Running in Extreme Heat: How Hot Weather Is Changing Marathon Training and Race Day

Healthy Hearty HabitsAug 15, 2026

Running in Extreme Heat: How Hot Weather Is Changing Marathon Training and Race Day

Marathon training has always demanded discipline, but rising temperatures are adding another variable that runners can no longer afford to ignore.

A training run that once felt routine can become significantly harder when temperatures and humidity climb. Pace slows, heart rate rises, sweat losses increase and recovery can take longer. On race day, those effects can become even more important because thousands of runners may be exposed to heat for several hours.

The answer isn’t necessarily to avoid running in warm conditions altogether. Instead, coaches and athletes are increasingly treating heat as another training variable—one that needs to be measured, respected and incorporated into race strategy.

For marathoners, that means the traditional question of “What pace can I run?” increasingly has to be accompanied by another:

“What pace can I safely sustain in these conditions?”

For a broader look at how exercise, training intensity, recovery and everyday movement fit together, see the complete guide to physical activity and exercise.

Why Heat Makes Marathon Running Harder

Running already produces a substantial amount of metabolic heat.

Your body has to get rid of that heat while simultaneously supplying working muscles with oxygen and maintaining cardiovascular function.

Hot weather makes the process more difficult.

As environmental temperature rises, the body relies increasingly on sweating and evaporation to cool itself. High humidity can make this especially challenging because sweat evaporates less efficiently.

The result can include:

Higher heart rate at the same pace
Increased perceived effort
Greater sweat losses
Faster dehydration
Reduced running pace
Increased thermal strain
Longer recovery requirements

Runners therefore need to recognize that environmental conditions can change the difficulty of a workout even when the distance and planned pace remain exactly the same.

Temperature Isn’t the Only Thing That Matters

A common mistake is to look only at the thermometer.

Two runs at the same temperature can feel dramatically different depending on humidity, wind, sunlight and other environmental factors.

Important variables include:

Air Temperature

Higher temperatures increase the body’s cooling challenge.

Humidity

High humidity makes sweat evaporation less effective.

Solar Radiation

Direct sunlight can increase the overall thermal load.

Wind

Air movement can improve evaporation and cooling, although conditions vary depending on speed and direction.

Clothing

Heavy or poorly ventilated clothing can interfere with heat dissipation.

This is why measures such as Wet Bulb Globe Temperature (WBGT) can be more informative than temperature alone when assessing heat stress. Environmental conditions should be considered as a combination rather than as a single number.

Why Marathon Pace Changes in Hot Weather

One of the most important lessons for runners is that pace and effort aren’t always interchangeable.

Suppose a runner normally completes an easy run at 5:00 per kilometer.

On a cool morning, that pace might feel comfortable.

On a hot and humid day, maintaining 5:00/km could produce substantially greater physiological strain.

Trying to force the same pace can turn an easy training run into a much harder workout.

That principle becomes particularly important during marathon training.

A slower pace in difficult weather does not necessarily mean a loss of fitness.

It may simply mean the environment has changed the cost of maintaining that pace.

Runners who are learning to adjust intensity can also benefit from understanding how shorter workouts can still provide meaningful exercise benefits, particularly when conditions make longer sessions more demanding.

Heat Acclimatization Is Becoming Part of Marathon Preparation

One of the body’s most useful responses to repeated heat exposure is heat acclimatization.

With gradual exposure to exercise in hot conditions, the body can adapt to handle thermal stress more effectively.

Heat adaptation can develop over roughly one to two weeks of repeated exercise in hot conditions, although the exact response varies between individuals and circumstances.

Heat acclimatization has become an important consideration for endurance athletes preparing for competition in hot environments.

The important word is gradual.

Trying to prove toughness by immediately performing hard workouts in extreme heat is not the same thing as structured heat adaptation.

How Runners Can Train for Heat

A practical heat-training approach starts with controlled exposure rather than maximum effort.

A runner might gradually introduce warm-weather running while reducing intensity.

For example:

Begin with easier sessions.
Keep the duration manageable.
Monitor how the body responds.
Gradually increase exposure.
Maintain appropriate hydration.
Avoid deliberately pushing toward heat illness.

Pushing to the point of heat exhaustion does not improve heat tolerance. Heat adaptation should therefore be viewed as training—not as a test of suffering.

Recovery also matters during this process. Runners can learn more about the role of recovery in how rest and recovery support healthy physical activity.

Should You Run During the Hottest Part of the Day?

Not necessarily.

There is an important distinction between training to tolerate heat and unnecessarily exposing yourself to dangerous conditions.

Running earlier in the morning or later in the evening can reduce exposure to the day’s highest temperatures and strongest solar radiation.

For most marathon programs, the priority should remain consistent training.

