SPECIFIC MUSCLE FUNCTION
TORSO
rectus abdominus (stomach): The major outer muscle which goes from breast bone to pelvic bone, it appears like a sheath-like material. It is a muscle of flexion, like the biceps. Supports stomach wall.
external obliques (waist): The major muscle of rotation in the torso, extending from the middle of the ribs to connection tissue in the middle of the back. Rotates body.
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erector spinae (lower back): Major muscles of extension in lower back working with the external obliques to bend, lift, and twist.
gluteus maximus (buttocks): The major muscle of the buttocks that splits in two parts from the back of the top of the waistline and across the buttocks area and attaches at the front of the thigh. Extends and rotates the thigh also bracing the knee when it's extended. Antagonistic to itself, like deltoid.
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UPPER TORSO
trapezius: An outer muscle of the neck and upper back, it extends from the top of the back of the neck to the top of the shoulders and the side of the shoulder blade. Supports neck and maintains proper posture holding shoulders back.
rhomboids: A major muscle that extends from the shoulder blade to shoulder blade attached to the spine. Pulls shoulders back.
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latissimus dorsi (back muscles): The broadest muscle of the back that starts from the base of the spine and attaches to areas of the shoulder blades (scapulae), and to the shoulder joint, anchoring to the spine of the middle back. Pull the arm toward the center of the body in rotation and draws the shoulder down and backward. Like all muscles, their function is coordinated with others. They help sustain erect alignment and to lift up the ribs. Among the consequences of their improper use, or failure to develop them, is the sunken chest, which limits the needed area for the functions of the lungs, heart, and other vital organs, and poor breast contour.
pectoralis major (chest muscles): A major muscle that extends from the breast bone to the shoulder. Flexion, rotates the arm and pulls the arm toward the center of the body.
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SHOULDER
deltoid (shoulder cap muscles): A thick triangular muscle which is divided in three sections and coordinate the movement of the shoulder and arm, abducting, or moving away from the body. Note the three sections (front, top and back) and these muscles have little to do with shoulder alignment or posture, which results from back, abdominal and chest muscles.
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UPPER ARM
biceps brachia (front of upper arm): A major muscle that is split in half, extending from the shoulder joint to the elbow. Flexion, bending the arm.
triceps brachia (back of upper arm): This major muscle is split into three parts. The triceps extend from the base of the forearm to the shoulder (scapula). This muscle is responsible for stability and extension of the arm.
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FOREARM
The forearm is constructed of four muscles. The primary functions involve movement of the hand, along with flexion and extension of the fingers. Antagonistic to each other.
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LEGS
quadriceps femoris : includes four major muscles on the front of the thigh. extension of the leg.
rectus femoris : middle of the thigh starting at the top of the hip bone connecting at the base of the knee cap (patella).
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vastus lateralis : largest. Starting at the top of the leg bone (femur) to the outside of the knee cap.
vastus medialis : starting at the top of the leg bone and ending on the inside of the knee cap.
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vastus intermedius: starting at the top of the outside thigh across the thigh ending at the inside of the knee.
Inferior development of these, and bad muscle habits in daily use, affect the function of the entire body musculature. The shape of the leg is directly affected by quadriceps daily use.
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biceps femoris (hamstring, back of thigh): one muscle divided into two parts (heads), leg flexion.
gastrocnemius and soleus (calf muscles): located from the posterior section of the lower femur to the intersection at the heel. plantar flexes ankle joint, flexes knee joint.
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