In any CORE exercise the most important thing to focus on is ensuring your are properly engaging and isolating the targeted abdominal muscles without allowing any surrounding muscles to provide assistance in the required movements. This is one of the most common mistakes that occur while performing abdominal exercises for one of many reasons: the person does not know how to properly isolate the abdominal muscles (the pelvic tilt), weakness in the abdominal musculature; therefore, the person is not able to hold the abdominal contraction throughout the course of the exercise, allowing the surrounding muscles to provide assistance in finishing the last couple repetitions. Improper isolation of the abdominal muscles, or lack of, during a CORE exercise can lead to increased strain on the surrounding tissues, most commonly the muscles of the low back (quadratus lumborum and erector spine.) If pain is felt during any CORE exercise that means that the abdominal muscles are not being effectively isolated and the exercise should be stopped.
An exercise to help teach proper isolation of the abdominal muscles while adding dynamic movement of the limbs is the dead bug. This exercise starts by lying supine (on your back) on a mat with your feet flat on the floor and knees bent. Before beginning this exercise you must ensure that you are comfortable with proper execution of the pelvic tilt (see article titled “The Pelvic Tilt”), as it is the main component of this and every other CORE exercise. Once you are lying supine with knees bent and feet flat on the floor, perform a pelvic tilt so that your low back is lying flat against the mat and transverse abdominis (TA) muscle is properly engaged. Next, raise your feet up off the floor while keeping your knees bent at 90 degrees; therefore, you should be in a position with a 90 degree angle between your hips and your thighs (quadriceps) and 90 degree angle in your knees with toes pointing to the ceiling. Due to the basic anatomy of the body, naturally when you raise your feet up off of the floor your low back will want to curve and raise up off the floor; however, this is where strength in your TA muscle is important to maintain a contraction and keep your back lying flat on the floor.
Once you have your knees up and TA muscle activated, straighten the left leg and lower it towards the floor while keeping the right leg bent at 90 degrees. Follow that movement with straightening the right leg and bring the left leg back into the 90 degree bent position. Continue to alternate lowering each leg to the ground for a total of 10 reps; however, if you begin to feel your low back lift off of the floor discontinue the exercise, rest, and try again.
Once this exercise becomes to easy the addition of opposing dynamic arm movements allows for increased difficulty. Begin with arms straight up overhead and while lowering the left leg to the floor also lower the right arm to the floor, keeping the right leg and left arm still. Continue the exercise by bringing the left leg and right arm back to their starting position, then lowering the right leg and left arm to the floor. Perform this for a total of 10-15 reps depending on TA strength and ability to keep your low back flat on the floor.
Remember to perform each repetition at a slow comfortable pace to ensure proper isolation of the abdominal muscles and to avoid unnecessary irritation of the surrounding musculature.