Ergonomics Exam 1
ergonomic task analysis: data collection
- Task→ a unit of work, one part of the whole job - Subtask→ one component of a task · Continuous→ tracking or monitoring, controlling a system with predefined parameters o Ex→ water delivery man driving the truck · Discrete→ procedural tasks, single trigger event (cause and effect) o Ex→ water delivery man opening rear door of truck · Rule based→ can be continuous or procedural, requires a decision, "if X then do Y"
what type of posture is the goal or ergonomics?
- a neutral posture - We are strongest and fastest in neutral posture o Blood flow is optimal here and NOT restricted o It allows recovery of the tissues that are being used frequently
Physiological demands of static and dynamic work
- ex: repetitive work and material handling o Increased pulmonary ventilation o Increased HR/BP o Increased blood flow to working muscles o Skeletal muscle contract/relax
what is RWL men and women?
- inclues 90% males - 75% females
PDC Character of work: sedentary - occasional - frequent - constant
- occasional: 10 lbs - frequent: negligible - constant: negligible
PDC Character of work: light - occasional: - frequent: - constant:
- occasional: 20 lbs - frequent: 10 lbs and/or walk/stand/ push/pull - constant: negligible
PDC Character of work: medium - occasional: - frequent: - constant:
- occasional: 20-50 lbs - frequent: 10-25 lbs - constant: 10 lbs
PDC Character of work: heavy - occasional: - frequent: - constant:
- occasional: 50-100 lbs - frequent: 25-50 - constant: 10-20 lbs
PDC Character of work: very heavy - occasional: - frequent: - constant:
- occasional: over 100 - frequent: over 50 lbs - constant:over 20 lbs
ergonomic task analysis- task analysis - effective therbligs
- people doing something to move system forward § Reach § Move: moves with object § Grasp: hand grabs object § Release: object released from grasp § Preposition: place in proper position for next use § Use: object operated as intended § Assemble: two or more items placed together § Disassemble: items taken apart
what areas are included in quick exposure screen?
1. back (neutral, flex, excessive flex or twist) 2. shoulder/ arm (what level) 3. wrist/hand (straight or deviated; repetition) 4. neck (bent or twisted) 5. lighting 6. vibration 7. stress 8. time on task 9. weight (light, medium, heavy) 10. drive vechile
OSHA W1 awkard postures
1. bending back 30 degrees 2. UD wrist 30 degrees 3. wrist extension 45 degrees 4. wrist flexion 30 degress 5. bending and extending neck
ergonomic task analysis: preparation
1. establish objective and obtain support 2. job description 3. job requirements 4. symptom survey 5. risk prioritization from workers perspective
what are some regions looked at in the OSHA W1 score?
1. neck/shoulder 2. back/trunk hip 3. elbow/ wrist/hand 4. leg/knee/ankle
ergonomic task analysis- phases
1. preparation 2. data collection 3. task analysis
what components are included in the OSHA W1 screen?
1. repetition 2. awkward hand posture 3. force 4. contact stress 5. vibration
what are some typical anthropometric measurements
1. stature 2. eye height 3. eye height seated 4. buttocks to popliteal 5. hip breadth 6. popliteal height 7. sitting elbow height 8. elbow-fingertip length 9. knee height 10. shoulder breadth
when is peak strength range?
25-35 - slower or no decline until 40s followed by acceleration
how much fitness reduction ages 25-65 years
30%
how much less efficient is arm work verses leg?
30%
what is most effective range for lifting?
40-60
Haddon Matrix
A way of conceptualizing injury prevention strategies based on the phase and whether the strategy is targeted to the host, the vehicle, or the environment - pre-injury - injury - post-injury
characteristics of standing work
Greater reach Body weight exerts forces Less room than seated Legs absorb forces (vibration) Lower lumbar disc pressures Lordosis evenly distributes pressures Low muscular activity Trunk muscle power Increased cognitive attention 8% energy expenditure (kcal consumed) over supine, 4% over sitting Standing work station does not combat cardiac risk factors Hydrostatic handicap: peak plantar pressures, walking and fidgeting, varicose veins 50% or more of shift Venous and circulatory insufficiencies Peripheral blood pooling
Anaerobic work
High intensity, short-duration exercise in the absence of oxygen - lactic acid build up
Aerobic work
Low intensity, long-during exercise in the presence of oxygen - O2 supply sufficient and prevent lactic acid
where is more weight able to be accepted in a carry, elbow or knuckle height?
