Two 'stubborn old Marines' remain the last of the 'Groundpounders,' the runners who have run every Marine Corps Marathon

Retired Marine colonels Will Brown and Al Richmond have run 39 consecutive Marine Corps Marathons, since its debut in 1976. This Sunday they'll run No. 40. They keep going and going and going .... My story for ESPN.com's Endurance Sports section: http://espn.go.com/sports/endurance/story/_/id/13934285/endurance-sports-last-remaining-groundpoundes-ready-their-40th-marine-corps-marathon