Gene Lee Final
Ganglion is a Greek word meaning
"a knot of tissue."
MMH often produces
"overexertion"
Ganglions are often seen
-In and around tendons -In the palm of the hand -At the base of the finger
Heavy Work: Intensive work may place stress on all of the systems of the body including
-Muscular - extensive exertion -Cardiovascular - need to pump blood to muscles as work is performed -Respiratory - need to perform gas exchange -Nervous System - through needed innervation of muscles for required movements
The types of work that we've discussed include any combination of the following types of work
-Physical Work •Heavy•Moderate•Skilled -Mental Work
Foot rests
-Reduces fatigue and back-strain. -Relieves stress on legs, back and neck. -Promotes circulation in legs and feet. -Promotes proper posture and comfortable seating.
Anthropometry Measurement positions:
-Standing upright naturally (slumping effect) -Standing upright erect (2 cm difference) -Seated erect -Lying supine (tallest measurement)
What makes a task efficient?
-When the task is designed such that the physical and mental abilities of the body are commensurate with the physical and mental demands of the task. -The most appropriate muscle groups are used for task performance -A refresh rate is such that it permits the muscles to consistently recharge for optimal task performance
Design Applications of Anthropometry
-Workplace design -Equipment design -Hand tool design -Product design
The anthropometrics associated with rotation or motion for a joint include
-extension -flexion -abduction -adduction
Alternative names of Cumulative Trauma Disorder (CTD) include
-repetitive strain injuries (RSI) -Work Related Muscular Skeletal Disorder (WMSD) -various other terms
Types of Anthropometric data:
-segment lengths -segment mass, volume, weight, density -segment center of mass -range of motion -strength capabilities
Any useful model of MMH should include the following parameters:
1) Body Weight of individuals doing the task (range) 2) Weight of load 3) Vertical start and end positions of a lift 4) dimensions of the load 5) frequency of handling 6) *gender
Primary Causes of MMH Back Injuries
1) Overexertion - Lifting loads that are too heavy or at improper heights. 2) Improper lifting - Lifting done that's not in the saggital plane 3) Fatigue - Not allowing adequate recovery from exertion in order The question that persist in industry is HOW MUCH CAN PEOPLE LIFT SAFELY?
Flaws in the Assumptions of 1981 NIOSH Guide
1) Two handed lifting 2) Lifting in the sagittal plane (in front of the body) - no twisting 3) Good handholds 4) Balanced load 5) Less than 30 inches in width 6) Good footing 7) Good environment (humidity, temp, etc.) 8) Unrestricted posture. -The assumptions that are most frequently violated are WHAT??
Data Collection Procedure
1. Determine the applicable body parts 2. Determine the user populations 3. Determine the percentile to consider 4. Calculate the appropriate dimensions 5. Determine the range of adjustability
Design rules
1. Use data for the primary user group 2. Design for universal operability•reach distances, clearances, etc. 3.Design to accommodate a large range of users (90-95%) - except in certain cases 4.Design for extreme individuals
Overexertion injuries of all types in the US occur at a rate of about
500,000 workers per year (1 in 20 workers)
Percentage of people in physically intensive tasks that have suffered back problems.
60 - 70%
Assuming normality, 90% CI:
= mean + 1.65 standard deviation
Assuming normality, 95% CI:
= mean + 1.95 standard deviation
While working at home,
Allow room for a computer, telephone, fax or other necessary equipment. File space may also be needed. Do not try to use the kitchen or dining table.
The Most Common CTD:
Carpal Tunnel Syndrome
Most important piece of furniture for home/office Ergonomic design is the
Chair; Consider the type of chair that the individual is using, lumbar support, foot rests.
Intersection Syndrome and Dequervain's Syndrome
Chronic inflammation of the tendon and muscles on the side of the wrist and the base of the thumb.