If an unusually hot afternoon makes a planned workout unsafe or excessively stressful, moving the session to a cooler time can be the smarter choice.

Training Pace Should Become More Flexible

Marathon training plans often prescribe specific paces.

Those numbers are useful, but they should not become a reason to ignore environmental conditions.

A sensible approach is to consider:

Target pace + perceived effort + environmental conditions

For example, an easy run should still feel easy.

A tempo session should resemble the intended physiological effort rather than becoming a race against the thermometer.

And a long run should develop endurance without unnecessarily turning into a survival exercise.

Consistency matters more than forcing performance during unusually difficult weather.

Long Runs Become a Critical Heat-Management Test

Long runs are where heat management becomes particularly important.

A marathoner may spend two, three, four or more hours exercising depending on pace and experience.

That creates prolonged exposure to:

Heat
Sweat loss
Sun
Fluid demands
Energy expenditure

Long runs therefore provide an opportunity to practice the entire race-day system.

That includes:

Drinking
Fueling
Clothing
Pace management
Cooling
Route planning
Recognizing early signs of excessive heat stress

The goal is not simply to finish the training run.

It’s to learn how your body responds.

Hydration Is Important—but More Isn’t Always Better

Hydration is one of the most discussed aspects of running in heat.

But the advice shouldn’t be reduced to “drink as much as possible.”

Fluid requirements vary substantially between runners.

They depend on:

Body size
Sweat rate
Temperature
Humidity
Running pace
Duration
Clothing
Individual physiology

Excessive fluid intake can create a dangerous condition known as exercise-associated hyponatremia, in which blood sodium becomes excessively diluted.

The objective is therefore appropriate hydration—not maximum hydration.

Why Electrolytes Matter

Sweat contains electrolytes, including sodium.

Long-duration exercise in hot conditions can result in substantial sweat and electrolyte losses.

Sports drinks and other electrolyte-containing products can help some runners replace both fluids and electrolytes during prolonged exercise.

However, individual needs differ.

Rather than blindly copying another runner’s hydration strategy, marathoners should practice their nutrition and hydration approach during training.

Practicing drinking during training can help athletes become more comfortable with their race-day strategy.

Don’t Experiment With Hydration on Race Day

A marathon is not the place to test a completely new hydration product.

If you’re planning to use:

Sports drinks
Electrolyte products
Gels
Salt-containing products
Different bottles or hydration systems

practice with them beforehand.

Your gastrointestinal system needs time to adapt to prolonged fueling as well.

The simplest race-day strategy is usually one that has already been tested repeatedly during training.

Cooling Is Becoming a Bigger Part of Race Strategy

When temperatures rise, cooling can become as important as hydration.

Depending on the event, runners may encounter:

Water stations
Ice
Wet sponges
Misting systems
Shade
Cooling stations

Cooling strategies can complement acclimatization and hydration during hot-weather road racing.

Runners can also think about cooling before the start, during the race and immediately afterward.

Pre-Cooling Before a Hot Marathon

Pre-cooling refers to strategies intended to reduce body temperature or thermal strain before exercise begins.

Depending on race conditions and available resources, runners may use approaches such as:

Cooling towels
Cold drinks
Ice
Shade
Air-conditioned environments before the start

The objective is to avoid starting the race already overheated.

However, any strategy should be tested during training rather than introduced for the first time on race morning.

Race-Day Warm-Ups May Need to Change

A long warm-up isn’t always appropriate in extreme heat.

For a marathon, the race itself provides a prolonged period of exercise, so excessive pre-race exertion can unnecessarily increase body temperature.

In very hot conditions, only a minimal warm-up may be appropriate.

This is one area where runners may need to abandon the idea that every race should begin with the same routine.

Clothing Matters More Than Ever

In hot weather, clothing becomes part of performance strategy.

Useful characteristics include:

Lightweight materials
Breathability
Good ventilation
Comfortable fit
Moisture management
Appropriate sun protection

A lightweight hat can also help reduce direct solar exposure.

Lightweight, breathable clothing can make warm-weather running more manageable, while hats and sunscreen can provide additional protection.

What About Sunscreen?

Sun protection matters during long outdoor training sessions.

A marathon can expose runners to several hours of sunlight.

A broad-spectrum sunscreen appropriate for exercise can help reduce sun exposure, while hats, sunglasses and clothing can provide additional protection.

Runners should follow the product’s application and reapplication instructions.

How Heat Changes Race Strategy

A hot marathon requires more than simply slowing down by a few seconds per kilometer.

The entire race strategy may need adjustment.

That can include:

Starting conservatively
Running by effort
Monitoring conditions
Taking fluids at appropriate opportunities
Using available cooling
Avoiding unnecessary surges
Adjusting expectations

The biggest mistake is often trying to run the race you prepared for in cool weather when the actual environment demands a different strategy.

