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The human body has over 600 muscles, which are soft tissues that help us move, breathe, swallow and stay alive. Muscles are attached to the bones of the skeletal system and make up roughly half of a person's body weight. They contract to produce movement at joints, where two or more bones meet. Muscles are sometimes classified by the type of function they perform, such as abductors, flexors or extensors. They can also be grouped by their location, such as chest, leg or back muscles. The muscular system is responsible for two types of movements: voluntary movements, which are actions we control, and involuntary movements, which happen automatically without us thinking about them.
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What You'll Learn
Forearm supination and pronation
Pronation and supination are two unique movements that can only be performed in the forearms and hands. They allow the human body to rotate the hand so that the palm is facing up or down. The forearm has a unique anatomy that enables these movements, with complex interactions between bones, muscles, and joints in the arm. The forearm consists of two main bones: the radius and ulna, which are connected to the wrist. The distal radioulnar joint links the forearm to the wrist, allowing the radius to rotate around the ulna.
During pronation, the distal end of the radius rotates around the ulna from its position on the lateral side of the wrist to the medial side. This action turns the hand, wrist, and forearm by almost 180 degrees, so that the palm faces backward or down. The pronator teres and pronator quadratus muscles in the forearm work together to achieve pronation by pulling on the radius bone.
Supination is the opposite movement, turning the palm forward or up. The supinator muscle of the forearm and the biceps brachii of the upper arm supinate the forearm by pulling on the radius. These muscles rotate the radius in the opposite direction of the pronator muscles, moving the distal end of the radius back to its position on the lateral side of the wrist.
The range of motion from pronation to supination is crucial for many daily tasks, such as opening doors, using tools, turning a screwdriver, or opening a jar. It also affects grip strength and dexterity.
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Dorsiflexion and plantar flexion
The human body has over 600 muscles, and these muscles help us move, breathe, swallow, and stay alive. The prime mover, or agonist, is the muscle that provides the primary force for a given action. For example, in dorsiflexion, the tibialis anterior is the prime mover. Antagonist muscles oppose the prime mover by providing resistance or reversing the movement. For instance, in plantar flexion, the gastrocnemius is the prime mover, while in dorsiflexion, it acts as the antagonist.
During plantar flexion, the lower muscles and tendons work together to maintain balance and stability. If one of these muscles or tendons fails, it can result in an injury and reduced range of motion. These injuries can range from Grade I sprains, which involve slight ligament damage and minimal swelling, to Grade III sprains, which are complete ligament tears with significant swelling and pain.
Understanding muscle function terminology, such as dorsiflexion and plantar flexion, is crucial for comprehending the various roles that different muscles play in each movement. These terms allow for a precise description of the complex interactions between muscles, tendons, and joints that enable the human body's remarkable range of motions.
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Protraction and retraction
Scapular Protraction and Retraction
The scapula, or shoulder blade, can move in six directions, and protraction and retraction are two of these movements. Scapular protraction occurs when the scapula moves laterally away from the spine. This movement is also called scapular abduction and is performed by the serratus anterior, pectoralis major, and pectoralis minor muscles, all located in the chest and side of the torso. Exercises that involve reaching away, such as push-ups or mountain climbers, demonstrate scapular protraction.
Scapular retraction, on the other hand, is when the scapula moves closer to the spine. This movement is also known as scapular adduction and is important for exercises like the row and bench press. It provides additional support for the shoulder and increases power and muscle mass. The trapezius, rhomboids, and latissimus dorsi muscles of the back are responsible for scapular retraction.
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Superior and inferior rotation
The terms elevation and depression refer to movement above and below the horizontal. Elevation refers to movement in a superior direction, such as a shoulder shrug. Depression refers to movement in an inferior direction, the opposite of elevation.
Superior rotation can be felt when you pick up a heavy load, such as a book bag, and carry it on one shoulder. To increase its weight-bearing support, the shoulder lifts as the scapula superiorly rotates.
Inferior rotation occurs during limb adduction and involves the downward motion of the glenoid cavity with upward movement of the medial end of the scapular spine.
The hip can also be subject to superior and inferior rotations. For example, a sufficiently strong and isolated bilateral contraction of any hip flexor muscle will either rotate the femur toward the pelvis, the pelvis toward the femur, or both actions simultaneously.
In the context of the ankle, dorsiflexion refers to flexion, so that the foot points more superiorly. Plantarflexion refers to extension at the ankle, so that the foot points inferiorly.
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Flexion and extension
Extension, on the other hand, is a straightening movement that increases the angle between two bones of a joint. Extension of the elbow increases the angle between the ulna and the humerus. Extension of the knee straightens the lower limb. In the upper limb, all posterior motions are extension, including movements of the arm at the shoulder, the forearm at the elbow, the hand at the wrist, and the fingers at the metacarpophalangeal and interphalangeal joints. For the vertebral column, extension involves a posterior-directed motion, such as straightening from a flexed position or bending backward.
Both flexion and extension movements can be seen at the hinge, condyloid, saddle, and ball-and-socket joints of the limbs. Hyperextension is the abnormal or excessive extension of a joint beyond its normal range of motion, which can result in injury. Similarly, hyperflexion is excessive flexion at a joint, which can also lead to injury.
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Frequently asked questions
Forearm supination and pronation. Supination is rotating the forearm so the palm is facing forward or up, and pronation is rotating the forearm so the palm is facing backward or down.
Neck flexion. This is accomplished primarily by the sternocleidomastoid muscles, with assistance from the longus colli and the longus capitis.
Plantar flexion. This is depressing the foot.
Abduction. This is a movement away from the midline.
Flexion. This involves decreasing the angle between the bones (bending of the joint).
