For most of my adult life, my exercise time was, by priority, martial arts, bicycling, then running. Running was just cross-training, though I did a couple of 5K's 10+ years ago. As I got older into my mid-40's, martial arts diminished, and I cycled more, up to 75 miles/week at my peak.

A new marriage, a long, bike un-friendly commute, and late-in-life kid means time is at a premium. Now I run more than anything, and a couple times a week seems plenty. It's always harder, more intense than cycling, but after a couple of years I'm used to it. My cardio is great, my joints don't mind it too much. I want to get out on the bike more on nice days, but if I don't that's ok, too.

If you're already running 8 miles a session and do just one ride at a moderate pace for recovery- you're doing awesome!