Mechanical Loads on Human Body Dr. Sana Altaf BsPT(LMDC), MsOMPT(RIU)

REVIEW ! Compression force? Tension ? Shear force ? EXAMPLES & DIRECTION !

Factors affecting outcome of acting forces ?

Factors Duration Direction Magnitude Distribution of forces*

Mechanical stress

Stress Pressure Force divided by area on which it acts. Stress represents internal force distribution. Force distributed over a given area. Pressure represents force acting external to the body.

CERVICAL THORACIC LUMBAR SACRAL COCCYGEAL In which section of vertebra, weight is transmitted the most ? CERVICAL THORACIC LUMBAR SACRAL COCCYGEAL

But the amount of stress present is not directly proportional to the Weight ? Lumbar Compression stress maximum ? But the amount of stress present is not directly proportional to the Amount of weight borne

WHY ???

BECAUSE WEIGHT BEARING SURFACES GREATER THAN HIGHER VERTEBRAS OF LUMBAR SPINE ARE GREATER THAN HIGHER VERTEBRAS

Causes Low back pain Discogenic Postural Muscular strain OA Cancer etc ....

Any Sawal ?

Torsion, Bending & Combined Loads

BENDING Complicated type of loading Compression and axial forces are applied to a structure – *SPINE* COMPRESSION FORCE --- TENSION FORCE

TORSION Torsion occurs when twist occurs along its longitudinal axis, when one end is fixed.

Combined Loading When more than one type of (pure form) loading occurs.

THE EFFECTS OF, loading

Magnitude and direction of force • Deformation When an external force is applied to the human body, several factors influence whether an injury occurs Magnitude and direction of force Area over which force is distributed Load-deformation curve * Yield point (elastic limit) Failure

Ultimate failure point Elastic limit Yield Point (Plastic region) Deformation

Repetitive vs. Acute Loads Repetitive loading Acute loading Macrotrauma Microtrauma

Repetitive loading Repeated application of sub acute load that is usually of relatively low magnitude. Example: Foot hits the floor during running Chronic injury / stress injury Causative mechanism is called ‘micro trauma’

Acute loading Application of single force of sufficient magnitude to cause injury. Example: fall, RTA Causative mechanism is called ‘macro trauma’

ELECTROMYOGRAPHY

 Electromyography (EMG) is a technique for evaluating & recording the electrical activity produced by skeletal muscles. Instrument - electromyograph Recording - electromyogram A resting muscle does not show recordable electrical potential, but with increase force of contraction, amplitude of potential increases. An electromyograph detects electrical potential generated by muscle cells when these cells are electrically or neurologically activated EMG is best done in a specially constructed shielded room to prevent interference.

DYNAMOGRAPHY

Dynamography Force and pressure platforms interfaced with computer, measure ground reaction forces. Primarily employed in gait research, starts, takeoffs, landings and balance.

Vector Quantity Scalar Quantity Physical quantity that possess both magnitude and direction. Physical quantity that is completely described by its magnitude.

Vector Composition Vector Resolution

Assignment Write all definitions given in this chapter. Assignment marks will be included in test .