# Isolating the upper, middle and lower pecs (chest)



## Arnold (Jan 14, 2005)

This is a very common question and debated topic, personally I believe that it is not possible to isolate any part of a single muscle, i.e. the pectorial major.

The following "article" explains in great detail why this is not possible. Credit goes to Belial from another board (I do not know his real name).




> The existence of the so-called "upper", "lower", "inner" and "outer" pectorals along with the assertion that it is possible to isolate one or more of these to the relative exclusion of the others in training, are among the most firmly entrenched myths in Strength Training and Bodybuilding circles. In fact none of these truly exist as either separate and distinct muscles or regions in a functional sense. Even though it could be argued that there appears to be a structural distinction between the upper and lower pectorals (and some anatomy texts do in fact support this distinction though not all do) because the pectoralis-major does originate from both the sternum and the proximal or sternal half of the clavicle along it???s anterior surface (it also has connections to the cartilages of all the true ribs with the frequent exception of the first and seventh, and to the Aponeurosis of the external oblique muscle), this is considered to be a common (though extensive) origin in terms of the mechanical function of the muscle. Thus the pectoralis-major is in fact for all practical purposes one continuous muscle with a common origin and insertion, and functions as a single force-producing unit. The terms upper, lower, inner and outer are imprecise and relevant only in order to make a vague subjective distinction between relative portions of the same muscle for descriptive purposes. They are vague and imprecise terms because there is no clearly delineated or universally defined border between them.
> Further it is not physically possible either in theory or practice to contract one region of a single muscle to the exclusion of another region or regions (as a Biomechanics Professor of mine once demonstrated to a bunch of us smart-ass know-it-all???s taking his course, using EMG analysis). When a muscle contracts it does so in a linear fashion by simultaneously reducing the length of its constituent fibers and thus its overall length from origin to insertion. Even where a single muscle is separated into multiple functional units that are clearly defined such as the triceps (which are referred to as ???heads??? by Anatomists and Biomechanists), because they share a common point of insertion in order for one head to shorten all must shorten. This only makes sense if you think about it because otherwise there would be ???slack??? in one when the other shortened, which as we know does not occur. Note that there are some special cases where one head of a muscle must actually lengthen when the other shortens (e.g. the posterior head of the deltoid in relation to the anterior head during the positive stroke of fly???s), the point however is that even in these special cases there is no ???slack??? because there is in fact contractile activity (whether concentric or eccentric) throughout the muscle.
> 
> That is not to say however, that all fibers in different areas, or heads are necessarily shortened to the same degree during a particular movement. Depending on the shape of the muscle, the joint geometry involved, and the specific movement being performed, fibers in one area of a muscle or head may be required to shorten more or less than in others (or even to lengthen) in order to complete the required movement. For example during a decline fly though muscle fibers in all regions of the pectoralis-major must shorten as the upper arm is drawn towards the median plane of the body, because of the angle of the arm in relation to the trunk the fibers in what we commonly refer to as the lower pecs will have shortened by a greater percentage of their overall length than those in the upper region of the muscle by the completion of the movement. Conversely when performing an incline fly there is greater shortening in the fibers towards the upper portion of the muscle than in the lower.
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