Chronic cardio easily trumps all those factors. Half an hour twice a week is probably the most anyone should do, but it's pretty pointless as far as health in concerned. If you want to be a competitive endurance athlete and destroy your body in that pursuit, it's your own choice. But your knees will be done by age 50, if you don't drop dead of a heart attack before then. A weekly sprint is more than enough to keep in sufficient shape, even to the point of being able run a marathon in a moment's notice should you feel the need. An overtrained body is at a serious disadvantage to a well-rested and properly built frame. Moving slowly at a steady pace, as in a medium speed walk, for a few hours a day is sufficient for most of the week, along with two or three strength training days and that one sprinting session. I'm just telling you what's in the Primal Blueprint. See for yourself.