Test 2Lectures 9-15

Lecture 9Physiology- Fueling and cooling system: blood vessels

o Food = Fuelo Combustion of fuel takes place with oxygeno Combustion yields energy for mechanical movement

- Blood vessels move supplies (oxygen, carbs, fat derivatives) to combustion sites (muscles and organs)

- Blood vessels move byproducts out (lactic acid, CO2, water, heat) for dissipation by skin and lungs- Respiratory System: provides oxygen for metabolism and dissipates byproducts

o Moves air to and from lungs (some absorbed into blood stream)o Removes CO2, water, heat from blood into air for exhaleo Air inhaled and exhaled by pumping thorax via muscles connecting ribso The volume of air exchanged in the lungs depends on the requirements

associated with the work being performedo Vital capacity: maximal inspiration

Is a function of age, training, body size, position, gender Females have 10% less than males Untrained people only have 60-80% the capacity of athletes

o Residual capacity: amount of air left when forcing an expirationo Vital + Residual = total capacityo Pulmonary ventilation: movement of gas in/out of lungso At rest we breath 10-20 times/minuteo Light exercise: tidal volume increased, not frequencyo Hard exercise: tidal volume and frequency increases

- Circulatory System: carries oxygen from lungs to cells that use and removes metabolic byproducts (CO2, heat, water) (works in a closed loop)

o Body’s transportation system for blood and cardiovascular system o Takes away by-products: CO2, water, heato Blood

Red blood cells take oxygen to tissue and remove CO2

White blood cells fight germs and infection Plasma is solution in which blood cells are held Platelets stop bleeding

o Atrium and ventricle: in left and right halves of hearto Blood flows from atrium to ventricleo Chambers DO NOT send blood back and forth o 2 Circuits of blood circulation

Systemic System (left to right): Blood with oxygen and nutrients passes through the left atrium, pumped out of the left ventricle, flows through arteries/capillaries to muscles/other organs, come back to heart through veins

Pulmonary System (right to left): blood with CO2 comes in from the right atrium, is pumped out of right ventricle through two arteries (one for each lung) so CO2 is exhaled, and blood re-oxygenated

Returns to left atriumo Capillaries: transport blood into muscles, if muscles need more blood, blood

vessels dilate, if other organs need blood capillaries are constricted

o Blood supply: Quickly distributed as necessary for proper muscle and organ function through blood vessel dilation and constriction

Muscles over digestion, skin over muscleso Heart response to work

Increase stroke volume – effective for moderate work Increase heart rate – once stroke volume is maxed, increasing heart

rate is main way to increase cardiac output At rest about ½ of the volume in the ventricle is ejected, other ½ stays

in the heart At rest, output of adult is about 5L/min During heavy work, can raise to 25L/min

- Metabolic System: supports chemical processes in the body that yield energyo Energy inputs are nutrients (food and drink)o Energy released through metabolism, process of yielding energyo Energy measured in joules (J) or calories (cal

4.2J = 1cal 1J = 1Nm

o Basal metabolism: energy to functiono Resting metabolism: without worko Work metabolism: due to additional energy needed to work

Physical Work- Only possible when there is energy to support the muscular effort needed- Energy required for muscular effort comes from nutrients being metabolized in

presence of oxygen (aerobic metabolism) or without oxygen (anaerobic metabolism)- Workload: Ratio of capacity to demands

o Physiological, physical, mentalo Workload is the energy required by the body to do worko Energy expenditure rate of work is linearly related to oxygen consumption and

heart rateo Three ways to measure workload

1. Oxygen consumptiona. Linear relationship between oxygen consumption and energy

expenditureb. For every liter of oxygen consumed a person releases on average

about 4.8kcal of energy2. Heart rate

a. # of heart beats per minuteb. Highly correlated with oxygen consumptionc. Easier to measure than oxygen consumption, but not as reliabled. Often measured using portable telemetry device while worker

wears a set of electrodes on chest3. Borg Ratings of Perceived Exertion (RPE)

a. Scale from 6-20b. 6 being no exertion at all, 20 being maximum exertion

NOTE: All measures could be affected by heat, humidity, psychological stress, cognitively complex work, noise