Lower acceptable with carry at elbow versus knuckle height
characteristics sitting work
Posterior tilt and reduced lumbar lordosis Flexion moment about lumbar spine P - posterior ligament tension, anterior disc wedging, inc disc pressure (upright), lower disc pressure in relaxed/reclined sitting - In more "slumped" posture see less muscle activity (dec % sub-max voluntary contraction) - Prolonged sitting and back pain - puts uneven pressure on discs with kyphotic posture seen As increase flexion angle in sitting, greatly increase pressure in third lumbar disc
Ergonomics
The study of workplace equipment design or how to arrange and design devices, machines, or workspace so that people and things interact safely and most efficiently.
when do you design for average?
WHEN ADJUSTABILITY IMPRACTICAL - Use where adjustability is impractical, e.g. auto steering wheel, supermarket check-out counter, etc. § Where design is NON-CRITCAL, e.g. door knob
OSHA W1 force
a. Lifting more than 75 lbs at any one time; more than 55 lbs more than 10x day; or more than 25 lbs below knees, above shoulder, or at arms length more than 25x per day b. Pushing/puling more than 20 lbs of initial force (e.g equivalent to pushing a 65 lb box across tile floor or pushing a shopping cart with five 40 lb bags of dog food) c. Pinching an unsupported object weighing 2 or more lbs per hand, or use of an equivalent pinching force for more than 2 hours total per day Gripping an unsupported object weighing 10 lbs or more per hand
compare stress on spine and energy expenditure with: 1. squat lift 2. stoop lift 3. free
a. Squat lift- less compressive force if load fits between knees b. Stoop method- less energy expenditure vs. squat lift, less compressive if large load c. Free- style- semi-squat load rested on thigh; least stressful in energy cost
OSHA W1- contact stress
a. Using the hand or knee as hammer more than 10 times per hour or more than 2 hours total per day
OSHA W1- vibration
a. Using vibrating tools or equipment that typically have moderate vibration levels (such as jig saws, grinders, or sanders) for more than 2 hours total per day
WHAT IS THE MAXIMUM ACCEPTABLE OF DISCOMFORT AGREED UPON FOR WORK DISCOMFORT?
bord 1-3
muscle Contraction types
concentric, eccentric, isometric
Physiological demands static work
ex: standing and sitting o Pulmonary ventilation constant o Cardiac output steady o Increased intramuscular pressure o Decreased blood/nutrient flow o fatigue
strength
external application of force or torque by a body segment to an outside object
relationships between speed of contraction and force
inverse relationship; as speed increases force decreases
Gender Difference in strength
n Females mean 67% of males mean across mm groups (Roebuck et al, 1975) n Specific muscle groups 35% to 85% (Chaffin and Anderson, 1991) - Higher female : male ratio for » LE Lifting » Pushing » Pulling - Lower female : male ratio » Bending » Shoulder work
NIOSH MMH- percentage of injuries - lifting injuries - push-pulling - holding/ carrying
o 50% lifting injuries o 9% push-pulling o 6% holding/ carrying
average strength compared to 31-35 y/o - 51-55 - 71-75
o 80% at 51-55 o 60% at 71-75
occupational health
o A continuum of health care from pre-hire to retire § Serve employees and employers of by continuously matching the worker with the work
recommendations when lifting
o Avoid over-exertion (get a feel for load by turning, tilting, pushing) o Stand as close to load as possible with legs slightly apart o Bend hips and knees as comfortable as possible o Lift slowly and steadily- do not jerk speed o Keep load close- carry against thigh and abdomen o Do not twist/turn
Physical therapists and functional training
o Barrier accommodations or modifications o Environmental or work task adaptation o Ergonomic stressor reduction o Device and equipment use and training o Assistive and adaptive device or equipment training during IADL o Orthotic, protective, or supportive device or equipment training during IADL o Prosthetic device or equipment training during IADL functional training programs o Back schools o Job coaching o Simulated environments and tasks
risk factors in ergonomics
o Biomechanical descriptions o Body regions o Ergonomic exposure o Ex- stooping posture, high force loads
MMH- biomechanical models
o Biomechanics- physics to determine stress o Large mm forces to counter small external loads o Computer models for compression, force and shear o L5/S1- vertebral segment is critical link in compression forces o Limited to analysis of infrequent tasks with high forces o Goal- limit tasks within compressive tolerance of spine
