Larsen was the co-founder of Running USA, now Mammoth Track Club. Most recently, in 2013 he was inducted into the USATF Hall of Fame. His most notable athlete is Mebrahtom Keflezighi, the 2004 Olympic Silver medalist in the Marathon. Building on that success, Keflezighi won the 2009 New York Marathon. Previous to that Larsen coached the UCLA Cross Country and then Track teams between 1979 and his retirement in 1999. UCLA Head Track and Field Coach. He perpetuated the UCLA winning ways with two consecutive NCAA Men's Outdoor Track and Field Championshipsin 1987 and 1988, along with 9 conference championships. In 1995 he was named the Coach of the Year by the United States Track Coaches Association. In 2003 he joined the Hall of Fame for that same organization.On December 5, 2009 Larsen was awarded the Robert Giegengack Award, signifying the person who has "made an outstanding contribution to the development and success of USA Track & Field and the larger community of the sport."