How Muscles Grow

I am interested in researching what are the real factors that cause muscle hypertrophy. The following are pretty much what i know but they too could be wrong.

1) Actual breaking down/tearing of the muscle. I would like to know more on how this works (ie-at what point does a muscle begin to breakdown, etc)

2) Something to do with ATP depletion. I know very little on this and would like to know more.

I have also heard about sarcoplasmic growth as well as increased capilary growth.

If you know of any more, or could explain any of the above better, that would be very appreciated.

Ok, i'm in line to get an exercise physiology degree in August so I had to take a few classes in this so I'll give you the short version. Hypertrophy is caused by tearing down and rebuilding of muscle fibers. The first phase in training is neuromuscular adaptation. The nerves get used to the training, which sends signals to increase tendon, ligament and other soft tissue strength. This phase ususally last around 3-8 months depending on biological age and training age (how long you have trained earlier in life, previous athletic status, etc). After a while, your neuromuscular system will become more efficient to the point where testosterone will move into the muscle cell into the DNA in the nucleus and tell the cell to synthesize (produce) more protein. The protein is then used in the muscle by your muscle protein Actin and Mysosin. These are the myofibrils that actually slide together to cause what is called a muscle contraction. Its often called the sliding filament theory. Anyhow, this is part of hypertrophy. It is known that during hypertrophy your fibers actually get larger. Some scientist believe that it also produces more fibers, but this is still being researched. But, what is known is that you DO NOT produce more muscle cells. This cell cannot multiply and is peaked out around your early 20's for males. Keep in mind that you can target hypertrophy by your method of training. While strength training will cause muscle growth, its not the usual method used by builders. They prefer high volume, high intensity w/ short rests. This method stimulates your bodies own Human Growth Hormone which is known to cause increased protein synthesis, increase lipolysis (fat processing), decreased muscle glycogen usage (which spares your muscle's glucose stores) and increases glucose usage (which is glucose or carbs circulating in your blood). It basically makes your body an efficient machine. Hoped that helped..

Oh, also, you said something about sarcoplasmic growth,, well that falls into this. The sarcomere is the actual muscle cell and in this are the actin, myosin, cross bridges, etc. They do grow, so maybe thats what your referring to.

Capillary growth does occur also. As you may know, this is the area of exchange where deoxygenated blood moves from the arteries to the veins and prepare for return to the heart and pulmonary circuit. This, over time, becomes more efficient, stronger and larger in order to handle the increased blood flow during and following training.

FYI..the pumped feeling and appearance during training is due to the cell leaking cellular fluid through the cellular membrane into interstitial space!!!