Central Fatigue: Impairment of Activation
o Central nervous system drive o Motivation, sense of effort o Integrity of the descending motor command o Perceived effort o Static exertion: increases with fatigue o Decrease in voluntary motor drive
anthropometrics- designing for extremes of population- maximum and minimum
o Design for max 95th percentile males and 5th percentile females § E.g.- doorways, escape apparatus, ladders § This value is commonly the 95th percentile male for target population o Design for the minimum population when a minimum value accommodate almost everyone § E.g. control panel buttons and the forces to operate them § This value is commonly the 5th percentile female for target population
endomorphy
o Dominate economy- digestive viscera · Predominance of soft tissue throughout various of body · Mass concentration near body center · Large round head · Short thin neck · Broad, thick chest · Short arms and legs · Large abdomen
· Ectomorphy
o Dominate economy: § Linearity, fragility o Frail, delicate body structure o Relatively large cranium o Small face o Pointed shin and sharp nose o Ling slender neck o Longa rms o Ling thin legs
mesomorphy
o Dominate economy: § Muscle, bone, connective tissue o Physique is heavy, hard, and rectangular o Massive muscles and large prominent bones o Long strong neck o Thoracic trunk dominant over abdominal volume o Broad shoulder with heavy, prominent clavicles o Muscular arms and legs
external and internal tissues loading
o External o Gravity o External objects o Internal o Counteract external o Equilibrium o Biomechanical disadvantage o Contributes to most cumulative trauma
Metabolic Factors in Fatigue
o Formation of lactic acid: decreased pH o Decreased phosphocreatine o Increased calcium (Ca++) o Decreased ATP hydrolysis o Hinders formation and detachment of cross bridges
Components of occupational health
o Functional job analysis o Conditional job offer o Post-offer medical screening o Worker-job matching § Injury prevention education § Ergonomics § Techniques training/ conditioning o Job entrance o Injury- immediate care; functional testing; modified duty; full duty or job change; education o Return to work o Job change or promotion
muscle work in occupational activity - heavy dynamic work - manual material handling - static postural work - repetitive work
o Heavy dynamic work- moving the body o Manual material handling- static and dynamic- lifting, pushing, pulling o Static postural work" local muscular load, large, and small groups o Repetitive work: local muscular, small groups
· Steps to apply arthropometric data
o Identify important dimensions- hip breadth for chair seat o Identify user population- children, women, U.S. population, world population o Determine principles to use- e.g. extremes, average adjustable o Select the range to accommodate- any, 90%, 95% o Find relevant data o Make modifications- adult heavy clothing adds about 4-6 inches linear
Static (isometric) strength
o Initial sarcomere shortening o No change in muscle length o Body segments do not move o All forces acting on body parts are in equilibrium o Easily measured o Much available normative data o Reasonable estimate of maximal exertion for slow eccentric body motions o Poor estimates of fast concentric or ballistic type movements
O2 uptake mena and women on bike erg
o Male: 15 kcal/min o Females: 10 kcal/min
Maximum oxygen Uptake
o Maximum rate of O2 consumption o Measure max O2 supply and utilization o Measure of work capacity for prolonged work o Intensity of work and endurance are related to max O2 uptake
heart rate - leg work - arm work -workers
o Measure of circulatory load o Leg work: 100-105 bpm o Arm work: 90-95 bpm o Age dependent § Physically active workers § Usual working HR: 90-100 bpm § Max HR for 1 hour: 120-130 bpm § Few workers HR > 110—120 bpm
Dynamic Strength
o Muscle length changes o Body segment movement o Time variables related to effort and external effect o Velocity (m/sec) o Acceleration (m/sec2) o Difficult to test o Controlled velocity (isokinetic) o Controlled mass or repetition (isotonic)
ambient conditions workspace design
o Physical environment workplace conditions o Climatic conditions could effect work § Temperature § Light § Noise § Vibration § Air quality o Workers exposures to adverse conditions o Workers acclimation to adverse conditions o Protection required
