I’m writing this article to display some of the discrepancies that I see with wrist based heart rate tracking. I will also be using this article to show why I think the Garmin Forerunner 235 does a pretty decent job in the heart rate tracking department if you wear it correctly (correct wear is important). At this moment, no wrist based heart rate tracking tech that I’ve worn (including the Forerunner 235) does a better job than a chest strap. A chest strap will always be more reliable. I took the Garmin Forerunner 230, 235, and Vivosmart HR on a 5K run at the same time. I then overlaid the heart rate data onto a graph so we all could look at this together.
Recording and Plotting the Data
I was asked last week if I thought the Garmin Forerunner 235 was a reliable heart rate tracking device. I believe it is with the caveat, “still not as reliable as a chest strap.” However, it is probably one of the best wrist based HR trackers that I have worn (I’ve worn the Polar A360, Fitbit Alta HR, Fitbit Charge HR, Vivosmart HR, and Fitbit Charge 2). So, I decided to strap on my Forerunner 235 on my left arm, put the Garmin Vivosmart HR on the right arm, then hold my Forerunner 230 in my hand while connected to a TICKR HR monitor. Below are the results.
Breaking The Data Into Sections
I made this image nice and big so we can see how equipment is tracking. The blue line is the Forerunner 230 connected to the TICKR HR monitor. The Orange line is the Forerunner 235 taking samplings on the left wrist. The Purple Line is the Vivosmart HR taking samplings on the right wrist. On first look, things seem really bad. We will quickly move to the next graphic below. I was doing things with the Forerunner 235 to show you how important strap and arm tension are for reliable reporting.
I am going to break this lesson/observation down into three sections. At no point did I make any adjustments on the Vivosmart HR. It stays nice and snug on my right wrist without any fiddling around or unnatural flexing. However, I did quite a bit of fooling around with the Forerunner 235 just to show how easy it is to influence the accuracy of the wrist based HR tracking. My sole purpose here is to support my earlier claim that the 235 is decently reliable as a wrist based Heart Rate tracker if you wear it correctly.
Section 1, Lesson 1
Looking closely at section 1 in our graph above, we can see the 235 is performing very poorly. The Vivosmart HR isn’t doing much better either. We see heart rates immediately shooting up into the 170’s while our blue line (Wahoo TICKR) is tracking my heart rate correctly. This isn’t an error of the Forerunner 235, it is user induced error right now.
The Watch Band
There is another big difference between the Forerunner 230 and 235 besides heart rate tracking; the Forerunner 235 comes with a flexible band. The band on the Forerunner 230 is much like a standard watch band. The 230 band is hard and does not flex at all. Garmin then uses a different band with the Forerunner 235 that stretches more than a normal band would. This was done for a reason, and isn’t just some watch band upgrade.
Wearing The Band Correctly
There are two ways I wear my Forerunner 235 band. I wear it looser when not doing activities. The 235 does a good job tracking regular activities this way and it doesn’t feel extra tight on my wrist. Looking at the image of the watch on my wrist, I move the watch band 2 to 3 holes tighter when running. This takes us to section 1. In section 1, I was wearing my Forerunner 235 loose as if for everyday use. At the end of section 1 in our graph, I tightened up my band by 3 holes. As you can see, the heart rate comes right back in line with what the 230 is reporting. Make sure you have the band nice and snug when you go out for a run.
Section 2, Vivosmart Inaccuracies
In section 2, we see the Forerunner 235 is now doing a much better job tracking our Heart Rate at the wrist. The 235 is lining up very well with our reports from the Wahoo TICKR. The Vivosmart HR, not so much. This is the problem I have with most activity trackers that also do Heart Rate. These fitness trackers have a harder time reaching the upper heart rate limits when in use.
Section 3, Lesson 2
In our last section and what I’m calling lesson 2, we look at the tension in your wrist. I noticed this problem when riding my bike with the Forerunner 235. When I was on top the handlebars with a tense wrist, or reaching for a water bottle with my right hand, I would notice a drop in reported heart rate. That led me to find a problem with wrist/hand tension.
Sprinting With Tense Hands
On this test, I did two sprint intervals. Well, I wouldn’t call them sprint intervals, more like running a 7 minute mile interval. I wanted to raise my heart rate quickly while clenching my fist. The red box on the graph is where I start to increase my running speed while clenching my fist on the arm with the 235. The red circle is where I maintain the pace, but now relax my hand and arm. The heart rate on the 235 fails to elevate when you are tensing up, but does begin to rise as soon as you relax that arm. Keeps those hands relaxed if you want accurate reporting!
I wanted to write this article because I wanted something to refer or link people to when I bring this up in the future. Wrist based heart rate tracking isn’t as reliable as tracking heart rate with a chest strap. The technology is getting better as we move into the newer equipment, but it isn’t flawless. Heart Rate tracking at the wrist is only accurate enough if we keep our hands and wrists relaxed (that is just having good running form) and we make sure the device is nice and snug on the wrist. Keeping the device snug on the wrist helps the sensors stay in contact with your arm and reduce the bouncing that leads to inaccurate or double HR reporting.
Extra Graphs From Garmin Connect
Just for a little extra data, here are screen shots from my Garmin Connect pages with each device. You can dig into that data a bit more if you want to.
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