Why Humidity Makes Running Harder
Humidity makes running feel harder because it interferes with your body’s main cooling system: sweat evaporation.
When you run, your muscles generate heat, and your body releases sweat to help regulate your temperature. In dry conditions, that sweat evaporates from your skin and carries heat away, effectively cooling you down. But in humid weather, the air is already saturated with moisture. This makes it harder for sweat to evaporate. Instead of cooling you, sweat tends to sit on your skin or drip off, meaning your body holds onto more heat.
So if you find yourself overheating sooner or struggling to hit your usual paces in humid conditions, it’s not a loss of fitness. It’s simply your body working harder to deal with heat it can’t release as efficiently.
Practical Tips for Running in Humidity
Timing
Run early morning or later evening, when temperatures are cooler and humidity is often lower.
Avoid the midday heat, when heat stress is highest.
Gear
Wear lightweight, moisture-wicking fabrics to help sweat evaporate.
Minimise coverage where possible (shorts, singlets, light colours).
Route Planning
Choose routes with shade and access to water fountains.
Consider multiple loops so you can refill water or stop if needed.
Consider training on the treadmill for a controlled environment.
How to Control Pace and Effort in Humidity
Pace becomes a less reliable measure of effort in humid conditions. If you stick to pace targets that don't consider the humid conditions, you’ll likely push your heart rate too high and fatigue much faster. That’s why it helps to switch your focus from pace to effort.
Use RPE Instead of Pace and Adjust Pace Targets
RPE (Rate of Perceived Effort) is simply how hard a run feels on a scale from 1–10.
In humid conditions, effort is a better guide than pace because it reflects what your body is actually experiencing. An easy run should still feel easy, even if the pace on your watch is slower than usual.
Accept the slower pace and don't be afraid take the ego out of it. As long as the effort stays in the right range, you’ll still get the intended training benefit without overloading your body.
Understanding Heart Rate in Humidity
The same principle applies if you’re using heart rate to guide your runs.
Cardiovascular drift is the gradual rise in heart rate that happens during prolonged runs, even when your pace stays the same. In all conditions, as you run, factors like rising body temperature and fluid loss reduce the amount of blood your heart pumps with each beat, so your heart compensates by beating faster to keep delivering enough oxygen to your muscles.
The effect of humidity on this: When humidity is high, cardiovascular drift happens earlier and more strongly. Your heart rate rises faster even if your pace hasn’t changed, and the same pace can start to feel harder than it would without the humidity. This is a normal physiological response.
So if you do use heart rate to guide your training, you’ll need to slow your pace to stay within the intended effort zone of your session. This again ensures the effort remains appropriate and you still get the correct training benefit.
Adjusting Your Training Plan During Humid Periods
The goal of every session in your plan is to deliver a specific training adaptation, whether it's to build your aerobic base fitness through easy miles, or sharpen speed and pace with an interval or tempo session. Here's how to adapt your sessions.
Session Type | What to Adjust |
Easy Runs | Slow down. Focus on the time the run would normally take rather than the exact distance. For example, if a 5K easy run usually takes you 30 minutes, try running for 30 minutes at an easy effort and ignore the distance covered. |
Long Runs | Same as above. If your long run includes sections at a faster effort (e.g. marathon pace effort), keep the structure and timing of the efforts, but allow the pace to slow to match the conditions. If extreme, it’s also reasonable to shorten the number or duration of the faster segments. |
Tempo / Intervals | Keep the session structure but allow your pace targets to slow to match the intended effort. If conditions are extreme, reduce the number of reps or pause and take extended recoveries to keep the session controlled. |
Rest Days | Fuel and hydrate well with electrolytes. |
Hydration and Fueling in Humidity
You may be sweating more than you think
Sweat rate in humidity can reach 1–2 L per hour (or more).
Humid air slows sweat evaporation, so sweat sits on your skin instead of cooling you.
Your body responds by sweating even more to try to cool down.
Result: Many runners underestimate how much fluid they’re losing.
Don’t wait until you feel thirsty
By the time you feel thirsty, you can already be dehydrated which can:
Raise heart rate
Increase perceived effort
Reduce performance
Tip: Start runs well hydrated and sip fluids regularly throughout the entire day and week.
Replace electrolytes, not just water
Sweat contains important minerals:
Sodium
Potassium
Magnesium
Drinking only water can dilute blood sodium, which may worsen cramping and fatigue. Replace electrolytes as well as fluid. Electrolytes become particularly important for runs longer than 60 minutes in humidity.
Fueling also matters more
Hot conditions can increase glycogen use, meaning you may burn through fuel faster. To avoid bonking:
Take gels, chews or mid-run snacks slightly more frequently during long efforts
Carry an endurance drink (such as Skratch) to boost carb intake while simultaneously covering the higher fluid and sodium needs that come with humidity.
Race Day in Hot & Humid Conditions
You may be expecting a humid race day depending on the location and time of year you’ve chosen. If you’ve been training in similar conditions, your body will likely be better prepared. However, if humidity is predicted to be higher than expected on race day, you may need to adjust your expectations and focus on hydration. Our heat racing tips will apply here – see the article below for more guidance.
Heat and Humidity Acclimatisation
If you're training and racing in a persistently hot and humid climate –acclimatisation will work. Your body will adapt and get used to the conditions, and over 2–3 weeks the same effort will start to feel noticeably easier.
If you're training in cool conditions but racing in humidity – deliberately exposing yourself to some heat and humidity during training, or using a steam room and sauna regularly after training helps your body get used to handling higher temperatures and humidity.
If heat is just temporary during a heatwave or a vacation – protect your training by adjusting based on effort.
It’s important to remember that heat acclimatisation is a training stimulus in its own right and places additional physiological stress on the body. It shouldn’t be stacked on top of increases in mileage or intensity.
Final Takeaways
The most important thing is to listen to your body and prioritise safety in extreme conditions. Focus on effort rather than pace, keep on top of hydration and adjust your expectations if your pace needs to be slower than usual.