bio mechanics of lifting

8/6/2019 Bio Mechanics of Lifting

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Biomechanics of Lifting

Graduate Biomechanics


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Lifting

Varied Forms and Purposes

Component of ADLs

Occupational Task

Training for StrengthEnhancement

Competitive Sport


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Lifting - Forms ofLifting Up

Lifting Down

Pushing

Pulling

Supporting

Rising to Stand

SittingBending


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Lifting

Injury

Why so much interest inlifting ??


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Lifting

Workplace Injury

Incidence of Lifting-related Injury 2% of workers yearly

21% of all workplace injuries

33% of workplace health care cost


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Lifting-Related Injury

Economic Impact

*** Billions ***


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Common Sites for Lifting Related

Injury

Incidence Rates: (i.e. frequency of injury)

#1 Low Back

#2 Wrist and Hand

#3 Upper Back

#4 Shoulder

#5 Knee

#6 Elbow


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Low Back Pain

Second leading cause of physician visits

Third ranking cause of surgery (250,000 + yearly)

Fifth ranking cause of hospitalization

15% of adults experience episode each year

Lifting-related Injury is the

Leading Cause of Low BackPain !


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Lifting

Roles of the Clinician

** Treatment **

What Can be Done ?

** Prevention **


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LiftingInjury Prevention

** Many Issues **


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Potential Areas Influencing Risk

The Lifter

The Load

The Task

The Conditions


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The LifterFactors Influencing Risk

Anthropometrics

Strength

Endurance

Range of Motion

Technique Sensory

Health Status


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The LoadFactors Influencing Risk

Weight

Size and Shape

Load Distribution

Grip Coupling


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The TaskFactors Influencing Risk

Complexity

Workplace Geometry

Frequency

Duration


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ConditionsFactors Influencing Risk

The Workplace Environment


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Lifting Technique- Common

Elements

What do all forms of Lifting Have in Common ??

Imposed LoadsMotion - Inertia

Joint Torques

Joint CompressionJoint Shear


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Biomechanics of Joint Motion

The Biomechanical Model

External Torque

The External Torque andintended direction of motiondetermine the Internal Torque

InternalTorque

If External Torque > Internal Torque TrunkFlexionIf Internal Torque > External Torque TrunkExtension

If External Torque = Internal TorqueEquilibrium


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Load - magnitude

Position of Load

Upper Body MassPosition of Upper Body

Inertia

External Torque

The External Torque is Determined

by:


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The External Torque is Determined

by:COG

Axis

Line of Gravity

Moment Arm

Torque = (Total Load) * (cosine of Slope * Moment Arm)

Total Load = Mass of HAT + External Load


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The External Torque is Determinedby:

COG

Axis

Line of Gravity

Moment Arm


Body Mass = 150 #HAT = 60 % of BMLoad = 50 #Trunk Angle = 60 degMoment Arm = 1.2


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Biomechanics of Joint Torque

External Torque

Body Mass = 150#

Load = 50#HAT = 60% of Body Mass

COG Distance = 1.2

Trunk Slope = 60 deg


Torque = (90# + 50# ) * (.5 * 1.2 )

External Torque = 84 ft/lbs

External Torque


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External Torque

External Torque = 84 ft/lbs

External Torque

How Much Internal

Torque is Needed toproduce Equilibrium ??

84ft/lbs


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External Torque

External Torque

How Much Internal


84 ft-lbs

How hard do the extensor musclehave to work to produce the neededinternal torque ????

Muscle MomentArm = .15

InternalTorque


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External Torque

External Torque

How Much Internal


84 ft-lbs

Internal Torque = MMA * MuscleForce

84 ft-lbs = .15 * Muscle Force

Muscle Force = 84 ft-lbs / .15

Muscle MomentArm = .15

InternalTorque


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Joint Compression

Body Mass = 150#

Load = 50#

HAT = 60% of Body Mass

Moment Arm = 1.2

Trunk Slope = 60 degMuscle Moment Arm= .15

Joint Compression = HAT + Load + Muscle ContractioJoint Compression = 90# + 50# + 560#

Joint Compression = 700#

Joint Compression

How about Joint Compression ??


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Joint Compression

Additional Factors

Motion speed of lift

Rotation Transverse Plane


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Lifting Technique

COG

What can be done to

decrease low backstress ?(1) Lighten the Load


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Lifting Technique

COG

What can be done to


(2) Change theposition of theLoad


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Lifting Technique

COG

What can be done to


(2) Change theposition of theLoad

(3) Change theposition of theBody


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Lifting Technique

Torque Torque

Bad Good

COG

COG


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NIOSH

National Institute for Occupational

Safety and Health

* Work Practices Guide to Manual Lifting, 1981


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NIOSH

What do they do ??

Define risk associated with lifting

Define safe lifting conditions

Publish lifting guidelines and standards for

the workplace

Inspect workplace for safe lifting conditions

Impose penalties for hazardous lifting

conditions


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NIOSH - Hazardous LiftingDependent on:

Weight of Object

Location of Object COM at beginning of

lift

Vertical travel distance of object

Frequency of Lift (lifts per minute)

Duration of lifting


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NIOSH StandardsAction Limit and Maximum Permissable Limit

AL:Tolerated by 99% of males and

75% of females

L5/S1 compression below 3400N

Energy cost below 3.5 kcals/min

**If any exceeded - some risk of

injury

MPL:Tolerated by 25% of males and 1% of

females

L5/S1 compression above 6500N

Energy cost above 5 kcals/min

**If exceeded severe risk of injury


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NIOSH Standards

Below AL - Stress tolerated by most workers

Above AL and below MPL - Risk of injury

such that task re-design or change in worker

may be necessary

Above MPL - Unacceptable risk...Must re-

design task

bio mechanics of lifting

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