I was going to post this as well. I have heard that Tiger's original knee problem started when he was f'n around with Navy Seals training, and everything sort of cascaded from there. I have also heard the whispers about Biogenesis etc., and frankly, none of that is hard to believe if it turns out to be true.
But even without the speculation/rumor of steroids, if the Navy Seals training thing is true, that itself is just so ridiculously dumb I don't even know where to start. I know it's all unverified, but the stories have been out there for a while now and it's well-known he idolized his career-military dad and his insanely inflated ego was peaking around that time as well. I never bought into this idea that his swing was somehow too violent and caused his injuries; yes, he torqued hard on that left knee, but unless he already had a serious injury there, it should not have led to multiple surgeries and left him in a debilitating state (after all, he's not the only guy with a hard post-up and swivel on the left side). It makes more sense that he had the original (non-golf-related) knee injury, compensated by changing his swing, and was simultaneously bulking up and further altering his swing which then led to further injuries (back, etc.).
Honestly, I'm not sure why he's even out there at this point. He's not competitive, he seems to aggravate some old injury or ailment every other round, and he's just a side-show to the actual tournament most of the time. I don't ever doubt that he still has the ability to compete at the highest level (as he occasionally shows), but putting together 4 solid competitive rounds seems to be beyond his physical abilities at this point (for health reasons). None of that is going to get better as he gets on the other side of 40. For someone who has always been of the mind that he wants to be the best or he doesn't even want to be out there, he really only seems to have 1 option at this point.
I can't imagine Tiger ever playing the Senior Tour. He seems more like a "retire into a life of business ventures and golf course design" kind of guy. The Senior Tour was originally a place for legends to basically cash in during the twilight of their careers at a time when the money in golf was finally getting pretty sweet (given that most of the legends played during a time when they didn't make all that much, all things considered). But in the modern era, most of these guys make so much money during their playing days, they really don't need to go out on what's clearly a secondary tour during their retirement years. These days, it seems like the "Champion's Tour" (I hate that name, BTW) is more like a career extension option for middle-of-the-road tour players who need to keep cashing a check for as long as possible. There are obviously some notable exceptions, but most of the time, I basically watch those tournaments to see if I can recognize some obscure former Tour players (the "hey, I remember that guy!" factor) and also to see how old I can feel (also known as, "that guy is on the SENIOR tour now??? Jesus, I'm old....).