I had this some time back. I was dipping my toe into photography, working on composition, framing, clarity, technique, learning the different features on my small, cheap camera... I was considering a photography course locally.
Suddenly he says, out of nowhere, "I fancy getting into photography."
Buys a £500 fucking camera.
Takes a few snapshots - his usual AWFUL style, chopping people's heads off, zooming so far in you can see their nostril hairs - a few snaps of trees, heavily edited them so they looked completely wonky, like a child had hammered the keys, then put the camera in a box and forgot about it.
The problem was I couldn't really articulate what made me so angry. The splashing of the cash? The fact he had no intention to actually learn? The way he sort of... took it from me? Obliterated my tiny point-and-click and murmurings about a cheap 6 week course at the local college? I mean, yeah, I still could have gone, but I realised just how poor my camera was next to his. And yes, I could have borrowed his... and maybe that was it. I didn't want to borrow his camera. I'd been thinking of getting my own.
Anyway. I lost interest.
On the other hand, I am the gym-goer; weightlifting, strength stuff. I'd actually quite like him to get into it but he curiously won't, and that amuses me a little. Not that I think I am better than him or anything, but just that yes, I have this, and you won't catch up with me ;)
YANBU OP, even if it's hard to articulate why. He might think he's being friendly and fun and bonding with you over becoming a running nerd, but heartrates and protein calculations are only fun for the person doing them. It's gym protocol 101. Don't bang on about it to someone else.
Try and separate what you do - run for pleasure - with what he does - run to be a runner-nerd. Train your brain to see them as two different activities, like train-spotting and pole-dancing, so that when he talks you can try and see what he's talking about as a whole different thing to what you do.
But beyond that I've no tips, I'm still simmering about the camera.