Video Lecture Notes: Kinesiology Principles, Bone & Cartilage Biomechanics — Vocabulary

Vocabulary flashcards covering key terms from lectures on force, lever systems, bone and cartilage biomechanics, and skeletal muscle mechanics.

Force

A push or pull that can cause motion; measured in Newtons (N); arises in action–reaction pairs per Newton's third law.

Newton's Third Law

For every action, there is an equal and opposite reaction; forces come in pairs.

External forces

Forces acting from outside the body; include contact and non-contact forces.

Internal forces

Forces generated within the body by tissues (e.g., ligaments, tendons, bones) that influence internal loads.

External contact forces

Forces between objects in contact (e.g., normal contact force, friction, fluid contact).

External non-contact force

Gravity is the primary non-contact force studied; it acts through the center of gravity (COG).

Ground Reaction Force (GRF)

A contact force from interaction with the ground; typically acts parallel to the normal contact direction at the interface.

Tensile force

A pulling force acting at the ends of an internal structure (e.g., ligaments, tendons).

Compressive force

A pushing force acting at the ends of structures (e.g., bones and joints).

Shear force

A transverse force that acts parallel to the analysis plane and can cause angular deformation.

Torque (moment)

The turning effect produced by a force; depends on the force and the moment arm.

Moment arm

Perpendicular distance from the pivot to where the force is applied; longer arms yield greater torque for the same force.

Muscular torque

Torque generated by muscles to rotate a limb around a joint (e.g., biceps at the elbow).

Lever system components

Load, Effort, and Fulcrum (pivot).

First-class lever

Fulcrum lies between the load and the effort; trade-off between distance and force.

Second-class lever

Load lies between the fulcrum and the effort; acts as a force multiplier.

Third-class lever

Effort lies between the load and the fulcrum; favors speed and ROM; most muscle attachments are this type.

Concentric contraction

Muscle shortens under tension; causes movement toward the insertion point.

Eccentric contraction

Muscle lengthens under tension; controls or slows movement.

Isometric contraction

Muscle length remains constant under tension; joint angle unchanged.

Haversian system (osteon)

Fundamental structural unit of compact bone.

Cortical bone

Outer high-density bone layer.

Cancellous bone

Inner porous, lattice-like trabecular bone.

Anisotropic

Material properties that vary with direction.

Loading modes of bone

Compression, Tension, Shear (and combinations like bending and torsion).

Stress

Force per unit area; a measure of internal forces within a material.

Strain

Deformation of a material in response to stress.

Elastic region

Load deforms bone but it returns to original shape upon unloading.

Plastic region

Deformation remains after unloading; continued loading can lead to failure.

Yielding

Point at which material undergoes permanent deformation leading toward failure.

Tension (key concepts)

Loads applied outward from a structure; lengthens the structure; maximal tensile stress occurs when load is perpendicular to the structure.

Compression (key concepts)

Loads applied toward the surface; shortens the structure; maximal compressive stress occurs when load is perpendicular.

Shear (key concepts)

Load applied parallel to the structure; causes angular deformation; shear stress interacts with other loading types.

Three-point bending

Bending with three forces creating a bending moment along the bone (e.g., distal/proximal tibia scenarios).

Four-point bending

Two inner loads create a constant bending moment between them.

Torsion

Twisting load that involves elements of multiple loading modes and causes a shear fracture pattern along a neutral axis.

Fatigue fracture

Fracture from a single overload or repeated loading at lower levels leading to microdamage over time.

Wolff's Law

Bone remodels in response to the forces placed upon it, adapting to functional demands.

Bone remodeling drivers

Gravitational forces (body weight) and muscle pull influence remodeling.

Moment of inertia

Resistance to changes in rotational motion; greater MOI makes a structure stiffer to bend about a given axis.

Bone geometry factors

Length, cross-sectional area, and tissue distribution influence mechanical behavior.

Aging bone changes

Bone density decreases with age; cancellous loss and cortical thinning occur; typical rates vary by gender.

Sex-based geometry changes

Men: periosteal bone formation increases; endocortical formation decreases. Women: periosteal formation decreases; endocortical formation increases.

Aging bone changes (rates)

Approximate annual bone density loss: males 0.5–0.75%, females 1.5–2.5%.

Cartilage avascular

Articular cartilage has limited blood supply, leading to limited healing capacity.

Articular cartilage composition

Hyaline cartilage surrounding joint ends; composed of chondrocytes, collagen, proteoglycans, and water.

Chondrocytes

Cells that manufacture and maintain the cartilage extracellular matrix.

Collagen

The main structural protein providing tensile strength; abundant in cartilage; anisotropic.

Proteoglycans

Large molecules that regulate water content and matrix stability in cartilage.

Water (cartilage)

60–85% of cartilage; essential for nutrition, load distribution, and lubrication.

Viscoelasticity

Cartilage exhibits both viscous and elastic behavior under load.

Creep

Time-dependent deformation following an initial rapid deformation under load.

Stress relaxation

Under constant deformation, stress decreases over time to maintain deformation.

Permeability

Ease with which fluid can move through cartilage; cartilage is porous with relatively low permeability.

Fluid film lubrication

A thin lubricating film separates surfaces; load is supported by pressure in the film.

Boundary lubrication

Close-contact lubrication where a gel-like boundary layer reduces wear; viscosity increases.

Wear: fatigue wear

Wear from accumulation of microscopic damage under repetitive loading.

Wear: interfacial wear

Material transfer or damage at bearing surfaces due to interface interactions.

Chondromalacia patella

Cartilage softening under the patella often linked to abnormal loading and knee pain.

Skeletal muscle layers

Epimysium (outer), Perimysium (around fascicles), Endomysium (around individual fibers).

Myofibril

Rod-like structures inside a muscle fiber containing the contractile machinery.

Sarcomere

Repeating contractile unit within a myofibril; site of actin–myosin interaction.