Biomechanics of Living Tissues

The Rigid Framework of the Body

Long BonesDesigned for large movements: extremities

Short BonesTransferring forces & Shock absorption

Flat BonesProtection

Irregular BonesSupport, protection & leverage

Sesamoid BonesOverlap within tendons to decrease stress or

increase leverage

Form of Bone

Mechanical Stress

Function of Bone

Long BonesEpiphyseal

CartilageEndochondral

Ossification:Cartilage is

replaced by BoneMechanical StressGrowth in diameter

Adapt with Mechanical Stress

A joint or Articulation:Any place where two bones meet or join

Function of JointJoin bones togetherControlling the motion allowed between them

Joint ClassificationJoint Structure: Fibrous, Cartilaginous, SynovialJoint Function:

Synarthrodial (immovable)Amphiarthrodial (slightly movable)Diarthrodial (freely Movable)

Joint CavityFormed by articular capsuleA sleeve of ligamentous tissue surrounds the

jointSynovial fluid

Syn “like” & Ovium “egg”LubricationHydrostatic shock absorbingNourishing & cleaning

Not easily movedMovements of the bones in planes other than

those defined by the Degrees of FreedomMovement of the articulating surfaces away

from each other through shear dislocation (sliding laterally) or traction dislocation (pulling apart)

FlexibilityRange of Motion possible acc. DoFHow easily this motion can occur

Reciprocal convex and concave (Compressive & Shear)

Ligaments (Tensile force & Bending Loads)

Reciprocal convex and concave (Compressive & Shear)

Ligaments (Tensile force & Bending Loads)

Tendons & Muscles (like Ligaments)

Reciprocal convex and concave (Compressive & Shear)

Ligaments (Tensile force & Bending Loads)Tendons & Muscles (like Ligaments)Pressure within the joint cavityR.O.M

Extensibility of multiple-joint muscles

Bulkiness of soft tissues or clothing

Reciprocal convex and concave (Compressive & Shear)Ligaments (Tensile force & Bending Loads)Tendons & Muscles (like Ligaments)Pressure within the joint cavityR.O.M

Extensibility of multiple-joint musclesBulkiness of soft tissues or clothing

MobilityFriction within the joint Inertia & tension in the muscles (esp. antagonist)Wearing or damage to the articular cartilage or synovial

joint

The Motors of the Body

Ability to Actively Shorten & Produce Tension

Smooth, Skeletal, & CardiacThe Structure of Skeletal Muscle

Movement, Posture Maintenance, heat production, Protection, Pressure Alteration to aid circulation

Micro and Macro Structures of MusclesThe Sarcomere is the basic contractile unit of

muscle

IsometricConcentricEccentric

AgonistAntagonistStabilizerNeutralizerSynergist

IsometricConcentricEccentric

AgonistAntagonistStabilizerNeutralizerSynergist

A single stimulus from the motor neuron:

When a muscle contracts Pull on each attachments with equal forceLine of pull

Physiological Cross Sectional AreaSeries ArrangementsParallel Arrangements

PCS

Longitudinal vs. PennateSee next page !

PreStretch

Stimulus Duration

Fatigue

Fiber Type:

Type I SO 50 – 55 %

Type IIA FOG 30 – 35 %

Type IIB FG 15 %

Control of the Musculoskeletal System

Three types:Sensory, afferentMotor, efferentInterneuron, connector

Number of Active Motor UnitsRate of Stimulation

Recruitment PatternFirst: Small & Slow TwitchThen: Large & Fast Twitch

Initial Strength GainTraining the nervous systemImprove its ability to recruit more motor units

Extroceptors

Interoceptors

Visceroceptors

Propriceptors (from Musculoskeletal system)

Involuntary response

Have some protective functions

DetectStretch or relative change in muscle length

ResponseMuscle spindle is activated to RESET the tension

Slow stretch results in slow rate stimulationControlling the posture involuntarily

In SportsBackswing or any prestretch prior to movementEccentric Muscle contraction to slow the

movementSlower movements in flexibility exercises

Detect

Tension within the tendon

Response

Inhibition of muscle contraction

Protects muscle from rupturing or tearing

Strength gains due to increase it threshold by

CNS

Vestibular Systems: Balance SenseChanges in motion of the head or its

accelerationPosition of the head relative to the

gravitational forceTonic neck reflexes

Neck flexion: Pulling action of armsNeck extension: Pushing action of arms

Pacinian corpusclesreceptors for touchChange in joint positionsLarge pressure is sensed: Extensor thrust

reflex (e.g. Landing: eccentric contraction of knee extensors)

Cutaneous pain receptorsPain is sensed: Flexor or withdrawal reflex

Crossed extensor reflexCombination of Flexor & Extensor Thrust

Shahram Lenjan Nejadian