Is it due to perfect ass?

I usually pick dancers for LD based on their looks and then keep extending the dances based on LD for first song. But sometimes I take dances from not so good looking dancers but still they r average looking but fit body.But turns out couple of those dancers are the best in ass department. But I won't extend the dances beyond two because I cannot control. I LDKed within 2 songs.Usually it takes 6 to 7 songs to happen. It's just becos of perfect sized and well toned ass for me and the sensual grinding.I asked both girls do you work out a lot.Their reply was they do weight lifting. Does it happen to you ?