MMH- physiological models
o Physiological: frequent task must account for body weight, gender, start and end of lift o Poor formula agreement o 33% max aerobic power (MAP) average for 8 hours o Max efficiency higher weights, lower lifting range
work rest cycle formula
o R- rest required in minutes o T- total work time in minutes o W- avg. energy consumption or work in kcal/min o S- recommended avg. energy expenditure
definitions: rate, magnitude, duration
o Rate- how fast energy is being applied to tissue o Magnitude- how much energy is transferred to tissue o Duration- how long energy is applied to tissue
Muscle Fatigue
o Reduction in ability to exert voluntary force o Neuromuscular adaptation to prevent serious damage o Dependent on type of loading required o Is it high or low intensity o Is it sustained or intermittent o Is is muscle activity static or dynamic
OSHA W-1: repetition
o Repeating the same motions every few seconds or repeating a cycle of motions more than twice per minute for more than 2 consecutive hours in work day o Using input device such as keyboard or more in steady manner more than 4 hours
Goals of Ergonomics
o Safety o Efficiency (productivity) o Human comfort
Anthropometrics- designing for motion
o Select the major body joints involved o Adjust your measured body dimensions to real world conditions § e.g. relaxed standing/sitting postures, shoes, clothing, hand tool reach, forward bend, etc. o Select appropriate motion ranges in the body joints, § e.g. knee angle between 60-105 degrees § Avoid twisting, forward bending, prolonged static postures, and holding the arms raised
what length and bout of work is best for physiological recovery?
o Shorter work with shorter rest periods better physiological recovery and lower stress than longer with work rest ratio o Important for scheduling work: rest periods to maximize recovery and minimize stress
what is smallest and largest percentile length of muscle contraction and maximum muscle length
o Smallest possible contraction length: 60% resting length o Longest elongation: 160% of resting length o Maximum force at 120-140% resting length
root problems in ergonomics contributing to problem
o Source or problem o Workspace design o Work space o Tool design o Ex- bench too low, bad location of bins, improper tools
tertiary prevention
o Strategies to minimize post-injury effecs o Post-injury injury analysis o Immediate, long-term, and support counseling
APTA STATEMENT OF PT ROLE OCCUPATIONAL HEALTH
o The role of the physical therapist in occupational health includes examination and evaluation of individuals with work-related risk factor(s), impairments, activity limitations, participation restrictions, or other health-related conditions which prevent individuals from performing their occupational pursuits in order to determine a diagnosis, prognosis, and implement intervention as necessary. The examination includes the history, systems review, and tests and measures. The physical therapist in occupational health evaluates the data from the tests and measures to determine the diagnosis and prognosis, and to determine the interventions that will be utilized to alleviate the work-related risk factors
Personal Factors affecting strength
o Wide variability between people: strongest person 6-8 times that of weakest (Chaffin and Anderson, 1991) o Genetics o Body dimensions o Training o Motivation o Gender and age
work pulse men and women
o Work pulse <= 35 bpm for men and 30 bpm for women
design process anthropometrics
o Workspace and equipment design § Specify population § Accommodate users- 90% o Population § Statistical § People with common characteristics · Occupations · Geographical locations · Age groups
what is most common recommendation for lifting?
o bend knees, keep back straight and lift with legs; ALSO LEAST FREQUENTLY USED - tough older people with ROM - boxes not small enoguh to get between legs
what muscle groups strength declines most rapidly and most slowly
o handgrip and knee extension largest decline o trunk and elbow flexion least change
ergonomic task analysis: ineffective therblings
o not doing any work, slowing the system down § Search § Select § Position: place object in proper position for use § Inspect § Plan § Unavoidable delay § Avoidable delay § Rest to overcome fatigue § Hold: retention of object after grasp, with no movement
metabolic cost of work
o total energy spent doing work (job or task)- leters O2, Kcal
what in lift cycle are compressive forces highest?
