Below is some great exercises you can do specifically for your lower abs. This workout should be at least 2 to 4 sets for 15 to 20 repetitions. This workout can be done on a separate day but works best in combination with your entire ab workout. 

1. Incline Leg Raise

Execution

1. Lie supine on an inclined abdominal bench with your legs down.

2. Raise your legs at the hips and pull your thighs toward your chest, keeping your knees slightly bent.

3. Slowly lower your legs back down to the start position.

Muscles Involved

Primary: Rectus abdominis (lower).

Secondary: Obliques, hip flexors (iliosoas, rectus femoris).

Range of motion: To maximize muscle contraction on the way up, raise your knees as high as possible toward your chest. To keep tension on the abs, do not lower your legs all the way down or allow your feet to touch the floor.

2. Hanging Leg Raise

Execution

1. Hang from a chin-up bar using your hands, or place your elbows in a pair of ab sling (these attach to the bar to support your body weight); your legs hang down.

2. Lift both knees, together and slightly bent, toward your chest.

3. Slowly lower your legs back down to the start position without swinging.

Primary: Rectus abdominis.

Secondary: Obliques, hip flexors (iliosoas, rectus femoris).

Range of motion: Raise your knees as high as possible to maximize muscular effort. As you lower your legs down, keep your knees slightly bent to maintain tension on the abs.

3. Knee-Up

Execution

1. Sit on the edge of a flat bench, legs hanging down with knees slightly bent, and grip the bench behind you.

2. Raise your knees up toward your chest, keeping your legs together.

3. Lower your legs back down until your heels almost touch the floor.

Muscles Involved

Primary: Rectus abdominis.

Secondary: Obliques, hip flexors (iliosoas, rectus femoris).

Range of motion:

Raise your knees up until your thighs almost touch your abdomen. As you lower your legs down, stop before your heels make contact with the floor to keep tension on the muscles.

4. Reverse Crunch

Execution

1. Lie on a flat bench, position your feet so you have a 90-degree bend at your knees and hips, and grasp the bench behind your head for support.

2. Lift your pelvis off the bench until your feet point to the ceiling.

3. Lower your legs back to the start position.

Primary: Rectus abdominis.

Secondary: Obliques, hip flexors (iliosoas, rectus femoris).

Range of motion:

Contract your lower abs to lift your pelvis up off the bench, raising your legs until your toes point to the ceiling.