Carpal Tunnel Syndrome
Common and troublesome condition that interferes with the use of the hand
Assessment of Energy Expenditures: Direct Measure
Direct: computerized measurement of gas exchange - using computers, mouth pieces, etc.
Estimating % of Energy Required •Percent Heart Rate Change
Energy Required is correlated to the % Change % Change = (HRtask - HRrest ) / ( HRmax - HR rest)
__________ are used to obtain lengths, widths, breadths, and joint angles of the human anatomy
Expensive anthropometric tools
Task-Related CTD Risk Factors
Force Frequency Awkward Joint Posture Vibration Excessive Grip or especially Pinch strength (5 times grip) Extreme temperatures Long work shifts w/o work breaks
Confidence Intervals
Generally Confidence intervals (CI) are established which attempt to accommodate 95% or 90% of the population (counter top).
Moderate Work
Generally characterized by exertions that do not exceed 40% of the workers muscular capability or aerobic capacity May include: -Light assembly work -Some material handling
Light Work
Generally involve mild physical exertions to perform a physical task These task may include -Various activities in the office environment -Monitoring tasks
In the physics definition of work (W = Fxd) - true work takes place only when there is displacement of a given weight.
In the occupational sense, work will be defined as the expenditure of measurable (subjective or objective) human resources for a given activity.
Tenosynovitis
Inflammation of the sheath surrounding the tendon (tendinitis of the tendon sheath lining)
Skilled Work
Involves the use of cognitive abilities in conjunction with physical work (generally light to moderate) to perform a learned task. These activities may include -Welding -Soldering -Computer Technician work -Keyboard or computer work
It is also important to consider rotation of joints
It is also important to consider rotation of joints
Environmental Factors include
Lighting and noise
the primary cause of back related injuries in occupational settings
Manual Material Handling Tasks
Ergonomic Mouse
Reduces unnecessary repetitive finger and hand movements. Reduces excessive load on fingertips. -- By reducing pinch force, the user can reduce the risk of Carpal Tunnel Syndrome.
•There are several models to predict the energy costs of various types of MMH tasks. •Although each of the models have disadvantages and advantages it is important to exercise caution when using a model for predicting work load.
SQUAW MMH SQUAW
CTS: IMPACT IN INDUSTRY•115,400 Reported cases of CTS in 1988 (5 times as many as in 1981)•48% of the victims were unable to return to work•Average rate of CTS in general industry -0.8 cases per 1,000 workers•Average rate in high risk industry -15% to 20% of employees
SQUAW SQUAW CTS SQUAW
The body is an engine that provides muscle power to perform work.
SQUAW TRUE MUSCLE POWER SQUAW Basically, the body uses oxygen, which enters through the lungs, to burn fuel, which has entered through the digestive system. The energy is converted into the kinetic and chemical energies required for sustaining body functions. This conversion is know as METABOLISM.
Pushing is generally easier on your back than pulling. Use your arms and legs to provide the leverage to start the push.
SQUAW pushing
Tendinitis:
Tendon disorder caused by inflammation of the tendon and its sheath
Energy Consumption is measured in kilojoules (1 kCal = 4.187 kJ)
The amount of energy consumption is indirectly measured by measuring the oxygen consumed in the body (1 liter of oxygen is consumed in the human body for a turnover of 20 kJ of energy: know as the calorific value of oxygen)
Usually, snapping and clicking in the finger occurs with this disorder
Trigger finger; occasionally, a digit will lock either fully bent or straightened
Circumference
a closed measurement that follows a body contour
Ergonomics in the office should be viewed as
a continuous improvement process
If your job involves heavy labor or manual material handling, you may be in
a high list category
Reach
a point-to-point measurement following the long axis of the arm or leg
Distance
a straight line, measurement between landmarks on the body
Trigger finger is caused by
a thickening on the tendon catching as it runs in and out of the sheath.
Resting pulse:
average heart rate before the work begins
Working pulse:
average heart rate during the work.
