repetive strain injuries, ergonomics and tools

8/7/2019 Repetive Strain Injuries, Ergonomics and Tools

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REPETITIVE STRAINREPETITIVE STRAININJURIES,INJURIES,

ERGONOMICSERGONOMICSandand

TOOLSTOOLS



midmid--1800s, Wojciech Jastrzebowski 1800s, Wojciech Jastrzebowski

coined the wordcoined the word ergonomicsergonomics-- the study or science of workthe study or science of work

1984, Chaff in & Anderson)1984, Chaff in & Anderson) -- today,today,science of ergonomics more oft en ref ersscience of ergonomics more oft en ref ers

to f itt ing the task to the personto f itt ing the task to the person-- task ref ers not only to work but task ref ers not only to work but recreat ional act ivit ies, sports, hobbiesrecreat ional act ivit ies, sports, hobbies

Ergonomics also considers the Ergonomics also considers the hu manhu manfactorfactor or hu man eng ineering or hu man eng ineering

-- cognit ive and decision making cognit ive and decision making performance of hu mansperformance of hu mans



ErgonomicsErgonomics

There is no definit ionThere is no definit ion

NO ONE TOOL WORKS FOR ALL JOBSNO ONE TOOL WORKS FOR ALL JOBS

NO ONE TOOL FITS ALL USERSNO ONE TOOL FITS ALL USERS If the tool fits, feels right and serves itsIf the tool fits, feels right and serves itsfunct ion, more than likely its the right one funct ion, more than likely its the right one f or the job, regardless if its t ermedf or the job, regardless if its t ermed

ergonomic. ergonomic. Best Rule Best Rule -- Bend the tool , not the wrist Bend the tool , not the wrist

-- use good post ureuse good post ure



Main Health Concerns & ToolsMain Health Concerns & Tools

Musculoskeletal Injuries / Repet it ive StrainMusculoskeletal Injuries / Repet it ive StrainInjuriesInjuries

RSIRSI more of t en result of bad post ure more of t en result of bad post ure when using tool or workstat ionwhen using tool or workstat ion

Carpal Tunnel Syndrome is a diagnosisCarpal Tunnel Syndrome is a diagnosis

RSI is a descript ion of mechanism of injury RSI is a descript ion of mechanism of injury

or encompasses many diagnosis such asor encompasses many diagnosis such asCTS, ulnar nerve entrapment,CTS, ulnar nerve entrapment,deQuervains syndrome. TOS, t ennisdeQuervains syndrome. TOS, t enniselbow, t endonit is.elbow, t endonit is.



RSIRSI

caused by many factorscaused by many factors

-- physical fitness statephysical fitness state

-- body sizebody size

-- muscle tensionmuscle tension

-- work habitswork habits

-- stressstress

-- long hours of work/activitylong hours of work/activity-- lack of breakslack of breaks

-- bad ergonomicsbad ergonomics

-- poor & static posturepoor & static posture



RSI and Comput ersRSI and Comput ers

RSI does not occur only with data entry RSI does not occur only with data entry

Web surfing is a common causeWeb surfing is a common cause

-- how longhow long-- post urepost ure

-- slouchingslouching

-- arm stretched out arm stretched out -- rest ing elbow on desk, arm of chairrest ing elbow on desk, arm of chair



Ergonomics and Basic ConceptsErgonomics and Basic Concepts

Have good post ureHave good post ure

Circulat ionCirculat ion

-- hand exercises, hand clencheshand exercises, hand clenches-- ergonomic ball squeezesergonomic ball squeezes

If feeling numbness, t ingling or pain inIf feeling numbness, t ingling or pain inyour arms, wrists or handsyour arms, wrists or hands -- YOU ARE YOU ARE

ALREADY INJURED ALREADY INJURED, not developing RSI, not developing RSI Living with pain, working through it,Living with pain, working through it, walking it off not an opt ion walking it off not an opt ion

-- take regular breaks, exercise, Rxtake regular breaks, exercise, Rx



RSI Risk Factors and Hand ToolsRSI Risk Factors and Hand Tools

ForceForce

Awkward post ure Awkward post ure

Stat ic post ureStat ic post ure Contact stressContact stress

Vibrat ion Vibrat ion

Repet it ionRepet it ion Cold Temperat uresCold Temperat ures



FORCE and WEIGHTFORCE and WEIGHT

Weight of tool det ermines f orce needed toWeight of tool det ermines f orce needed tooperat eoperat e

Heavy hand or power tools > 10 lbsHeavy hand or power tools > 10 lbs

-- require high levels of f orce to hold andrequire high levels of f orce to hold andcontrol toolcontrol tool quick muscle fatigue quick muscle fatigue

Distribution of weight may affect forceDistribution of weight may affect force

-- further center of gravity away from handle,further center of gravity away from handle,

more force needed to hold and operatemore force needed to hold and operate-- tool wt. distribution may make tool rotatetool wt. distribution may make tool rotate

when used, requiring increased musclewhen used, requiring increased muscle

usage to counteract rotation.usage to counteract rotation.



