msd and physiology

8/14/2019 Msd and Physiology

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CUMULATIVE TRAUMACUMULATIVE TRAUMA

DISORDERDISORDER

SITI ZAWIAH MD DAWALSITI ZAWIAH MD DAWALDEPT OF ENGINEERING DESIGN ANDDEPT OF ENGINEERING DESIGN AND

MANUFACTUREMANUFACTURE

UNIVERSITY OF MALAYAUNIVERSITY OF MALAYA


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Sometimes called repetitive motionSometimes called repetitive motion

injuriesinjuries

Or work related musculoskeletal disorderOr work related musculoskeletal disorder

Are injuries to musculoskeletal system thatAre injuries to musculoskeletal system that

develop gradually as a result of repeateddevelop gradually as a result of repeatedmicro-trauma due to poor design and themicro-trauma due to poor design and the

excessive use of hand tools and otherexcessive use of hand tools and other

equipmentequipment


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Leading to problemsLeading to problems

Repetitive motion disorderRepetitive motion disorder

Carpal tunnel syndromeCarpal tunnel syndrome

TendinitisTendinitisTenosynovitisTenosynovitis

White fingersWhite fingers


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Common SymptomsCommon Symptoms

PainPain

Joint movement restrictionJoint movement restriction

Soft tissue swellingSoft tissue swelling


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TenosynovitisTenosynovitis

Inflammation of the tendon sheaths due toInflammation of the tendon sheaths due to

overuse or unaccustomed use ofoveruse or unaccustomed use of

improperly designed tools.improperly designed tools.

The wrist is bent especially in palmerThe wrist is bent especially in palmer

flexion or ulnar deviation (or both)flexion or ulnar deviation (or both)

Example inserting screw in holes,Example inserting screw in holes,

manipulating rotating control.manipulating rotating control.


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TendinitisTendinitis

If the inflammation spread toIf the inflammation spread to

the tendons it becomesthe tendons it becomes

tendinitistendinitis


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Carpal Tunnel SyndromeCarpal Tunnel Syndrome

Disorder of hand caused by injury of theDisorder of hand caused by injury of the

median nerve inside the wrist.median nerve inside the wrist.

Repetitive flexion and extension of theRepetitive flexion and extension of the

wrist under stress may cause inflammationwrist under stress may cause inflammation

of the tendon sheaths.of the tendon sheaths.

The sheaths, sensing increased friction,The sheaths, sensing increased friction,

secrete more fluid to lubricate the sheathssecrete more fluid to lubricate the sheaths

and facilitate tendon movement.and facilitate tendon movement.


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The resulting build up of fluid in the carpalThe resulting build up of fluid in the carpaltunnel increased pressure which in turntunnel increased pressure which in turncompresses the median nerve.compresses the median nerve.

Symptoms include impaired or lostSymptoms include impaired or lostnervous function.nervous function.

Numbness, tingling, pain and loss ofNumbness, tingling, pain and loss of

dexteritydexterityType of work job requiring high force andType of work job requiring high force andshort cycleshort cycle


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Trigger FingerTrigger Finger

Is the form of tendinitis resulting from theIs the form of tendinitis resulting from theindex finger is used excessively forindex finger is used excessively foroperating triggers.operating triggers.

The condition seems to occur mostThe condition seems to occur mostfrequently if the handle of the tool orfrequently if the handle of the tool ordevice is so large that the distal phalanxdevice is so large that the distal phalanx

(segment) of the finger has to be flexed(segment) of the finger has to be flexedwhile the middle phalanx must be keptwhile the middle phalanx must be keptstraight.straight.


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White FingerWhite Finger

Results from excessive vibration fromResults from excessive vibration from

toolstools

A similar effect can occur as a result ofA similar effect can occur as a result of

exposure to cold termed Raynauldsexposure to cold termed Raynaulds

syndrome.syndrome.


