/r/Strava and a bunch of the cycling ones like /r/Velo and /r/bikepacking, not very optimistic that there's much intersection between existing subsribers and those willing to leave Reddit for Lemmy but I can always live in hope!
I've been missing /r/trailrunning for much the same reason! There is [email protected] at least, but is much less active than /r/running was. When I mentioned Lemmy over there before I gave up on Reddit I was down-voted to oblivion. I was disheartened how little people there seemed to care. Still, given more time I imagine more people will come over.
Similarly, r/AdvancedRunning and r/RunningShoeGeeks are all that I really miss about Reddit. I'm thinking I'll probably just check in once a week or so on the desktop. They've been great resources for my running and I haven't found any non-Reddit community that's even close.