The ideal ballerina body is a small head, long neck, short torso and long, lean legs. Unfortunately, all of these things are genetic and unchangeable. If you are not lucky enough to have been born this way, don't worry, technique and talent are also huge factors in becoming a ballerina and can help you to overcome any physical imperfections.
Whether your are just naturally flexible or as a result from training, flexibility is key in ballet. You must also have enough muscle strength to control and hold each position. Knees that hyperextend (joints that flex past 180 degrees) or bow backward are considered a desirable trait for a ballerina. This helps to produce a more visually pleasing line of the legs when en pointe.
A good turn out of your legs originating from the hip joint through the knee all the way to your ankle and foot is also required. Classical ballet positions are all based on a turn out, so a good one is absolutely necessary since it allows for better extension in the leg in the side or rear positions.
The degree of turnout is measured in first position--standing flat on the feet with the heels together and the toes rotated outward toward the sides. The perfect turnout is measured at 180 degrees, where your toes are pointed straight out to each side, forming a perfect half circle if a line were to be drawn from one foot to another. Most dancers do not have a perfect turnout. The degree to which you are able to rotate your hips outward is genetically determined; however, there are several ballet exercises that can be done to help stretch and strengthen the hip joints and muscles needed to achieve a fuller rotation at the hip.
High arches in your feet are desirable since it is more esthetically pleasing and often times allows you to achieve a more pointed foot. Most ballerinas have wide, square feet. Not generally born with feet of this shape, they are formed into this shape from years and years of practice as young children.
Even if you are lucky enough to have a perfect ballerina body, if you lack talent and technique you will not succeed in the ballet world. The ability to perform dance combinations precisely and quickly is key. In order to do so, dancers must have a strong abdomen and back as well as strong feet, ankles, legs and knees. It takes years and years of practice and work to condition your muscles to achieve the correct positions.
Ballet is the basis for all dance technique. Someone without a solid ballet background will often find themselves struggling to achieve a proper "line." One's "line" is critical in ballet. The line is the appearance your body parts (head, arms, shoulders, waist, pelvis, legs, feet) give when in a ballet position. A pleasing line is much sought after by ballerinas and is achieved through practice and technique. A solid background in ballet also helps to strengthen muscles, ensuring a lower risk of injury.
Because the ballerina body is so specific and success in the art lies heavily on not just talent and technique but what your body looks like, eating disorders are prevalent in many women and men. In order to change their shape or maintain their ballet body, many dancers resort to anorexia or bulimia.
Anorexia is psychological and physiological disorder that is based in a person's desire to be thinner than what their normal body weight would naturally be. Most anorexics will stop eating to lose or maintain their ideal weight. Anorexics also commonly compulsively exercise to keep their weight down. All of this leads to severe malnutrition and extensive damage to the body, including your bones and heart.
Bulimia is an eating disorder in which one over eats or binges and then follows it with a self-induced purge or vomit. Many sufferers also use laxatives or diuretics to rid their systems of any remaining food. Bulimia causes extensive damage to the mouth, teeth and throat, as well as the kidney and heart.