Loop the resistance band around the balls of your feet inside the band. Lie down on the floor facing up, extend legs forward, and place your fingertips behind your ears (as opposed to interlacing the fingers behind the head; you might end up pulling on the neck and shoulders as you fatigue).
Feeling the resistance of the band, rise up off your shoulder blades, pulling your navel to spine and closing the ribcage, pull your left knee in toward your chest as you twist your right elbow to meet your knee (right leg remains extended forward and lifted off ground). Keep your elbows wide open to increase your range of motion and deepen your twist, exhale at the end of the movement to get your naval in tighter.
Switch sides, alternating the left elbow to right knee, aiming to touch the elbow to knee each rep, feeling the opposition of the push and the pull of the legs to activate the low abs and obliques.