Complex sentence: In terms of difficulty Elena advanced the sport of gymnastics extended its limits and is one of a select few to have introduced a new move and/or trend on each piece of apparatus.
Split into simpler sentences: In terms of difficulty Elena advanced the sport of gymnastics extended its limits. Indeed, Davydova advanced the difficulty of gymnastics through the introduction of her moves, and is one of a select few to have introduced a new move and/or trend on each piece of apparatus.