It's certainly not related to hacking, but on the other hand, there's always that broad "satisfies our intellectual curiosity" banner that you have to hold things to. Although it was short and to the point, it caused me to reevaluate something I had taken for granted, so personally I think it fit the bill.
Plus, I have a suspicion that the overlap between people who work out and people who go to hacker news is larger than you might think. I know that jogging, for instance, helps me focus, and I've heard other coders say the same. But I think I'm getting a bit tangential.
Mostly, the idea seems oddly artificial to me. I use my muscles when I want to do something with them, like go for a walk, or go hiking, or swimming, but not just for the sake of using them. Sort of how I approach coding, too...
I don't know what you mean by recreational hiking, but it's hard to see how greater strength wouldn't help. For me, that means a load of 25-50 lbs on my back, moving swiftly across rough terrain. Core stability is paramount, and with weights you can develop that and be ready when you go on a trip.
I wouldn't be surprised if that were true, but I haven't been able to track down any solid information on it. There are a lot of articles talking of research showing elderly runners and elderly former runners suffer less disability in terms of doing those sorts of daily tasks than their non-running cohorts.
http://findarticles.com/p/articles/mi_m0NHF/is_2_21/ai_10117...
As with biking / jogging / rowing, I find that a proper weight workout also helps me stay focused after finishing up.