It is very important to remember that anthropometric guidelines represent
averages of populations and that this information should simply be used as a gage not as a hard and fast rule - -Be prepared for occasions that are exceptions.
Primary complaint of sedentary workers is
back problems.
Ganglion Cysts are
balloon-like sacs, which are filled with a jelly-like material
Physical anthropology is concerned with
body characteristics of individual persons or groups
The causes of CTD are
complex and no single factor can be identified
Carpal Tunnel Syndrome results from
compression of the median nerve within the wrist area
Work pulse:
difference between the resting and working pulses.
Anthropology is the science concerning
human and their biological and social aspects
Anthropometry is a branch of physical anthropology dealing with
human body measurements, including - body size - range of movement - muscle strength
Split Ergonomic Keyboards are designed with separated left/right keys to
improve arm positioning and relieve neck and shoulders, providing a neutral posture.
Measurement of oxygen uptake during a given task can be used where the subject
inhales air from the atmosphere and exhales it through a mask connected by tubing to a large brown bag (Douglas bag). After the empty bag is filled with expired air the test is terminated. The oxygen content of the air in the bag can be compared with that of the atmosphere to determine the amount of oxygen metabolized by the subject. If the time taken to fill the bag is known, the subject's rate of oxygen uptake can be calculated. Also if oxygen content of expired air can be determined, amount of oxygen used and the amount of energy generated can be determined.
Manual Material Handling
involves any type of manipulation of an object or load. Manipulation may be in the form of pushing, pulling, lifting, or adjusting.
Curvature
is a point-to-point measurement following a contour
The human is / is not not a very efficient animal in terms of mechanical work.
is not For instance about 30% of energy consumed is turned into mechanical work and the remaining 70% is turned into heat.
In fact low back pain is recognized as
leading cause of morbidity and lost productivity in the workforce today.
The operating space of a limb is a factor of its
length and the angle of rotation of its joint
Approximately 2/3's of overexertion injury claims involved
lifting loads
Overexertion was claimed as the cause of
lower back pain by over 60% of people suffering from it.
The amount of muscular work performed can be assessed by
measuring the amount of oxygen used.
CI are based on
normal distributions and the old empirical rule.
Anthropometry is a branch of
physical anthropology
Ergonomic Keyboards are designed to
promote proper posture of the forearm and hand via •Fitting natural contour of the hand and fingers •Reducing pressure required for key activation
While sitting, the feet should be able to
rest firmly and flatly on the floor or foot support as to reduce the amount of pressure on the thighs
Height
straight line, point -to-point vertical measurement
Depth
straight line, point to point horizontal measurement running fore-aft the body
Breadth
straight line, point-to-point horizontal measurement running across the body or a segment
Problems of heavy work are generally seen in
strength intensive tasks such as firefighting, construction working, etc. This type of Work is limited by energy consumption and cardiac capacity.
Total recovery pulse (recovery cost):
sum of heart beats from the end of work until the pulse returns to its resting level
Total work pulse (cardiac cost):
sum of heart beats from the start of the work until resting level is restored.
Work efficiency is severely inhibited by work spaces which challenge
the anthropometric limitations of employees.
Effective office ergonomics produce a work area that is
the appropriate work height and supports the limbs for task performance
Manipulation of a load, even a light weight, may cause a strain because
the body is required to stretch, bend, twist, or straighten using fingers, arms, trunk, and/or legs.
Leg support is critical to distribute and reduce the load on
the buttocks and the back of the thighs.
