Traditionally, exercises devoted to strengthening and toning the abdominal muscles were performed using high repetitions (50-100+).  A few months back, I read an interesting article, "The Science and Evolution of Abdominal Muscle Training," written by Phil Campbell and published in OnFitness, which challenged this concept.  Campbell purports that we rethink our approach to developing this muscle group.

To lay the foundation for his argument, Campbell refers to the physiological process involved in building muscle tissue.  He explains that micro-fiber tears have to occur in the muscle in order for it to adapt, and thus, rebuild and get stronger.  This process begins when you perform an exercise that taxes the targeted muscle group(s).

The problem with the traditional approach to improve abdominal fitness, explains Campbell, is that, by nature, the abdominal muscles are designed to be efficient and to endure the repeated demands placed on them throughout the day (even while sitting your abdominal muscles are recruited to keep your torso upright).  The "row" configuration of the abdominal muscle group allows for some of the rows to rest while others are contracting, hence, contributing to the high endurance capacity and efficiency of this muscle group.  Campbell points out that you would have to do several sets of 100 repetitions back-to-back to create the micro-fiber tears needed to start the adaptation process required to increase strength.  He argues that this could subsequently lead to a "wearing-out" of your spine in the long-run, resulting in back problems and discomfort.

Campbell's solution is to work the abdominal muscles in a "less efficient" way.  That is, separate the training exercises into upper and lower abdominal workouts.  He suggests that you work your upper abdominal muscles first by performing 4 sets of 20 repetitions of upper-body quarter crunches followed by working your lower abdominal muscles through completing 2 sets of 20 repetitions of leg raises.  The idea is to exhaust the upper abdominal muscles so that they cannot be engaged to assist the lower abdominal muscle group.

When performing the upper abdominal muscle group exercises, Campbell suggest either using a weight machine that only allows you to perform upper-body quarter crunches or to place a free weight on your chest while you lie on your back with your feet elevated on a bench.  He suggests you choose a weight that will be difficult, yet doable for the recommended number of sets and repetitions.  Campbell recommends that this abdominal program be performed 3-4 times per week.

Developing strong abdominal muscles not only has an aesthetic appeal, but is necessary to improve your ability to perform day-to-day activities.  A strong core will lower your risk for back discomfort and injury.  It will also improve your quality of life and increase your years of independent living.

Note:  Before beginning an exercise program or increasing the intensity level of a current routine, a physician's approval should be obtained, especially for older adults and those at risk for or who currently have chronic health conditions.

Resource:
OnFitness, January/February 2010, pp. 40-45, "The Science and Evolution of Abdominal Muscle Training," Campbell, P.