Kinesiology: Joints and Levers

Uniaxial Joint

Joint with one degree of freedom, moving in one plane (e.g., hinge, pivot).

Biaxial Joint

Joint with two degrees of freedom, moving in two planes (e.g., condyloid, saddle).

Multiaxial Joint

Joint with three degrees of freedom, moving in three planes (e.g., ball and socket).

Open Kinematic Chain

Movement where the distal extremity is unattached and freely moveable in space.

Closed Kinematic Chain

Movement where the distal extremity is fixed to an object or the ground.

Unloaded joint function

relaxed, open, unstressed

Loaded joint function

forces or stress being applied, compressed, under tension/distraction, bending, torsion, shearing

Arthrokinematics

Passive range of motion based strictly on anatomical joint structure.

Arthrokinetics

Active range of motion considering the forces, momentum, and resistance causing movement.

Non-Pathological End Feels

Normal anatomical limitations to joint movement: bony, soft, or firm/springy.

Pathologic Range of Motion

Abnormal joint movement categorized as hypomobile or hypermobile.

First-Class Lever

Lever system best for balance, with the fulcrum between weight and force.

First-Class Lever Example

The vertebral column acting against gravity.

Second-Class Lever

Lever system best for power, with weight between fulcrum and force.

Second-Class Lever Example

The act of plantarflexion at the ankle.

Third-Class Lever

Lever system best for ROM and speed; the most common lever in the body.

Mechanical Advantage

The efficiency of a lever measured by effort required to overcome resistance.

Newton's Law of Inertia

An object remains at rest or in motion unless acted upon by an external force.

Newton's Law of Acceleration

Acceleration is proportional to force magnitude and inversely related to object mass.

Newton's Law of Action/Reaction

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