Muscle Mechanics, Fiber Arrangements, and Classification

Flashcards on muscle actions, skeletal muscle contraction mechanics, fiber arrangements, naming rules, and functional roles.

Isometric

An externally controlled muscle action where total muscle length stays the same under tension ($R = F$), with no movement, such as wall sits or planks.

Isokinetic

A muscle movement performed at a constant fixed speed regardless of the resistance (same speed, resistance), typically used in rehab settings.

Isotonic

A muscle action in which tension of the muscle remains the same throughout the entire range of motion (variable speed, same resistance).

Skeletal Muscle Contraction

A process where shortening of the sarcomere occurs from both ends toward the center, causing shortening of the whole muscle; contractile force produced by the sarcomere is transmitted to bone to produce joint motion.

Length-Tension Relationship

The principle stating that a muscle's ability to generate force depends on its length before contraction.

Optimal Length (Resting Length)

The muscle length where actin and myosin have the best overlap, creating the maximum number of crossbridges.

Parallel Fiber Arrangement

Muscle fibers arranged parallel to the length of the muscle, built for range of motion, with a small cross section (small force) and long length (large length change).

Pennate Fiber Arrangement

Shorter muscle fibers arranged obliquely to the tendons (like a feather), built for force production, with a large cross section (large force) and short length (small length change).

Parallel Flat Muscles

Thin and broad parallel muscles that spread force over a large area to provide stability, such as the rectus abdominus and external oblique.

Parallel Fusiform Muscles

Spindle-shaped parallel muscles with a central belly that tapers to tendons on each end, such as the semimembranous, semitendinous, and biceps brachii.

Parallel Strap Muscles

Parallel muscles uniform in diameter with almost all fibers arranged in a long parallel manner, such as the sartorius.

Parallel Radiate Muscles

Triangular / fan-shaped parallel muscles that represent a combination of flat and fusiform muscles, such as the pectoralis major and trapezius.

Parallel Sphincter Muscles

Circular parallel muscles that surround openings, such as the orbicularis oris.

Pennate Unipennate

Pennate muscle fibers running obliquely from a tendon on one side only, such as the biceps femoris, extensor digitorum longus, and tibialis posterior.

Pennate Bipennate

Pennate muscle fibers running obliquely from both sides of a central tendon, such as the rectus femoris and flexor hallicus longus.

Pennate Multipennate

Pennate muscles containing several tendons with fibers running diagonally between them, such as the deltoid.

Muscle Movement Principle

When a muscle contracts, it attempts to pull the bones at both ends closer to one another, where usually the less stable bone moves toward the more stable bone.

Agonist Muscle

The primary mover muscle that is most responsible for a specific joint action.

Antagonist Muscle

Muscles located on the opposite side of the joint from the agonist.

Stabilizer

Muscles that fixate or stabilize an area allowing a limb or body segment to exert force and move, such as the abdomen obliques.

Synergist

Guiding muscles that assist the primary mover (agonist) in performing a joint action.

Neutralizers

Muscles that counteract or neutralize the action of other muscles to prevent undesirable movements.

Muscle Naming Characteristics

Distinctive characteristics by which muscles are named, including shape (deltoid, rhomboid), size (gluteus maximus, gluteus minimus, teres minor), number of divisions (biceps brachii, triceps brachii), direction of fibers (external oblique, internal oblique), location (rectus femoris, subscapularis), point of attachment (coracobrachialis, sternocleidomastoid), action (erector spinae, supinator), action and shape (pronator quadratus), and action and size (adductor magnus).