Muscle is one of the few tissues in the body that is highly dynamic, capable of growing or shrinking depending upon the level of strength training. The growth of muscles is called hypertrophy. Like many human endeavors, muscle growth has become an aesthetic as well as a practical matter, but regardless of the intentions, it involves complex physiological reactions that can be maximized for efficiency once they are understood.
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Skeletal muscles are made up of thousands of cylindrical muscle fibers bound together by connective tissue. Inside each fiber are small filaments called myofibrils. This is where the basic unit of contraction, the sarcomere, resides. The sarcomere is made out of bands that pull the rest of the tissue in closer during a muscle contraction. This requires an input of energy from the cells.
Any intense and strenuous exercise, especially weightlifting, causes acute trauma to the muscles, and damage begins to proliferate within the fibers. The flow of calcium within cells is an important part of muscle contractions, but according to one paper in the “Proceedings of the National Academy of Science” by researchers from Columbia University, tiny channels in muscles start to leak calcium as they grow tired, weakening contractions.
Once muscles become damaged from weightlifting, the body immediately attempts to repair them. This disruption activates satellite cells operating on the fringe of the muscle fibers. These satellite cells proliferate to the site of the injury and become fused together with the muscle fibers. This is explained in a paper entitled “How Do Muscles Grow?” by Young sub Kwon, M.S., and Len Kravitz, Ph.D., from the University of New Mexico.
Satellite cells add to the myofibrils, which causes them to increase in thickness and number. This activity is regulated by hormones called growth factors. These are the hormones that stimulate satellite cells to produce gains in muscle fiber size. They are very important for the incorporation of different kinds of molecules and nutrients into the actual muscle tissue. The actual key to muscle growth, however, varies from person to person. Genetics are a huge influencing factor, but so are age and gender.
Protein is the most important nutrient in the construction of new muscle fibers because myofibrils are actually made of protein. There are about eight amino acids that the body cannot make naturally; these must come from protein in the diet. When protein is consumed, it's broken down into building blocks called amino acids during digestion. These amino acids are crucial: The DNA carries the code that reconstructs protein by placing these amino acids in a certain order. The proteins then carry out many of the functions of the body, including muscle contraction. Some amino acids are excreted from the body every day, so you'll have to consume enough to build muscles in addition to replacing the ones that were lost naturally.