There may be no direct 1:1 solution at this time, but you can do a lot with IFTTT and Webhooks. So long as your fitness tracker's host service (Apple, Fitbit, etc.) supports IFTTT, you could -- for example -- send a post to Mastodon with whatever information you desired. I do something similar with Untappd since there's no direct integration with Masto at this time.
EDIT: I believe these are the guidelines I used to figure out my own integration. https://hyperborea.org/journal/2017/12/mastodon-ifttt/
I don't think people appreicate the old axiom "when you look into the abyss, it also looks into you" in this case. For a long time, corporate social media algorithms drove what content you saw. This tended to be "outrage" content, because as others have mentioned, it gets clicks. But marinate in that long enough and YOU become the source of the outrage clickbait. The algorithm starts people down that path until their mentality becomes self-reinforcing. They post what they're used to posting -- angry stuff. And they seek out more even without behind-the-scenes manipulation of their feed. Now imagine all those Twitter refugees landing in the Fediverse with that kind of outlook. It's not surprising that outrage and bile are trending.
The way to break this cycle is... just ignore it. I have an extensive list of keyword filters on Mastodon. It screens out 99% of the political content. I just don't want to see it. I'm here to engage with people who share the same passions and hobbies as myself. THAT'S what makes my Fediverse social media experience better. It's not a magical function of crossing the corporate/open-source boundary. I have to be responsible for curating my feed according to what I want to seek.
The same goes for Lemmy. I'm using Leomard as my client on macOS, and it allows me to block out any Lemmy instances I don't want to see. And I set my default view to "subscribed," not "local" or "all." That prevents me from getting psychologically drenched with whatever angry or trollish content might be lurking in those feeds when I open the client. I also sort by "new" rather than "hot," "most comments," etc. It's great that people have opnions about things, but I find relying on up/downvotes to be a poor way of discovering the content I want.
Long story short (too late): your social media experience in the Fediverse is yours to shape. If you rely on the defaults and flow with the tide, you'll likely end up somewhere you don't want to be. If you trim your sails and take the wheel, there are all sorts of wonderful destinations out here.
Don't use other people's anger and unhappiness as your compass.