats/minute in temperature from 24C to 32C.
Imagine the high level of HR in high temperature over 32C and 90% humidity!
We need to listen and look after our body to teach our body to respond more efficiently in the heat and humidity and be able to survive.
Eat and Drink Right, Train Well, Feel Great!