No kidding. It's like he got serious about working out or something after he left Michigan State. In college I wouldn't say he was out of shape but he was a bigger, slower, more plodding runner that relied more on being physical.
In the NFL he's slimmed down, very elusive, and changes directions quickly while still having a lot of the power. It's been very impressive. Also a shame he's missed a lot of time due to injuries and being an idiot though.