Whole-Body Capacity- Maximum physical work capacity (MPWC)

o Maximum rate of energy productiono Short-Term Work Capacity (aerobic capacity or VO2max)

Maximum expenditure for a few minuteso Varies as a function of duration

- Whole body fatigue is experienced with 8-hour energy requirements exceed 33% maximum (30-50% of aerobic capacity)

- Occurs because body cannot consume enough oxygen to keep up with energy requirements

- The potential for fatigue is based ono Effort levelo Effort timeo Recovery time

- Indicators of fatigueo Slight tirednesso Wearinesso Exhausted (difficulty staying awake)o Worn outo Reduced muscular performance

- Engineering controls to reduce fatigueo Redesign jobo Provide job aidso Design for the least fit

Physical loads that are within strength and endurance capacities for 5% female

o Provide accommodations Conveyor belts to reduce carrying Automated material-handling devices to reduce lifting

o Rest break as a fraction of total work time = (PWC-Ejob)/(Erest – Ejob) PWC – physical work capacity of the workers Ejob – energy requirement for job Erest – 1.5 kcal/min

o Resulting fraction is multiplied by 8hrs to determine total break time in a shifto Preferably divide total break time over course of 8hr shift

Lecture 10Simplified Anatomy

- Bones: internal framework- Muscles: generate force and movement- Ligaments: connect bones - Tendons: connect muscles to bone- Joints: degrees of freedom to move, synovial fluid, types: ball and socket and pivot- Cardiac: your heart, only self-exciting muscle in the body, don’t have to tell it to beat- Smooth: digestive muscles, not under voluntary control, anything close to gut - Skeletal: under voluntary control, tell them when/how to move- Muscles

o Each muscle is made up of thousands of muscle fibers surrounded by connective tissue, blood vessels and nerve fibers

o Generates force and produces movemento Contraction of muscles allows bones to act like leverso Muscles can also perform eccentric contractions when they are lengthened

involuntarily (when you hold something too heavy and your muscles start to give away)

- Muscle Fibers:o Each fiber is made up of parallel cylindrical myofibrils (each fiber is like needles

and threads)o Myofibrils are made up of sacromeres (cross sections) which form a repeating

pattern along the length of the myofibril

o Sarcomeres are the contractile units of skeletal muscle. You can tell if your muscles are contracting or expanding by seeing if the sacromeres are getting smaller or larger

- Muscular Effort - Dynamic (moving)o Rhythmic alternation between contraction and relaxation of muscleso Muscle acts as a pump to the blood circulationo Continuously supplied with sugar and oxygen, and waste products are removed

- Muscular Effort - Static (needs a lot of blood but doesn’t get a lot)o Prolonged state of contraction (postural stance)o Muscles are tense, not relaxedo Blood vessels compressed and blood no longer flowso Muscle does not receive sugar or oxygen, waste products not removed

- Muscle Fatigue: o Influenced by strength and contraction time – not enough recovery timeo Leads to oxygen deficit, lactic acid build up, waste build up/no nourishmento Controlling muscle fatigue

Allow for strongest posture Minimize static muscle loading Provide handles for carried objects (reduce moment arm) Rest breaks Job rotation

How the back works- Spine is the major support structure, reaching from neck to hip area- Spine: series of separate bones (vertebrae) 24 total, 7 cervical, 12 thoracic, 5 lumbar,

and sacrum and tailbone - Discs: separate vertebrae

o Help to cushion spinal loadingo Compression, flexion, lateral bending, torsion

- Spine houses and protects spinal cord - The muscles of the back and of the stomach support the back in different postures and

create motion- All movements of the back require muscular effort- Natural position of spine is S-shaped- Types of curves in spine

o Cervical Lordosis: inward curve at the neck o Thoracic Kyphosis: outward curve at the mid backo Lumbar Lordosis: inward curve at lower back

