You’ve set off at a slow pace and you’re breathing comfortably. You complete a nice 5K in a relaxed time and your body feels like it could go again.
But wait… you check your Strava data, and something doesn’t look quite right.
“Why is my heart rate high on easy runs?”
If you see an unexpected spike in your heart rate on an easy run, it can be both disconcerting and discouraging (if you are using heart rate as a performance indicator).
But the truth is that there are many factors that can influence a runner’s heart rate, and the rate you saw yesterday may differ from the rate you’ll see tomorrow.
In this guide, we dig a little deeper to address what can cause a high heart rate on an easy run.
What Causes A High Heart Rate On A Run?
We’re going to avoid the most obvious factor, which is a sudden increase or decrease of intensity.
It shouldn’t come as a surprise to anybody if your heart rate takes off when you turn on the burners to finish strong in a race with an aggressive negative split.
Let’s focus on some of the more abstract factors. The things that might not be obvious while you’re running, but can actually result in a dramatically different heart rate on the same predictable slow run.
Hot and Humid Weather
One of the most common reasons for a high heart rate on easy runs is hot and humid weather. Runners who live in areas where it’s common to see summertime conditions might be tempted to give up on heart rate as a performance indicator altogether.
The reason for this is because as your body temperature rises, it has to work harder to cool down. In order to do this, the heart pumps more blood per minute, and therefore has a higher heart rate.
Heat is also dehydrating, which can make your body work even harder to cool down.
Unfortunately, we don’t get to pick and choose the weather when we set out on our morning run.
If you are using heart rate to ensure that the run stays ‘easy’, the only solution here is to reduce speed to compensate for the extra work your body is having to do to stay cool.
Dehydration
If we had to diagnose an abnormally high heart rate on an easy run, the first thing we’d want to check is hydration levels.
Given that dehydration makes the body work harder to regulate temperature, it’s no surprise that many runners find their heart rate skyrockets when they’re running in a state of dehydration. This could be from as something as simple as the common cold.
In order to determine if this is your problem, you can monitor both weight and heart rate before and after a run with a Sweat Test. Remember, hydration levels fluctuate throughout the day, so make sure you collect accurate data.
Dehydration is the enemy of all runners.
Always ensure that you take on sufficient water before (and during) your run. If you are going on a longer run, it is even more important to re-hydrate along the way.
Caffeine
Dehydration can cause a higher heart rate on an easy run, and the combination of caffeine and dehydration is a match made in hell.
Many of us swear by a cup of coffee before our runs.
And many of us are familiar with the caffeine-packed energy gels that are classic mid-run fuel fodder over a long distance.
What some runners forget is that caffeine can have a significant impact on heart rate.
It directly affects the central nervous system, and raises your blood level of epinephrine. In basic terms… it gives you a shot of adrenaline.
Some people are more susceptible to caffeine than others. Some of us can wolf down six cups of coffee and barely flinch, while others only need a very small amount to feel a clear physical effect (often described as the caffeine jitters).
If you’re anything like us, your first reaction is “but caffeine gives me energy.” However, if you are using caffeine to get through your easy runs on busy days when sleep was limited, don’t be surprised to see that your heart has had to work harder to get the job done.
Which brings us to…
Lack Of Sleep / Exhaustion / Fatigue
Running with a tired body works against so many of our goals as runners: speed, distance and consistency among them. This goes doubly for ‘easy’ runs… almost triply because we want those types of workouts to be consistent and reliable, without wild swings in heart rate.
If you are exhausted, your body is going to do everything it can to protect itself. This means conserving body fat for later, so the only source of fuel available for runs is carbs.
If you’re not eating enough carbs throughout the day (especially within an hour or two before the run), then your heart rate is likely higher than it needs be on easy runs, forcing you to run slower if you want to stay in lower heart rate zones.
It’s simple math: with carb stores low, fatigue sets in and you’re forced to slow down to match the effort level. No longer able to sustain a speed that allows you continue burning excess fat, your heart rate increases as extra oxygen is needed to make up for lack of stored energy. You might even experience shortness of breath as your body is forced to work harder to meet the oxygen demands of running.
The best solution for exhaustion? Fix sleep quality and quantity! You’ll be amazed at what you accomplish when you’re not spending the day in a zombie-fied state.
High Altitude
Again, there’s not much you can do about this.
If you know that you’re going to be running at an increased altitude, one of the things that you should be aware of is the effect this will inevitably have on your heart rate.
There’s no defying altitude.
The decreased atmospheric pressure at higher altitudes means that your body requires more oxygen than usual to function correctly, which makes the heart work harder. This is why it’s crucial to adjust your running accordingly – you’ll need to re-adjust your pace to compensate.
We can’t imagine there’ll be many applicable readers for this, but if you’ve just swapped your location for one of high altitude and you’re wondering why your heart rate is higher on an easy run – this will be the reason!
What Can I Do To Lower My Heart Rate On Easy Runs?
If it’s obvious to you that you are doing something wrong (dehydration, exhaustion), then it should be fairly easy to remedy the problem. Ideally, these issues will be nipped in the bud before they cause serious problems; if not, what can you do once you’ve already overdone it?
Your body needs carbs. There’s no getting away from that. If you’re running on fumes… fuel up!
The best pre-run foods include bananas, bagels and toast – oatmeal is even better than ‘regular’ breakfast cereal.
Nuts are also another great source of carbs during easy runs – almonds or peanut butter sandwiches would work well – so long as digestion isn’t an issue for your runs.
Better nutrition, sufficient hydration and proper rest are the best solutions to a sudden uptick in heart rate on easy runs.
However, over the longer term, the best answer we can give you is: more running.
Consider low heart rate training (the MAF method) to build up your base fitness levels so that you can push further.
The fitter you are, the better your VO2 Max will become, and the less work your heart has to do to sustain the same pace.
This is particularly the case if you are carrying excess weight. By burning off that extra weight, you will see a significant reduction in heart rate when performing the same run at the same pace.
