Chest Strap v Wrist Based HR Accuracy

Introduction

I am lucky, I get to test some of the very best heart rate monitor watches on the market. I quickly know which will be best sellers and which will fail to appeal. Often their success or failure is a result of the watch’s heart rate functionality and accuracy. A few years ago Mio rocked the heart rate monitoring world with their unique and innovative WRIST BASED heart rate sensors. Powerful LED’s on the back of the watch that acquire the user’s pulse rate directly from the wrist … finally strapless heart rate monitoring had arrived.

How accurate are they?

In less than 3 years almost all the major brands have released wrist based heart rate watches. Suunto are the only brand with their offering still under development (Dec 2016) but I expect to see the Spartan HR released in early 2017. I decided some time ago to perform accuracy tests on the wrist based models comparing them to a traditional chest strap style heart rate sensor. My control models vary, either the Polar H7 or BlueLeza heart rate sensor paired to either the Suunto Spartan Sport, Polar V800, Polar M450 or Garmin Edge 820.

Below are the results of TWO of these tests.

Test 1 > is the TomTom Spark 3 (wrist based HR) & Garmin Vivosmart HR+ (wrist based) versus the BlueLeza chest sensor paired to a Suunto Spartan Sport as the control model.

Test 2 > is the same control tested against the Garmin Vivoactive HR+ (wrist based HR)

I have performed more similar tests. Please click the links below for further details.

Test 3 > Polar M200 (wrist based) versus Polar M450 with Polar H7 chest strap

Test 4 > Garmin Vivoactive HR (wrist based) versus chest strap sensor and Garmin Edge

Test 5 > TomTom Adventurer (wrist based) against Garmin Edge 820 with BlueLeza chest strap

Test 6 > Garmin Forerunner 35 (wrist based) v Polar M450 with H7 chest strap

Test 1

Test Equipment Used

Interval Training on Turbo Trainer

The session

The graphs below show the heart rate data acquired from an interval training session performed on a turbo trainer. The session starts with 3 x STEADY (zone 3) intervals each of 2-3 minutes. This is followed by 1 x HARD (zone 4) interval for 1 minute. The session closes with one more STEADY (zone 3) interval for 2 minutes and finishes with a final HARD (zone 4) peak for 1 minute. 

The Graphs

Graph 1 for the TomTom Spark3, shown below, is identical to the heart rate Graph 2 acquired using the  Suunto Spartan Sport with BlueLeza chest strap heart rate sensor (CONTROL). Unfortunately Graph 3 acquired using the the Garmin Vivosmart HR+ has large chunks of data missing and several erroneous spikes …

Graph 1 – TomTom Spark 3 (wrist based HR)

tomtom-touch-very-accurate-interval-training-turbo-heart-rate

Graph 2 – Control Graph (chest strap to Suunto Spartan)

intervals-turbo-trainer-control-heart-rate-from-chest-strap

Graph 3 – Vivosmart HR+ (wrist based)

Heart Rate graph from Vivosmart HR+

Test 1 Conclusions

I was astounded by how accurate the TomTom Spark 3 was. It is clear it duplicates all the major peaks and troughs experienced during the interval test. There are NO periods of inaccuracy of error. The same was found during a 6M test run and 20M bike test ride. As a result of this test the TomTom Spark 3 was awarded 98% for heart rate accuracy.

Unfortunately, the same cannot be said for the Garmin. I was disappointed with these results as this did NOT reflect what I’d found in the Forerunner 235 or Vivoactive HR. There are obvious periods where the heart rate has erroneously dropped to less than 50% actual HR. Similarly, there are periods where the recorded HR have spiked. As a result of this test the Vivosmart HR+ was awarded a heart rate accuracy score of 8/10. However, please see the FURTHER TESTING below. It would appear the Vivosmart HR+ works VERY WELL for constant effort sessions, as opposed to intervals with rapidly changing intensity …

Test 2

Garmin Vivosmart HR+ versus Chest Strap

I wanted the Vivosmart HR+ to have performed better so I decided to investigate further. Here are two graphs showing another 50 minute turbo trainer interval. The products on test were the Garmin Vivosmart HR+ (wrist based HR) versus a Suunto Spartan Sport with BlueLeza Bluetooth traditional chest strap style heart rate strap as the control