- Standing: lordotic (inward)- Sitting: kyphotic (outward)

o Advantages: rest your legs, don’t need as much blood flow (muscles recover)o Disadvantages: curve of spine, disrupts organs

- The neck contains top 7 vertebrae (cervical) o Each vertebrae move a little over 10 degrees to move side to sideo Your neck can move 90 degrees in each wayo The position and movements of the neck are controlled by a complex of about

three dozen muscles which attach from the skull and cervical vertebrae to bones all around the base of the neck

Working of the arms and hands- Upper arm controlled by shoulders and forearm- Holding arms without support requires static effort gives way to fatigue- Forearm controls finger and hand movement (these muscles connect via tendons from

elbow to wrist)

-- Abduction: move body part away from midline- Adduction: move body part towards midline- Flexion: bend towards body, make smaller angle- Extension: away from body, larger angle- Medial: inward toward midline of body- Lateral: outwards away from midline of body

- Supination: face up- Pronation: face down- Torque = moment arm (meters) X load (newtons)

o Reduce either moment arm or load to decrease torque o B is worse

Lecture 11 & 12

Anthropometry – the science of measurement of body size- Anthrop(s) – human- Metricos – of or pertaining to measurment- Variability in dimensions comes from

o Ageo Gendero Race and ethnicityo Generations

- Where to find the datao Civilian and military databases, other bookso US military: problem: gender and race/ethnicity

- Types of data:o Structural: measures while body is static, not movingo Functional: measures while body is doing some work (reach)

- Some body dimensions are highly correlated, stature and leg length - Determine the user, body dimensions, percentile range and population (let the small

person reach and large person fit)- Design Principles:

o Custom fit individual (near impossible)o Several fixed sizeso Make it adjustable (fit 5% Female to 95% male)o Design for extremes (escape hatch -100% F, brake pedal width 50% length

5%F, control knob 5%F, stretcher 99% M)o Select persons whose bodies fit the last design (last resort)

- Principle of adjustability to design or redesigno When you need to accommodate a range of users, and fit depends on

adjustment- Principle of adjustability to accommodate

o Adjust worker position relative to workplace (height adjustable chair to make reaching easier, platforms)

o Adjust work piece (life tables, jigs, pallet jacks)o Adjust the tool (adjustable length handles)

- Principles for designing for extremeso When a minimum or maximum allows everyone else to be accommodated

(doorway clearance – 95% male stature)- Average

o This is done to save money (the idea is that most people won’t be too uncomfortable)

- Americans with Disabilities Act of 1990: requires design accommodation’s for less able, accommodate wheel chairs

Lecture 13Manual Material Handling (MMH)

- Most significant cause of back problems- Back Problems

o Increased muscle fatigue to hold postures for long timeo Flattening of the lower back when we sit downo Discs may degenerate and lose their strength (flattened)o Allows nerves to be strained and pinchedo Unnatural postures speed up deterioration of discs

MMH Tasks- Biomechanical

o Calculate force on body joints (especially low back L5/S1)o Design for 5% strength capacity of compressive forceso Good for occasional lifts

- Physiologicalo Calculate energy consumptiono Design for least fit person – 33% VO2maxo Good for MMH over shifto We can measure energy consumption in three ways

1. Oxygen consumption2. Borg scale3. Heart rate

- Psychophysicalo Subjective evaluation of strengtho Maximum load with out strain, discomfort, fatigue = Maximum acceptable

weight of load (MAWL) o Design for %5 female MAWLo Good for occasional and over shift

- MAWL Tableso Maximum acceptable weight load increases with horizontal distance, increases

with lift distance, increases in walking distance, and varies depending on lift locations and frequencies

o In these tables they are using horizontal distance (box from body), distance of lift, and frequency (one time every eight hours, etc.)

