Biomechanics of Living Tissues

The Rigid Framework of the Body

Long Bones Designed for large movements: extremities Short Bones Transferring forces & Shock absorption Flat Bones Protection Irregular Bones Support, protection & leverage Sesamoid Bones Overlap within tendons to decrease stress or increase leverage

Form of Bone Mechanical Stress Function of Bone

Long Bones Epiphyseal Cartilage Endochondral Ossification: Cartilage is replaced by Bone Mechanical Stress Growth in diameter Adapt with Mechanical Stress

A joint or Articulation: Any place where two bones meet or join Function of Joint Join bones together Controlling the motion allowed between them Joint Classification Joint Structure: Fibrous, Cartilaginous, Synovial Joint Function: Synarthrodial (immovable) Amphiarthrodial (slightly movable) Diarthrodial (freely Movable)

Joint Cavity Formed by articular capsule A sleeve of ligamentous tissue surrounds the joint Synovial fluid Syn “like” & Ovium “egg” Lubrication Hydrostatic shock absorbing Nourishing & cleaning

Not easily moved Movements of the bones in planes other than those defined by the Degrees of Freedom Movement of the articulating surfaces away from each other through shear dislocation (sliding laterally) or traction dislocation (pulling apart) Flexibility Range of Motion possible acc. DoF How 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 cavity R.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 cavity R.O.M Extensibility of multiple-joint muscles Bulkiness of soft tissues or clothing Mobility Friction 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, & Cardiac The Structure of Skeletal Muscle Movement, Posture Maintenance, heat production, Protection, Pressure Alteration to aid circulation Micro and Macro Structures of Muscles The Sarcomere is the basic contractile unit of muscle

Isometric Concentric Eccentric Agonist Antagonist Stabilizer Neutralizer Synergist

Isometric Concentric Eccentric Agonist Antagonist Stabilizer Neutralizer Synergist

A single stimulus from the motor neuron:

When a muscle contracts Pull on each attachments with equal force Line of pull Physiological Cross Sectional Area Series Arrangements Parallel Arrangements

PCS Longitudinal vs. Pennate See next page !

PreStretch Stimulus Duration Fatigue Fiber Type: Type ISO50 – 55 % Type IIAFOG30 – 35 % Type IIBFG15 %

Control of the Musculoskeletal System

Three types: Sensory, afferent Motor, efferent Interneuron, connector

Number of Active Motor Units Rate of Stimulation Recruitment Pattern First: Small & Slow Twitch Then: Large & Fast Twitch Initial Strength Gain Training the nervous system Improve its ability to recruit more motor units

Extroceptors Interoceptors Visceroceptors Propriceptors (from Musculoskeletal system) Involuntary response Have some protective functions

Detect Stretch or relative change in muscle length Response Muscle spindle is activated to RESET the tension Slow stretch results in slow rate stimulation Controlling the posture involuntarily In Sports Backswing or any prestretch prior to movement Eccentric Muscle contraction to slow the movement Slower 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 Sense Changes in motion of the head or its acceleration Position of the head relative to the gravitational force Tonic neck reflexes Neck flexion: Pulling action of arms Neck extension: Pushing action of arms

Pacinian corpuscles receptors for touch Change in joint positions Large pressure is sensed: Extensor thrust reflex (e.g. Landing: eccentric contraction of knee extensors) Cutaneous pain receptors Pain is sensed: Flexor or withdrawal reflex Crossed extensor reflex Combination of Flexor & Extensor Thrust

Shahram Lenjan Nejadian