I know this exercise might look easy, but if you're actively pulling and engaging the right muscles, it's very effective and great for building a strong core. Remember, core means the back of your torso as well as the front.
Suggested sets and reps: 8-15 reps, 2-4 sets, 3 times per week.
T.M.G. TRANSVERSE ABDOMINALS / HIP FLEXORS
NO POLE OPTIONS:
Dumbbells - Lie on the floor with arms stretched overhead while holding the dumbbells, lift one or both legs at a time holding a hollow body position.
Standing Cable Crunch - Keep the rope or handle about forehead level and bend forward.
Ab curl machine - Follow the instructions on the machine.
Hanging leg raises - These are not suitable for beginners, and if you're new to this exercise, start with the legs bent working up to extended legs as shown below.