Tool Weight Tool Weight

Ideally, should be able to operat e toolIdeally, should be able to operat e toolwith one handwith one hand Weight of tool (esp. f or repet it ive use)Weight of tool (esp. f or repet it ive use)

should not exceed 2.2 lbs or 1 kgshould not exceed 2.2 lbs or 1 kg Cent er of gravit y should be aligned with cent erCent er of gravit y should be aligned with cent er

of gripping hand (except ionsof gripping hand (except ions grinders, axes,grinders, axes,sawssaws heavy to decrease usage f orce heavy to decrease usage f orce -- these these should not weigh more than 5.1 lbs or 2.3 kg toshould not weigh more than 5.1 lbs or 2.3 kg toreduce arm f at igue)reduce arm f at igue)

Tools heavier than 2.2 lbs or 1 kg or poorly Tools heavier than 2.2 lbs or 1 kg or poorly balanced tools should be support ed by count erbalanced tools should be support ed by count er--balances or > 5.1 lbs suspended f rom ceilingbalances or > 5.1 lbs suspended f rom ceiling

Studies have shown that tools weighingStudies have shown that tools weighingfrom 2from 2 3.85 lbs or 0.9 to 1.75 kg feel3.85 lbs or 0.9 to 1.75 kg feel

just right for most workers. just right for most workers.



FORCE, GRIP and HANDLESFORCE, GRIP and HANDLES

Grip or handle size of tool may affect amount Grip or handle size of tool may affect amount of f orce needed when operat ing toolof f orce needed when operat ing tool

If handle or grip size is too small or large,If handle or grip size is too small or large,

great er f orce needed to operat e toolgreat er f orce needed to operat e tool-- Handle size directly affects grip capacit yHandle size directly affects grip capacit y

Handle too narrow, higher muscle contract ionHandle too narrow, higher muscle contract ionf orces needed to hold and operat e toolf orces needed to hold and operat e tool

Handle too wide, less abilit y to generat e gripHandle too wide, less abilit y to generat e gripf orce or muscle contract ionf orce or muscle contract ion-- may result in putt ing operator in awkwardmay result in putt ing operator in awkward

posit ion (i.e., operator must bend or f lex posit ion (i.e., operator must bend or f lex

wrists to maintain a grip on tool handle)wrists to maintain a grip on tool handle)



FORCE, GRIP and HANDLESFORCE, GRIP and HANDLES

Tools with longer or thicker handles require Tools with longer or thicker handles require less f orce.less f orce.

Longer handle allows operator to generat e Longer handle allows operator to generat e

more leverage with a smaller f orce at a great ermore leverage with a smaller f orce at a great erdistance.distance.

Thicker handle allows more surf ace f or grasping Thicker handle allows more surf ace f or grasping

or increased torque (screwdriver)or increased torque (screwdriver) Wider handles (pliers & wrenches) allow gripWider handles (pliers & wrenches) allow gripf orce to be distribut ed over a larger surf ace,f orce to be distribut ed over a larger surf ace,decreasing the grip strengthdecreasing the grip strength



Tool Handle SelectionTool Handle Selection

No hand tool perfect f or every job orNo hand tool perfect f or every job orevery personevery person

What works f or one person may be aWhat works f or one person may be aproblem or result injury f or anotherproblem or result injury f or another

Each person has his/her opt imum gripping Each person has his/her opt imum gripping diamet erdiamet er



The OK MethodThe OK Method

Radwin & Haney, 1996Radwin & Haney, 1996 average personsaverage personsopt imum grip diamet er is approximat ely opt imum grip diamet er is approximat ely 1.5 inches1.5 inches

Ask person to make OK sign using Ask person to make OK sign using thumb and index finger.thumb and index finger.