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How to evaluate the level of CTDHow to evaluate the level of CTD

Starts with surveying the workers toStarts with surveying the workers to

determine their health and discomfort atdetermine their health and discomfort at

workwork

Body discomfort chartBody discomfort chart


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Muscles, through the tension they exertMuscles, through the tension they exert

when contracting, make physical workwhen contracting, make physical work

possible. There are three types opossible. There are three types of

muscle in the bod :muscle in the body:

1. Smooth muscle1. Smooth muscle

2. Cardiac muscle2. Cardiac muscle

3. Skeletal muscle3. Skeletal muscle


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Smooth muscle is found in the intestines andSmooth muscle is found in the intestines and

makes possible the movements essential for themakes possible the movements essential for the

digestion of food (peristalsis). It is also found indigestion of food (peristalsis). It is also found in

the walls of blood vessels where it is involved inthe walls of blood vessels where it is involved in

the regulation of blood pressure and blood flow.the regulation of blood pressure and blood flow.

It is not normally considered to be underIt is not normally considered to be underconscious control. Cardiac muscle has a specialconscious control. Cardiac muscle has a special

structure and constitutes the bulk of the heart.structure and constitutes the bulk of the heart.

The energy required for muscle contraction isThe energy required for muscle contraction is

obtained from phosphate compounds in theobtained from phosphate compounds in the

muscle tissue. These compounds are formedmuscle tissue. These compounds are formed

from the breakdown of food.from the breakdown of food.


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Skeletal MuscleSkeletal Muscle

Described as striated, stripDescribed as striated, strip

Voluntary muscleVoluntary muscle

Voluntary because contraction is underVoluntary because contraction is underconscious controlconscious control


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A myofibrilA myofibril


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MyofibrilMyofibril

Representing series of dark and lightRepresenting series of dark and light

bands and consisting of unit calledbands and consisting of unit called

sacromeresacromere

A sacromere represents the smallestA sacromere represents the smallest

functional unit of a skeletal muscle fibrefunctional unit of a skeletal muscle fibre

and consists ofand consists of -thin filament actin-thin filament actin

-thick filament -myosin-thick filament -myosin


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Sliding filament theory of muscle contractionSliding filament theory of muscle contraction


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A model of the circulatory systemA model of the circulatory system

The Cardiovascular

System


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Industrial Applications ofIndustrial Applications of

PhysiologyPhysiologyImprovement of productivity is always a priority, a mainImprovement of productivity is always a priority, a maingoal is to determine acceptable work rate for a given job.goal is to determine acceptable work rate for a given job.Industrial engineers have developed methods forIndustrial engineers have developed methods fordesigning manual jobs in a systematic way. Thesedesigning manual jobs in a systematic way. These

techniques enable them to specify time standards, ortechniques enable them to specify time standards, orstandard times for the completion of tasks and tostandard times for the completion of tasks and todescribe the physical load of tasks by means ofdescribe the physical load of tasks by means ofperformance rating. Therefore standards levels ofperformance rating. Therefore standards levels ofproduction can be defined.production can be defined.

Application of physiological methods in industry is usefulApplication of physiological methods in industry is usefulfor:for:

Measurement of workloadMeasurement of workload

Investigating mental stressInvestigating mental stress

Nutrition and em lo ee level of fitnessNutrition and employee level of fitness


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Physiology response to workPhysiology response to work


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Physiology methods:Physiology methods:

Applied in industry to evaluate the physical demands ofApplied in industry to evaluate the physical demands ofjobs in terms ofjobs in terms ofenergy expenditure.energy expenditure.

When an individual begins a work task from rest, heartWhen an individual begins a work task from rest, heartrate and oxygen consumption increase to meet the newrate and oxygen consumption increase to meet the newdemands:demands:

Begin working - immediate requirements for energy areBegin working - immediate requirements for energy aremet by local energy stores. (ie. muscular)met by local energy stores. (ie. muscular)

Stop working - HR and OX levels return to initial levelsStop working - HR and OX levels return to initial levelsbut extra oxygen needed to replenish muscle storesbut extra oxygen needed to replenish muscle stores(oxygen debt) during recovery period.(oxygen debt) during recovery period.

