Injuries come from stupid training. Most people do chest, bis, tris, back, delts, traps, legs but forget to work stabliser muscles, rotator cuff exercises etc... It's true that strength and muscle size increase at a faster rate in comparison to tendons etc... But that doesn't mean that you forget about those important exercises that help to protect you from injury. So it doesn't matter if you're on or off. Genetics play an important role as well but smart training is what's important.