-- measure inside diamet er of the Omeasure inside diamet er of the O

-- measurement indicat es opt imum gripmeasurement indicat es opt imum gripdiamet er of a hand tool f or that diamet er of a hand tool f or that individualindividual

-- tool may need customizat iontool may need customizat ion



HANDLESHANDLES

Most hand tool grips and handle shouldMost hand tool grips and handle shouldbe designed f or a power gripbe designed f or a power grip

Pinch grip requires excessive fingerPinch grip requires excessive finger

pressure and more muscle f orcepressure and more muscle f orce



HANDLE SHAPEHANDLE SHAPE

Poor wrist posit ioning can diminish gripPoor wrist posit ioning can diminish gripstrength.strength.

St udy (Terrel & Purswell, l976) f ound that St udy (Terrel & Purswell, l976) f ound that grip strength is decreased by 27% whengrip strength is decreased by 27% whenwrist is held in f lexion, 23% in ext ension,wrist is held in f lexion, 23% in ext ension,17% in radial deviat ion and 14% in ulnar17% in radial deviat ion and 14% in ulnardeviat ion.deviat ion.




Tools with bent or angled handles or tools withTools with bent or angled handles or tools withpistolpistol--grips are beneficial when the f orce is exert edgrips are beneficial when the f orce is exert edin a straight line in the same direct ion as the in a straight line in the same direct ion as the straight ened f orearm and wrist, especially whenstraight ened f orearm and wrist, especially whenthe f orce must me applied horizontallythe f orce must me applied horizontally




Tools with straight handles are f or tasks where Tools with straight handles are f or tasks where the f orce is exert ed perpendicular to the the f orce is exert ed perpendicular to the straight ened f orearm and wrist straight ened f orearm and wrist

-- i.e., when f orce must be appliedi.e., when f orce must be applied vert icallyvert ically

Shaped tools such as bent Shaped tools such as bent--handle tools are handle tools are effect ive where most of the tasks are done ineffect ive where most of the tasks are done in

the

same

plane

and heig

ht as the

arm

& hand.the

same

plane

and heig

ht as the

arm

& hand. Crucial ergonomic tool use and design principle Crucial ergonomic tool use and design principle

Bend the tool, not the wristsBend the tool, not the wrists



TOOL HANDLE DIAMETERTOOL HANDLE DIAMETER

Should be cylindrical or oval in crossShould be cylindrical or oval in crosssect ion with a diamet er between 1.18 andsect ion with a diamet er between 1.18 and1.77 inches.1.77 inches.

For precision work, the recommendedFor precision work, the recommendedhandle diamet er is between 0.2 and 0.5handle diamet er is between 0.2 and 0.5in.in.

For great er torque, handle diamet erFor great er torque, handle diamet ershould be 2.0 to 2.4 in.should be 2.0 to 2.4 in.



Tool Handle LengthTool Handle Length

Handle too short Handle too short unnecessary unnecessary

compression in the middle of the palmcompression in the middle of the palm

-- handle should extend across the entirehandle should extend across the entirebreadth of palmbreadth of palm

-- handles longer than 3.9 in. to 4.7 in. willhandles longer than 3.9 in. to 4.7 in. will

reduce negative effects of compressionreduce negative effects of compression

-- rounded handles minimize palmrounded handles minimize palm

compressioncompression



Separat ion between HandlesSeparat ion between Handles

Pliers, tongs, crimpers, cutt ing tools have Pliers, tongs, crimpers, cutt ing tools have two handlestwo handles

Recommended distance between handlesRecommended distance between handlesof tool is between 2.0 and 2.6 inchesof tool is between 2.0 and 2.6 inches

-- this range fits both males and femalesthis range fits both males and females

Tools with larger or smaller handle spansTools with larger or smaller handle spanswill reduce ones maximum grip strengthwill reduce ones maximum grip strengthand may contribut e to onset of CTSand may contribut e to onset of CTS



HANDLE MATERIAL & TEXTUREHANDLE MATERIAL & TEXTURE

Should be made of nonShould be made of non--slip, nonslip, non--conduct ive and compressible mat erial.conduct ive and compressible mat erial.

Text ured rubber handles provides good gripping,Text ured rubber handles provides good gripping,

effect ively reducing eff ort needed to use tooleffect ively reducing eff ort needed to use tooland prevents tool f rom slipping out of hand.and prevents tool f rom slipping out of hand.

Glossy coat ings and highly polished handlesGlossy coat ings and highly polished handlesshould be avoided.should be avoided.

Avoid tools that have finger grooves Avoid tools that have finger grooves

-- finger grooves should be customized to the finger grooves should be customized to the users fingers.users fingers.



