Growth, as used as a term to discuss the human body, has a number of meanings. In general terms, growth is the process towards full development and physical maturity. At a biological organism level, growth represents the change in a cell from a simple to a more complicated structure. All human cells are formed with mechanisms that foster growth, and all cell creation taken together combines to define the growth of the human body.

Growth in the human body is regulated by a remarkably complicated group of internal components that are linked to the particular hereditary traits of the individual, which are compartmentalized in the genetic structure of every person, and coded in the DNA contained within each gene. These internal components, both with and in response to external factors such as the environment and exercise, regulate human growth processes through the release of the growth hormone, known as somatotropin.

Hormones are chemicals produced by the body to regulate its own cellular processes and organ function. Many hormones are commonly the subject of interest in a sport science context; erythropoietin (EPO) is the substance secreted by the kidneys that signals increased production of erythrocytes (red blood cells) for increased oxygen transport in the bloodstream; adrenaline is the hormone produced by the adrenal gland, located near the kidney, during periods of excitement or stimulation to increase circulation and muscular activity.

The growth hormone is produced by the anterior pituitary gland, a small structure located inside the skull. The main endocrine gland is the pituitary gland, a structure that permits the flow of a hormone directly into the bloodstream. It is often referred to as the "master gland" of the body, as it regulates the performance of other glands. The release of growth hormone by the pituitary gland is the most important regulator of physical development, as this chemical will determine the rate of cell growth, sexual development, and physical traits.

The process initiated by the release of growth hormone from the pituitary gland sets into motion a complicated series of biochemical relationships. The growth hormone is a compound known as a polypeptide, which comprises 191 different amino acids, the formation material from which proteins, the building blocks of muscle and tissue formation, are made. The sequence of the amino acids within each polypeptide is determined by the individual genetic code of the person, which is contained in the DNA. Increases in the release of growth hormone by the pituitary gland boost the synthesis of protein, and correspondingly impact both the speed of cell growth and metabolism. Conversely, natural release of the growth hormone declines from a peak at age 20; by age 40, the typical adult produces only 40% of the growth hormone available at peak. For this reason, supplement forms of human growth hormone have attracted significant attention in the athletic community as well as with the general population.

While the growth mechanisms of the body may be set into motion and regulated by the hereditary impulses determined by the genetic structure of every human, factors external to the body are as important to growth. Diet, including foods, vitamins, and minerals, is the most important of these growth-impacting factors. If a dietary deficiency exists with respect to a particular aspect of growth, the impulses sent to the body to increase cell formation through hormonal release will be ineffective. An example of this contrast is found in bone growth. Calcium, in combination with vitamin D, is essential to the creation of osteoblasts, the building blocks of skeletal cells. The release of growth hormone from the pituitary gland may send a signal to the bones to create more cells, but if the raw materials for construction are inadequately supplied, there will be insufficient growth. The existing structure will also experience a reduced capacity to repair itself.

Environmental factors may also affect growth. The exposure of young children to toxins such as air pollution has a proven inhibiting effect upon the growth of the entire physical structure, including the cardiorespiratory system and skin.

The long bones of the body such as the femur (thigh bone) and the humerus (upper arm) are designed to grow to mature size over a period of years. The increases in length, circumference, and density of such bones are facilitated in part by the physis (growth plate), the portion made of developing tissue located near each end of these long bones; the epiphysis is the head or the extremity of the bone. The growth plate function is to regulate the pattern of shape and development of the mature, fully formed bone, a maturation process that begins at birth and is generally completed by age 20. As the growth plate is the last portion of the bone to harden into maturity (a process known as ossification), it is more vulnerable to injury. Damage to the growth plate of a youth that is not properly treated can result in shortened or deformed bones in adulthood.

When the human growth hormone became the subject of intense scientific research in relation to its potential use as a nutritional supplement, particular

The pituitary gland regulates the secretion of the growth hormone into the blood stream. The release of the growth hormone decreases after age 20.
emphasis was placed upon those sports where physical size and strength are at a premium. The growth hormone has been synthesized, and is widely distributed under the acronym HGH; human growth hormone has also been extracted from the pituitary glands of cadavers for this purpose. A wide range of scientific studies has confirmed that in its natural as well as in its synthetic form, human growth hormone will tend to permit the increase in physical strength and endurance when combined with a focused training program. The hormone generally stimulates the liver to produce a chemical known as IGF-1, which has the dual effect of stimulating the production of myoblasts, a key to the development of muscle growth, and facilitating cartilage and bone cell growth. Additional human growth hormone appears to generally increase the metabolism of fats, proteins, and carbohydrates.

The period within which human growth hormone has been examined scientifically is relatively short; definitive conclusions regarding the safety of its use as a supplement are not yet available. However, it is clearly a potential performance-enhancing substance, and it is a prohibited substance in elite athletics of all types. Human growth hormones in supplement form are also listed as a prohibited substance by the World Anti-Doping Agency (WADA).

SEE ALSO Diet; Growth hormones; Health; Muscle mass and strength.