Some individuals are stocky with heavy bones; others are thin with fines bones; others exhibit gradations between the two extremes. One way to characterize the diffences in body build was proposed by Sheldon many years ago. According to his now well recognized scheme of classification, the are three basic somatotypes: ectomorphic, endomorphic, and mesomorphic. The ectomorph is an individual who is especially tall and fragile, with a large surface area, thin muscles and subcutaneous tissues, and slightly developd digestive viscera.

The endomorph has a relative preponderance of soft tissue throughout the body, with large digestive viscera and accumulation of fat and with large trunk, thighs, and tapering extremities. The mesomorph- the well proportioned individual - has a relative preponderance of muscle, bone and connective tissue, usually with a heavy, hard physique and rectangular outline.

Since many individuals cannot be readily categorized as belonging to one of three somatotypes, Sheldon developed a rating scheme to indicate the relative dominance of each. As an example, an extreme ectomorph would be classifieds as 1-1-7 (that is, endorphy 1, mesomorphy 1, and ectomorphy 7).

Body Chemistry
Protoplasm- the stuff of the cell- is a jellylike substance. There is nothing unique about its constituent elements or, for that matter, many of its compounds. In other words, the chemical key to the mystery of life resides in the way all the atoms and molecules are arranged and put together.

The chief compound of protoplasm is just water (H2O), which is usually present to an extent of about 75 % by weight. The other inorganic constituents may be characterized as chemical salts. The most important are the chlorides, phosphates, and sulfates of sodium, calcium, magnesium and potassium. These compounds are commonly referred to as electrolytes.

The organic constituents of protoplasm may be categorized as carbohydrates, lipids, proteins and nucleic acids. Carbohydrates (sugars and starches) serve a reserve fuel and,to a lesser degree, as structural elements; proteins serve as enzymes and collectively as the basic fabric or molecular back-bone of the cells,nucleic acids (DNA and RNA) act as chemical information in metabolism and in the genetic code.