Arthrology, Myology & Biomechanics

Sagittal Plane

Divides the body into left and right portions; movements occur forward and backward (flexion and extension).

Frontal Plane

Divides the body into front and back portions; movements occur side-to-side (abduction and adduction).

Transverse Plane

Divides the body into upper and lower portions; movements generally involve rotation.

Fibrous Joints

Bones connected by fibrous connective tissue, allowing little to no movement (e.g., skull sutures).

Cartilaginous Joints

Bones connected by cartilage, allowing limited movement (e.g., pubic symphysis).

Synovial Joints

Joints with a cavity filled with synovial fluid, allowing a large amount of movement.

Three Major Accessory Motions

Roll, Glide (or slide), and Spin.

Isometric Contraction

Muscle produces tension but does not change length, and the joint does not move.

Concentric Contraction

The muscle shortens while producing force, typically overcoming resistance.

Eccentric Contraction

The muscle lengthens while producing force, typically controlling or slowing down movement.

Agonist (Prime Mover)

The main muscle responsible for producing a specific movement.

Antagonist

A muscle that performs the opposite action of the agonist.

Synergist

A muscle that assists the prime mover in producing or controlling the desired movement.

Fixator / Stabilizer

A muscle that stabilizes a body part or joint so another movement can occur efficiently.

Neutralizer

A muscle that prevents an unwanted movement caused by another muscle's action.

First-Class Lever

The fulcrum is between the force and resistance (Force — Fulcrum — Resistance).

Second-Class Lever

The resistance is between the fulcrum and force (Fulcrum — Resistance — Force).

Third-Class Lever

The force is between the fulcrum and resistance (Fulcrum — Force — Resistance); most common in the human body.

Newton's First Law (Law of Inertia)

An object at rest stays at rest, and an object in motion stays in motion unless acted upon by an external force.

Newton's Second Law (Law of Acceleration)

Acceleration depends on force applied and mass, expressed as F = ma.

Newton's Third Law (Action/Reaction)

For every action, there is an equal and opposite reaction.

Torque Formula

Torque = Force × Moment Arm (T = F × d).

Mechanical Advantage Formula

MA = Resistance Force / Effort Force.

Static Balance

Maintaining balance while the body is stationary.

Dynamic Balance

Maintaining balance while the body is moving.

Factors Increasing Stability

Wider base of support, lower center of mass, center of mass inside base of support, and greater mass.

Center of Mass (COM)

The point where the body's mass can be considered to be concentrated.

Muscle Spindles

Sensory receptors that detect changes in muscle length and rate of length change.

Golgi Tendon Organs

Sensory receptors that detect tension or force in tendons.

Open Kinetic Chain

The distal end of the limb (end of the limb) is free to move.

Closed Kinetic Chain

The distal end of the limb is fixed or in contact with a stable surface.