Test Equipment Used

Heart Rate Graphs from Test

Comparing heart rate reading from chest strap and off the wrist

The short training session was broken down as follow : (a) 10 minute warm up – (b) stopped to sort music – (c) 4 x 1 minute full power sprints – (d)  5 minute steady at 140 bpm – (e) 2 x 1 minute full power – (f) steady 120 bpm and (g) cool down

Conclusions

It was some time ago that I performed my first test of strapless heart rate accuracy testing the orginal Vivosmart HR with a BlueLeza chest strap and Garmin Edge. The results of that chest strap versus off the wrist comparison can be found here. This time I have approached it a little more scientifically using the turbo trainer I can control the precise level of exertion and time. I am CONFIDENT the chest strap recording is 100% accurate. It reflects the effort and intensity of each interval exactly how it was perceived at the time. There are no erratic spikes or drops in signal. Unfortunately, the same cannot be said for the Garmin Vivosmart HR+. Yes, it generally appears to follow the trends of the session, but it is in not as smooth as I would have hoped it would be. The Max HR at 162 compared to 163 is good. The Average heart rate compares well at 119 for the Garmin compared to 120 from the chest strap on the Suunto.

Areas of Concern

The areas that concern me most were the warm up (a). This was a steady 110-120 bpm with no sudden changes in intensity. That is NOT what we can see from the first 10 minutes of the graph. The 4th interval (c4) has been lost all together. And interval (e1) has been split in to two?

95% Accuracy for 95% of the time

From these short test I have drawn the same conclusion. Off the wrist heart rate monitoring is undoubtedly convenient, but it currently lacks the ACCURACY of chest strap acquired heart rate readings. It’s only a ball park figure, but I suggest an average accuracy of 95% can be expected for approximately 95% of the time. If you are mostly interested in the BIG PICTURE, average HR over a period of time, calories burnt, time spent (approximately) in different HR zones off the wrist heart rate sensing is brilliant. In other words, if you are just trying to stay active, get fit and get healthy, it’s perfect. If that’s the case, please take a look at Polar A360, Fitbit Charge 2 and Garmin Vivosmart HR

Chest Strap for 99.99% – 100% Accuracy

However, if like me, you rely on accuracy and you want to see the full heart rate graph accurately recorded second by second, off the wrist is currently NOT quite good enough. Maybe you want to know EXACTLY where your heart rate peaked during an interval, climbing a hill, sprinting to the line or maybe your coach needs to see how long and how quick your heart rate recovered. If this sounds like you, for the time being, it has to be a chest strap offering 99% to 100% accuracy.

NOTE > we did find that the heart rate acquired from the Vivoactive HR and Forerunner 235 was better than this Vivosmart HR model? This may be because they have wider, flatter backs to the watch providing a more secure base for the sensors to acquire a good reading. The same can be said for the TomTom Runner 2 / Spark 3 and the Polar M600. It might be that this narrow style of the Vivosmart HR is more prone to minor movement on the wrist ? or possibly allowing light in?

Further Testing …

(updated Feb 2017)

A Facebook friend of ours, Wayne Lyle, has been kind enough to send these heart rate traces to us. They show the heart rate acquired from a Vivosmart HR+ (wrist based) and a Forerunner 230 (chest strap). What Wayne found, similar to our own tests, was that the Vivosmart HR+ was VERY GOOD for steady intensity efforts. For training sessions where the heart rate remains fairly constant he found 99% accuracy, if not more. Only when he introduces INTERVALS with short bursts of high intensity and rest did he start to see deviations from the chest strap recordings …

Heart Rate from Forerunner 230 (Chest Strap)

Heart Rate from Vivosmart HR+ (wrist based)

More to come soon …

I will conducting more technical reviews in to the accuracy of the modern OFF the WRIST heart rate monitors in the next few weeks.

Tristan – HeartRateMonitor.co.uk

Date – 7th November

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