In many industrial tasks, physiological response to work:In many industrial tasks, physiological response to work:

Warm up period Steady stateWarm up period Steady stateRecovery periodRecovery period


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Measurement of the physiological cost ofMeasurement of the physiological cost of

workwork

Classic method of determining energyClassic method of determining energyexpenditure at work involves the measurementexpenditure at work involves the measurementof oxygen uptake using the Douglas bag:of oxygen uptake using the Douglas bag:

Oxygen content of the in the bag can beOxygen content of the in the bag can be

compared to that of the atmosphere tocompared to that of the atmosphere todetermine the amount of oxygen metabolized bydetermine the amount of oxygen metabolized bythe subject. Rate of oxygen uptake can bethe subject. Rate of oxygen uptake can becalculated with the time the subject takes to fillcalculated with the time the subject takes to fillup the bag. From the rate of oxygen uptake, theup the bag. From the rate of oxygen uptake, therate of energy expenditure can be calculated.rate of energy expenditure can be calculated.Above method is well established butAbove method is well established butinconvenient and causes interferences. Manyinconvenient and causes interferences. Manycompact instruments now available: Oxylog &compact instruments now available: Oxylog &

Respiration Monitor BeltRespiration Monitor Belt

I di t M fIndirect Measures of energy


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Indirect Measures of energyIndirect Measures of energy

expenditureexpenditureHeart RateHeart Rate

likened to a signal, which integrates the totallikened to a signal, which integrates the totalstress on the body and can be used as anstress on the body and can be used as an indexindexof the physiological cost of work.of the physiological cost of work.

Heart beat rate is known to increase as a functionHeart beat rate is known to increase as a function

of workload and oxygen uptake.of workload and oxygen uptake.Individuals can have the same rate but completelyIndividuals can have the same rate but completelydifferent levels of oxygen because the maximaldifferent levels of oxygen because the maximaloxygen uptake varies between individuals.oxygen uptake varies between individuals.

cannot be used to estimate energy expenditurecannot be used to estimate energy expenditurerequirements of a job therefore is often used asrequirements of a job therefore is often used asan indirect measurement of energy expenditure.an indirect measurement of energy expenditure.

easier to measure then oxygen uptakeeasier to measure then oxygen uptake


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Relationship between HR and oxygen uptake mustRelationship between HR and oxygen uptake must

be determined when evaluating physiologicalbe determined when evaluating physiological

workload using heart rate.workload using heart rate.Both have to be measured simultaneously in theBoth have to be measured simultaneously in thelab at a number of different sub-maximallab at a number of different sub-maximalworkloads. This is to calibrate the heart rate workloads. This is to calibrate the heart rate VO2 relationship for a worker.VO2 relationship for a worker.

Workers hearts rate measured in the field canWorkers hearts rate measured in the field canbe converted to an estimate of oxygen uptakebe converted to an estimate of oxygen uptakewith reference to the lab data. (Linearwith reference to the lab data. (Linearrelationship between the two variables)relationship between the two variables)

Estimates of energy expenditure can then beEstimates of energy expenditure can then becalculated.calculated.

Close correlations between these two methodsClose correlations between these two methods

of estimation suggest that HR measurement ofof estimation suggest that HR measurement of

reviousl calibrated sub ects can ivereviousl calibrated sub ects can ive

S bj ti B RPE S l


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Subjective measures Borg RPE ScaleSubjective measures Borg RPE Scale

(Ratings of perceived exertion)(Ratings of perceived exertion)

Well-known rating scale for subjectiveWell-known rating scale for subjectivemeasures. Subjective measures worthwhile frommeasures. Subjective measures worthwhile fromcost benefit and practical viewcost benefit and practical view

Workers are asked to rate the level of exertionWorkers are asked to rate the level of exertionthey perceive when carrying out a task on athey perceive when carrying out a task on a

scale from 6 to 20 (corresponding to minimumscale from 6 to 20 (corresponding to minimumand maximum heart rates of 60 and 200).and maximum heart rates of 60 and 200).