- Lifting – most dangerous MMH activityo Correct way to lift is straight-back, bent kneeo If load can’t fit between your knees, stoop or freestyle is better. Stoop requires

less energy than straight back lift because less muscles- Object Characteristics for lifting

o Size – influences forceso Shape – bags have higher MAWL because they are carried closer to body and

require less forceo Stability – center of gravity outside centerline is BADo Handles

- NIOSH lifting equation: calculate RWL (recommended weight limit)o National Institute for Occupational Safety and Health (NIOSH)o Used for lifting tasks: two hands without mechanical assistanceo DON’T USE: one hand, over 8-hours, wheel barrow/person (assistance),

carrying/pushing/pulling, seated/kneelingo RWL: weight of load could be performed during 8hour shift with low risk of

back paino RWL= LC x HM x VM x DM x AM x FM x CM

LC – Load Constant Metric: 23kg. US: 51lb.

HM – Horizontal Multiplier Distance of the hands away from the midpoint of ankles

VM – Vertical Multiplier Distance of the hands above floor

DM – Distance Multiplier Distance between object’s starting point and ending point

AM – Asymmetry Multiplier Twisting of the body, looking straight ahead is zero and

twisting up to 90deg FM – Frequency Multiplier

How often the object is being lifted CM – Coupling Multiplier

The quality of the hand to object coupoling – handles are besto Lifting index (LI) = Load Weight (L)/ RWL (goal <1)

LI provides a relative estimate of the level of physical stress associated with a particular manual lifting task

If LI is greater than 1, redesign because we don’t know who is going to be doing the task. This represents increased risk of low-back pain and injury for some workers. Wickens calls this the Action Limit (AL). If LI is over 3, you must redesign. It represents high risk of low-back pain for most workers. Wickens call this the maximum permissible limit (MPL)

o Healthy workers refers to workers who are free of adverse health conditions that would increase their risk of musculoskeletal injury

- Engineering Controlso Reduce weight of objectso Allow pushing or pulling instead of carrying o Lift/carry aidso Improve NIOSH multipliers o Decrease distance of box from body

- Controlling MMH Problemso Work/rest scheduleso Job rotationo Worker selectiono Training – weak but criticalo Back belts do not work

Lecture 14Neck Strain

- Even in the upright position, there is a constant tension on the muscles of the neck to keep the head balanced vertically

- Psychological stress contributes to neck muscle tension- Loads to the shoulder are transmitted to the neck muscles

Causes of neck strain- Placement of work materials- Arm posture- Visual problems

Rules for avoiding neck strain- Avoid high frequencies of extreme twists or tits of the neck and head- Avoid long period of fixed postures of the head and neck- Periodically support the arms or wrists- Posture of the neck should be so that the gaze angle is in the range of 5-20 degrees

Shoulder strainCauses of shoulder strain

o Jobs involving repeated or prolonged abduction of the armsSolutions

o Keep the upper arms close to the bodyo If repeated or prolonged extensions, flexions or abductions of the arms are

required, armrests or palm rests may relieve some of the stressElbow strain

- Unhealthy posture: elbow bent, like in typing posture- Tension is around the ulnar nerve that wraps around the elbow- There is little protection of the ulnar nerve from external forces (such as resting on a

hard surface)

- Lateral Epicondylitis: Elbow tendon disorder where there is radiating pain from elbow down to forearm caused by tendon strain (tennis elbow). Throwing motions.

