Secure a pair of Ab straps over a pull-up bar. Reach your arms through the straps so that the upper arm is being supported by the strap. Grab the top part of the strap with your hands and with your knees slightly bent.
Initiate the movement by contracting your core and raising your knees toward the ceiling.
Continue to contract your core and raise your legs until your knees are slightly above the line of your hips.
As you perform the movement, make sure that you do not sway forward or backward by keeping your back and core tight.
Reverse the motion by lowering your legs back to the starting position under control.
Pause and repeat.