MEM 634ERGONOMIC DESIGN

4.1 Strains associated with Load Handling– Exerting force and energy in lifting objects with hand(s) strains hands, arms ,

shoulders, trunk and legs(if standing).– Same parts also under stress in lowering ,pushing, pulling-diff direction and

magnitures of external and internal force and torque vector.– Primary area of concern: low back(especially disc on lumbar spine)-spinal

vertabrae, connective tissue, muscles– Tension strains can be in form of: linear elongation, bending movement or

twisting torque– Loading:activities on external objects-lifting,holding etc– Strains:static or dynamic-fast or slow,short or long period,regular or inregular

interval– Sources of strain:sports,leisure, occupational activities

4.2 Assessing Body Capabilities Related to Material Handling

– Energy to move or keep objects from moving must be generated within the body and exerted in terms of force to the outside objects

– Ability to lift material over hours is limited by metabolic and circulatory capabilities

– Ability top lift heavy objects just once or occasionally is limited by generate large force capabilities.

– Assessment of human abilities: psychophysical and biomechanical method– Psychophysical measurements

• Relies on assumption that human can sense and integrate perception of strain on all body function and capabilities

• Overall assessment of acceptability, suitability and willingness to perform stressful task

– Biomechanical measurements• Spinal compression

-calculation of compression strain is complicated because human spine is not straight column and changes with different trunk posture- Thus, the strains in spinal column were treated as static.

• Involvement of torso muscle- study in activation of various muscle within the trunk in movement-muscle that develop force vectors that run between inferior and superior parts of the trunk are:right and left dorsi,right and left erector spinae,right and left internal and external obliques, right and left rectus abdominus- use EMG to identify which muscle involved and sequence and intensity of muscle to work.- Depending on lifting task-height,distance from body, speed and sideways displacement –sequence and magnitude of muscle activation are recorded

• Intraabdominal Pressure- IAP changes with trunk loading and motion conditions.- (Freivalds 1989) researchers estimated IAP will carry 15% of strain and recommends for suitable lifting condition had largely relied on observing devp of pressure build up- (Marras and Mirka 1996;Kumar 97) states that IAP does not reduce spinal compression loading

• 2D vs 3D activities-initial research assumed that lifting would be done directly in front of trunk (symmetrical) lift-2D task.- but most of lifting involves activities to one or the other side of body,requiring twisting motion about spinal joints-it was apparent that human body perform less for nonsymmetrical work-supported by recording of 3D lumbar motions, evaluation of EMG signals of torso muscles and models of distributed muscle activities and spinal compression

• Unexpected loadingunexpected loading of body may lead to overexertion injury

• Material handling other than lifting- Most research in material handling has dealt with lifting and lowering activities (force vector in operator hands is vertical)- But many activities involves horizontal pulling and pushing of a load.

4.3 Back Injury and Pain – Injury happens if limit of maximal strain of tissues are exceeded– May happen in a single strenuous effort, an accidental trauma-but often

repeated loadings add up to accumulative overloading.– Low back pain (LBP) –indicator of overexertion of the body– Major difficulty in recognizing and analyzing back injury is that it may happen

without generating any pain because neither the facet of the apophyseal nor the intervertebral discs have pain sensitive nerves.

– Actual reason of LBP are not clear. Some factors contributes:degenerative disc disease, congenital anomalies,spondylolisthesis, difference in leg length and pevious injuries