APA3131 Exam

Biomechanics

The application of mechanical principles in the study of human organisms

Bernardino Ramazzini

Developed the idea that if you are paying people on how much work they can get done, they are going to compensate with their bodies to produce the most work possible.

Occupational Biomechanics

The study of the physical interactions of workers with their tools, machines, and materials to enhance the worker's performance while minimizing the risk of musculoskeletal disorders.

Ergonomics

The profession that applies theoretical principles, data, and methods to aspects of workplace design to optimize human well-being.

Domains of Specialization

Cognitive, Organizational, & Physical Ergonomics

Cognitive ergonomics

Concerned with mental processes such as perception, memory, reasoning, and motor response, as they affect interactions among humans and other elements of a system.

Organizational ergonomics

Concerned with the optimization of sociotechnical systems, including their organizational structures, policies, and processes.

Physical ergonomics

Concerned with human anatomical, anthropometric, physiological, and biomechanical characteristics as they relate to physical activity.

Areas of application (physical ergonomics)

Manufacturing, construction, mining, agriculture, health care, office work, meat processing.

Musculoskeletal disorders

Injuries and disorders of the musculoskeletal system that are caused or aggravated by various hazards or risk factors in the workplace

Human-centered

All designable components of a system, product or service are fitted to the characteristics of the intended users, operators or workers, rather than selecting and/or adapting humans to fit the system, product or service.

"Fitting the job to the person, not trying to find a person that fits the job."

RACE model

Workflow to organize MSD prevention process.

4 components of the RACE model

Recognition

Assessment

Control

Evaluation

Prepare (RACE model)

Engage a team, represent different perspectives.

Recognize (RACE model)

Recognize MSD hazard exposures (force, repetition, awkward postures, duration, vibrations). Can hazard be eliminated now?

Proactive measures

Recognize and anticipate hazards. Goal is to prevent MSDs before they occur.

Reactive measures

Address existing workplace hazards. May be conducted as the result of a workplace incident or injury.

Assess (RACE model)

Determine if exposure to hazard warrants change. 2 levels of assessment.

Simple Assessment

Hazard assessment tools (e.g., NIOSH Lifting Index)

Full Assessment

Detailed risk assessments (e.g., Digital Human Modelling)

Hazards

Sources of potential harm to a worker

Control (RACE model)

Identify root causes of high-risk exposures, determine appropriate control to mitigate risks, follow hierarchy of controls.

Hierarchy of Controls (from most to least effective)

Elimination, Substitution, Engineering Controls, Administrative Controls, PPE

Elimination (Hierarchy of Controls)

Physically remove the hazard

Substitution (Hierarchy of Controls)

Replace the hazard

Engineering Controls (Hierarchy of Controls)

Isolate people from the hazard

Administrative Controls (Hierarchy of Controls)

Change the way people work

PPE (Hierarchy of Controls)

Protect the worker with personal protective equipment

Evaluate (RACE model)

Was control effective?

CSA Z1004-12 Workplace Ergonomics

Act, Plan, Check, Do.

"Do" step = RACE model

Acceptable task vs unacceptable task

Continuum, need to draw the line somewhere

Threshold Limit Value (TLV)

Where to "draw the line." Typically based on 25th percentile female workers (i.e., 75% of women are capable of doing the task).

Injury Risk

Increases when task demand exceeds tissue capacity

Connective Tissues

Tissues that separates and supports all other tissue in the body (I.e., bones, ligaments, tendons, fascia, cartilage).

Balance of forces determines what?

The direction of motion

What do forces do to objects in static equilibrium?

Cause local changes in shape (i.e., deformation)

Deformation

A change in the shape or size of an object due to an applied force

Types of forces

Tension, compression, bending, sheer, torsion, combined loading

Stress

A measure of the average force per unit of area (N/m^2)

Stress formula

Sigma = F/A

Strain

A normalized measure measure of the degree of deformation (unitless)

Strain formula

(Epsilon) e = delta l/l

Elastic Region

The material strains without permanent deformation

Yield point

When permanent deformation occurs

Failure point

When the material fails

Strength

Maximum stress withstood before failure

Yield strength (Oy)

The stress at which plastic deformation begins

Ultimate strength (Ou)

The peak stress before fracture or rupture occurs

Stiffness

Resistance to deformation (Elastic Modulus/ Young's Modulus E)

The ratio of stress to strain

Uniaxial tension or compression forces

Steep slope is...

