I hear what you guys are saying ... that regular season is more like a normal jogger running the Boston marathon versus adding an extra lap to one's daily routine. Ok, I concur there.
But here's where I disagree. During Robert Parish's offseason, he'd also practiced martial arts, just like Kareem. Well coincidentally, he also played into his early 40s. And Karl Malone's workout, albeit it was a more normal bodybuilding type of work, also extended his career quite a bit.
Thus, I believe that in general, many pro players do *take it easy* during the off season and don't treat their bodies like its their greatest investment. Remember Artest and his cognac sips, during games. Granted, that's a extreme case but I believe in general, taking it easy, see Charles Barkley's current rotunda shape, is more the norm.
And where the extra training, even for slubs like myself, pay off is when I'm ask to help someone move. I have virtually unlimited energy for the task where everyone else is bushed in no time. Likewise, a good martial arts summer regimen will show up in the fall, with all that added hand-eye body coordination training and endurance.