they are the devils work. Try to do a superman on it and you will be in agony for a long time. I've got pretty good core strength, if I say so myself, can happily pull off front levers no trouble, but trying this nearly killed me, laughing hurt so much. Made me think it worked non climbing related muscles, hence the pain, so doubtful that it will help climbing much. Best thing is to train front levels with different leg positions, or do chin ups with your legs straight out in front of you, and hang weights off your toes. Much harder than it sounds.