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Human body shape is a complex phenomenon with sophisticated detail and function. The general shape or figure of a person is defined mainly by the molding of skeletal structures, as well as the distribution of muscles and fat. Skeletal structure grows and changes only up to the point at which a human reaches adulthood and remains essentially the same for the rest of his or her life. Growth is usually completed between the ages of 13 and 18, at which time the epiphyseal plates of long bones close, allowing no further growth (see Human skeleton).
During puberty, differentiation of the male and female body occurs for the purposes of reproduction. In adult humans, muscle mass may change due to exercise, and fat distribution may change due to hormone fluctuations. Inherited genes play a large part in the development of body shape.
Due to the action of testosterone, males may develop these facial-bone features during puberty:
- A more prominent brow bone (bone across the centre of the forehead from around the middle of eyebrow across to the middle of the other)
- A heavier jaw.
- A larger head size. 
- More prominent chin.
- Larger nose bone. (testosterone thickens the brow and "upper bridge of the nose")
Because females have around 1/4 the amount of testosterone of a male, these features do not develop to the same extent. Hence female faces are generally more similar to those of pre-pubertal children.
Skeletal structure frames the overall shape of the body and does not alter much after maturity. Males are, on average, taller, but body shape may be analyzed after normalizing with respect to height.
Widening of the hip bones occurs as part of the female pubertal process, and estrogens (the predominant sex hormones in females) cause a widening of the pelvis as a part of sexual differentiation. Hence females generally have wider hips, permitting childbirth. Because the female pelvis is flatter, more rounded and proportionally larger, the head of the fetus may pass during childbirth. The sacrum in females is shorter and wider, and also directed more toward the rear (see image). This sometimes affects their walking style, resulting in hip sway; The upper limb in females have an outward angulation (carrying angle) at elbow level to accommodate the wider pelvis. After puberty, hips are generally wider than shoulders. However, not all females adhere to this stereotypical pattern of secondary sex characteristics. Both male and female hormones are present in the human body, and though only one of them is predominant in an adult, the other hormone has effects on body's shape to some extent.
Fat distribution, muscles and tissuesEdit
Body shape is affected by body fat distribution, which is correlated to current levels of sex hormones. Muscles and fat distribution may change from time to time, unlike bone structure, depending on food habits, exercises and hormone levels.
Estrogen causes fat to be stored in the buttocks, thighs, and hips in women. When women reach menopause and the estrogen produced by ovaries declines, fat migrates from their buttocks, hips and thighs to their waists. Later fat is stored in the belly. Thus females generally have relatively narrow waists and large buttocks, and this along with wide hips make for a wider hip section and a lower waist-hip ratio compared to men. Hormonal and genetic factors may produce male-like distribution of fat in women i.e. around the belly instead of buttocks and thighs.
Estrogen increases fat storage in the body, which results in more fat stored in the female body. Body fat percentage recommendations are higher for females, as this may serve as an energy reserve for pregnancy. Males have less subcutaneous fat in their faces due to the effects of testosterone; testosterone also reduces fat by aiding fast metabolism. Males generally deposit fat around waists and abdomens (producing an "apple shape") due to the lack of estrogen.
Testosterone helps build and maintain muscles through exercise. On average, males have around 10 times more testosterone than women. Prominent muscles of the body include the latissimus dorsi, trapezius, pectoral muscles (muscles critical for a strong erect posture) as well as biceps and triceps in the arms and quadriceps and hamstrings in the thighs.
Females have enlarged breasts due to functional mammary glands, which develop from puberty onward due to the effects of estrogen. Mammary glands do not contain muscle tissue. The shape of female breasts is affected by age, genetic factors, and body weight.
Being overweight or underweight causes change in the human body's shape as well as posture and walking style. This is measured using Body Mass Index – BMI or waist circumference. Depending on the BMI, a body may be referred to as slim, overweight, or obese. New computer based measurement, such as the Body Volume Index – BVI, specifically measure body shape and where weight on a person's body is distributed. This can determine different risk factors for people with different body shapes.
The fats and carbohydrates in food constitute the majority of energy used by the body. They are measured cumulatively in the USA and many other places in calories and in kilojoules in some other parts of the world.
Body posture and gaitEdit
Body shape has effects on body posture and gait, and has a major role in physical attraction. This is because a body's shape implies an individual's hormone levels during puberty, which implies fertility, and it also indicates current levels of sex hormones. A pleasing shape also implies good health and fitness of the body.
Impact on healthEdit
According to the Heart and Stroke Foundation of Canada, those people with a larger waist (apple shaped) have higher health risks than those who carry excess weight on the hips and thighs (pear shaped). People with apple shaped bodies who carry excess weight are at greater risk of high blood pressure, Type 2 diabetes and high cholesterol.
Fitness and exerciseEdit
Different forms of exercises are practiced for the fitness of the body and also for health. It is a common belief that targeted exercise reduces fat in specific parts of the body —for example, that exercising muscles around the belly reduces fat in the belly. This, however, is now proven to be a misconception. Spot reduction exercises are not useful unless you plan proper exercise regime to lose overall calories. But exercising reduces fat throughout the body, and where fat is stored depends on hormones. Liposuction is surgery commonly used in developed societies to remove fat from the body.
Social and cultural idealsEdit
The general body shapes of female and male bodies both have significant social and cultural symbolism. Physical attractiveness is closely associated with traits that are considered typical of either sex. The body mass index (BMI), waist-to-hip ratio, and especially waist-to-chest ratio in men have been shown in studies to rank as overall more desirable to women. Wide shoulders, a muscular upper body and well-developed upper-arm muscles are all traits closely associated with masculinity, similarly to other specifics of the male sex, like beards. These traits are seen more sexually attractive to women and also associated with higher intelligence, good leadership qualities and better health.
Classifications of female body sizes are mainly based on the circumference of the bust-waist-hip (BWH), as in 36–24–36 (inches) respectively. In this case, the waist-hip ratio is 24/36 = 0.67. Many terms or classifications are used to describe body shape types:
- V shape: Males tend to have proportionally smaller buttocks, bigger chests and wider shoulders, wider latissimus dorsi and a small waist which makes for a V-shape of the torso.
- Hourglass shape: The female body is significantly narrower in the waist both in front view and profile view. The waist is narrower than the chest region due to the breasts, and narrower than the hip region due to the width of the buttocks, which results in an hourglass shape.
- Apple: The stomach region is wider than the hip section, mainly in males.
- Pear or spoon or bell: The hip section is wider than the upper body, mainly in females.
- Rectangle or straight or banana: The hip, waist, and shoulder sections are relatively similar.
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