Can You Isolate the Lower Abs?

By Brad Schoenfeld, PhD(c), CSCS

Most people find it difficult to add appreciable muscle to the lower ab region. While the upper abs generally respond rather easily to intense training, the lower portion always seems to lag behind. This has a lot to do with the structure of the ab muscles. The rectus abdominis is a tapered muscle; it is wide at the top and narrow at the bottom. Consequently, because there isn’t much muscle to work with (about 1/3 the amount muscle in the lower abs as compared to the upper abs), developing the lower ab region can be a challenging proposition.

For women, developing the lower abs tends to be especially problematic. Due to the monthly cycle and associated bloating, the muscle in the lower abdominal region is continually stretched. With each successive cycle, it stretches further and further. Making matters worse, for those who have endured pregnancy, the rigors of childbearing distends the pelvis even more—and for an extended period of time, no less. The cumulative effects of these events cause the lower abs to become more pliable, often producing the dreaded “pelvic bulge.”

Given these issues, gym goers are constantly seeking ways to selectively isolate their lower abs. Some even advocate training the upper and lower abs on separate days. They contend that, by alternating workouts in this fashion, you can avoid over-training the abs and achieve superior development. However, while such an approach may sound logical, it’s actually misguided.

The truth is, it’s impossible to completely isolate the upper abs from the lower abs; the anatomical composition of the abs simply doesn’t afford this ability. Contrary to popular belief, the rectus abdominis isn’t a group of independent muscles, rather, it is one long muscular sheath that runs from just below your chest bone all the way down into your pelvis. Thus, the upper and lower abs are not separable; you can’t train one part without affecting the entire muscle. Every exercise that you perform will, to some degree, target both areas of the muscle complex.

Within limits, however, you can alter the activation of the muscle in the upper versus lower portion of the abs. Here's why.: the rectus abdominis is partitioned by the tendinous intersections (this is what gives the abs the “six pack” appearance). What’s more, the upper and lower abs are innervated by different nerves, providing a mechanism for selective activation.

The key to targeting the lower aspect of the rectus abdominis is to initiate a posterior pelvic tilt. Exercises that facilitate this movement include the reverse crunch and hanging leg raise. The key here is to concentrate on raising your pelvis up towards your stomach—not simply raising and lowering your legs. This is a tricky proposition because the pelvis has a very limited range of motion and, if strict attention is not paid to proper form, your hip flexors will tend to take over during exercise performance. You must focus on putting maximal effort into each contraction, forcing the lower portion of the abs to execute the movement.

The ability to target the lower ab region is supported by research. One of the best studies on the subject was performed by Sarti and colleagues (1), who divided participants into two groups: a high physical activity group that had trained seriously for at least 1.5 hours, 3 days a week for 3 years, and; a low physical activity group that did not. Each of these two groups performed a crunch and a reverse crunch. EMG readings were obtained to determine muscle activity in the upper vs. lower ab region. Exercise performance was monitored by fitness pros and the groups were then further subdivided into correct and incorrect performers based on the participant’s ability to perform the exercises properly. Interesting finding: only the physically active participants deemed “correct performers” were able to target their lower abs! These findings suggest that it might take a bit of practice to really nail proper performance of the movement, but once you do results are bound to follow.

Bottom line: the upper and lower abs can’t be isolated from one another. Regardless of which ab exercises you perform, you’re always working both the upper and lower areas (and even your obliques, too). That said, by performing exercises that allow for a posterior pelvic tilt during dynamic spinal flexion you can selectively target the lower ab region. With proper performance and dedication over time, you can maximize lower ab development.

Reference
1) Sarti MA, Monfort M, Fuster MA, Villaplana LA. Muscle activity in upper and lower rectus abdominus during abdominal exercises. Arch Phys Med Rehabil. 1996 Dec;77(12):1293-7.