Do you have it on tight enough? Mine leaves a divot in my wrist for at least 30 minutes after removing the watch. Does whatever software you use give you the raw HR data (one HR value for each data point it recorded)? If not, send me a .FIT file and I can dump it into excel for you. I just checked the HR data for my last ride and there are a few dropouts, but other than that it all seems like reasonable data. (But I'm not targeting specific HR zones, so what would I know...)
Are you using Data Recording = Smart, or Every Second? It could be doing weird things if you're on a trainer and it thinks you're recording an outside activity (Bike vs Bike Indoor)
Thanks, Dan. Right now it's on Smart. Do you recommend switching to Every Second?
I keep it on Smart and only use Every Second if I'm trying to record a new trail with maximum precision (like to add an unmapped trail to a topo map for a race).
Back to your original question - what kind of discrepancy are you seeing? Is it reading consistently higher than your actual HR? Is it zig-zagging high-low-high-low? Is it not giving HR data for random clusters of data points? On the trainer or outdoors? Using the Indoor setting if on the trainer?
I just started using the watch last week, but I'm noticing that the numbers don't line up with actual exertion (IE - yesterday during an extended recovery block on the trainer, the watch was consistently showing HR at 160+, and then it didn't change when I started riding hard again. It also goes the other way, where the HR is way lower than the effort -- 90 BPM when I'm running). That's all been indoors, which maybe is the issue? Unless I'm running inside, I'm setting the activity for Other, since the watch doesn't offer an Indoor Bike option. It's less of an issue for indoor running, but still some discrepancies.
I have a Forerunner 235, too. I would definitely try using the Bike Indoor setting when you're on the trainer and Run Indoor on the treadmill, since Other, Bike, and Run all think you're outside, and the Smart recording feature is looking for changes in the GPS location to decide when to record new data points (ie, if you're biking at 15mph down a straight rail trail, it won't record many points, but if you suddenly start going into singletrack and your speed and direction vary, it will record more points)
You have to manually add the Indoor modes to your watch settings. Click the red button, then go to Menu, Settings (not Activity Settings), then Activity Profiles, and scroll down to Bike Indoor. Change Hide to Show. Do the same for Run Indoor.
Try that. It may not actually improve the HR problem, but those modes are definitely there specifically for use on stationary trainers, so Garmin must have had a reason to add them.
Thanks, Dan - I'll do that! I ran outside today, and for the most part the numbers seemed way more accurate. Got a bit wonky toward the end - seemed to be stuck on 167 for several minutes - but otherwise it was in line with RPE.
Just seeing this - I've had similar issues with my Garmin 235. I don't use HR religiously when training so I haven't made too much effort to troubleshoot, but this is a helpful thread.
I’m having similar issues with my 935 - on an outdoor run yesterday, I was absolutely, honestly in an E2 conversational-pace zone but the watch kept screaming that I was hitting 165, 170, 175...not a chance. I gave up and ran by feel but I’d like to actually use and trust HR zones more.
Erin, I used to have a chest strap that synced with the forerunner 920. It was way more accurate, but it died a couple years ago and I transitioned to training by RPE. Post-pregnancy, I wanted to use HR as I got back into real training. A new strap ended up being the same cost as the 235. I did some research and found plenty of reviews that said the HR was accurate enough to be useful so I went with that. But I'm not totally convinced yet (though it's been better using the Indoor Bike setting).