Running in the Heat: What You Need to Know About Heart Rate Training

When the weather heats up, so does your heart rate — even if your running pace stays the same. For runners who rely on heart rate training, this can be confusing and frustrating. But it’s not a sign that you’re unfit or training incorrectly. It’s simply how your body responds to the heat.

Let’s break down what happens to your heart rate on hot days, why it matters, and how to adjust your training so you don’t sell yourself short.

Why Heart Rate Rises in the Heat

On a cooler day, your heart’s main job is to pump blood to your working muscles. But when it’s hot, there’s another demand: cooling your body down.

Here’s what happens in the heat:

• More blood is redirected to your skin to release heat.

• You sweat more, which reduces blood volume.

• Less blood is available for your muscles.

• Your heart has to pump harder and faster to meet both needs.

So even if you’re running at the same pace and effort, your heart rate will be higher.

The Common Mistake Runners Make

Many runners slow down when they see their heart rate creep into a higher zone on hot days. While this makes sense at first glance, it often reduces the effectiveness of your training.

For example:

• If you normally run Zone 2 at a certain pace, and in the heat that pace pushes you into low Zone 3, you don’t necessarily need to back off.

• As long as your effort (rate of perceived exertion) and pace feel right, it’s fine to spend some time in that slightly higher zone.

Slowing down too much can limit running economy and reduce the training adaptations you’re aiming for.

When You Should Back Off

There are times when a higher heart rate is a genuine red flag. Pay attention to the difference between heat-driven changes and signs of fatigue or illness.

• If your resting heart rate is elevated first thing in the morning, that may indicate fatigue or overtraining — in that case, reduce intensity.

• If you feel unusually fatigued or unwell during your session, listen to your body and adjust.

But if you’re feeling fine, running well, and it’s just hot outside, you don’t need to overcorrect.

How to Train Smarter on Hot Days

Here’s how to make heart rate training work when the temperature rises:

• Track more than just heart rate — use pace and RPE to confirm intensity.

• Don’t panic if you drift into a higher zone.

• Accept that heart rate will be slightly elevated on hot days.

• Focus on consistency and adaptation, not chasing perfect numbers.

By understanding why heart rate behaves differently in the heat, you’ll avoid sabotaging your training and keep making progress.

Building Aerobic Fitness for the ADF

For anyone preparing for the ADF or police, running performance and aerobic capacity are critical. That’s why I recommend combining heat-smart heart rate training with a structured program like my Beep Test Training Guide. It’s designed to help you build the aerobic base you’ll need to not only pass but excel at entry standards.

If you want to understand why simply scraping by on fitness tests isn’t enough, check out this blog on ADF PFA Standards: Why the Minimum Isn’t Enough.

Final Takeaway

Heat puts extra demands on your cardiovascular system. That means your heart rate will often be higher even when your effort and pace feel normal. Instead of slowing down unnecessarily, trust your body and your training data.

Use heart rate as a guide — not a rulebook. On hot days, stay focused on how you feel, keep an eye on your pace, and don’t let the numbers trick you into holding back.