Estrogen also plays a role in growth hormone production, the anabolic and lipolytic effects of which have been well elucidated. The bottom line is that without adequate estrogen, growth hormone levels will suffer, making it more difficult to both gain muscle mass and lose bodyfat. As an added benefit, estrogen enhances growth hormone receptor expression, further potentiating its effects in the body. In laymen’s terms, growth hormone works better in the presence of estrogen.
One should also expect an increase in Glut-4 translocation. Located within skeletal muscle, Glut-4 is a carrier protein which helps transport nutrients from the cell surface to inside the cell, where they can then be used for recovery and growth. Unless activated, Glut-4 remains within the cell, hibernating until it receives a signal to rise to the surface. However, under certain conditions Glut-4 can be rather stubborn, refusing to come up to the cell surface in adequate quantities even when signaled to do so. Estrogen improves the translocation (movement) of Glut-4 to the cell surface, permitting greater amounts of nutrients to permeate the cell barrier, where they will ultimately be used for muscle growth and repair.
As one of the most powerful suppressors of muscle growth in the human body, myostatin interferes with the growth process on multiple levels, one of which is by blunting mTOR—a central regulator of cell metabolism, growth, and proliferation. Even small elevations of this muscle destroying protein can make it more difficult to maintain currently existing muscle tissue, let alone acquire additional size and strength. To give you an idea of how powerful myostatin is, animals which have been genetically altered to ensure the absence of the myostatin gene exhibit drastically increased levels of muscle mass over their genetically intact peers. In many cases these animals will grow over 100% more lean tissue than non-treated animals; a massive increase to say the least.
However, we don’t need to be the object of genetic engineering in order to manipulate myostatin levels within the body. In clinical studies designed to evaluate the effects of training on myostatin in men and women, the elevated estrogen levels found in women were shown to have myostatin inhibiting effects in muscle tissue by down-regulating myostatin mRNA expression and reducing serum LAP/propeptide levels. This down-regulatory effect makes estrogen anti-catabolic in nature and therefore, a valuable component of the growth process.