When summer hits, runners start paying attention to the weather.
But there’s one mistake almost everyone makes: They only look at the temperature.
Humidity is just as important … and sometimes more.
Understanding the difference can help you train smarter and avoid burnout.
What Heat Does to Your Body
Heat raises your core temperature.
To cool you down, your body:
- Sends more blood to your skin
- Makes you sweat
- Increases heart rate
That means less blood is available for your working muscles, which makes every pace feel harder.
What Humidity Does
Humidity affects how well sweat works.
When the air is humid:
- Sweat doesn’t evaporate
- Your body can’t cool itself
- You overheat faster
That’s why a 75° humid day can feel worse than a dry 85° day.
Why Humidity Feels So Brutal
Sweating is your body’s air conditioner.
If the air is already full of moisture, sweat just sits on your skin instead of cooling you down. Your heart rate climbs, effort spikes, and fatigue shows up fast.
How to Adjust Your Running
On hot or humid days:
- Slow your pace
- Shorten your run
- Take walk breaks
- Run earlier or later
Trying to push through high heat and humidity is a shortcut to burnout.
Use Effort, Not Numbers
In summer, effort matters more than pace.
Your heart rate and breathing tell the real story. If it feels hard, it is hard, even if your watch says otherwise.
The Bottom Line
Heat stresses your body. Humidity blocks cooling.
Together, they make running feel way harder than it should.
Respect both, and your summer training will stay on track.