This question crops up all the time! You are out for an easy run, but when you get home and check the heart rate data from your sports watch, it looks very high. How can this be? Am I ill? Do I need to see a doctor? How is it possible for my heart rate to be that high when it seemed like I was going for a really slow run?
For example, at an easy, conversational pace, you’d expect the average forty year old runner’s heart rate to be around 140-150bpm (beats per minute). At this effort level, you’d be able to say a sentence of about this length without having to gasp for breath in the middle. But when you look at the data, it says 170-190bpm, which would be more appropriate to a Zone5, max effort 5K or interval session! Weird right?
Firstly, let’s state that if the data is correct, and your heart rate really is very high while running at an easy effort, you should definitely get yourself checked out out by a doctor.
However, before you get too excited and rush to get an appointment at the clinic, do a few sanity checks on the data first and understand how easy it is for the data to be completely wrong!
Look at the heart rate graph
Does your heart rate look like this most times you run? Does it shoot up at the beginning and stay high the whole way like in the picture (A) above?
Or does it look like the picture (B) above, where the heart rate rises gradually throughout the run?
Or perhaps it jumps around erratically, suddenly going from a low heart rate to a high heart rate, even though you were maintaining the same pace throughout?
Assuming you are running at the same pace throughout the run, you’d expect to see something like Exhibit B. So why are you seeing something different?
Problems normally caused by optical wrist-based heart rate monitors
Most of the problems I see in this area stem from people using the optical heart rate monitor on their sports watch without setting the watch up correctly.
There is a sensor inside the watch with strong LED lights either side of it. The sensor looks at changes in the reflected light level caused by the blood pulsing past it. For this to work properly, the watch needs to be set up correctly on the arm. If it’s not, it can start measuring your cadence instead!
Cadence monitor instead of Heart Rate monitor!
What happens to your wrist when you run? Your arm is counter-balancing the movement of your legs and thus your wrists are moving forwards and backwards at the same rate as your feet are taking steps. The number of steps you take each minute is called Cadence. This normally doesn’t change much throughout your run.
When you are using a wrist based heart rate monitor instead of a chest strap sensor, the watch needs to be snug against your wrist, otherwise slight movements in the watch position caused by the arm movements are determined to be changes in light levels. Since that’s exactly what the sensor in the watch is looking for, it can easily lock on to these instead. In this case, the graph will look just like Exhibit A above. Or if perhaps it will get confused and jump between the two, with a few minutes showing real heart rate and few minutes showing cadence instead.
How to get a more accurate reading from an optical heart rate monitor.
Here are your options to fix this.
First, try tightening the strap. If you can quickly and easily slide your finger under the strap, it’s too loose. Tighten it until your finger gets a bit stuck when trying to slide under the strap. This will mostly likely fix the issue.
If the strap is already tight, but you are still measuring your cadence, or getting erratic readings, try shoving the watch up your arm a bit towards the elbow. This will move it on to a thicker bit of flesh, with more blood flow and a snugger fit.
Another option is to switch the watch to the other arm. Most people are right handed, but wear their watch on the left. However their left wrist will be slightly thinner due to less strength from the hand bias. See if your other wrist gives a more reliable reading.
Finally, if you still can’t get a reading that looks right, apart from seeing a doctor, you could try a chest strap sensor instead. Most decent sports watches will support one. They need to be wet to work well, so soak the strap before you leave, but they are generally accepted to give a good reading, especially at the high effort levels required in 5K races, interval sessions or Maximum Heart Rate Stress Tests that help you determine your heart rate training zones.
I hope you found that useful. If it solves your issue, please let me know on the Facebook page or drop me a message on the website messenger chat.