Late Monday afternoon, while typing, I developed sharp pains in my left wrist. It hurt! I couldn’t type, though changing wrist position with a gel pad helped. Maybe, I thought, it was something with some recent mountain biking. Or maybe it was the high intensity CrossFit cleans I was doing. Whatever, it was obnoxious.
So I sort of splinted it with my weightlifting wrist wraps and then I waited to see what it would do.
It kept hurting, but another mountain bike ride didn't make it worse.
Maybe, I think, it’s an inflammatory arthritis of some kind. I’ve a family history and some intermittent personal history to worry about. Who knows.
I go to my morning CrossFit anyway. (Hmm. I wrote that one at 54. Now I’m 56…) Today the workout is muscle cleans and push press — about 180 of em. Great. That’s gonna hurt. I do the first 80-90 with a straight wrist, which is extra work. Then, between sets, I realize my wrist isn’t hurting any more. I do the next 90 with the usual wrist extension.
There’s some mild aching as the endorphins fade, but then nothing. Twelve hours later it’s slightly sore with unusual motions. 
If a patient came into my office with wrist pain back in the 90s I might have recommended ice, a splint at night, and some gentle range of motion exercises. Today somebody smarter might suggest something like the Dynaflex Pro. I don’t think anyone would recommend high intensity high repetition wrist extension weightlifting.
That’s what helped though.
I do not understand my increasingly aged body, and I don’t think I’m the only mystery. I suspect nobody really understands joints and backs. Once upon a time we recommended bed rest for sore backs, then we recommended activity and exercise; I personally did well with relatively intense weight and flexibility training. More recently, mountain biking made my anterior knee syndrome slightly worse, but deep squats seemed to have no effect and conventional rehab seems to have helped. Today there’s the wrist.
Pity the poor physician who has to make a recommendation for someone’s sore wrist. It doesn’t work to say “I really have no idea”. It would be nice to know what’s going on though.
 I can make up a theory. I have reason to suspect I’m prone to dumping calcium into sore tendons and tissues — a counter-productive response that promotes inflammation. Bad genes I guess. Maybe the vigorous activity promoted clearance of some local calcium deposits. Maybe a stuck tendon sheath loosened up. Maybe the gods had mercy...
Update 5/1/2023: Almost 8 years later I can see this was probably the start of wrist involvement in my mixed-type arthritis. It became an on and off problem over the next 8 years. I'm on HCQ to slow progression and the symptoms seem to be dose responsive. It's annoying but not bad. When it's more bothersome I do "true pushups" or ring pushups or more reps at lower weights.