The FIRST program seems well suited for those training for multi-sport events like the duathlon and triathlon. The founders of the program participated in trathlons, so it makes sense. You see this connection when you research training programs for triathletes. For example, check out this training runs for triathaletes: The Big Three - Key Running Sessions for Triathlon In this case, tha author recommends three key runs - a multi-pace track session, a hill work-out, and a long run.