November 21, 2015
If you are a runner and also enjoy having the latest advances in technology, perhaps, like me, you already purchased the Garmin Forerunner 225 (FR225), the first watch of the Garmin family incorporating a cardiac optical sensor to monitor your heartbeats or heart rate without the need for a chest band.
The Garmin Forerunner 225 is a small clock, lightweight, incorporating a number of appeals as a graphic interface and distance meter, pace, cadence, and allowing you upload your training to the web via Bluetooth without using cables connected to the computer. But the appeal of this piece is its Mio Heart Rate technology, which allows to monitoring the pulse from the wrist. Here, we present an exercise we do to try to determine the accuracy of this new technology.
To perform this exercise, we compare measurements of Forerunner 225 (FR225) with respect to measurements of Garmin 310XT and Garmin Fenix 2, which we could say are relatively recent (the second one) and old (the first one) technology watches. The comparison was made on 2 separate runs, each of 8 km, where a relatively stable pace between 5:20 min/km and 5:30 min/km remained. Both runs were started around 6:00 pm and under the same path in the Mirador Sur Park, starting at Km. 0. The table below summarizes the general statistics of these exercises (click table to enlarge).
As noted, Test 1, which compares measurements of FR225 versus 310 XT, indicates a significant difference in heart rate measurements. That is, while the FR225 reports an average heart rate (Avg HR) of 130 bpm, the 310XT reports an average heart rate significantly higher of 170 bpm.
The following graphs show these results in more detail. In both graphs, the blue line measures the pace test at each point in time. As can be seen, the pace was to maintain stable around 5:30 min/km. The gray shaded region shows the evolution of heart rate throughout the course (about 44 minutes). For the Garmin 3010XT, we see that the heart rate evolves in a manner expected; i.e. maintains a slightly increasing trend between 150 bpm and 180 bpm. For the Forerunner 225, we see that the heart rate showed very significant oscillations. Specifically, during the first 13 minutes of the test, the FR225 reported a stable heart rate slightly below 150 bpm. Then, between 13 and 30 minutes, heart rate plummeted to almost 100 bpm. Finally, the FR225 reported an increasing trend during the last 15 minutes, similar to that of the 310XT. This oscillation caused the FR225 report at the end of the test an average heart rate of 130 bpm, much lower than the 170 bpm reported by the 310XT.
My experience as a runner tells me that it is very unlikely that my heart rate has dropped to 100 bpm for about 15 minutes at mid test. But it is valid to ask whether the measurement given by the 310XT is closer to the correct measurement than the measurement of FR225, since we consider that the 310XT has a somewhat older technology. To answer this question we conducted a second test, similar to the previous one, but this time comparing the measurement of FR225 regarding that of the Garmin Fenix 2. The result can be displayed in the following graphs.
The above graphs show a similar result to the first test result. While Fenix 2 indicates a heart rate with an upward trend over time (similar to 310XT), the Forerunner 225 shows sudden oscillations that could be altering the measurement result. After indicating a measurement slightly above 150 bpm during the first 13 minutes of running, heart rate measurement of Forerunner 225 drops significantly to almost 100 bpm, but this time for a shorter time period of about 10 minutes. After 22 minutes, the Forerunner 225 resumes the upward trend in the measurements, but this time reporting a heart rate close to 200 bpm. It is worth noting that in the last 10 minutes of the race the pace was a little faster, descending from 5:30 min/km to 5:00 min/km.
In conclusion, these tests show very interesting results. Measurements of heart rate for Garmin 310XT and Fenix 2 were very similar. Both show a slightly increasing trend over time and a similar average heart rate of 170 bpm on the 310XT and 169 bpm on the Fenix 2. However, the Forerunner 225 showed an average heart rate significantly lower than that of other watches, of 130 bpm in the first test and 159 bpm in the second test. Another interesting point is that the Forerunner 225 seems to tend to underestimate the heart rate measurements at relatively low paces and to overestimate these measurements as the runner accelerates the pace. So we see that in the second test the Forerunner 225 yields a measurement closer than of the Phoenix 2, although still below this.
The oscillations having the Forerunner 225 in the heart rate measurement could be causing an underestimation of the results and for sure this will not be accepted by the most demanding runners. So if you purchased a Forerunner 225, think twice before calling your coach shouting: Hallelujah!