start of lift
Global Corporate Challenge- the effect of presenteeism and absenteeism in workplace
§ Absenteeism- 4 lost days § Presenteeism- 57.7 lost days · Coming to work and working less than full capacity § Absenteeism- $150 billion § Presenteeism- $1,500 billion
work efficiency
§ All energy used for productive work · Heat (70%) · Static unproductive efforts § Efficiency= work output/ energy consumptoion x 100
skeletal muscle and work variables
§ Contraction type: static verse dynamic § Tension production: loading · External loading · Internal lading § Contraction velocity § Fatigue
Goals of ergonomic intervention
§ Give the body the best mechanical advantage § Manage the pacing and duration of the job tasks § Manage muscle fatigue, starting with the distal-most muscles used § Promote and maintain circulation § Consider the cognitive workload § Involve the workers in solution § Our bodies are designed to move
Anthropometric- horizontal and vertical reach in workplace
§ Horizontal reach: 5th percentile female elbow-fingertip length and shoulder-grip length (15.7" - 21.9") § Vertical reaches: 95th percentile male knee height and 5th percentile female shoulder height (47.8"-23.4" recommended frequent work zone 32.5")
ergonomic task analysis: risk prioritization
§ Identify job factors § Body region § Tasks associated § Frequency of task performance
o Ergonomic Job Analysis/ Evaluation
§ Is application of body of knowledge about human abilities, human limitations and other human characteristics that are relevant to design § Interventions is the application of that knowledge to the design of tools, machines, tasks, jobs and environments for safe, comfortable, and effective use
object effect size on lifting
§ Length § Impact MAWL (max acceptable weight) § Energy expenditure § Spinal stress: keep width as small as possible (vertical sheer/ compression increase with width), load COG moves further from L5/S1, light large objects >small heavy objects (due to distance from individual) o Shape- MAWL higher for bags than boxed o Load distribution/ stability: COG outside midline- lateral bending moment, vertebral rotation; shifting COG reduces MAWL (lifting limit) o Handle- safer and less stressful able to increase MAWL
what male and females dimensions typically vary and are greatest in populations?
§ Men greater in all except hip breadth and length of knee-buttock § Women exceed skin fold thickness § Soft tissue distribution: women greater fat proportion and central fat deposition
what are some assumptions in regard to lifting
§ SQUATTING (DEEP) is superior § Load close to body § Lower compression and shear forces § Uniform stress distribution
what are some some examples of work efficiency in tasks 1. shoveling 2. using heavy hammer 3. stairs 4. push cart 5. cycling 6. walking level
§ Shoveling 3% § Using heavy hammer 15% § Stairs: 23% § Push cart: 27% § Cycling 25% § Walking level 27%
ergonomic task analysis: objectives
§ list overall objectives of job/task analysis § identify personnel involved with the job being studies § develop a plan and identify interactions with other personnel § obtain support for study at level of the worker, supervisors, and management identify activities to be conducted, plan and timeline these activitie
ergonomic task analysis: job description
§ tools, materials equipment required § critical demands of the job § specific duties and tasks § what are the outcomes for evaluation § what behaviors, skills, knowledge and experience are most important § physical demand characteristics
ergonomic task analysis: job requirements
§ worker's description of what they do (body regions and physical stresses) § organizational factors § physical effort (Borg RPE 6-20) § type of work § frequency § worker's description of hazardous tasks
secondary prevention
· identifying and intervening in persons with risk factors for health events o Prevent other injurues in another area of body after they have had one already (ex- shoulder injury and don't want them to compensate and cause back problem) o Conducting workplace risk assessment o Injury management team can intervent when risk identified o Duty modifications
epidemiological triad
· interrelated triangle approach to assessing a job and the health conditions surrounding it considers three factors: o Person/worker->health, personality, arthropometrics o Environment-> physical, social, work demands o Task-> kinetic energy; what the indidivual does at his/her job
Primary prevention
· preventing adverse events in health individuals o Ex- eating healthy, exercising, no smoking o Developing and implementing policies and procedures o Coordinating employee assistance programs o Providing recommendations for environmental/ workspace design strategies to prevent injuries o Conducting research in workplace to reduce potential risk and prevent injuries
Anthropometrics
· the study of people in terms of their physical dimensions · The application of specific physical measurement techniques on human subjects in order to design standards, specifications, or procedures · Key factor that fits people into their workplace