Cont....

THE NUCLEAR DOMAIN
In order to understand why or how muscle can respond regionally, it is important to understand the underlying biology of muscle cells or fibers themselves. An individual muscle is much more than just fibers attaching at tendons or bones with a single muscle-nerve interaction. Neuromuscular compartments, which can be described distinct regions of a muscle, are each innervated by an individual nerve branch and therefore containing motor unit territories with a unique set of characteristics. In other words, different portions of one muscle may be called into play depending on the task demands of the situation.

Furthermore, this compartmentalization is evident at the subcellular levels. There is something that muscle biologists refer to as the DNA unit or nuclear domain. The nuclear domain can be defined as the theoretical volume of cytoplasm associated with a single myonucleus. In English, that means each nucleus controls its own little territory. What happens in one part of a muscle fiber does not necessarily happen in other parts of a muscle.

WHAT DOES THIS ALL MEAN?
Does this mean we can all shape our bodies to look like Lee Labrada? No! But we can still shape our muscles to some degree. It may take some tweaking here and there. Mere comparison of the physiques of Olympic weightlifters and bodybuilders demonstrate what effects different training regimens have. You don't normally see a large teardrop (vastus medialis) muscle or prominent sartorius (long strap muscle that starts at the hip and crosses the front of the thigh) muscle on Olympic weightlifters, do you? Certainly, diet and genetics plays a role in the size and shape of the muscle. However, the issue of androgen use may negate any differences in the type of training performed. So at this point, all we can really say is that the different athletes in the strength/power sports demonstrate strikingly different phenotypes or physiques and that these differences are due to many factors (i.e. training, diet, genetics, drugs).

However, if you're a natural bodybuilder (somewhat of an oxymoron), the use of different angles, grips, and exercise selection may produce different hypertrophic responses in different muscles as well as within different regions of a muscle.

PRACTICAL ADVICE ON HOW TO TARGET A SPECIFIC REGION OF MUSCLE
Keep in mind that the following recommendations are based on the limited data available; and it would behoove you to utilize the principle of variation in your training regimen. Nonetheless, you add these variations to your training program as part of an overall training scheme:


1) pectoralis major - if you're interested in developing the upper portion (clavicular head) relatively more so than the sternocostal portion, it is best to do a narrow grip incline bench; if you want to target the sternocostal region relatively more than the clavicular region, a narrow grip on the decline bench is best. And furthermore, for the greatest activation of the entire pectoralis major muscle, then the wide grip bench press is the king of the chest exercises.

2) biceps brachii - if you want to target the short head (medial side), you can do supination exercises with your elbow flexed to ~120 degrees (bend your arm so that your forearm is nearly touching your biceps) or you can do unilateral dumbell curls with your palms up; if you want to target the long head more, try doing unilateral dumbell curls (i.e. hammer curls) with your palms in a neutral position or you can do supination movements (turning of the palms upward) with your elbows extended past 90 degrees (i.e. your arm is between a right angle and fully straightened).

3) triceps brachii - to target the distal portion of the triceps brachii group, French presses (dumbell press overhead) will do wonders; interestingly, isokinetic elbow extensions seem to target the proximal and middle portions of the triceps.

4) rectus abdominus - for the upper abs, curl-ups or crunches are best; for the lower abs, posterior pelvic tilt exercises will help tremendously!

5) quadriceps femoris - the "quads" are actually four separate muscles each having the same function, except the rectus femoris, which also performs hip flexion. Although, regional adaptations occur in each of these muscles, it isn't clear which exercises target each region the best; however, for maximal stimulation of the "entire" quad, doing leg extensions with the leg outwardly rotated (toes pointed out) seems to work best!


The previously described exercises are to be used as an adjunct to your training program. They are not meant to be the exclusive exercises for these bodyparts. It is evident that your muscles are much more complex than just a bunch of fibers attaching at an origin and insertion. In order to maximally stress the muscle unit as a whole, it is imperative that you do a variety of exercises. Of course, if you're in a performance sport such as powerlifting, emphasis should be placed on those exercises specific to the sport; but in bodybuilding or general fitness, you've got more room to experiment with different exercises. So get back to the lab more affectionately known as the gym and do some experimenting!




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REFERENCES
Alway, S.E. et al. Regionalized adaptations and muscle fiber proliferation in stretch-induced- enlargement.
Journal of Applied Physiology. 66:771-781, 1989.
Antonio, J. and W.J. Gonyea. Muscle fiber splitting in stretch-enlarged avian muscle. Medicine and Science in Sports and Exercise. 26:973-977, 1994.
Barnett, C. et al. Effects of variations of the bench press exercise on the EMG activity of five shoulder muscles. Journal of Strength and Conditioning Research. 9:222-227, 1995.
Brown, J.M.M., C. Solomon, and M. Paton. Further evidence of functional differentiation within biceps brachii. Electromyography and Clinical Neurophysiology. 33:301-309, 1993.
Carey Smith, R. and O.M. Rutherford. The role of metabolites in strength training. European Journal of Applied Physiology. 71:332-336, 1995.
English, A.W., S.L. Wolf, and R.L. Segal. Compartmentalization of muscles and their motor nuclei: the partitioning hypothesis. Physical Therapy. 73:857-867, 1993.
Hall, Z.W. and E. Ralston. Nuclear domains in muscle cells. Cell. 59:771-772, 1989.
Housh, D.J. et al. Hypertrophic response to unilateral concentric isokinetic resistance training. Journal of Applied Physiology. 73:65-70, 1992.
Kawakami, Y. et al. Training-induced changes in muscle architecture and specific tension. European Journal of Applied Physiology. 72:37-43, 1995.
Narici, M.V. et al. Changes in force, cross-sectional area and neural activation during strength training and detraining of the human quadricpes. European Journal of Applied Physiology. 59:310-319, 1989. Roman, W.J. et al. Adaptations in the elbow flexors of elderly males after heavy resistance training. Journal of
Applied Physiology. 74:750-754, 1993.
Sarti, M.A. et al. Muscle activity in upper and lower rectus abdominus during abdominal exercises. Archives of Physical Medicine and Rehabilitation. 77:1293-1297, 1996.
Signorile, J.F. et al. Effect of foot position on the electromygraphical activity of the superficial quadricpes muscles during the parallel squat and knee extension. Journal of Strength and Conditioning Research. 9:182-187, 1995.
Tesch, P.A. Muscle Meets Magnet. published by Per. A. Tesch, Stockholm, Sweden. 1993.

And I'm spent :cool:

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