Mechanical Loads on Human Body Dr Sana Altaf

Mechanical Loads on Human Body Dr. Sana Altaf Bs. PT(LMDC), Ms. OMPT(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 • Force divided by area on which it acts. • Stress represents internal force distribution. Pressure • Force distributed over a given area. • Pressure represents force acting external to the body.

In which section of vertebra, weight is transmitted the most ? 1. 2. 3. 4. 5. CERVICAL THORACIC LUMBAR SACRAL COCCYGEAL

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

BECAUSE WEIGHT BEARING SURFACES 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

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

üVector Composition üVector Resolution

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