The amount of zone 2 that one should get is frustratingly large. I love my cardio - more than most, but it can be a real struggle to fit that in when you have a young family. I'm doing great on the strength training side, but the time demands of cardio are hard!

It doesn't help that when I do get outside that I tend to go "comfortably hard" and I'm in the no-man's-land somewhere between zone 2 and 5, not really capitalizing on the full benefits of either regime yet maximizing fatigue.