Apple Watch not syncing with iPhone

[Apex]

I start my activity with my iPhone but won’t activate my Apple Watch for heart rate or any data.

i need to start another activity on my watch itself making two active recorded. 

Any ideas how this can be resolved?

[Hayley_Oborn]

I always start the workout / activity on my Apple Watch and then once complete it’ll sync with my iPhone and then upload to Strava

[Apex]

So they don’t actually start on both devices?

I want to have riding data displayed while I ride.