I use the kind that hangs on the top of a door frame. I do 15 min bursts, off and on for about two hours. then I hang, with the bicep part of my arm flat (90 degree angle on the elbow), then do core work, pulling my knees to my chest, and then twisting to put one knee on the opposite side of my body, to the chest. to the left, both knees up, then to the right, count as one. I do that till I tire, then drop to the ground for "bow and toes" routine. I never get on my back for sit-ups, and I like to think (in as much modesty as I can use here), that I have a pretty decent core routine. hope I could help. stick with it man. its a great work out. I do escrima (sinwale all the way!), and my core work out really helps with kali endurance.