Myhlback, who started for the Karlslunds IF, made his debut in the Val di Fiemme in December 2003 in the cross-country skiing world cup and took 26th place in the sprint. His first race in the Scandinavian Cup he ran in December 2004 in Veldre , which he finished in first place in the sprint and thus achieved 13th place in the overall standings at the end of the season. In March 2005 he achieved his first top ten place in the World Cup with ninth place in the sprint in Drammen . At the end of December 2005 he won the sprint at the Far East Cup in Changchun . In the 2006/07 season he came in four World Cup appearances, three times in the points. He achieved his best place in the World Cup with sixth place in the sprint in Changchun. At the end of the season, he achieved 32nd place in the Sprint World Cup. At the season highlight, the Nordic World Ski Championships 2007 in Sapporo , he finished 22nd in the sprint. He completed his 11th and last World Cup race in March 2007 in Stockholm , which he finished in 39th place in the sprint.