Understanding Muscle Actions and Anatomy for Fitness

A muscle can act in all joints it crosses.

From a fixed point during muscle contraction, insert a mobile point during muscle contraction.

Trapezius: Occipital bone and the spinous process of C7 and all thoracic vertebrae. Clavicle, spine, and acromion.

Action: Superior: elevates scapula. Lower: lowers the scapula. Medial: adducts.

Deltoid: Clavicle, acromion, and spine of the scapula. Tuberosity of the humerus.

Action: Posterior: shoulder extends. Anterior: flexes shoulder. Medial: abducts the shoulder.

Latissimus Dorsi: Spinous process of T7 to T12 and lumbar vertebrae. Intertubercular sulcus of the humerus.

Action: Extends, abducts, and medially rotates the shoulder.

More Round: Same action as the latissimus dorsi.

Rhomboid Major and Minor: Raise and abduct the scapula.

Levator Scapulae: Elevates the scapula.

Rotator Cuff Muscles: 4 muscles:

• Subscapularis - front
• Supraspinatus - back
• Infraspinatus - back
• Teres Minor - back

Rotation: 3 lateral and 1 medial.

Biceps Brachii: Long head: supraglenoid tubercle; short head: coracoid process. Tuberosity of the radius.

Action: Elbow flexion, supination, and flexion.

Brachialis: Front of the humerus. Coronoid process of the ulna.

Action: Elbow flexion.

Coracobrachialis: Coracoid process. Body of the humerus.

Action: Adduction and flexion of the shoulder.

Triceps Brachii: Infraglenoid tubercle (long head), lateral humeral (lateral), and medial aspect of the humerus (medial), posterior face of the humerus.

Action: Extension of the elbow; long head also extends the shoulder.

Anconeus: Humerus to the olecranon and lateral epicondyle of the ulna.

Action: Extension of the elbow.

Abdominal Muscles: 4 muscles.

Action: Compression of the abdomen. Flexion of the trunk, except for the transverse muscle. Lateral inclination to the right and left. Rotation of the trunk: right oblique internal and external, left side is the opposite.

Chest:

Pectoralis Major: Clavicle, sternum, and cartilage from ribs 2 to 6. Crest of the greater tuberosity of the humerus.

Action: Flexes, adducts, and medially rotates the shoulder.

Pectoralis Minor: Ends of ribs 3, 4, and 5. Coracoid process of the scapula.

Action: Pulls the scapula forward and down.

Serratus Anterior: From the scapula to ribs 8 and 9. Medial margin of the scapula.

Action: Pulls the scapula forward and down, separating the ribs and aiding in scapular abduction.

Back:

Erector Spinae: Composed of 4 muscles: spinalis and longissimus, iliocostalis.

Action: Lateral inclination of the trunk (contracted unilaterally) and trunk extension (bilaterally).