Wrist strain- Unhealthy postures

o Hands bent backwardso Hands bent outwards

- Compression of the contents of the carpal tunnel (tendons, nerves and blood vessels) may damage the median nerve

Wrist tendon injuries- Tendon tear = strain- Some tendons are surrounded by a sheath- Sheath has lubricant called synovial fluid- With overuse synovial fluid may be reduced, causing friction between tendon and sheath

(inflammation)Carpal Tunnel Syndrome

- 9 tendons and the median nerve are running through the carpal tunnel- Unnatural postures combined with high frequency and/or high forces can lead to tendon

swelling and compression of median nerveRisk factors associated with hands/wrists problems

- Poor postures that constrict the carpal tunnel pathways- High force- Pressure resulting from repeated contact on hard surfaces or sharp edges- High repetition

Vibration Syndrome: (aka white finder/Raynaud’s syndrome)- Finger blanching due to close of finger arteries- From forceful gripping of vibrating tools

Vibration- Two major types of vibration exposure

o Whole body vibrationo Hand-arm vibration (HAVS)

- Controlling hand-arm vibration exposureo Select tools with lowest vibration o Maintain toolso Damping gloveso Minimize grip forceo Alternate tasks: vibrating -> non vibratingo Limit daily use of vibrating toolso Long rest breakso Limit number of days tools are usedo Add springso Increase stiffnesso Reduce velocity

Controls of arm/hand disorders- Support or rest the arms and hands- Avoid highly deviant arm and hand postures- No hard or cutting edges of chair, table and work surfaces- Varied tasks in terms of motion patterns- Rest breaks

Work Systems and Hand Tools- Ulnar Nerve (blue) out side of hand, pinky/half ring finger- Median Nerve (orange) thumb, fingers/finger tips, palm- Dorsiflection: top of hand moves back towards body- Palmar Flexion: palm moves down

Hand tools

- Most common hand tool related injuries are associated with knives, wrenches and hammers

- Just holding a tool creates static loads in forearm, upper arm, neck, shoulder, back- Posture is determined by

o Tool designo Seated or standing work height of persono Work surface orientationo Work surface height

- Principles of hand tool designo Neutral posture (straight wrists)o Bend tool, NOT wristo Use power grips for tasks requiring forceo Use pinch grips for tasks requiring precisiono Provide adequate grip span (men and women generate the most force with a 7-

8 cm opening for open handle tools)o Provide finger and glove clearanceo Eliminate pinch pointso Avoid tissue compressiono Avoid repetitive finger action (trigger finger: moving fingers difficult and gets

locked in one position)o Safe operationo Remember lefties and variable hand sizeso Minimize/ eliminate vibration

Lecture 15Work Station Design

- ANSI/HFES 100-2007 Human Factors Engineering of Computer Workstations- ISO Series 9241

o New title: “The Ergonomics of Human-system Interaction”

- Ergonomic Design: Product/equipment, job aid, user selection (less desirable), training- Standing: no heel cause forward leaning and increase torque on spine

o Hips parallel to floor, equal weight on both feeto Shoes should be half to full size bigger for standing worko Purchase shoes after work (feet swell during day)o Keep weight off heels

- Floorso Hard floors cause fatigue, metal gratings worsto Carpet is best, reduce standing heart rate, compressibility 3-5%

- Slips and Fallso Slips in heal strike (fall back) and push offs (fall forward)o Trips when foot swingo Step on air when floor level change goes unnoticed

- Video Display Terminal (VDT) o Distance from eye to screen adjustable (15-32 in)o Screen tilt-able (5-15) to eliminate reflectionso Center of screen 15-25 below eye levelo Keyboard angle 5-15 (7-11 preferred)o Keys should have feedbacko Standardization on keyboard

- Chair Designo Adjustableo Weight supported by two bones (ischial tuberosities)o 25% weight supported by feeto Not contouredo Upholstery should give about 25mm (not too soft)o Curved front edgeo Slope backwards 1-5 deg (forward slant gives knee problems)

Seat Dimensions- Seat Height

o Measure from work height not from flooro Work slightly below elbow heighto Use footrests for shorter workers, if necessary

- Backrestso Must be adjustable and should be spring loadedo Concave shape to provide lumbar support

- Armrestso They take weight off your backo Wrist supports for typing work

- Legs/Pedestalo Seat should swivel except when operating pedalo Swivel permits micro adjustment to prevent fatigueo Must have 5 horizontal supports to prevent tippingo Wheel base about 300 mm in diameter (maximum 350 mm)