Tiger's body is failing because:
he trained incorrectly (see running miles in combat boot, adding a ridiculous amount of muscle weight)
led an extremely stressful double life
attended specialized Navy SEAL training courses
Jack didn't need to train because- like Rory- he didn't need to-- the gym doesn't give you swing speed-- fast twitch muscles, sequence and how you torque the club does. But the gym does improve those area's, and help them 'work' deeper in the round--and help you have a longer, more enjoyable life...
How bout this weekend at the Honda--Gary Woodland loses to Rickie Fowler--how do you explain that? Should Rickie add more muscle to keep up with Woodland's driving distance? Of course not--you know why? Because Rickie already KILLS it, and has a Varsity short game to Woodlands JV--
The short game, judging slope, wind, etc will always be the equalizer.
The game has changed in that golfers are now forced to be athletes- forced to become athletes because of the amount of effort it takes to play at the highest level--travel, scheduling, pro-am, off the course engagements..
-eat impeccably
-exercise regularly, smartly, and with proper professional guidance
-manage your schedule
Bottom line is you don't have to train like an NFL corner back to compete on the PGA Tour--simply because it's useless--it doesn't help golf.
The USGA has effed the game because they didn't control the ball and driver head--that's the bigger issue.