Such ratings are often used in conjunction withSuch ratings are often used in conjunction withobjective measures. High positive correlationobjective measures. High positive correlation

between HR and RPE are usually foundbetween HR and RPE are usually foundSubjective measure should be used with cautionSubjective measure should be used with cautionbecause of proneness for distortion -because of proneness for distortion -experimenter effect (biasness)experimenter effect (biasness)


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Physiological methods have been used to evaluatePhysiological methods have been used to evaluatephysical workload in many jobs both in industrialized andphysical workload in many jobs both in industrialized anddeveloping countries. Physiological methods reflect thedeveloping countries. Physiological methods reflect the

effort that the worker puts into the work system rathereffort that the worker puts into the work system ratherthan the output of the system itself. They are indexes ofthan the output of the system itself. They are indexes ofthe effect of work on the worker rather than the effect ofthe effect of work on the worker rather than the effect ofthe worker on the output of the work system.the worker on the output of the work system.

Workload measurements are important to identify undulyWorkload measurements are important to identify undulyheavy tasks, to evaluate traditional work methods and toheavy tasks, to evaluate traditional work methods and toarrive at more efficient methods of work. (Especially inarrive at more efficient methods of work. (Especially indeveloping countries, which rely heavily on manualdeveloping countries, which rely heavily on manuallabor.) There are many studies where physiologicallabor.) There are many studies where physiological

methods are used to evaluate and redesign manualmethods are used to evaluate and redesign manualtasks of all kinds. It is also used to optimize the design oftasks of all kinds. It is also used to optimize the design oftools.tools.

Physiological methods can also be applied to thePhysiological methods can also be applied to theinvestigation of light work, to detect the presence ofinvestigation of light work, to detect the presence of

mental stress. (heart rate increases when under mentalmental stress. (heart rate increases when under mental


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Calculation of rest periods in manual workCalculation of rest periods in manual work


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Oxygen dependent system can usually function for asOxygen dependent system can usually function for aslong as nutrients are available. Oxygen is obtained fromlong as nutrients are available. Oxygen is obtained fromthe air ventilating the lungs and is transported to all partsthe air ventilating the lungs and is transported to all parts

of the body by the blood but the body has a very limitedof the body by the blood but the body has a very limitedcapacity to store oxygen.capacity to store oxygen.

When there is insufficient oxygen available the oxygenWhen there is insufficient oxygen available the oxygenindependent system would produce energy. It is aindependent system would produce energy. It is a

valuable system, which enables work to be carried out atvaluable system, which enables work to be carried out ata high for short periods interspersed with time. Thisa high for short periods interspersed with time. Thisbackup system is inefficient and produces less energybackup system is inefficient and produces less energyper glucose energy than the oxygen dependent system.per glucose energy than the oxygen dependent system.It also produces waste products, which cause acidity ofIt also produces waste products, which cause acidity of

muscles cells to increase.muscles cells to increase.Work capacity depends on the ability to take up oxygenand deliver it to the cells for use in the oxidation offoodstuffs. Thus ability to work at a high rate isassociated with high oxygen uptake.


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The oxygen uptake or metabolic activity does not increaseThe oxygen uptake or metabolic activity does not increasesuddenly at the onset of work. There is gradual smoothsuddenly at the onset of work. There is gradual smoothincrease in oxygen uptake. During these first few minutesincrease in oxygen uptake. During these first few minutesof work the muscle use energy thatof work the muscle use energy that does not requiredoes not requireoxygenoxygen. (Called anaerobic metabolism or oxygen. (Called anaerobic metabolism or oxygenindependent process)*. Oxygen uptake does not reach aindependent process)*. Oxygen uptake does not reach a

stable level until several minutes after work has begunstable level until several minutes after work has begundepending on how hard the work is, this usually takesdepending on how hard the work is, this usually takesabout 5 minutes. Eventually a steady state level isabout 5 minutes. Eventually a steady state level isreached. This steady state represents the bodys aerobicreached. This steady state represents the bodys aerobic(oxygen fuelled process) response to the demands of(oxygen fuelled process) response to the demands of

increased workload.increased workload.

