Don't want your run workout to get beat, then don't train by heart rate in the heat!
As you may know, I live in Thailand - which happens to be a rather hot country!
This is great for me as I love running in the hot weather! Suns Out. Guns Out. Right!?
But there is one drawback from running in hot conditions (aside from the fact that I get sunburnt easily!)...
If you've ever been running in hot weather, you've probably noticed it's harder than running in cool conditions.
So, how does this affect the kind of training runs we do and how we measure them?
Well, one of the most popular metrics we use in our training is our heart rate (HR). Doing workouts based on heart rate zones can be extremely beneficial as we can hit the correct intensity levels correct and reap the maximum benefits from the workout.
Source: runnersworld.com
However, if you live somewhere hot, then planning your workouts by heart rate may not always be the best plan.
When you run in the heat, your heart is doing overtime, as it's required to move blood to your muscles and also to your skin to keep you cool.
This causes your heart rate (HR) to be 5-10% higher, but not because you’re running too fast or that it gives a true indication of the exercise intensity.
At 60 to 75 degrees, heart rate increases by two to four beats per minute. From 75 to 90 degrees, heart rate increases up to 10 beats per minute, and humidity increases it even more. Perceived effort is accordingly much greater as both the temperature and the humidity rise.
But trying to lower your HR can mean you run too slow and not at your intended intensity.
So, if we're not gonna use HR, what else can we do to measure out workout intensity aside from heart rate?
Alternatives to Using Heart Rate in the Heat
When you run in the heat, there are 3 other metrics you can use to make sure your training is in the right zone:
1. Your Breathing
You can measure how easy or hard it is to breathe on a scale of 1-10, with 1 being super easy and 10 being that feeling when you're completely out of breath and gasping for air!
What you'll notice in hot weather is that although your heart rate may be higher than normal, your breathing should be at the correct difficulty. As most of the runs we do should be easy miles, your breathing should reflect this and it should be fairly easy to breathe
2. The RPE Scale
This involves you judging the effort that you're putting in. Again working on a scale of 1-10 with 10 being sleep-like activity and 10 being full-gas!
3. The Talk Test
Another option is to use the talk test. This is based on how many words or sentences you can get out of your mouth during your run. At max effort you should be unable to speak (as you simply try to get some oxygen back in your lungs!
Unlike the RPE Scale and your breathing, the talk test is a little bit less subjective. After all it's quite easy to see how well you can speak.
To illustrate the difference between running in the heat and "cool" weather, let's compare 2 runs that I recently complete.
Case Study: Hot vs Cool Weather
Before we dive in, it's worth noting that when I use the word "cool", we're talking about Thailand "cool"! The temperature around midday can be 35 degrees and the cooler weather in the evening maybe high 20s. So, although it's not "cool" in the same way as other places around the world, the difference is still notable.
Run 1 - 14th September 2021
The first run we'll look at was a fairly hard 8k effort which I did around 7pm, after the sun had gone down and so it was a little bit cooler. According to my Garmin Forerunner 945 the temperature was 32 - although we can't be sure how accurate that is!
In any case, it was noticeably cooler than in the afternoon!
Now let's compare this 8k run with 21k run I did a few days later...
Run 2 - Saturday 18th September 2021
This was my long run for the week of 21km. I set off around 10am and finished just after 12pm - so pretty much in some of the hottest part of the day. And ir was pretty hot that day up in the high 30s!
Normally, you'd expect that the quicker your pace, the higher your heart rate would be.
But what we can see from this data is that even though I ran the 21k run at almost 1 minute/km slower than the 8k effort, my average HR was a little bit higher.
THE WRAP UP
So, back to the original question in the title, "Should we train with heart rate in hot weather?"
Although I've shown you one comparison here, I'm sure you'll agree that running in hot weather does need more effort and you do have to work harder.
If you're training and running in hot conditions then it might be worth considering using either your breathing, the talk test or the RPE scale to get you into the correct zone of intensity.
What do you guys think? Do you always train with HR in hot weather? Does it affect you? Do you notice any difference?
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