actually just probably 5 years ago, almost every team had a featured back who played almost all the 1st and 2nd downs. He would only be spared in the 3rd down if it is a passing down and he did not have good hands. Naturally, such a RB would carry the ball about 250-300 a season and would take a lot of pounding. That was why RB's average NFL career was less than 5 years. Recently, teams are more willing to use more than 1 RB to share the workload. A common scheme is to play two backs alternately. The most successful example, in my momory, was Denver Broncos committee several years ago. Mike Anderson ran over 1000 yards and scored 10 TDs, while Tatum Bell ran almost 1000 yards and scored 9 TDs.