The primary areas of physiological and biomechanical concern for MMH has been
the lower back, specifically the disks of the lumbar spine. However, this is not the only region of the back that can be negatively effected by inappropriate or excessive MMH
To construct a confidence interval you must first know
the mean and standard deviation for a data set:
Carpal Tunnel Syndrome occurs when
too much pressure is put on the median nerve that passes through the wrist area
To Prevent Shoulder Problems
work with the hands near the waist level and close to the body •If the hands have to be positioned above shoulder level, their -elevation above the shoulders should be no more than 35 degrees. -Hand loads should not exceed 0.4 kg and the posture should be held for no more than 20 seconds for each work minute -select taller workers for workplaces that can not be modified
Anthropometric Planes:
•1. Coronal (Frontal) Plane - the plane dividing the body into equal/unequal front and back parts. -The terms anterior and posterior relate to this plane •2. Medial (Lateral) Plane - the midline plane dividing the body into left/right halves. The terms medial and lateral relate to this plane •3. Transverse (cross horizontal) Plane - the horizontal plane that divides the body into upper (cranial) and lower (caudal) parts. -The terms superior and inferior relate to this plane. •4. Oblique Plane
The empirical rule states that approximately
•68.76 % of the data set will be within 1 s.d. •95.65 % of the data set will be within 2 s.d. •99.73% of the data set will be within 3 s.d.
1991 NIOSH Lifting Guide
•A decade later, NIOSH revised the technique for assessing overexertion hazards of manual lifting. •The new document no longer contains two separate weight limits but has only one •Recommended Weight Limit (RWL). •It represents the maximal weight of a load that may be lifted or lowered by about 90 % of American industrial workers, male or female, physically fit and accustomed to physical labor. •This new equation resembles the 1981 formula for AL, but includes new multipliers to reflect asymmetry and the quality of hand-load coupling. The 1991 equation allows as maximum a "Load Constant" (LC) - permissible under the most favorable circumstances -- with a value of 23 kg (51 lb.) •RWL = LC*HM*VM*DM*AM*FM*CM •LC - load constant of 23 kg or 51 lb. •** Each remaining multiplier may assume a value [0,1]
Factors Affecting ROM:
•Age-decreases very slightly between 20 &60 •Gender-Female exceed male in all joints except the knee •Race-no concrete data available •Body build-slender body has a wider ROM than obese one •Exercise-exercise increases ROM •Occupation-can increase ROM •Fatigue-restrict ROM due to motivation and muscle strength •Joint/nerve disease-can restrict or immobilize •Right vs left-little variation, small difference in arm rotation •Body position-adjacent or neighboring body parts can affect ROM •Clothing & personal equipments
Home / Office Ergonomic Tools
•Arm / Wrist Support •Ergonomic Computer Equipment- Ergonomic Keyboard- Ergonomic Mouse- Anti-Glare Screen •Arm Rests-Shoulder muscles remain relaxed. -Comfort in back, shoulders, neck, elbows and wrists. •Wrist Rests-Wrists kept in neutral position on soft cushions. -Wrist support reduces pressure on the wrist and minimizes lateral deviation. •Ergonomic Keyboard•Eliminates awkward postures of the hands, wrists and arms. •Allows the wrist to remain in neutral posture
Desk should
•Be approximately 26" in height and at least 24" deep, •Allow sufficient leg clearance •Rounded edges on desk
Factors Affecting Muscle Strength:
•Biological-age, gender, race, body build/position, handedness, fatigue, exercise, health, diet, drugs, diurnal variations •Environmental- altitude, acceleration •Psychological-motivation, emotional state •Occupational-occupation, clothing/personal equipments, workspace
Symptoms of Carpal Tunnel Syndrome
•Burning •Tingling •Numbness •Loss of muscle strength •Difficulty grasping objects •Pain
Biomechanical Approach to MMH
•Determines what a person's biomechanical system can physically do •Attempts to establish the physical stress imposed on the musculoskeletal system during a lifting action •Stresses serve as the criteria upon which the capacity of lift is based
Physiological Approach to MMH
•Determines what a person's cardiovascular system can physically do •several criteria such as oxygen consumption, heart rate, pulmonary ventilation volume or percent of physical work capacity, can be used as indices of heaviness of work performed •Energy expenditure while lifting loads serves as the criteria
some useful guidelines to prevent CTD include the following
