Thanks for posting about this. The Apple Watch cannot be used as a heart rate sensor for activities recorded on the Strava iPhone App. In order to upload your Apple Watch recorded heart rate data, you would need to record the activity using your Apple Watch.
You can pair a compatible bluetooth heart rate sensor with your Strava iPhone App if you wish to record with your iPhone. See more information here on how to do it and what's compatible.
I hope that's helpful information - please let us know!
Seriously? I have heard so many good things about Strava that I just signed up to give it a try. I have been using Runkeeper for years, and it is totally able to use the Apple Watch heart rate sensor when recording activities on the iPhone app (by having the Runkeeper app open on the Apple Watch at the same time). This really needs to be fixed.
Why is it always advised here that there are other ways? Or you can use a heart rate sensor from another manufacturer. But that is not the point. It should be possible to record the tour with the iOS app and use the Apple Watch as a heart rate sensor. I wonder what the problem is here? Is it so difficult to programme?
If your goal is HB info in your Strava saved activity and iPhone display on your bike, you can record your session with your watch as linked by the moderator and record a simultaneous session on your iPhone. At the end of the ride, save the watch session and discard the phone session. Did it this morning, works great, just have to pause in two places - if you pause.
Note: Apple would have to broadcast HB info via bluetooth according to standard for Strava to have a clean implementation like the OP requests.