Core exercises can strengthen and tone the abdominal muscles. These muscles are more difficult to shape. Typically, there may be stubborn deposits of fat remaining in the stomach area, even after you have lost most of your excess weight. If you want a nicely shaped six pack, you need to take core exercises seriously. You can choose from a series of exercises.

Sit-ups are the best known core exercises used to shape the tummy. Lie on the ground or on a yoga mat, keeping your knees bent and the feet on the mat. Your hands should be held at the back of your head.

Tighten your abs and lift your head and shoulders off the mat, making sure the feet remain on the ground. Remain in the air with your abs tightened for 1 to 3 seconds and return to your initial position. Repeat the move 10 to 20 times.

The crunches are similar to sit-ups. The initial position is the same, with the back on the mat and knees bent. The hands will be kept crossed on the chest or at the back of your head.

Inhale and lift your head and shoulders by tightening your abdominal muscles. Stay in this position for a few seconds, exhale and return to the starting position.

The crunches may replace the sit-ups; choose the sit-ups if you experience neck pain.

Leg lifting is a type of exercise that will work on your lower abs.

Lie on a yoga mat with your hands behind your head or crossed on the chest. Tighten your abdominal muscles and squeeze your buttocks. Lift both your legs off the floor, maintaining them straight or bending them slightly. Lower the legs to 1 inch to the floor, so that the abdominal muscles are still tight and then repeat the lift. Perform 5 series of 10 leg lifts.

A pull-up bar can also be used to vary the intensity of the exercise. The bar should be attached to a wall behind you (e.g. over the door). Grab the pull-up bar with your hands and hang with your legs straight; make sure your body is not swinging by stabilizing your upper body. Your shoulders should be in a neutral position and there should be a bit of space between your ears and the shoulders. Keep your back and abs tight and lift your knees to your chest. To add more intensity, you can also raise your straight legs to 90 degrees, using your lower abs. Maintain this position for 3 seconds and then lower your legs. Repeat 10 times.

A jack knife sit up is a more complex sit-up, involving all abdominal muscles.

Lie on your mat, with the legs straight on the mat and your hands to the sides. Lift your feet and head at the same time. Maintain this position for 3 seconds and then lower your feet and head.

Lie on your mat with your stomach and head touching the ground. Lift your legs and head at the same time, keeping your legs straight.

Remain in this position for a few seconds and then lower your legs and head to the ground. Repeat 10 times.