For a rookie, he sure shredded some pretty good defenses last year, there is no doubt that he can be one of the top 5 RBs in the NFL. Capers was talking about much of last year's team being rookies, and guys playing double the season that they did in school, the end of the year takes it's toll.
So with, more time and conditioning under their belts, improvement is inevitable.
As far as injuries, with experience and training players learn how to keep from getting hurt,
hopefully that's the case with 37DoubleD.