When the work stops, the oxygen uptake returns slowly toWhen the work stops, the oxygen uptake returns slowly tothe resting level prior to work. During this slow return afterthe resting level prior to work. During this slow return afterwork, the oxygen debt incurred during the onset of workwork, the oxygen debt incurred during the onset of work

(area A) is repaid (area B).(area A) is repaid (area B).


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* The anaerobic metabolism is* The anaerobic metabolism is inefficientinefficientbecause:because:

It uses nearly 20 times more fuel thatIt uses nearly 20 times more fuel thataerobic metabolism.aerobic metabolism.

Produces waste products (lactic acid),Produces waste products (lactic acid),

which may accumulate in the workingwhich may accumulate in the workingmuscles rather than being carried away bymuscles rather than being carried away bythe blood.the blood.

Lack of energy supplies, lack of fuels andLack of energy supplies, lack of fuels andaccumulation lactic acid in the musclesaccumulation lactic acid in the musclesinvolved willinvolved will lead to fatigue andlead to fatigue andcessation of work.cessation of work. This will also resultsThis will also results

inin aching of musclesaching of muscles..


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Fatigue is due to lack of carbohydrates or fluids oFatigue is due to lack of carbohydrates or fluids orthe accumulation of waste products. The mosthe accumulation of waste products. The mostimportant factor in the prevention of fatigue is theimportant factor in the prevention of fatigue is themaintenance of blood flow to the active muscles.maintenance of blood flow to the active muscles.Jobs should be designed to reduce theJobs should be designed to reduce therequirements of static muscle loading, such asrequirements of static muscle loading, such asgripping, extended reaches and awkward postures.gripping, extended reaches and awkward postures. The lowest possible percentage of the muscles maximum isometric,The lowest possible percentage of the muscles maximum isometric,

or static, effort should be designed for in situations where static effortor static, effort should be designed for in situations where static effortis part of the job, such as in tool use.is part of the job, such as in tool use.

Lower tension or effort in muscles results in less impairment of bloodLower tension or effort in muscles results in less impairment of bloodflow, the muscles will take longer to fatigueflow, the muscles will take longer to fatigue

Dynamic or rhythmic muscle contractions are preferred becauseDynamic or rhythmic muscle contractions are preferred becausethey allow blood to flow between contractions. However, if thethey allow blood to flow between contractions. However, if theintensity and rate of contraction is high enough, the inter mittenintensity and rate of contraction is high enough, the inter mittenmuscle blood flow may still be inadequatemuscle blood flow may still be inadequate

Recovery or rest period is needed to replenish the energy stores.Recovery or rest period is needed to replenish the energy stores.The duration of rest will depend on how much fatigue has developed.The duration of rest will depend on how much fatigue has developed.

M i t k


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Maximum oxygen uptakeMaximum oxygen uptakeVO2 max is a term been used to describe an individualsVO2 max is a term been used to describe an individualscapacity to utilize oxygen (maximal aerobic capacity).capacity to utilize oxygen (maximal aerobic capacity).

it is usually observed that oxygen uptake increases asit is usually observed that oxygen uptake increases asthe work rate is increased. relationship is approximatelythe work rate is increased. relationship is approximatelylinearlinear..

Oxygen consumption and heart rate do not continue toOxygen consumption and heart rate do not continue toincrease indefinitely. A point is reached where increasesincrease indefinitely. A point is reached where increases

in work rate is not accompanied by increases in oxygenin work rate is not accompanied by increases in oxygenuptake the individual is assumed to reach hisuptake the individual is assumed to reach hismaximum level of oxygen uptakemaximum level of oxygen uptake and cannot sustain aand cannot sustain aharder pace.harder pace.

