Heat Acclimation For Runners | How To Adjust To Running In Hot Weather

Updated: Nov 11

Photo by: Michael Kappeler/dpa/Alamy via Nature.com

Athlete: Sviatlana Kudzelich

Historically increasing temperatures and global warming will impact your running performance now and into the future.

Since 1980, the average temperatures in the United States have climbed with furious consistency. Last summer was notably warm, with the number of 90 plus degree days peaking at 88 in Charlotte, NC, 30 days in Boston, 98 days in Sacramento, and 121 days in Miami, according to The Weather Channel.

As runners, it's important to be familiar with the term heat acclimation and understand that it's essential to allow the body time to adjust to hot temperatures. However, with this rate of change, is it time we seriously consider embracing the hot training days on the horizon, or do we opt for early mornings, night runs, or forgo both and opt for the treadmill?

Watching Olympic runners succumb to the heat last summer was disheartening. The officials' altered start times had little effect on those who had to drop from the race. Faces of agony seen uncharacteristically early in both the men's and women's marathons were a stark reminder that our atmosphere is changing.

Although steps have been taken to curb climate change, the likelihood that amateur, sub-elite, and professionals alike will have to become accustomed to "running hot" seems like the way of the future.

What Is Heat Acclimation?

Heat acclimation, or heat acclimatization, "is the improvement in heat tolerance that comes from gradually increasing the intensity or duration of work, or effort, performed in a hot setting," according to the CDC. As a runner, it's essential to take heat acclimation seriously because of the detrimental effects on health that can lead to serious internal injury or death in extreme circumstances.

It can take approximately 1 - 2 weeks for an individual to adjust to training loads in heat. (This is an estimate, and we advise that athletes and runners that train 5-6 days a week for more than 30 - 45+ minutes a session consider allowing 1 - 3 weeks to adjust safely)

*If an athlete has a break in the training of 5-7 days, or runs inside on the treadmill to avoid the warm temperatures, it will be necessary to reacclimatize to the heat.

How Can Runners Acclimate To Running In The Heat?

Heat acclimation can take as little as two weeks, but again, we advise using caution, allowing more time to adjust depending on the climate in your region.

When you begin the process of acclimatization, it's best that you temporarily reduce your training volume and intensity. Adjust your pace (think easy milage) and reduce the time spent in the elements.

If your training requires a hard, race-paced effort, cut the amount of time spent running at pace and fill the void with easy mileage. If the training schedule calls for a long run, but the temperatures are warmer than expected, temporarily reduce the run by mileage or time to avoid the risk of heat-related illness.

This cutback won't affect or limit your abilities as an athlete. Still, it will protect your body from potential adverse effects from attempting to maintain your typical paces without acclimating first.

What Happens When Runners Don't Acclimate To The Heat?

If a runner does not allow their body to acclimate to the heat safely, they place themselves at risk of minor and severe health complications, including:

  • Cramping

  • Heat rash (skin irritation from sweating)

  • Fainting (heat syncope)

  • Rhabdomyolysis (rapid deterioration, rupture, or death of muscle fibers)

  • Heat exhaustion

  • Heat stroke

When exposed to heat at rest, our body can more easily accommodate hot temperatures. However, when we are training, our body generates heat and tries to cool itself by sweating. When the temperatures increase, our body struggles to keep up with this cycle and can quickly overheat, leading to one or more of the above conditions.

What Are The Signs And Symptoms Of Heat-Related Illness?

Thirst - Thirst is the body's way of protecting itself from heat and dehydration. If you're thirsty, it's often a sign that you are already dehydrated. Review this article to assess if you are adequately hydrating during training. *You may need to consider increasing your fluid intake if you're training when it's hot out.

Cramping or muscle weakness - Our muscles require appropriate hydration to contract and relax efficiently during training. When a runner is dehydrated, these muscle functions can be significantly impaired. If not addressed, it may lead to muscle strains or a condition such as rhabdomyolysis.

Dizziness, headache, or nausea - The body has difficulty circulating blood with prolonged heat exposure due to dehydration. Dehydration can increase blood viscosity (or thickness), limiting the body's ability to circulate blood to essential organs such as the brain. This can lead to dizziness, headache, nausea, or fainting if an athlete has not acclimatized appropriately.

Dark-colored urine or significantly reduced urine output - When adequately hydrated, urine output should appear pale yellow. When we are dehydrated, our kidneys will attempt to hold in as much fluid as possible, which increases the concentration of the output, making it appear dark yellow and perhaps have a more pungent odor.

Heavy sweating - The body is designed to self-regulate all bodily functions, including regulating temperature. One of the quickest ways the body can compensate for overheating is sweat. However, sweating profusely is a sign that the body is struggling to keep up. *If you notice that you or a fellow athlete is sweating profusely, it's essential to take action. If you or a fellow athlete stops sweating in hot conditions, it may be necessary to contact emergency personnel.

Elevated body temperature and changes to skin appearance - Commonly, when an athlete is experiencing a symptom of heat-related illness, they will present with hot skin, rash, or perhaps clammy skin.

What To Do If You Or Another Athlete May Be Experiencing A Heat-Related Illness


Treatment for heat-related illness varies depending on severity. For minor concerns such as cramping, it's important to increase fluid intake (water) and perhaps introduce supplements such as electrolytes. *It’s essential to assess if adequate fluid and electrolytes are being consumed before, during, and after activity to reduce the chance of cramps when training or racing.

If an athlete has become thirsty during training or an event and is experiencing cramping, it's best that the athlete rests while slowly sipping water. Depending on the severity of the cramping, it may be worth forgoing training for the rest of the day to avoid adverse effects. If an athlete continues to train once cramping sets in, they may be at risk of breakdown of the muscle fibers, leading to muscle strains or worse (rhabdomyolysis).

Dizziness, headaches, or nausea

For moderate concerns such as dizziness, headaches, or nausea, which may be symptoms of heat exhaustion, the runner must be removed from the elements. Move the runner inside, find a shaded area, or form a makeshift canopy with t-shirts or towels.

Drink cool water in small sips to slowly bring the body temperature down. Use cold compresses such as cooling towels or soak a shirt in cool water and drape it over the athlete. *If there is any question about the symptoms an athlete is experiencing, call for emergency assistance, as time is of the essence to prevent severe damage.

Heat Stroke

If you suspect a runner is experiencing a heat stroke, immediately remove them from the elements and call 911. Apply a cold compress to areas of the neck, groin, and armpits, remove clothing, and elevate feet. Irreversible damage can occur in as little as 30 minutes if proper care isn't administered.

*Drinking water, if a runner is experiencing a heat stroke, can cause drastic swings in electrolyte levels, so it's best to consult with emergency personnel on the phone prior to pushing fluids. If a runner has taken in too much fluid and not enough electrolytes, they may be at risk of hyponatremia, which is a serious condition that can lead to heart rhythm irregularities. This is why it's important to account for both fluid and electrolyte intake to optimize performance and hydration status.


Centers for Disease Control, accessed 15 April 2022,


Clevland Clinic, accessed 15 April 2022,