How to Adjust Your Marathon Training Plan for High Humidity and Heat

Why Heat and Humidity Make Running Harder

Your body cools itself by evaporating sweat. When humidity is high, sweat evaporates less efficiently, making it harder to regulate body temperature. As a result:

• Your heart rate increases at the same pace.
• You sweat more and lose fluids faster.
• Your perceived effort rises.
• Recovery takes longer.

It is completely normal for your pace to slow during hot and humid conditions.

Run by Effort Instead of Pace

One of the biggest mistakes runners make is trying to hit their usual pace regardless of the weather. Instead, use:

• Heart rate zones.
• Rate of Perceived Exertion (RPE).
• Conversation pace for easy runs.

If your easy pace normally is 5:30/km, don't be surprised if it becomes 5:50-6:10/km on a hot, humid day.

Reduce Training Intensity When Necessary

You don't have to skip workouts, but you should be flexible.

• Reduce interval volume by 10-20%.
• Take longer recovery between repeats.
• Convert tempo runs into steady efforts if conditions are extreme.
• Postpone key workouts if there is a heatwave.

Consistency beats forcing one difficult session.

Train During Cooler Parts of the Day

The safest times to run are:

• Early morning.
• Late evening.

Avoid the hottest hours, especially when temperatures exceed 30°C or humidity is exceptionally high.

Hydrate Before, During and After Your Run

Hydration becomes much more important during summer training.

• Drink regularly throughout the day.
• Carry water on runs longer than 60 minutes.
• Include electrolytes for longer sessions or heavy sweating.
• Replace fluids after your workout.

Dark urine, dizziness and headaches are signs you may already be dehydrated.

Adjust Your Long Runs

Long runs create the greatest heat stress.

• Start before sunrise when possible.
• Plan routes with water fountains.
• Loop back regularly for drinks.
• Slow your pace from the beginning.

Remember that completing the planned duration is usually more important than maintaining a specific pace.

Wear Clothing That Helps You Stay Cool

• Light-coloured technical clothing.
• Breathable fabrics.
• A lightweight cap or visor.
• Sunglasses with UV protection.
• Apply sunscreen before heading out.

Allow Time for Heat Acclimation

Your body gradually adapts to hot weather over one to two weeks. During this period:

• Expect slower paces.
• Keep most runs easy.
• Increase exposure gradually.

As your body adapts, you'll sweat more efficiently and tolerate the conditions better.

Know When to Stop

Stop running immediately if you experience:

• Dizziness.
• Confusion.
• Chills despite hot weather.
• Loss of coordination.
• Nausea or vomiting.

These can be warning signs of heat illness and require immediate cooling and medical attention if symptoms persist.

Frequently Asked Questions

Should I skip workouts when it's extremely hot?

If conditions are dangerous, move the workout indoors, train earlier, reduce the intensity, or postpone it. Missing one workout is better than risking heat illness.

How much slower should I run?

There is no fixed adjustment. Focus on effort rather than pace. Many runners naturally slow by 10-30 seconds per kilometre or more in hot and humid weather.

Can training in the heat improve performance?

Yes. Gradual heat acclimation can improve your body's ability to regulate temperature and may benefit endurance performance, provided training is managed carefully.

Final Thoughts

Training in heat and humidity requires flexibility, not stubbornness. Adjust your pace, reduce intensity when needed, hydrate well, and prioritise recovery. Marathon fitness is built through consistent training over months, and smart adjustments during hot weather will help you arrive at race day healthier and stronger.

Once you've adapted your training, the next question is what to actually do differently on race day itself — see our marathon race-day heat strategy for pacing, cooling and fuelling adjustments specific to the day.