•Engineer products to allow machinery to do highly repetitive tasks; leave more variable task to human operators •Spread the load over as many muscle groups as possible to avoid overloading the smaller muscle groups •Design tasks to permit gripping with the fingers and palm instead of pinching •Avoid extreme flexion or extension of the wrist. •Design work surface heights, orientations, and reach length to permit the joints to remain as close as possible to their neutral positions for maximum muscle strength. •Keep forces low during rotation or flexion of the joint. •Use power assists is forces are high. Avoid repetitive gripping actions •Provide fixtures to hold parts during assembly so that awkward holding postures can be minimized. •Provide a variety of tasks over a shift, if possible •Minimize time or pace pressures •Give breaks •Reduce finger movement-The control of finger movement depends on many small muscles which can easily become fatigued, particularly during prolonged work with inadequate rest breaks. •Of particular interest is the posture of the shoulders, elbows, and wrists in during the work tasks and throughout the work shift
Anthropometric Tools
•High Tech Scanners •Photometric equipment •Hand Tools -Anthropometers - Straight link measurements -Calipers - Contoured surfaces -Measuring Tapes - Circumference measurements
Work Practices Characteristics
•Individual: -Measure of operating practices under the control of the individual worker •Organizational: -Measure of work organization such as plant size, medical staff, utilization of team work •Administration:-Measure of administration of operating practices - work safety incentive system.
Skilled work
•Just as with the design of machinery, the workplace should be designed as to allow for the most efficient operation of the human system. This is especially true in material handling tasks, lifting tasks, and control tasks. •To evaluate the effect of system efficiency, the characteristics of two aspects of the work environment, the human system and the external force or environment being acted upon, need to be looked at.
High risk occupations for CTS
•Keyboard & Data entry operators •Computer programmers/operators •Grocery store clerks •Meat packing/processing operators •Small parts assemblers/manufacturers •Carpenters •Sewing Machine Operators
Material/Container Characteristics
•Load - measure of force, pushing/pulling •Dimensions •Distribution of Load•Coupling - handles •Stability of load - e.g. location
Ergonomic Seating Requirements
•Lumbar support •Chair with a waterfall edge •Armrest •Slightly tilted seat pan (promotes proper posture) •Adjustability
Median vs Sagittal
•Median plane - the midline plane dividing the body into left/right halves. •Sagittal plane - the plane dividing the body into unequal left and right parts and parallel to the median plane.
Benefits of Efficient Task Performance?
•Minimize likelihood for injury •Increased output •Higher job satisfaction •Promotes effective ergonomics
Distribution of Work
•No arm or hand should be overused •This is often a tendency when workers are given the opportunity to set up their work areas; •Tendency is to overuse the dominant hand.
Worker Characteristics
•Physical - e.g. age, sex, anthropometry •Sensory - visual, auditory, or tactile senses •Psychomotor - measure of worker capability •Personality - e.g. risk taker •Health Status - previous injuries, fitness level •Leisure time activities
Tilted Seat Pan
•Promotes proper posture, particularly in the lower back
Factors Affecting Human Body Size:
•Race: individuals differ significantly •Age: maximum at 25-30 yrs, gradually decreases •Gender: female smaller than male counterparts •Occupation: heavy manual work vs office work •Long-term changes: WWI<WWII<Korean War •Clothing & personal equipment
Principles of Prevention of CTS
•Reduce Force -Reduce weights lifted or use mechanical aids -Keep loads as close to the body as possible -Reduce pulling and pushing forces •Improve Posture -Keep the natural curve of the spine intact -Lift loads at about waist height -Eliminate twisting motions -Avoid bending over continually •Reduce Repetitions -Eliminate unnecessary lifting -Improve material handling systems
Injury Prevention is accomplished by
•Rest Breaks -small muscles which can easily become fatigued, particularly during prolonged work with inadequate rest breaks. •Exercise -Stretching and light aerobic exercise -Joint Posture - Prevention of Upper Body Disorders•Of particular interest is the posture of the shoulders, elbows, and wrists during the work tasks and throughout the work shift.
