Complex sentence: He was the editor of "Mountain Bike Action Magazine" from 1986 to 1993, when he moved to Rodale's Mountain Bike magazine, which he brought to prominence before leaving that Executive Editor post in 2004.
Split into simpler sentences: He was the editor of "Mountain Bike Action Magazine" from 1986 to 1993. He then left to become Editor at Rodale's Mountain Bike magazine, which he brought to prominence before leaving in 2004.