Elbows are probably the things I focused most on in my training. All sorts of them. The legs are definitely important but what's also important is getting the ''same feel'' as if your punching most people who use an elbow strike have their elbows ''too far out'' the motions are wide without providing power so in that sense the torso comes to play as well but it's like anything else really if you can throw a powerful straight punch you already have 70-90% of the mechanics for an elbow strike of almost any kind.