Loop a long resistance band around a secure anchor point close to the floor. Ensuring a good distance between yourself and the anchor point place the other end of the resistance band around your feet. Lie face up, with your back flat on an exercise mat and your legs extended out in front of you with the band round your feet. There should be a good amount of tension on the band. This is your start position. Keeping your core braced and arms by your sides, bring your knees towards your chest, resisting against the band. Pause at the top of the movement before reversing back to the start position. Repeat for the required number of reps (or time).