Definitions for Heart Rate Values used in Assessment
•Resting pulse •Working pulse •Work pulse •Total recovery pulse (recovery cost) •Total work pulse (cardiac cost)
Waterfall Edge
•Results in termination of seat in back of thigh or lower leg •Prevents the obstruction of blood flow to the lower extremities
Categories in Office Ergonomics
•Seating •Desk/Work Area •Ergonomic tools •Environmental Factors
Lighting
•Should be adequate for reading, writing and computer use. •Both natural and artificial light should be directed to the side and behind the line of vision, not above or in front of it. •Use indirect lighting whenever possible
Effects of Carpal Tunnel Syndrome
•Significant median nerve sensory loss and motor loss •Muscle atrophy •Permanent nerve damage •Pain and discomfort
Divisions of Anthropometry:
•Static anthropometry-static body measurements, applications include seats design, furniture design, equipment design, etc •Dynamic anthropometry-operational measurements, applications include controls of equipments/ machines, reach envelope
Indirect Measures of Energy Expenditure include:
•Subjective measures of physical effort. - Borg RPE Scale ranging from No exertion at all to Maximal exertion. •Heart rate: -Change in heart rate -Continuous -Intermittent
Anatomical Directions/Positions
•Superior •Inferior •Anterior •Posterior •Medial •Lateral •Proximal •Distal
Lumbar Support
•Support for the lower region of the back •Promotes proper posture •Minimizes the load on the lower back
Common CTD's of the Upper Extremity
•Tendinitis •Tenosynovitis •Intersection Syndrome •DeQuervain's Syndrome •Trigger Finger •Thoracic Outlet Syndrome •Ganglion Cysts •Carpal Tunnel Syndrome
Anti-Glare Screens
•The long-term effects of monitor use include: eyestrain, fatigue, blurred vision, and headaches all result from working at less-than-perfect monitors and result in discomfort and lowered productivity. •Minimizes screen flicker. •Improves image resolution and has anti-radiation features.
Psychophysical Approach to MMH
•The premise of this approach is that people integrate and combine both biomechanical and physiological stresses in their subjective evaluation of perceived stress. -In this approach subjects are allowed to adjust a load to the maximum amount that they feel they can sustain without strain or discomfort and without becoming unusually tired or out of breath. -The maximum selected is called the maximum acceptable weight limit (MAWL) of the load •This is considered one of the most appropriate methods for establishing criteria for MMH tasks.
What can we do to minimize MMH related injuries
•Understand •Measure •Control
Work Area Layout
•Vertical Work Envelope-A semi-circle of radius •comparable to 65 cm above shoulder height for men and 58 cm above shoulder height for women •occasionally exceeding this by 15 cm is acceptable. •Horizontal Envelope-Rule: put the items that are used most frequently closest to you: 35 - 45 cm •distance is consistent with the range of forearm & hand -Put tools that are not used as frequently at 55 - 65 cm
Other Regions Impacted by MMH
•When considering the musculoskeletal structures within the trunk a variety of elements may be individually or collectively strained. •Tension strains can be in the form of linear elongation, or of bending movements or twisting torque •Shoulders and arms can also be impacted by MMH
Classification of MMH Characteristics
•Worker characteristics •Material/container characteristics •Task characteristics •Work Practices
Task Characteristics
•Workplace geometry - spatial properties of the task •Frequency/duration/pace •Complexity: measures of combined or compounding demands of the load; precision •Environment - noise, temperature
CTS: TREATMENT
•Wrist splints •Steroid injections •Anti-inflammatory agents •Rest •Surgery •Therapy / Exercise
Fudge factors not accounted for in direct anthropometric measurements
•heels of shoes •clothing •gloves, helmets, coats, etc.