The First Few Kilometers Matter

Many runners make the same mistake in difficult weather:

They start at their normal pace because they feel good.

But early in a marathon, adrenaline can mask the effects of heat.

The consequences may appear later.

A conservative opening can help preserve energy and reduce thermal strain.

When conditions are hot, patience becomes a performance tool.

Why Humidity Can Be Especially Challenging

Sweating is one of the body’s major cooling mechanisms.

But sweating only cools the body effectively when sweat can evaporate.

High humidity reduces the difference between the moisture on your skin and the surrounding air.

As a result, sweat may remain on the skin rather than evaporating efficiently.

That means a runner can be sweating heavily without receiving the expected cooling benefit.

Heat Can Change Your Heart Rate

As the body attempts to regulate temperature, cardiovascular strain can increase.

A runner may therefore see a higher heart rate while maintaining a slower pace.

This is another reason heart-rate and effort-based training can be useful during hot conditions.

The same numerical pace does not necessarily represent the same physiological workload.

Why Your Long Run May Feel Surprisingly Difficult

A common experience during hot-weather training is:

“I ran the same distance at almost the same pace, but it felt much harder.”

That doesn’t necessarily mean fitness has disappeared.

The environment changes the physiological demands of the session.

Heat can increase cardiovascular strain and fluid loss while reducing the body’s ability to dissipate heat.

The result is a training run that costs more effort than the same run in cooler conditions.

Heat and Recovery

Heat doesn’t stop affecting the body when the run ends.

A difficult hot-weather session can leave a runner feeling unusually tired.

Recovery should therefore include:

Cooling down
Replacing appropriate fluids
Eating adequately
Resting
Sleeping well
Monitoring how you feel before the next session

Hot-weather training can place additional demands on recovery, making it particularly important not to treat every difficult session as a reason to immediately increase training load.

When a Training Run Should Be Cancelled

There is no prize for completing a workout that has become unsafe.

Sometimes the correct training decision is:

Don’t run.

Alternative options can include:

Running indoors
Using a treadmill
Moving the session to a cooler time
Shortening the workout
Replacing it with easier exercise
Taking a rest day

When extreme weather makes outdoor training impractical, taking a break can sometimes be better for long-term consistency than forcing a session.

For runners looking for ways to maintain movement when a conventional workout isn’t practical, adding more movement to everyday life can provide another option.

Recognizing Heat Illness

Every runner should know the warning signs of heat-related illness.

Potential warning signs can include:

Dizziness
Unusual weakness
Headache
Nausea
Confusion
Fainting
Chills despite hot conditions
Unusual changes in sweating

Runners should slow down or stop and cool themselves if they develop concerning symptoms such as dizziness, unusual fatigue, chills or an inability to sweat despite the heat.

Heat Stroke Is an Emergency

Heat stroke is a serious medical emergency.

Signs can include:

Altered mental state
Confusion
Loss of consciousness
Severe overheating
Abnormal behavior

If heat stroke is suspected, the priority is immediate medical assistance and rapid cooling.

A runner should not attempt to “tough it out” or continue toward the finish line.

Race organizers and medical teams are responsible for providing appropriate emergency support, but runners also need to recognize when they should stop.

Why Race Organizers Are Changing Their Approach

Extreme heat doesn’t only affect athletes.

Race organizers also have to consider:

Start times
Course exposure
Water stations
Medical resources
Cooling stations
Volunteer safety
Emergency response
Weather forecasts

Competition organizers increasingly have to monitor temperature, humidity and other heat-related environmental measures during endurance events and make adjustments when conditions create significant risks.

Race Start Times Could Become More Important

Moving a race start earlier can reduce exposure to the day’s peak temperatures.

This is one reason many endurance events are scheduled around cooler periods of the day.

As organizers face more challenging weather patterns, start-time decisions may become an increasingly important part of race planning.

What Climate Change Means for Marathon Running

The broader issue goes beyond individual races.

Climate change is creating more frequent concerns about heat exposure across outdoor sports.

For marathon organizers, this can mean reconsidering:

Race calendars
Start times
Course design
Hydration infrastructure
Medical coverage
Heat policies

For runners, it means environmental preparation may need to become a standard part of marathon training rather than an occasional consideration.

Training for the Weather You Might Race In

One of the most useful concepts in heat preparation is specificity.

If your target marathon is likely to be hot, training occasionally in similar conditions can help you understand:

How quickly you sweat
How your pace changes
How much you need to drink
Which clothing works
How your stomach responds to fueling
How your heart rate behaves
How quickly you overheat

Warm-weather training can provide valuable familiarity before competition.

That experience can be valuable on race morning.

But Don’t Chase Heat for the Sake of Heat

There is a difference between preparation and unnecessary risk.

A runner doesn’t need to seek the hottest possible conditions to become heat-ready.

