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

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

4. Factors affecting outcome of acting forces ?

5. Factors
Duration
Direction
Magnitude
Distribution of forces*

6. Mechanical stress

7. 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.

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

10. 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

11. WHY ???

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

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

16. Any Sawal ?

17. Torsion, Bending & Combined Loads

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

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

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

21. THE EFFECTS OF,
loading

22. 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

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

24. Repetitive vs. Acute Loads
Repetitive loading
Acute loading
Macrotrauma
Microtrauma

25. 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’

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

28. ELECTROMYOGRAPHY

30.  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.

31. DYNAMOGRAPHY

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

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

36. Vector Composition
Vector Resolution

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