The band jack knife situp is an exercise targeting the abdominal muscles, particularly the rectus abdominis or six-pack muscles. The band adds resistance and continuous tension to this popular exercise, making it more challenging than a traditional situp. This exercise can be performed with either your feet on the floor or elevated on a bench. To do a band jack knife situp with your feet on the floor, start by lying flat on your back with your knees bent and your feet flat on the floor. Place a resistance band around your ankles and hold the ends of the band in your hands. Exhale and contract your abdominal muscles to sit up, bringing your knees toward your chest. Inhale and slowly lower back down to the starting position. To do a band jack knife situp with your feet elevated, start by lying flat on your back with your knees bent and your feet elevated on a bench. Place a resistance band around your ankles and hold the ends of the band in your hands. Exhale and contract your abdominal muscles to sit up, bringing your knees toward your chest. Inhale and slowly lower back down to the starting position.