Zjw - 50 miles a week is staggering. Congrats.
I run a few miles a few times a week now, in the heat of the summer, but I will start working in some long runs (10 - 20) when the weather breaks.
I am 59, so I do what I can to stay in shape without making anything worse.
I lifted weights for 5 - 6 years, and, after 4 resulting ortho surgeries, I have decided that God meant me to be a runner and not a weight-lifter.
I have been running for ~ 40 years and still love it.