How much the bust or hips inflect inward, towards the waist, determines a woman's structural shape.
The hourglass shape is present in only about 8% of women.
Breasts sag if the ligaments become elongated, a natural process that can occur over time and is also influenced by the breast bouncing during physical activity (see Sports bra).
They are produced in both men and women, but their levels are significantly higher in women, especially in those of reproductive age.
Besides other functions, estrogens promote the development of female secondary sexual characteristics, such as breasts and hips.
The hormones produced by the thyroid gland regulate the rate of metabolism, controlling how quickly the body uses energy, and controls how sensitive the body should be to other hormones.
Body fat distribution may change from time to time, depending on food habits, activity levels and hormone levels.The muscles most likely to be affected are the pectoral muscles, biceps and the triceps in the arms and quadriceps in the thighs. Muscle mass changes over time as a result of changes in testosterone and estrogen levels and exercise, besides other factors.