Body shape

Classical female and male faces

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) and a larger nose bone.[3]
• A heavier jaw.
• A high facial width-to-height ratio.[4] However some studies dispute this, and testosterone reduces cheekbone prominence in males.[5]
• A more prominent chin.

Because females have around 1/4 the amount of testosterone of a male, the testosterone-dependent features do not develop to the same extent.

Comparison between a male (left) and a female pelvis (right). Females generally have wider hips relative to males in the same population. (Images not to scale.)

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. The length of each bone is constant, but the joint angle will change as the bone moves.[6]

Widening of the hip bones occurs as part of the female pubertal process,[7] 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.[8] The sacrum in females is shorter and wider, and also directed more toward the rear (see image).[9] This sometimes affects their walking style, resulting in hip sway.[10] 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.[11] Males and females generally have the same hormones, but blood concentrations and site sensitivity differs between males and females. Males produce primarily testosterone with small amounts of estrogen and progesterone, while women produce primarily estrogen and progesterone and small amounts of testosterone.[12]

An adult man with a "V-shaped body"; pronounced shoulder width and expanded chest, both traits typically associated with male physique

Widening of the shoulders occurs as part of the male pubertal process.[7] Expansion of the ribcage is caused by the effects of testosterone during puberty.

The rear view of a naked adult woman with pronounced hip width and large buttocks, both typically associated with female physique

Body shape is affected by body fat distribution, which is correlated to current levels of sex hormones.[1] Unlike bone structure, muscles and fat distribution may change from time to time, depending on food habits, exercises and hormone levels.

Estrogen causes fat to be stored in the buttocks, thighs, and hips in females.[13] When females reach menopause and the estrogen produced by ovaries declines, fat migrates from their buttocks, hips and thighs to their waists.[14] Later fat is stored in the belly, similar to males.[15] 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 males.[16] 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.[17] Body fat percentage guidelines are higher for females, [18] as this may serve as an energy reserve for pregnancy. [19] Males generally deposit fat around waists and abdomens (producing an "apple shape").

Testosterone helps build and maintain muscles through exercise. On average, men have around 5-20 times more testosterone than women.[20] However, estrogen also help build muscle mass.[21] 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.[22]

Females have enlarged breasts due to functional mammary glands, which develop in puberty from the influence of various hormones such as thyroxine, cortisol, progesterone, estrogen, insulin, prolactin, and human growth hormone.[23] Mammary glands do not contain muscle tissue. The shape of female breasts is affected by age, genetic factors, and body weight. Women's breasts tend to grow larger after menopause, due to increase in fatty deposits caused by decreasing levels of estrogen. The loss of elasticity from connective tissue associated with menopause also causes sagging.[24]

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.

Dieting, in conjunction with exercise, may be used to bring and keep the BMI within a healthy or desired range. A person can calculate BMI, that is body mass index, to check that where they lie in terms of weight and height. A BMI between 18.5 and 24.9 is ideal. A person with a BMI below 18.5 is classed as underweight, above 24.9 is overweight and a BMI of 30 or higher is defined as Obese.

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 shape has effects on body posture[25] 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.[1] A pleasing shape also implies good health and fitness of the body. Posture also affects body shape as different postures significantly alter body measurements, which thus can alter a body's shape.[25][26]

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; these exercises may change body shape by improving muscle tone but any fat reduction is not specific to the locale. 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.