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One of the latest rages in the fitness industry is the plank exercise. In essence, plank refers to maintaining your body in a straight line from head to toe, as for example, in the up position of a push-up. Your body can also be in a plank position when facing sideways while supported on one arm. This exercise is touted as being very effective for developing the core (i.e. the abdominal, lower back, and sometimes hip muscles). In reality, however, the plank position is a very poor exercise for strengthening the core for several reasons.

First, the strength that you gain is isometric (static) strength, which isn’t transferable to dynamic strength. Understand that dynamic strength is more functional because it can be used in your daily movements. Static or isometric strength is very specific to a particular point in the range of motion and is effective mainly for holding purposes. This means it enables you to hold a position for an extended period of time.

This is why the plank exercise is effective only for developing static strength to hold the body in a straight line posture. It is not effective for enhancing any movements that use the core muscles, especially dynamic movements with the axis of rotation in the waist or hips. Thus, any value gained from doing the plank exercise is specific only to holding the position seen during the exercise.

Second, many people do not have the strength to hold themselves in a plank position. Some lack the arm strength, especially when doing the side plank while others lack the abdominal strength to hold a straight line position through the midsection. Some may be able to assume the position. However, in order to develop isometric strength, you must hold the position for five to six seconds. This compounds the difficulty of the exercise for some people.

Third, the plank exercise involves mainly the abdominal muscles when holding the push-up up position. It does not affect the lower back muscles and only partially the hip flexors. The side plank position, however, does involve all of the core muscles but not equally.

For these reasons, if you are truly interested in developing the core muscles not only for maintaining straight line body position posture but also to help improve your everyday movements, especially those involving bending and twisting, you do not want to do plank exercises.

Instead, you should do some of the standard exercises such as sit-ups, reverse sit-ups, reverse trunk twists, back raises, back raises with a twist, hip abductions, abductions, flexions, and extensions. There are no exercises that involve all of these actions to develop all of the core muscles.

If you want more information on the execution of these exercises and the muscles that they develop, see Kinesiology of Exercise. It is a very detailed book, well illustrated with muscle and exercise pictures and complete descriptions of not only how the exercise should be done but also what happens when you change grips, stance, and execution.