The human body contains three types of muscle: smooth, cardiac and skeletal. Skeletal muscles, which are responsible for locomotion and other body movements, likely come to mind first when you discuss muscles. You have more than 600 skeletal muscles in your body, in various shapes and sizes. The body's largest muscles perform the biggest tasks.
The gluteus maximus is the biggest muscle in the human body. The glutes, as they are commonly known, contain three muscles located at the back of each hip or buttock. The gluteus maximus is the largest and most superficial muscle of the group. It contributes most of the mass that can be seen as the buttocks. It must be large due to its roles in hip extension and lateral rotation, as well as in keeping the body in an erect position.
The latissimus dorsi is the widest muscle in the human body. In fact, the English translation of latissimus dorsi is "wide back." The latissimus dorsi, or lats, are fanlike muscles that begin at the spine, run from the thoracic vertebrae to the sacrum, and attach on the upper arm. The lats are responsible for shoulder and scapula adduction and rotation, along with a variety of other shoulder and shoulder-blade movements.
The sartorius is the longest muscle in the human body. The sartorius is a superficial muscle that begins at the outside of the hip, runs down the upper leg and ends at the inside of the knee. The name sartorius means "tailor," so-called because it's responsible for crossing the legs, traditionally a common position assumed by tailors while sewing. The sartorius helps to flex your knees and hips.