Click on the photos to view a video clip illustrating the proper way to perform the exercises described.
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Abdominal Exercises

The abdominal muscles work to compress the abdomen and flex the spinal column. Contraction of one oblique alone will laterally rotate the spinal column.

Abdominal Crunch

Lie on your back with knees bent and feet flat on the floor, shoulder width apart. Cross arms at the chest and focus eyes on the ceiling. Lift the shoulder blades off the floor, keeping head, neck, and back in a straight line during the entire exercise. Slowly return to the start position and breathe evenly throughout the motion. If further neck support is desired, place a towel behind the neck, grasping the ends of the towel in each hand.

Diagonal Crunch

Lie on your back with knees bent and feet on the floor, shoulder width apart. Cross arms at the chest and focus eyes on the ceiling. Without twisting the spine, lift the shoulder blades up by directing the right ear towards the left knee. Keep head, neck, and back in a straight line. Return to the start position and repeat in the opposite direction to work the other side. This exercise may also be done using a towel for further neck support.

Reverse Crunch

Begin with shoulder blades on the floor, and arms parallel at sides for support. Lift legs up and slightly bend the knees, keeping feet together. Next, tighten the abdominals and roll hips off the floor slowly, bringing legs toward the head. Maintaining a slow controlled movement, return to the start position. Concentrate on using only abdominal muscles for lift. Never let momentum in the hips and legs complete the repetition for you.

Back Exercises

The low back muscles act to extend the trunk and produce lateral trunk flexion.

Prone Back Extension

Lie in the prone position, with hands placed on the small of the back. Feet and hips should remain in contact with the floor throughout the exercise. Keeping the head, neck, and back in a straight line, lift the torso by contracting the lower back muscles. Return to the start position using a slow, controlled motion. Lift only as far as comfortable. Discontinue if any pain is experienced.

Advanced Back Extension

Start in the prone position, as in the Prone Back Extension exercise, but extend arms straight out above the head. Work the lower back muscles by lifting opposite arm/leg combinations. Limbs should remain extended without locking their respective joints. Only lift limbs to a comfortable level. Discontinue immediately if any pain is experienced.

Source:
The Total Trainer, Army Physical Fitness Research Institute, The U.S. Army War College Barracks, Pennsylvania.