Lie on back, with hands tucked behind lower back and elbows out to the sides, one leg straight, the other bent with knee up and foot resting on floor. 1 rep is: slightly lift elbows, flex core to lift shoulders and head just barely off the floor, keeping spine & neck neutral/straight. Do not curl neck. Hold for a count of 8. Relax. The idea is if the floor behind the head and shoulders were a scale, the flex just barely causes the scale to read zero. Very little actual motion.