I have both the Edge 520 and Forerunner 235. On the Forerunner forums they really knock the accuracy of the optical heart rate monitor. So I thought I'd pit the Edge 520 with the Garmin premium chest strap HRM against the Forerunner 235. The bike has the cadence sensor and the speed sensor. What I found was pretty interesting. The bike ride, as recorded by the Forerunner 235 was 45.38 miles, while the Edge 520 recorded it as 45.5 miles. I'm guessing the 520 with the sensors is the more accurate number, but the two units were still very close to one another.
The total time for the ride, as you might expect was the same for both units; 2:48:36. Both are set to autopause when stopped, but I still expected at least a small variation in time, maybe a few seconds, caused perhaps by one unit starting to record a second or two after the other. But that wasn't the case.
The average speed for both units was also exactly the same at 16.2 mph. The really amazing thing though was every time I looked at the watch and then at the 520 my heart rate was pretty much identical on both units. The average heart rate for the ride was also exactly the same for both units at 155 bpm. I think that's pretty impressive. So it seems, at least in this very unscientific test, the optical heart rate monitor on the Forerunner 235 is the equal to the Garmin premium soft strap HRM.
But there was one discrepancy in the numbers that I hope someone can explain to me. Even though all the metrics of the two units were basically identical the watch measured my calories burned as 1788, while the 520 had it at 1501 calories. That's a pretty big discrepancy. Why do you think those numbers are so different? The only thing I can think of that might account for the difference is when I set up the 520 I think I had to input some value for my biking skill, I'm not sure if I did that with the 235. Anyway I'd be interested in hearing your comments and ideas on this. This has been cross posted from the Edge 520 forums. Mods, if this is forbidden please delete.
Tom
