Can Clinton Portis still be an effective running back?

The Washington Redskins wasted little time in releasing veteran RB Clinton Portis after the conclusion of the 2010 NFL season, but can the free agent running back still be an effective player in the league going forward? The University of Miami product started his career with great promise after being drafted by the Denver Broncos in 2002. Portis accounted for 3,777 total yards and 31 scores before being traded to the Washington Redskins prior to the start of the 2004 season. Portis, who will turn 30 on September 1 this year, is a 9-year veteran and has rushed for over 1,000 yards in six of those seasons. However, throughout his career, Portis has had difficulty staying healthy. He has only played all 16 games of a season four times in his career. Last season, Portis only saw action in five games, rushing for 227 yards before shutting it down for the season due to injury. History proves that for the most part, running backs start to lose their effectiveness around the age of 30, a...