The meat we eat is the muscle of the animal. Muscles are of two types with two respective functions. The involuntary muscles are the smooth muscles of the blood vessels and digestive tract which do their jobs automatically and virtually continuously. These muscles are lacking in interspersed fat and are, therefore, very tough. The voluntary muscles are composed of many tiny fibers joined together by connective tissues in a fashion which is analogous to the wire cables used in building bridges. This type of formation is called straited. Muscles are composed of cells of sizes and shapes which vary according to the feed, age, sex, and type of animal.

The connective tissue cells are joined together into bundles by two types of connective tissue. White connective tissue, called collagen, is found in all the muscles of the animal; it is dominant in the more tender cuts of meat. Yellow connective tissue, called elastin, is predominant in the muscles which carry the heaviest load of constant strain and work.

The white connective tissue breaks up and becomes moist in cooking, whereas the yellow connective tissue requires mechanical means of tenderizing such as pounding, cubing, or grinding. The younger and less exercised an animal is, the less yellow connective tissue it will have and the more tender its meat will be.