My manager here at work has a PHD in Advanced Genetics, I was on about spanish players not getting many injuries(muscle injuries i mean), bone can't really be enhanced, in terms of strengthening anyway - no matter how much milk you drink :D, but he mentioned "i have read recently a book about genetic doping... scary stuff
maybe that's what they are doing
so even if they have muscular injuries, their muscles regenerate far more quickly than otherwise possible"
Sports injuries such as calf(oshea) and hamstring injuries, are very common over seasons, especially as you get older, where you are playing 2-3 games in 7-8 days. They never seem to get them.