There are limitations to human activity and the factorThere are limitations to human activity and the factor

believed to limits a persons work rate is the inability ofbelieved to limits a persons work rate is the inability ofthe heart and lungs to supply oxygen to the muscles at athe heart and lungs to supply oxygen to the muscles at asufficiently fast rate to meet the requirements of thesufficiently fast rate to meet the requirements of thework.work.

Increases in work rate can be met if energy is providedIncreases in work rate can be met if energy is providedby oxygen independent processes. However, these canby oxygen independent processes. However, these canonly be maintained for a short period because theyonly be maintained for a short period because they

Th l ti hi kl d dTh l ti hi kl d d


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The relationship workload and oxygenThe relationship workload and oxygen

uptakeuptake


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One main reason for the interest in workOne main reason for the interest in work

physiology is to consider variations in workphysiology is to consider variations in workcapacity between individuals. There iscapacity between individuals. There is

great variability in VO2 max betweengreat variability in VO2 max between

individuals and therefore there is aindividuals and therefore there is adistribution of VO2 max in the population.distribution of VO2 max in the population.

It is clear that tasks must be designedIt is clear that tasks must be designed

using VO2 max in a way similar to that ousing VO2 max in a way similar to that o

other anthropometric variables. Oneother anthropometric variables. One

important difference is physical condition.important difference is physical condition.


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Factors affecting work capacityFactors affecting work capacity

(Personal)(Personal)

Sh h th it f t i d h i lSho s ho the capacit for s stained ph sical


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Shows how the capacity for sustained physicalShows how the capacity for sustained physical

work depends upon the amount of physicalwork depends upon the amount of physical

conditioning.conditioning.


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A highly trained individual (runners) can sustain 50%A highly trained individual (runners) can sustain 50%of the maximal aerobic capacity for an 8 houof the maximal aerobic capacity for an 8 hour

working day, an average individual can sustain 35%working day, an average individual can sustain 35%and an untrained individual 25%and an untrained individual 25%

Cyclist, distance runners have a high VO2 max levels oCyclist, distance runners have a high VO2 max levels of70-80 ml of oxygen per kg of body weight. These70-80 ml of oxygen per kg of body weight. Theseindividuals lie in the extreme range of the populationindividuals lie in the extreme range of the populationdata. The average value is around 40 ml per kg perdata. The average value is around 40 ml per kg perminuteminute

It is generally believed that individuals can workIt is generally believed that individuals can workcontinuously over an 8-hour shift at a rate of 30 to 50continuously over an 8-hour shift at a rate of 30 to 50percent of their maximum capacity.percent of their maximum capacity.

In heavy manual work (In heavy manual work (egeg tasks requiring expenditure otasks requiring expenditure of2L of oxygen per minute), individuals with a high VO22L of oxygen per minute), individuals with a high VO2max (6 L of oxygen per minute) will be at an advantagemax (6 L of oxygen per minute) will be at an advantagebecause they will require fewer rest breaks. Individualsbecause they will require fewer rest breaks. Individualswith a lower VO2 max (2L of oxygen per minute) will bewith a lower VO2 max (2L of oxygen per minute) will beable to work only for short periods and will requireable to work only for short periods and will require

frequent rest breaks.frequent rest breaks.


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Variability between individuals alsoVariability between individuals also

increases with age. The table belowincreases with age. The table belowshows the maximal oxygen uptake for twoshows the maximal oxygen uptake for two

individuals from the age of 35 yearsindividuals from the age of 35 years

onwards. The oxygen uptake is given as aonwards. The oxygen uptake is given as apercentage of the greatest value attainedpercentage of the greatest value attained

for that individual.for that individual.

It can be observed that by the age of 65It can be observed that by the age of 65

years individual A was as fit as ever,years individual A was as fit as ever,

whereas individual B had a maximalwhereas individual B had a maximal

oxygen uptake of 65 % of his high value atoxygen uptake of 65 % of his high value at

the age of 35 years.the age of 35 years.


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