Running is simply the act of placing one foot in front of the other rapidly as you move from one point to another. However, running—especially marathon running—requires much more than basic movement.
To perform well in a marathon, a runner must understand factors such as humidity, atmospheric pressure, hydration, nutrition, and pacing. While it may seem sufficient to check only the temperature or the time of day for the race, many other factors can significantly impact your performance and safety.
Humidity, in particular, plays a crucial role in how your body feels and performs on race day. When the humidity is above 45%, you may start to notice a difference in your running efficiency; at 75%, the effects become much more pronounced, and at 100%, running can become extremely challenging and even dangerous.
How humidity affects running
This is because higher humidity prevents your sweat from evaporating efficiently, which hinders your body’s natural ability to cool itself. As a result, you may overheat more quickly and fatigue faster than expected.
Humidity makes running more difficult on warm days because the high moisture content in the air creates a sensation known as “apparent temperature,” making it feel much hotter than it actually is. This means your body has to work even harder to cool itself. It’s important to recognise that feeling sluggish or tired on a day with high humidity doesn’t indicate a lack of fitness or a lapse in mental toughness; it’s a natural physiological response to environmental stress.
When you run, your body temperature naturally rises, prompting your sweat glands to produce sweat to dissipate excess heat. Normally, this sweat evaporates from the skin, creating a cooling effect and helping to regulate your core temperature. However, in humid conditions, the air is already saturated with moisture, preventing your sweat from evaporating efficiently. As a result, the body’s cooling process is impaired, and you may feel overheated, sticky, and fatigued much sooner than you would in drier conditions. This can also increase your risk of dehydration, heat exhaustion, and even heatstroke if you’re not careful.
When your body continues to heat up and becomes dehydrated, it enters a survival mode, prioritising blood flow to your most essential organs and your skin to regulate temperature. At this stage, you might notice your heart rate climbing, your pace dropping, and your breathing becoming more laboured. Ignoring these early warning signs and continuing to push hard can be dangerous.
As your core and brain temperatures rise, your ability to accurately assess your own condition diminishes. This can lead to a breakdown in coordination, impaired judgment, and even confusion or disorientation. In severe cases, you may lose consciousness or experience heatstroke, which is a life-threatening emergency requiring immediate attention.
Factors affecting your susceptibility to humidity
Several factors can influence your susceptibility to humidity while running. Body size is one such factor: individuals with greater body mass tend to generate more heat and retain it more easily, due to both increased insulation and the extra energy required to move a heavier load. This increases the risk of overheating, especially in humid environments.
Your overall health, pre-existing medical conditions, and level of cardiovascular fitness also play a role. For example, people with heart or lung conditions may struggle more in humid conditions, as their bodies are less efficient at regulating temperature and oxygen intake. Age is another important consideration; older adults and very young runners are generally more vulnerable to heat-related illnesses because their bodies are less adept at temperature regulation.
Additionally, acclimatisation—how well your body has adapted to heat and humidity—can greatly impact your performance and safety. Runners accustomed to cooler, drier climates may find it particularly challenging to compete in hot, humid conditions. This is why it’s crucial to train in similar weather conditions before the race, allowing your body time to adjust its cooling and hydration mechanisms.
No matter your level of experience or preparation, it is essential to prioritise your health and well-being over race performance. Proper hydration is key: drink fluids before, during, and after the race, but avoid overhydration, which can also be dangerous. Adjust your pace according to the conditions, even if it means running slower than planned—your body will thank you in the long run.
Remain vigilant for early warning signs of heat-related illness, such as excessive fatigue, nausea, dizziness, headaches, tingling skin, muscle cramps, or confusion. If you experience any of these symptoms, it’s important to slow down, seek shade, and rehydrate. In some cases, the safest option may be to withdraw from the race, recognising that your health is far more valuable than finishing a single event.
Remember, there will always be other races and opportunities to challenge yourself.