Sit on floor or mat. Place dumbbell between feet. Lie supine with hands on floor over head.
While keeping feet together, simultaneously raise straight legs and torso. Reach toward raised feet. Return to starting position. Repeat.
Weight can also be held with hands and feet at same time. Keep knees straight throughout movement. Begin each repetition with upper back on floor to allow abdominal muscles to work dynamically. The Rectus Abdominis and Obliques dynamically contract only when actual waist flexion occurs. With no waist flexion, Rectus Abdominis and External Oblique will only isometrically contract to stabilize pelvis and waist during hip flexion. See Spot Reduction Myth and Lower Ab Myth.