training after knee replacement??

:confused: One of my friends who trains in wing chun with me is having a hip replacment and knows he will be able to get back to training after some recovery time, but then he has to get a full knee replacment( not knee reconstrution). and is unsure if he will ever be able to do the chum kil or dummy at full speed after the knee, he is only 41 and is very fit( bike rides, surfs, base jumps,sky dives) all of which he wont be able to do after the knee.

Has any one had a knee replacment and then been able to train after. and if so how long after the OP and could they train at 100percent ever again or if not how much was there training affected?

Any help would be great.thanks