Heat exposure should be gradual and appropriate to the athlete’s experience and circumstances.

The objective is adaptation—not exhaustion.

Gradual acclimatization is important, and pushing to heat exhaustion does not improve heat tolerance.

How Beginner Marathoners Should Approach Heat

New marathoners should be especially cautious because they may not yet know their sweat rate, fueling requirements or response to prolonged heat exposure.

A sensible approach is to:

Build aerobic fitness first.
Introduce warm-weather running gradually.
Keep easy runs genuinely easy.
Practice hydration and fueling.
Monitor symptoms.
Avoid forcing scheduled paces during extreme conditions.
Seek professional advice when appropriate.

There is no advantage in trying to imitate the heat-training practices of an elite athlete without considering differences in experience, training volume and individual circumstances.

What Experienced Marathoners Can Learn From Heat Training

Experienced runners can use warm conditions as a form of race-specific preparation.

A well-managed hot-weather session can reveal weaknesses that may remain hidden in cool conditions.

For example, a runner might discover:

Their planned pace is too aggressive.
They need a different hydration strategy.
Certain clothing causes excessive heat retention.
Their fueling plan doesn’t work at high temperatures.
They recover more slowly after hot long runs.

These lessons can be extremely valuable before race day.

A Practical Hot-Weather Marathon Checklist

Before Training

Check the weather.
Consider temperature and humidity.
Choose a cooler time if appropriate.
Plan your route.
Bring suitable fluids for longer sessions.
Wear breathable clothing.
Protect yourself from excessive sun exposure.

During Training

Start conservatively.
Run by effort.
Monitor how you feel.
Drink according to your practiced strategy.
Use shade where possible.
Stop if concerning symptoms develop.

After Training

Cool down.
Replace appropriate fluids.
Eat adequately.
Monitor recovery.
Allow additional rest if needed.

Before Race Day

Check the forecast.
Review the event’s heat policies.
Practice your race-day fueling.
Know where aid stations are located.
Prepare appropriate clothing.
Adjust your performance expectations if conditions demand it.

Frequently Asked Questions

Does Running in Heat Make You Fitter?

Heat exposure can produce physiological adaptations that improve heat tolerance, but it should be introduced gradually and safely. Heat training is not a replacement for normal endurance training.

Should I Run at My Normal Marathon Pace in Hot Weather?

Usually, forcing your normal pace in significantly hotter conditions is not a good strategy. Effort and environmental conditions should influence pacing.

How Long Does Heat Acclimatization Take?

Meaningful heat adaptations can develop over roughly one to two weeks of repeated exposure, although individual responses vary.

Should I Drink as Much Water as Possible?

No. Excessive drinking can be dangerous because it can contribute to exercise-associated hyponatremia. Hydration should be appropriate to the conditions, duration and individual needs rather than based on a goal of consuming as much fluid as possible.

Is Running in Humidity Worse Than Running in Dry Heat?

High humidity can make cooling more difficult because sweat evaporates less effectively. The actual impact depends on temperature, humidity, wind, sunlight and individual factors.

Should I Skip a Long Run Because It Is Extremely Hot?

If conditions are unsafe, changing the timing, shortening the session, moving indoors or resting can be the better choice. A single modified workout is preferable to a heat-related illness that disrupts weeks of training.

Does Heat Affect Marathon Race Times?

Yes. Hot conditions can increase physiological strain and make a given pace harder to maintain. Race strategy should therefore account for environmental conditions rather than relying solely on a cool-weather target time.

The New Marathon Skill: Managing the Environment

Marathon training has traditionally focused on mileage, pace, recovery, nutrition and strength.

Heat adds another layer.

The strongest marathon preparation increasingly involves learning how to manage the environment rather than simply trying to overpower it.

That means understanding how your body responds to temperature, practicing hydration and fueling, adjusting training intensity, using appropriate clothing and developing a realistic race strategy.

Most importantly, it means recognizing that slowing down can sometimes be the smarter performance decision.

When the Weather Becomes Part of the Race

A marathon is never run in a vacuum.

The course, elevation, wind, temperature, humidity and sunlight all become part of the challenge. As hot-weather conditions become a more prominent consideration for endurance events, runners have an opportunity to treat environmental preparation with the same seriousness they give to mileage and pacing.

Heat acclimatization can help the body adapt. Practiced hydration and cooling strategies can improve race-day preparation. Flexible pacing can prevent an ambitious target from becoming an unsustainable effort.

But none of those strategies replaces judgment.

The best hot-weather marathon plan is ultimately one that allows the runner to train consistently, recognize danger early and arrive at the finish line healthy.

Because when temperatures rise, the smartest runner isn’t necessarily the one who refuses to slow down.

It’s the one who knows exactly when slowing down is what keeps the race—and the training journey—on track.