TIP 6: DON’T ANCHOR YOUR FEET

Using sit-up boards with supports for the feet or having someone hold your ankles when you perform abdominal exercises increases the involvement of the hip flexors. It also affects normal recruiting patterns so that the hip flexors are activated before they should be, an effect which increases the stress on the lower back. 

For those who contend that them are no such things as lower-abdominal muscles consider that the abdominal muscles which extend below the belly button are controlled by two nerves which originate in the region of the first lumbar vertebra.

From a neurological standpoint, the abdominals can be classified as having upper and lower segments. Also. because the external obliques originate from the ribs and attach to the front of the pelvis, they can rotate the pelvis back and ensure ideal posture by preventing the forward pull of the hip flexors. Consequently, from a functional standpoint, the abdominals can be classified as having upper and lower segments, which function somewhat independently. 

Although many people do flutter kicks and leg extensions (pulling the legs "in” and then extending them while lying on their backs on a flat bend h) to work their lower abs, it should be noted that these are advanced exercises. If your lower-ab muscles aren’t strong enough, you’ll be working the stabilizing aspect of the lower abs rather than the fictional aspect of the lower-abs. In other words, unless you advanced in your lower-ab training, these exercises will work the lower abs only indirectly. You’ll be emphasizing the hip flexors and the muscles that control the postural position of the pelvis.

Better beginning and intermediate lower-abdomen exercises include reverse crunches (pulling the legs to the upper body rather than pulling the upper body to the legs) and reverse crunches done on an incline bench.

TIP 7: PERFORM LOWER-ABDOMINAL EXERCISES FIRST 

An abdominal workout should progress from the bottom up; that is, perform exercises for the lower-abdominal region before exercises for the upper- abdominal region.

The upper-abdominal muscles provide stability for the lower abs, and lower- abdominal exercises generally require more coordination than upper-abdominal exercises. If you fatigue the upper abdominals with exercises like crunches, you won’t be able to train the lower abs at an optimal intensity level. Thus, you should train the lower abs when you’re fresh and focused (but of course. not before doing heavy lifts that load the spine).