Heat and Heart Rate Zones: How Weather Can Affect Your Training HR

A popular approach to endurance training, both for runners as well as for other endurance athletes like cyclists, is heart rate training.

Heart rate training involves monitoring your heart rate during exercise and aiming to keep your heart rate within specific predetermined “heart rate zones,“ depending on your age, fitness level, workout goals, etc.

But, do you need to adjust your heart rate zones in the heat or cold? Keep reading to find out how heat and heart rate training are linked.

We will look at: 

  • What Is the Benefit of Heart Rate Zone Training for Runners?
  • Heat and Heart Rate: How Does Heat Affect Heart Rate Zones During Workouts?
  • Do My HR Zones Change In the Cold?
  • Does Dehydration Affect HR Training?

Let’s jump in!

A person checking their running heart rate in the heat.

What Is the Benefit of Heart Rate Zone Training for Runners? 

While there are pros and cons to each of the various approaches to training for runners and other endurance athletes, there are several notable benefits of heart rate training for runners or training by heart rate.

Brett Lato, the Manager of Training and Education at Polar, one of the leading companies at the forefront of heart rate monitoring technology for athletes, says that heart rate zone training can be an effective tool for runners at every fitness level. 

“Essentially, each heart rate zone represents a different level of intensity so runners can better understand how hard they are pushing themselves during a training session,” explains Lato.

“Precise knowledge of your training intensities can ensure you receive the desired effect from your sessions.” Lato says that there are many factors that impact your heart rate, including your fitness level and aerobic capacity. 

“Because your heart rate is personal, it’s important to determine your unique maximum heart rate to optimize your training zones,” advises Lato.

“Using a heart rate monitor is the most effective way to determine your maximum heart rate and personalized heart rate zones, so you can accurately track your progress over time.”

A person running with a heart rate monitor.

Heat and Heart Rate: How Does Heat Affect Heart Rate Zones During Workouts?

One of the downsides of heart rate training is that even for the same individual, the heart rate during exercise, or even during everyday life, can be impacted by a number of factors such as your stress level, hydration level, and even temperature.

This means that other factors can impact your heart rate while running or working out from just the workout intensity or type of exercise you are doing in and of itself.

In most cases, heart rate variability factors that impact heart rate are often not significant enough to have a massive impact on heart rate zone training.

This means that even though a slight elevation or depression of your heart rate from environmental factors won’t shift you into another heart rate zone, it can be helpful to consider these factors if you are using heart rate training.

In particular, running in the heat and humidity can increase your heart rate. Humidity makes running in hot temperatures even more taxing on the body because when the moisture content of the air is higher, it feels hotter.

A person running, looking at their running watch.

“Running in hot temperatures can challenge anyone, even elite athletes,” says Lato. “It’s important to make adjustments and tune into what your body needs to prevent risk, especially in high heat.”

Lato further explained how temperature affects heart rate training and increases your heart rate in general:

“Exercise generates heat and increases our body temperature,” says Lato. “As your body temperature increases, whether from exercise, heat or a combination of both, your heart must work harder to increase circulation in an effort to cool down.”

So, when you are exercising in an already hot environment, your body temperature can increase rapidly and exceed the “safe“ range.

As such, the body doubles down on the thermoregulatory mechanisms that are normally initiated during exercise to cool your body down: sweating and increased blood flow to the skin.

These are both energy-intensive processes, so your heart rate can increase.

This explains why your heart rate running might be higher in the heat and humidity, but just noting a higher heart rate during summer workouts or running in the heat isn’t necessarily enough.

A person bent over, looking at their running watch.

“If you get too hot while exercising, your body temperature can rise above normal, leading to heat exhaustion and other heat-related illnesses, like heat stroke,” warns Lato.

“You’re also more susceptible to dehydration, so it’s important to drink water to help control body temperature.”

Lato provides some advice for running in the heat:

“Be sure to pay attention to signs of dehydration and heat exhaustion when running in heat like dizziness, nausea, and headaches.

Your heart rate is another effective way to listen to your body during your training, especially in the heat to make necessary adjustments and continue running safely.”

In other words, even though you might be frustrated to see a higher HR on your HR monitor when running in the heat, you should use that biometric data to provide insight that your body is working overtime.

You should look at the heat index using a heat index calculator like the one here, which can help you determine the “real feel” of the heat and the impact of heat on heart rate.

A person looking at their fitness tracker.

Do You Need to Adjust Your Heart Rate Zones In the Heat?

“Because your heart rate will be elevated in the heat, you’ll find that you’re reaching higher zones with a slower pace, and that’s okay. ”

“When training in the heat, you may want to reduce your average speed rather than trying to maintain your regular pace at a higher heart rate,” advises Lato. “This can be done by slowing down or extending recovery periods during interval runs.”

While some runners may be concerned that slowing down will negate the purpose of HR training for runners, Lato says this isn’t true.

Rather, adjusting your HR zones in the heat is exactly what heart rate training is all about—using your heart rate to guide your training.

“You’ll find that even with this adjustment, you can still see benefits from following your heart rate zone training while reducing risk,” suggests Lato.

A person tying their shoe getting ready to run.

Do My HR Zones Change In the Cold?

Generally, it’s thought that the main impact of temperature on heart rate zones or heart rate training comes when it’s hot out, not cold.

“In cold weather, it’s possible your heart rate will slow. This means you may be able to maintain a faster pace or higher intensity at a lower heart rate,” explains Lato.

“Your heart rate zones will not change, but training in cold weather is a great time to improve your strength and endurance since you’ll be less fatigued.”

In other words, you might have to push your body a little harder to hit the same heart rate zones in the cold, but this is where you “win back” the adjustments in the effort you had to make with HR training in the summer heat.

A person looking at their running watch.

Does Dehydration Affect HR Training?

Some studies suggest that it’s actually dehydration—and the subsequent drop in plasma volume—that causes the impact of heat and heart rate we generally see (an increase in HR exercising in the heat), rather than the heat itself.

A weight loss of 1.5% due to dehydration can cause an increase in about 7 bpm of your heart rate. This is significant enough to impact your heart rate zones.

Thus, the best you can do to keep your fluid levels up while running in the heat will help minimize the heart rate elevation in the heat.

Lato says an increased heart rate can also be a sign of dehydration. 

According to Lato, “If you notice your heart rate increasing with no change in your pace or other variables, you should consider resting and increasing your fluid intake.”

Here again, is where using a heart rate monitor with your training can help guide your workouts and give you insights into your fitness.

A person looking at their running watch.

“A heart rate monitor is the most effective way to measure your intensity during training and track your progress over time.”

“Recognized as the gold standard in accuracy, Polar offers a suite of heart monitors and watches for every type of training and every athlete,” suggests Lato.

He provides a few suggestions of the best heart rate monitors for runners from the Polar running watches and fitness watches:

#1:Polar Pacer Pro

The Polar Pace Pro is the perfect companion for those beginning their training. 

#2: Polar Vantage V3

For those who want to take their training to the next level, the new Polar Vantage V3 offers advanced and precise optical heart rate tracking.

This includes the new breakthrough Polar Elixir™ biosensing technology which provides a comprehensive suite of training and recovery tools including blood oxygen saturation, wrist ECG, skin temperature, and more.  

If you are interested in using the heart rate training method, the first step you will need to take is to accurately calculate your heart rate zones. Learn how to calculate your heart rate zones here.

A person looking at their running watch.
Photo of author
Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a NASM-Certified Nutrition Coach and UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.