Kinematics and Kinetics in Biomechanics

Uniaxial joints

Joints allowing movement around one axis only.

Biaxial joints

Joints permitting movement around two axes.

Tri-/Multi-axial joints

Joints enabling movement around multiple axes.

Osteokinematics

Study of bone movement in joints.

Arthrokinematics

Movement between joint surfaces during motion.

Close-packed position

Joint position with maximal surface contact.

Open-packed position

Joint position with minimal surface contact.

Kinematic chain

Sequence of linked body segments in motion.

Open kinematic chain

Distal segment free to move independently.

Closed kinematic chain

Distal segment fixed, proximal segments move.

Kinematics

Study of motion without considering forces.

Translatory motion

Movement in a straight line.

Rotary motion

Movement around an axis.

Velocity in rotary motion

Speed of points varies with distance from axis.

Degrees of Freedom

Number of planes a joint can move in.

One Degree of Freedom

Joint movement in one plane only.

Two Degrees of Freedom

Joint movement in two planes.

Three Degrees of Freedom

Joint movement in three planes.

Accessory Motion

Movement not primarily intended, e.g., joint play.

Instantaneous Axis of Rotation

Axis around which rotation occurs at a moment.

Convex-Concave Rule

Describes joint surface interactions during movement.

Open-Packed Position

Joint surfaces maximally separated, less stable.

Closed-Packed Position

Joint surfaces maximally congruent, more stable.

Open Kinematic Chain

Distal segment moves against fixed proximal segment.

Closed Kinematic Chain

Proximal segment moves against fixed distal segment.

Ligaments

Connect bone to bone, providing stability.

Tendons

Connect muscle to bone, facilitating movement.

Bursa

Fluid-filled sacs reducing friction in joints.

Cartilage

Smooth tissue covering joint surfaces, reducing friction.

Fibrocartilage

Tough cartilage providing support and cushioning.

Elastic Cartilage

Flexible cartilage allowing shape retention.

Hyaline Cartilage

Smooth cartilage at joint surfaces for movement.

Isotropic Material

Exhibits uniform mechanical properties in all directions.

Anisotropic Material

Mechanical properties vary with direction of force.

Load/Force

External force applied to a material or structure.

Stress

Force per unit area within materials.

Strain

Deformation resulting from applied stress.

Viscoelasticity

Material property exhibiting both viscous and elastic characteristics.

Viscoelasticity

Material property showing time-dependent strain response.

Creep

Gradual deformation under constant force application.

Stress-relaxation

Decreasing force needed under maintained stretch.

Hysteresis

Different load-deformation paths for loading and unloading.

Strain-rate sensitivity

Energy requirement varies with loading speed.

Uniaxial joints

Joints allowing movement in one plane.

Biaxial joints

Joints allowing movement in two planes.

Triaxial joints

Joints allowing movement in three planes.

Hinge joint

Allows flexion and extension, e.g., elbow.

Pivot joint

Allows rotational movement, e.g., atlantoaxial.

Condyloid joint

Allows movement with two degrees of freedom.

Ellipsoidal joint

Similar to condyloid, e.g., radiocarpal.

Saddle joint

Allows movement in two planes, e.g., thumb.

Plane joint

Allows gliding movements, e.g., carpal bones.

Ball and socket joint

Allows multi-directional movement, e.g., shoulder.

Displacement

Distance moved in a specific direction.

Velocity

Rate of change of displacement over time.

Acceleration

Rate of change of velocity over time.

Force

Push or pull acting on an object.

Inertia

Resistance to change in motion state.

Torque

Rotational force around an axis.

Impulse

Change in momentum due to force application.

Friction

Resistance force opposing motion between surfaces.

Inertia

Resistance of an object to change its state.

Mass (m)

Amount of matter in an object, measured in kg.

Weight (wt)

Force of gravity acting on an object.

Pressure (P)

Force distributed over a given area (P=F/A).

Volume

Amount of space occupied by an object.

Density (ρ)

Mass per unit volume (ρ=mass/volume).

Torque (τ)

Rotary effect of a force (τ=Fd).

Impulse (J)

Product of force and time (J=Ft).

Force

A push or pull acting on an object.

Unit of Force

Metric unit is Newton (N).

Unit of Mass

Metric unit is kilogram (kg).

Unit of Weight

Metric unit is Newton (N).

Unit of Pressure

Metric unit is Pascal (Pa).

Unit of Volume

Metric unit is cubic meters (m³).

Unit of Density

Metric unit is kg/m³.

Specific Weight (γ)

Weight per unit volume (γ=wt/volume).

Collinear Forces

All forces lie on the same line.

Coplanar Forces

All forces lie on the same plane.

Concurrent Forces

Forces meet at the same point.

Force Vector

A vector quantity representing force magnitude and direction.

Free Body Diagram

Simplified drawing showing forces acting on a body.

C2

Law of Cosines formula for triangles.

Force of Gravity

Attraction between two masses due to gravity.

Center of Gravity (CoG)

Point where weight is equally balanced.

Center of Mass (CoM)

Point representing average position of mass.

Line of Gravity (LoG)

Imaginary line through CoG to ground.

Segmental CoM

CoM for individual body segments.

Base of Support (BoS)

Area beneath an object supporting its weight.

Newton's First Law

Object remains at rest or uniform motion unless acted on.

Inertia

Resistance of an object to change its state of motion.

Static Equilibrium

Balanced forces result in no motion.

Dynamic Equilibrium

Balanced forces result in constant velocity.

ΣF = 0

Sum of forces equals zero in equilibrium.

Στ = 0

Sum of torques equals zero in equilibrium.

Anatomic Location - Head

CoG located at sphenoid sinus.

Anatomic Location - Arm

CoG at medial head of triceps.

Anatomic Location - Hand

CoG at 3rd metacarpal.

Anatomic Location - Thigh

CoG at adductor brevis or magnus.

Anatomic Location - Whole Body

CoG one inch anterior to S2.