The lower abdominals may be the single most popular subject among fitness enthusiasts today. This is due to the fact that having flat, tight, lower abdominals is a highly desired look, but a very difficult look for most people to achieve. Many fitness professionals insist that there is no such thing as "lower abdominals", While others propose that exercises like crunches work the upper abs more and exercises such as leg raises or reverse crunches work the lower abs more.
Before continuing, first keep in mind that no abdominal exercise can "spot reduce" lower abdominal fat. Many people feel a need to perform special "lower ab" exercises, not realizing that the real reason they can't see their lower abs has nothing to do with their choice of abdominal exercise, and everything to do with an excess of fat and possibly digestive problems
Because of genetics and hormones like estrogen - the lower abdominal region is simply one of the first places most people store body fat. Therefore the same is true in reverse - lower ab fat is the last place to come off. Removal of lower abdominal body fat is a separate issue than lower versus upper abdominal muscle recruitment and body fat problems can only be addressed by creating a caloric deficit and addressing lifestyle factors. This requires proper nutrition, not special "lower ab" exercises.
Second, it's true that you cannot isolate the upper and lower abdominals from one another. Both upper and lower abdominals are activated during the performance of any abdominal exercise. The rectus abdominis is one long muscle, not two separate muscles. However, the nerve innervation of the upper and lower portions is different.
Although you cannot completely isolate upper and lower abs, research has used electromyography (EMG) testing to try and determine whether certain exercises can emphasize one section of the abs more than another. Results have shown very clearly that the obliques can be recruited more with specific exercises. However, data on lower versus upper abs is mixed.
For example, a 2001 study by Lehman and McGill published in the journal Physical Therapy said, "Differences between the portions of the rectus abdominis muscle are small and may lack clinical or therapeutic relevance." On the other hand, a study by Willett and colleagues at the University of Nebraska said, "our findings support the concept that abdominal strengthening exercises can differentially activate various abdominal muscle groups." A 2007 study by Eric Sternlicht found major increases in EMG activity (93%) of the lower abdominals simply by changing body placement on a swiss ball during the crunch exercise.
I believe it is very possible that the upper and lower abdominal areas can be emphasized to a greater degree by the choice of exercise. The abdominal region is somewhat unique because unlike muscles such as the bicep, the abdominals are divided by tendinous intersections which correlate to various segments of the spinal column. It has been proposed that these segments may be under separate neurological control.
As I learned in my internship from the Paul Chek Institute, as early as 1934, Joel E. Goldthwaite in his book "Body Mechanics in Health and Disease," determined that there was a difference between the control mechanisms of the upper abs versus the lower abs. In other words the "electrical system" that controls each section is innervated by different wiring.
Some years ago a TV special filmed a belly dancer rolling a few quarters up, down, sideways and diagonally across her belly. I have seen a similar feat with my own eyes as my brother can do a "belly roll" - an impressive feat of abdominal muscle control somewhat akin to a caterpillar inching its way across the floor, by rolling one segment of its body a time. Although this may simply be an individual trait and or a well-practiced skill, it's suggestive that different segments of the abdominals can function independent of each other, indicating that they may be on different neurological circuits.
Evidence of separate innervation may also be seen when a person with great upper abdominals experiences distention in the lower abdominal region, commonly known as a "pooch belly," despite low body fat. Explanations include gastrointestinal issues, bloating or food intolerances that allow the lower abdominal wall to protrude as a result of inflammation inside the gut. However, there may be a neuromuscular explanation as well. If the muscles that hold in the gut contents are weak or suffer from poor neural connections, the lower abdominal wall may bulge outward, independent of body fat levels.
There are many opinions on this controversy, as well as conflicting research data. Some experts believe strongly that "lower ab exercises" are just another fitness myth and that the case is simply closed. However, the abdominal and core region may be much more complex than just one long sheet of muscle running from the sternum to the pubic bone that contracts completely along its length or not at all. I believe we should keep an open mind to the possibility of being able to emphasize the upper or lower area to a greater degree, as some of the EMG studies suggest.
Assuming that the lower abdominals can be stressed to a greater degree with choice of exercise, this has significant implications for creating highly effective and individualized training programs.
Lower abdominals should be trained as follows:
(1) proper exercise sequence (lower abs first),
(2) proper selection
(3) proper progression.
A common mistake is when a beginner with weak lower abs attempts to do advanced exercises such as hanging leg raises. This demonstrates improper exercise selection and progression and will do nothing but build muscle imbalances. These imbalances will manifest in poor posture and lead to injury and low back pain.
Upper and lower abdominals can be tested and I outline two easy assessments to find out your level of lower abdominal conditioning in my Firm and Flatten Your Abs e book. When you take the upper and lower abdominal tests before starting the program, you will easily see the difference between the two and then you will know which areas to prioritize the most, which exercises you can safely begin with and how to get the best results possible from your training program.