Handles f or Garden / YardHandles f or Garden / Yard

Handle t ypes and placement are clinically Handle t ypes and placement are clinically proven beneficial f or prevent ion of lowproven beneficial f or prevent ion of lowback injuriesback injuries

3 main act ions take place when using 3 main act ions take place when using garden/yard tools:garden/yard tools:

-- lif t ing, pushing & pulling and twist inglif t ing, pushing & pulling and twist ing



Ergonomic Handles f orErgonomic Handles f or

Garden / YardGarden / Yard

T-grip / Straight h andle

D-grip h andle



DD--grip and Lif t ing grip and Lif t ing ( shovels, spades, pitch f orks, etc.)( shovels, spades, pitch f orks, etc.)

Biomechanically, lif t ing involves body as 3Biomechanically, lif t ing involves body as 3rdrd classclasslever.lever.

Adding D Adding D--grip midgrip mid--way down shovel handle way down shovel handle moves the fulcrum to lower hand, transferring moves the fulcrum to lower hand, transferring the eff ort to the long end of shovel, making it athe eff ort to the long end of shovel, making it a11st st class lever.class lever.

With increased leverage, a heavier load can be With increased leverage, a heavier load can be

lif t ed with great er ease.lif t ed with great er ease. DD--grip improves post ure, user can stand upgrip improves post ure, user can stand up

straight erstraight er With DWith D--grip limb alignment and hand posit iongrip limb alignment and hand posit ion

are neutralare neutral reduces fatigue and blisters reduces fatigue and blisters



Use of brooms, rakes, etc. involvesUse of brooms, rakes, etc. involvestwist ing mot ion.twist ing mot ion.

Adding a T Adding a T--grip midgrip mid--way down a gardenway down a garden

tool handle as well as at the upper endtool handle as well as at the upper endallows a great er range of mot ionallows a great er range of mot ion

A straight line of f orce f rom the shoulder A straight line of f orce f rom the shoulder

to the grip opens the space between the to the grip opens the space between the shoulders f or good post ure and reducesshoulders f or good post ure and reducesrisk of back and muscle strainsrisk of back and muscle strains

Neutral limb alignment and hand posit ionNeutral limb alignment and hand posit ion

helps reduce arthrit is and back painhelps reduce arthrit is and back pain

STRAIGHT of T-grip Handle



TT--Grip / Straight GripGrip / Straight Grip

Permits the wrist angle to remain in a nearPermits the wrist angle to remain in a nearneutral posit ion in the ulnar/radial plane.neutral posit ion in the ulnar/radial plane.

-- limits UD to max of 10limits UD to max of 10°° vs 35vs 35°° without without straight grip.straight grip.

-- minimizes compression of lunar nerve,minimizes compression of lunar nerve,blood supply, carpal ligaments,blood supply, carpal ligaments,t endons, etc. on ulnar side of wrist andt endons, etc. on ulnar side of wrist andless t ension on radial side t issues.less t ension on radial side t issues.



TT--Grip / Straight GripGrip / Straight Grip

Without straight grip, f orearm is end a supinat edWithout straight grip, f orearm is end a supinat edposit ionposit ion

Straight grip puts f orearm in pronat ed posit ion.Straight grip puts f orearm in pronat ed posit ion.

Results in shoulder being abduct ed.Results in shoulder being abduct ed.-- lif t ing normally involves shoulder abductorslif t ing normally involves shoulder abductors

Possible less or no involvement of supraspinat us with TPossible less or no involvement of supraspinat us with T--gripgrip

Allows trunk to remain in more upright posit ion during Allows trunk to remain in more upright posit ion during lif t ing lif t ing

-- decrease eff ort f rom ext ensor mmdecrease eff ort f rom ext ensor mm

May lessen blist er f ormat ionMay lessen blist er f ormat ion



POWER TOOL TRIGGERSPOWER TOOL TRIGGERS

To avoid hand & f orearm f at igue, look f or toolsTo avoid hand & f orearm f at igue, look f or toolsthat can be act ivat ed by either hand.that can be act ivat ed by either hand.

Frequent movements of index finger while Frequent movements of index finger while operat ing trigger poses considerable risk f oroperat ing trigger poses considerable risk f or

trigger finger and trigger thumb trigger finger and trigger thumb Trigger should have a mechanism that holds orTrigger should have a mechanism that holds or

locks it in place.locks it in place. A long trigger allows f or use of more fingers, A long trigger allows f or use of more fingers,

reducing discomf ort and minimizes risk f orreducing discomf ort and minimizes risk f orinjury.injury. Recommended trigger length is 2.0 inchesRecommended trigger length is 2.0 inches

repetive strain injuries, ergonomics and tools

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