Exactly this. Your VO2max will only increase appreciably with whatever the stress is that is causing it. It will increase minimally for all other activities, if at all. Expanding on the Lance Armstrong thing, his VO2max is insane *when riding a bike* but not while running. His energy efficiency (which VO2max is a subset of) is trained for riding a bike. While his energy efficiency for running is impacted by riding the bike, he would not be completely efficient for running unless he trained specifically for running and all other things being equal (which they never are). This is more a function of mitochondria rather than the "cardiovascular system," which really doesn't exist.
Originally Posted by Winterbike
People too weak to follow their own dreams will always try to discourage others.