Garmin Forerunner 225 with optical HR monitor


Just a short post on the accuracy of the new¬†Garmin Forerunner 225 running watch with in-built optical HR monitor and accelerometer. For the past 7 years I used a (much loved and used) Garmin FR 405 with a chest strap – close to the heart for the best accuracy. It’s seen me reliably through 5 marathons. Could the FR 225 match its accuracy? The answer is: as good as. After a 25 minute run with both the FR 225 and 405 with me (and the chest strap for the 405), the average reported by both was 147 bpm. The following shows the heart rate for the run from the two watches.


HR bpm 225 vs 405 (click to expand)


The 25 is blue and the 405 is orange. The difference is negligible. There was a lag of perhaps 2 or 3 seconds with the 225 Рi.e. it took maybe 2 or 3 seconds longer for the correct heart rate to display. For maybe 99%of runners that matters not a jot.

What about cadence? The 225 has a built-in accelerometer to record the cadence for a run. With the 405 I had a footpod attached to my shoe. This gives exact cadence, but the 405 records strides as opposed to steps. Garmin Connect web app now reports cadence as steps rather than strides, so it simply multiplies the strides by 2, resulting in always even numbers for the cadence – a slight 0.5 step inaccuracy on average (every other run will be 1 step out on average). Would the 225’s accelerometer match up given it is probably making more assumptions than with a footpod?


Cadence with the 405 (click to expand)


Cadence with the 225 (click to expand)

As you can see, there is a lot of variance with the 225. The 405, by contrast looks quite smooth. The 225 reported average cadence of 157 with the 405 reporting 160 (I’m not in great shape at the moment!). One run isn’t scientific enough to make a judgment. The 405 might have been rounded up from 159 and the 225 could have been 157.4 rounded down – or the gap might actually have been even wider. But I think if I want to do proper cadence analysis, I’ll be pairing the footpod with the 225, which is also supported.

Overall, I am very pleased with the switch to the new FR 225. GPS accuracy and lock speed were improved (no more waiting 5 minutes in the cold at the start of a run) and the watch works very well as a day-to-day watch. No more fiddling with the chest strap and spitting on the contact points, and no more early spikes in bpm. I’m not sure how much use I’ll make of the activity / step tracker, but I might keep an eye on the daily step counts to see how active I am from week to week, month to month, etc.

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