Q: Is it possible to selectively train your lower abdominal muscles?

A: Based on electromyographic (EMG) activity recorded during the performance of various abdominal exercises (e.g., crunches, reverse curls, leg lifts), individuals generally appear unable to differentially recruit the "upper" and "lower" abdominal muscles. In other words, individuals cannot trigger a contraction in one specific area of the abdominal muscles (either the upper or lower abs). Despite the common misconception among many fitness professionals and exercise enthusiasts, EMG data suggest that the upper and lower rectus abdominis act as a continuous sheath (i.e., one large muscle group). Contributing to the confusion is the fact that during certain abdominal exercises (e.g., leg lifts or other "hip flexor" exercises), individuals experience localized muscle fatigue and discomfort in the lower abdominal region. This situation occurs because the primary muscle used in hip flexion, the iliopsoas, originates deep below the lower portion of the rectus abdominis. The key point to keep in mind is that the phenomenon of local muscle fatigue and discomfort should not be misinterpreted as specific recruitment of "lower" abdominal muscles.

Source: Bryant, Cedric X. ACE FitnessMatters, January/February 2004.