Injuries are a matter of genetics and luck. Some players seem to have a body that can withstand the punishment that pro tennis puts on the body. Other players have genetic weak points that will eventually break over time.
I had to have a wrist surgery, due to torn cartilage. I'm a weekend warrior who doesn't get in a ton of court time, but SNAP, that cartilage was going to go no matter what I did.
We've seen fantastic players like Guga, Haas, Rafter, etc. etc. all have injuries that really hurt their performance in the long run. Are these guys less fit? I'd say they were all just prone to a specific injury.
Agassi has had a few close brushes over the years with his wrist. Aside from that, he has always said the key is playing as well as he does at his age is "getting lucky by being healthy." Agassi works like a dog, but even he accepts that you can't train being healthy.
And yes, every player (worth a damn) goes through extensive training in flexibility and strength to increase the odds that they won't get normal wear and tear injuries.
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