Heat Acclimation and Tips for Staying Safe

Updated: Jun 7

We are approaching that time of year again! Hot weather running provides a unique training stimulus. We can use that to our advantage but we also need to plan a few precautions to keep it safe.




How Does the Body Respond to Hot Weather Training?


Ass temperature rise, the effort required to run your usual paces will increase. This will be different for everyone but generally speaking, once you get above 55 degrees, you can expect a 1-3% decrease in performance for every 10 degree increase.

When the temperatures rise, multiple physiologic changes happen:

  • Heat and humidity will increase your baseline heart rate. Higher heart rates mean different training objectives (like your easy run just turned in to a tempo run)

  • In an attempt to cool your body, blood will be diverted towards your skin. This decreases the amount of blood and oxygen going to fuel your muscles.

  • Of course, you can expect to sweat more during the hot summer months. Sweating is our body's response to keep cool. As the sweat evaporates, we start to feel cooler.

  • However, in high humidity the sweat does not easily evaporate and this can make it feel hotter and increase perceived effort.

  • When you sweat more, your blood volume will slightly decrease meaning that there will also be a decrease in blood returning to the heart for distribution to the body.

It will take your body about 10 days to adjust to the demands of heat training.


How can you alter training?

Make the mental shift. I know, runners love pace targets but this is the time to run by perceived effort or heart rate.


Your goal for long runs is to improve aerobic fitness. That happens in a specific heart rate range. Use these tactics to make your training productive.

  • To run by heart rate, find your heart rate max (easy calculation is 220-age). Then keep your heart rate between 50-70% of your heart rate max.

  • To run by perceived effort, check in with your breathing. Your breathing should be even and not taxing. You know that easy feeling, right?

Use the weather as your guide. The dew point point because that is a good indication of how efficiently your body will be able to sweat for cooling effects.

It is an important consideration to avoid over training or mentally beating yourself up over missed paces. Use this guide to determine if you should proceed with your training run as planned or modify for safety.

Remember smart training is the best training!



Tips for Staying Safe In Hot Weather


1. Change the time of day that you are running


Run early in the morning (even before the sun comes up) or in the evening to take advantage of the coolest parts of the day.


In the past, summer training for our marathons meant starting runs at 4:30 in the morning on Saturday while it was still dark outside. This gave us a chance to be finished by 7:30am.


I know that getting up early isn’t for everyone. If you have a short run on the schedule, running in the evening before sunset should work.


Or, at the very least find a shaded trail to keep you out of the direct sunlight if you have to run mid day.


Make sure that you are visible if you are running at dusk or dawn. Neon colors or reflective gear will help drivers to spot you and steer clear.



2. Hydrate, hydrate, hydrate


Make sure that you are well hydrated before you go out for your run. This means setting a goal to drink between 80-120 ounces of water daily.


Set a goal to consume about 8-10 ounces of water in the hour before you start.


For runs longer than 40 minutes, you will want to carry water with you, drop a bottle at a point on your loop, or plan a route that will go past water fountains.


For runs longer than 60 minutes, you will also want to start thinking about electrolyte and sodium replacement. This comes down to runner’s preference: Nuun, Gatorade, sodium tablets. Stick to what works best for you.


3. Run with a buddy


If you are going to be outside for a medium to long run and the heat index is high, run with a buddy.


You may not pick up on some of the early signs of heat exhaustion but your running buddy may notice them.


If you don’t have a running buddy available, let a friend or family member know that you are going out for a run just in case you would get into trouble and may need a ride home.


4. Protect yourself


Wear your sun protection, light color clothing and know the symptoms of heat exhaustion and heat stroke. Sun screen and a hat will go a long way to protect your skin while lighter color clothing will provide some reflection of the heat.


Heat Exhaustion: Fatigue, nausea, headache, increased sweating, muscle cramps, confusion, anxiety, cool clammy skin, dizziness, fainting

  • What should you do? Stop exercising, get out of the heat and hydrate! Find a shady spot or move in doors. You can also mist your skin with cool water, lie down and elevate your feet. Your primary goals are to cool and re;hydrate.


Exertional Heat Stroke: Characterized by body temperatures above 105 degrees Fahrenheit, fainting/collapse, irritability, confusion, seizures

  • What causes this? Exertional heat stroke is a combination of metabolic heat production from exercise and environmental heat load.

  • This is in comparison to traditional heat stroke which occurs from passive heating (high temperatures) in non heat acclimated individuals.

  • It is important to note that dry skin and the absence of sweating are seen in traditional heat stoke. That is not an accurate way of identifying exertional heat stroke.


  • What should you do? This is a medical emergency that requires immediate action to prevent multi-system organ failure and/or death.

  • The first step is aggressive cooling by immersing the athlete in cold water then immediately transporting to a hospital for treatment.

  • If you do not have access to trained personnel or cold water for immersion, then call 911 for transport.


If you are interested in the nitty gritty and the research, this is another great article on the effects of humidity and heat on running


National Athletic Trainers Association Position Statement on Exertional Heat Stroke

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