Adrian Peterson suffered a serious knee injury on Christmas Eve in 2011. He didn't miss a game in 2012 and came within a first down of setting the NFL single-season rushing record.

But Peterson says that it is unrealistic to expect someone like Robert Griffin III, who underwent reconstructive knee surgery two weeks ago, to make a similar recovery.

"That's not fair," Peterson told at the Pro Bowl in Hawaii. "Everybody's body heals differently. That's something nobody is going to understand."

Actually, most thinking observers and fans do understand that. This is Griffin's second ACL repair and it would not surprise anyone if it took him longer to be ready to play than it took Peterson. Even if Griffin had not had the previous surgery it could take him longer to rehab than it took Peterson.

Peterson thinks that an ability to heal quickly has something to do with his heredity.

"This is also a matter of genetics," he said. "Look at my dad. And my mom's side, my aunts and uncles, they're all ripped. At 50 years old, they've got six packs and eight packs.

"My body just heals differently. I know it has a lot to do with rehabilitation and work ethic -- but I really credit my genetics for my recovery as much as anything else."

Peterson may have a point, although I am not aware of any scientific evidence linking being "ripped" to being able to heal knee tendons more quickly than the average human. More likely it points to a family culture of working hard to stay in shape and that carries over into injury rehab.