Chest strap heart rate monitors are the most accurate, followed by forearm optical sensors; devices below the forearm provide poor data during intense exercise.

“it's almost like there's really three I know you said there's two buckets you could really say it's anything on the chest amazing gold standard always going to be good as long as anything on the forearm I think we've established if you do the forearm right at least heart rate to heart rate is comparable we'll talk about the HRV variability and then anything below the forearm is sort of nonsense it's not great it's definitely not great especially if you're doing if you're lifting weights if you're doing interval training if you're doing anything high intensity you're doing change in Direction it's it's garbage you just get very poor data”