Your skeletal muscles are major muscles that are under your voluntary, or conscious, control. Along with bones and the anchoring connective tissue of tendons and ligaments, these muscles form your musculoskeletal system, which not only provides a framework for your body but also is responsible for movement. ThinkQuest.com notes that your musculoskeletal system contains 640 distinct skeletal muscles, and accounts for a large part --- 42 percent for males, 36 percent for females --- of your body mass.
Deltoid
The deltoid muscle is the wedge-shaped muscle of the shoulder, and is responsible for the rounded appearance on top where your arm meets your body. It is attached to the shoulder blade and collarbone on one end and the humerus --- or bone of the upper arm --- on the other. According to InnerBody, the deltoid also abducts the arm, helping lift it up and away from the body.
Pectoralis Major
The pectoralis major, a large, triangular muscle that extends over the upper front chest, begins at the breastbone and is attached to the clavicle, or collarbone. InnerBody says this muscle's major function is to move the arm across the body.
Biceps
The biceps brachii, in the upper part of the arm, connects to the scapula, or shoulder blade, and extends along the front surface of the humerus, attaching at the end to the radius, or lower arm bone. This muscle, which visibly contracts when you clench your fist, helps to flex your forearm and to bend your arm at the elbow.
Rectus Abdominis and Abdominal Obliques
The rectus abdominis --- the abdominal muscle --- extends vertically the entire length of the abdomen, running from the pubis to the cartilages of the fifth, sixth and seventh ribs. It flexes the spinal column --- particularly the lower back --- helps draw the beastbone towards the pelvis, and tenses the abdominal wall. This is the muscle you work when you do stomach crunches; you also use it when you forcibly exhale. The external abdominal oblique muscles lie on the sides and front of the abdomen. According to InnerBody, their main function is to flex the ribcage and spine, particularly when you are twisting sideways or bringing your shoulders forward. The University of New Mexico Extension states that the obliques run from the lower eight ribs to the pelvis and pubis.
Latissimus Dorsi
The latissimus dorsi is the strongest and largest muscle of the back. According to Get Body Smart, it covers the lower back, beginning at the lower half of the vertebral column and hipbone and tapering to a rounded tendon attached to the humerus. The latissimus dorsi muscle draws the upper arm down and back, rotates it inward and extends it at the shoulder.
Quadriceps Muscles
The quadriceps femoris muscle group extends over the front and sides of the thigh, connecting the femur --- or thighbone --- to the patellar tendon in front of the knee. InnerBody points out that the quadriceps femoris extends the leg at the knee. The rectus femoris, a long, cylindrical quadriceps muscle, runs down the front of the upper leg, and is particularly important for kicking and sprinting.
Gluteus Maximus
The gluteus maximus, the strongest muscle in the body, covers the buttocks and connects the ileum, sacrum and tailbone to the femur. Get Body Smart says it extends the thigh, laterally rotates it at the hip, and abducts it, moving it away from the midline of the body. InnerBody states that the gluteus maximus causes the leg to straighten at the hip in walking, running and climbing.
