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Mechano growth factor (MGF) is a variation of muscle insulin-like growth factor-1 (IGF-1) triggered by rigorous exercise and muscle damage. Structurally different than other growth factors such as IGF-1 that is synthesized by the liver, MGF enters muscle fibers to repair skeletal muscle tissue and prevent damaged cells from dying off. It adds stem cells into the muscle and is triggered by a pulse of stimulation after muscle tissues undergo significant mechanical stress. Genes for MGF are transcribed to a lesser degree as people age, which is why muscle mass decreases in the elderly, and certain diseases also interfere with the production of it. Supplements do not work as well for older people either because of the decrease in response to mechano growth factor.
The difference between mechano growth factor and IGF-1 is that a group of carbon molecules at the end of the protein, called a C-terminus, controls the release of signals that trigger secretion. When muscles are damaged, MGF is activated, triggers the formation of additional proteins, and enables healthy muscle cell nuclei to form into new tissues and muscle fibers. A more systemic type of insulin-like growth factor from the liver is also produced in higher quantities, aiding in the longer term repair process of muscles.
Injured muscles need to be repaired locally so the damaged cells do not die and lead to further degradation. The release of stem cells regenerates the muscle, and the process is very specific because the contracting elements, energy sources, nuclei, and fluid in the muscle cells, making up the fibers, need to be replenished as well. A lack of growth hormone can lead to deficiencies in mechano growth factor. Hormone replacement therapies, however, can trigger the release of MGH to help the elderly maintain muscle tone and benefit from physical exercise to some degree.
Bodybuilders have tried to inject mechano growth factor directly. Doing this does not have much effect because the substance degrades very quickly. To allow MGF to survive long enough, another substance called polyethylene glycol is injected, which protects the protein structure so that mechano growth factor is activated when weightlifters and other people undergoing rigorous exercise stress their muscles. Polyethylene glycol is used with many pharmaceuticals to deliver drugs to specific areas of the body as well. Used for many purposes, MGF supplements should be used wisely, because only the local area they are injected into will increase in muscle mass, but in a matter of weeks.