Of the six hundred muscles in the body the gluteus maximus is the largest. It extends the entire buttocks, from cheek to cheek.
The buttocks are termed "voluntary muscles". They are from the skeletal muscle family (the largest of the three types of muscles). On average males have 40-50% skeletal muscle and females have approximately 10% less than males.
The buttocks are comprised of three muscles. The largest of these being the gluteus maximus, followed by the gluteus medius, and ending with the smaller gluteus minimus.
Ligaments hold the bones together in the body. They are covered with cartilage.
The gluteus maximus (butt cheeks) are the largest and most powerful muscle of the body. We know weight training can alter the shape and size of muscles so it makes sense the largest muscle of the body can be shaped with exercise.
Whenever you sit or stand your gluteus maximus is responsible for keeping you upright. The gluteus medius and gluteus minimus hold you steady from leaning to the left or right.
To insure your cheeks are wider near the top and narrower at the bottom you must work all three muscles of the glutes. There are specific exercises to target each of these muscles individually as well as exercises that work all three at the same time.
Doctor William Sheldon categorized three body types. He referred to them as soma types. Each one requires a different diet as well as different workouts to alter the shape of the buttocks.
Age and genetics play a role in the shape and look of the buttocks. Everyone, regardless of age and genetics can make a significant change in the appearance of their posterior given proper diet and exercises.