A mesomorph is a muscular body type. It's one of three body types put forth in theory by William Sheldon in his book, The Atlas of Men, published in 1954. According to Sheldon, an American psychologist, the three possible body types for human beings are: mesomorph, ectomorph, and endomorph. Endomorphs are rounder and don't burn fat easily, while ectomorphs are slim and have fast metabolisms that enable them to burn fat quickly. Mesomorphs are considered to be the ideal body type as they tend to be able to maintain their correct body weight and are usually well proportioned.
Female mesomorphs have hourglass figures, while their male counterparts are rectangular in shape, with broad shoulders and a slim waist. A person with the mesomorph body type is muscular and tends to have shapely arms and legs. The bones in the face tend to be prominent. Mesomorphs are said to have wider faces than the other two body types. According to Sheldon, people with a mesomorph body type tend to have coarse rather than fine hair, good posture, and thick skin that tans easily.
Although the mesomorph has a natural, muscular fitness, he or she isn't likely to stay that way naturally. The aging process tends to slow down the mesomorph's efficient fat burning metabolism. Younger mesomorphs are usually able to eat whatever foods they want without gaining weight, but this characteristic tends to change as they age, unless they exercise regularly. Even older mesomorphs tend to be able to lose weight as easily as they gain it, though.
Too much fat in the diet tends to show in a fast weight increase in people with the mesomorph body type. Mesomorphs gain weight much more easily than naturally lean ectomorphs, although they also have the ability to lose it much faster than full figured endomorphs. Since mesomorphs also gain muscle easier than the other two body types, regular exercise can keep this type looking fit as long as the dietary fat intake remains moderate. Of the three body types, mesomorphs are the most likely to have and maintain a body that is height and weight proportionate.
Weight lifting is considered part of a good work out regimen for mesomorphs. Not only are they naturally muscular, but their bones tend to be large and strong. Although the mesomorph is the most athletic body type, caution should be taken not to overdo exercise or weight training. Otherwise, the muscles may be overly strained, which can lead to pain problems.