| Lord Monkcheese -> RE: Decline Bench query (May 8 2008 11:40:01) |
For a more scientific response, have a read through this article. I can't find any reference of where I originally found it but it's been sat in my Yahoo account since 2004 so it may have come from a post in MT.
It seems to be Mel Siff's response to a claim that isolation of specific parts of a muscle can't occur. Siff is of the camp that isolation cab occur as evidenced by EMG studies and biofeedback specialists.
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by: Maki Riddington
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 StrengthTraining 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 its 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 smarty 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.
***[Biofeedback research in some cases shows exceptions to this 'rule.' Surface EMGs often tell a very different story from invasive EMGs recorded with fine needles inserted deep into different regions of muscle. I trust that this biomechanics professor pointed this basic and very important fact out to all the students. If he failed to do so, he was in definite dereliction of his duty as an educator. Mel Siff]
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 flyes), 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 flye there is greater shortening in the fibers towards the upper portion of the muscle than in thelower.
Many proponents of the so-called "isolation" approach to training claim that this proportionally greater shortening of the fibers equates to greater tension in the "target" region than in others, and therefore stimulates greater adaptation; but this is completely at odds with the cross-bridge model of muscle contraction
which clearly shows that as fiber length decreases tension also declines due to increasing overlap and interference in the area of the cross-bridges.
Some also contend that the fibers called upon to shorten to a greater degree tend to fatigue faster than others and that therefore there is greater overall fiber recruitment in the region where this occurs, and thus a greater stimulus to growth; but there is no evidence to suggest that a fiber fatigues faster in one position
than in another in relation to other fibers in the same muscle. In fact it has been shown that Time Under Tension (TUT) is the determining factor in fatigue and not fiber length. In fact fiber recruitment tends to increase in a very uniform fashion throughout an entire muscle as fatigue sets in.
The ability to "isolate" a head, or region of a muscle to the exclusion of others by performing a particular movement, or by limiting movement to a particular plane and thus develop it to a greater degree, is a myth created by people who wish to appear more knowledgeable than they are, and has been perpetuated by trade magazines and parroted throughout gyms everywhere. It is pure nonsense and completely ignores the applicable elements of physiology, anatomy, and physics in particular. Quite simply the science does not support it, and in most cases is completely at odds with the idea.
*** [This collage of different facts to infer the conclusions reached is replete with some typical errors in logic and offers a large amount of information for critical comment. While it is correct to conclude that isolation of a region of muscle may not occur under most circumstances, EMG studies with needle electrodes show that activation of even a few musce fibres is possible, especially if biofeedback methods of training are used. Basmajian (in 'Muscles Alive') reports on one of his studies which shows that thinking about a muscle action can isolate control over small muscles like those in the thumb.
And, how does one explain the ability of that belly dancer on TV who used separate regions of her abs to shift coins and fold notes? I also have carried out EMGs studies and studied biomechanical models which clearly appear to militate against isolation of specific regions of muscle, but, when I witnessed this display, read work by biofeedback specialists and saw how some disabled folk could voluntarily activate certain muscle regions, I was compelled to be less dogmatic. I know that there os at least one biofeedback expert on this group - maybe he would care to add his comments.
One other issue is never raised - what of the possibility that nerve fibres are not simply simple conductors of sequential pulses of discrete action potentials, but also play a 'multiplexing' role in which one fibre or group of fibres carry many different messages at the same time, as is the case with technological telephone and optic fibre systems? How would the arriving messages influence local and adjacent regions of muscle? So far, this is sheer speculation on my part, but I would be interested to see if anyone has come across references which allude to this possibility. Mel Siff ]
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