But there are also tons of backs who just completely broke down. After the 2001 season, everyone thought that Marshall Faulk, at age 28 would eventually become the league's leading all-time rusher -- he was closing in on 10,000 yards and had broken off 4 straight 1300+ yard seasons. All of a sudden, he's less effective and hasn't hit 1000 since.
LT is great but with the number of touches (rush + catch) he gets each year, he has a strong potential to wear down -- he has averaged 400 a year -- Emmitt was closer to 350 with only 4 years total over 400. Dorsett was around 330 a year, with one year over 400.