I decided to make this comparison when reviewing last week’s slow run I saw that the average heart rate detected by my Garmin Forerunner 735XT was 171 beats per minute. Something was definitely wrong, and it was probably related to the fact that during an activity like running the wrist sensor is moved and loses accuracy. It could also be due to the gloves I use, as one of them is in contact with the watch during training. I therefore decided to test how much the detection of the sportwatch differed from a heart rate monitor, the Garmin Premium Heart Rate Monitor. To carry out the test I used two different watches, the Garmin Forerunner 735XT and the Garmin Forerunner 35, the latter connected with the heart rate monitor.

Running

The training recorded was an medium 12km, in which I had to maintain a constant pace of 3:37 min/km. Once the activity was completed, I superimposed the heart rate graphs as a function of time: As you can clearly see, the band (in red) has always been very precise in its measurement, showing the initial surge due to the start of the activity, while the clock (in blue) remains at 140 bpm until almost halfway through the workout, then makes a sudden jump and settles at 170 bpm, approaching the measurement of the band.

Cycling

Since I didn’t go to the athletics field because of snow, I trained at home today. I chose to warm up on an exercise bike, 15 minutes at a constant speed of 40 km/h. Despite the fact that the activity was not as long as running, I was able to obtain a homologous graph to that of the average. From the graph, it can be seen that both the wrist sensor and the band follow the same trend, remaining within a margin of less than 5 beats per minute difference.

To conclude

The conclusion I’ve come to, at least as far as running is concerned, is that for consistent results the band proves to be an excellent tool. With regard to other activities where the wrist sensor remains more or less stationary, such as cycling, its reliability increases considerably, narrowing the difference with the chest belt.