"lying? sorry I don't lie."
You just lied with that statement.
Anyway...
Some of the so called shaping exercises are more effective than the so called mass building exercises at building muscle. For example, the cable cross-over. The cable cross-over removes the primary weak links of the bench press, which means the pecs have to do all of the work to complete the motion. Muscle fibers are stimulated by the nervous system by way of alpha motor neurons. Each neuron may control only several muscle fibers or as many as a thousand or more. Each muscle fiber, however, is innervated by only one neuron. A neuron and the fibers it innervates are referred to as a motor unit. All of the muscle fibers in a motor unit (stimulated by the same neuron) tend to be of the same fiber type. You may have heard of the 'all-or-none' theory in regards to this subject. It states that all of the fibers in a motor unit must fire or none of them, although this may not be 100% true in certain cases (such as fatigue).
How does the neuron "innervate" it's associated muscle fibers? Well, the neuron "connects" to the fibers at their center (their length-wise center). To innervate them they transmit an electric current to the fibers, which travels out from the center of the fibers to their ends, thus setting off a contraction. That is a nut-shell how contraction works. What i am getting at here is that the actual exercise does not matter, it's the force of the contraction. Doing a flye, at maximum intensity, to failure, will produce the highest possible force of muscle contraction to the pecs! This means - more muscle growth. There are also other reasons that isolation exercises induce more localized growth than compound exercises (localized hormone release, sarcomere multiplication is series, etc).
About the whole burning thing, muscle burn has nothing to do with muscle fiber stimulation. The burn is, in fact, an effect of lactic acid accumulation. Lactic acid leads to a DECREASE of the force of muscular contraction. Lactic acid also interferes with ATP formation (inteferes with the glycolysis process). This means that less ATP will be around to actually fuel contractions - leading to further weakening.
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Complex problems have simple, easy to understand, wrong answers.
<font size="1">[This message has been edited by TheSupremeBeing (edited 06-05-2001).]</font>