More stiff (stress increases faster)

Isotopic material

Same material throughout, does not matter which direction you load it

Ductility/Brittleness

Ability to plastically deform without failure

Smaller plastic change is...

More brittle

Greater plastic change is...

More ductile

Toughness

Energy absorbed before failure

Bigger area = more energy = ...

Tougher material

Fatigue limit

Maximum stress withstood under repeated loading

Endurance limit

Maximum stress that a material can sustain repeatedly without failure

Linear elastic behaviour

A unique, specific relationship between stress and strain. Return to original shape instantaneously. Not dependant on the rate of loading.

Viscosity

A fluid property, resistance to flow

Elasticity

A solid material property, ability to return to its original size and shape

Viscoelastic

A characteristic of materials containing solid and fluid properties

Elasticity

A solid material property, ability to return to its original size and shape

Viscoelastic behaviour

Dependant of rate of loading, may return to original shape over time

Biological tissues are...

Viscoelastic

The Creep Test

Apply a constant load, plot the stress over time, plot the strain over time.

Elastic: deformation instantly recovers

Viscoelastic: deformation recovers gradually

The Stress-Relaxation Test

Apply and maintain a constant stretch, plot the strain over time, plot the stress over time.

Elastic: a constant stress is required

Viscoelastic: the stress required decreases over time

Biological tissues exhibit...

Creep and stress-relaxation

What affects material properties of connective tissues?

Load direction, shape, length, loading rate, age, use/disuse.

Anisotropic

Material properties that depend on the direction of loading

Increased strain rates...

= stiffer behaviour

Wolff's Law

No loading = weaker bones

Acute Injury Mechanism

One big load that goes over tolerance (e.g., a fall)

Chronic Injury Mechanism

Related to fatigue, smaller load applied repeatedly, eventually exceed tolerance which results in injury

Bone (mechanical function)

Support the body, protect organs, transfer forces, allow movement

Bone (metabolic function)

Reserve of ions, calcium, phosphate

Common bone injuries

Fractures, avulsion

Cartilage (function)

Transmits loads between bones, distribute forces over wider area, provide know-friction surface for articulation

Cartilage (injuries/disorders)

Osteoarthritis, bone spurs

Tendon (function)

Transmit tensile forces from muscle to bone, change line of action of a mucle

Tendon (structure)

Unidirectional fibres (stiffer), strong in tension, weak in shear

Tendon (common injuries)

Tendinitis (acute), Tendinosis (chronic), Avulsion (acute), Tenosynovitis (chronic)

Ligaments (function)

Attach bone to bone, increase joint stability, guide joint movement

Ligaments (structure)

Multidirectional fibres, can support large tensile loads but can also withstand some shear

Ligaments (common injuries)

Grade 1, 2, 3 sprains

Muscle (function)

Generate motion, joint stability, passive tensile force

Muscle (structure)

Active component wrapped in elastic component

Muscle (common injuries)

Fatigue, atrophy, contusion, strain

ROSA

Rapid Office Strain Assessment

PDA

Physical Demands Analysis

Physical Demands Description (PDD)

A document used by employers to objectively capture and describe the physical demands that are required to perform a particular job or role.

Disability management

Compares the physical demands of a job as it is currently performed to a worker's restrictions. If there is not a direct match, the worker is determined to be unable to perform the job or essential tasks that cannot be performed are downloaded onto another worker.

Disability Prevention

Compares the physical demands of the pre-injury job to a worker's restrictions. Where there is a barrier or mismatch, creative solutions are considered and the best one is implemented to remove the barrier(s) and allow full performance of the essential duties.

PDD Steps

1. Prepare, 2. Observation and data collection, 3. Reporting

Physical Demand Task Elements

Lift/lower, carry, push, pull, reach, grip, pinch, write, fine finger movement, sit, stand, walk, kneel, crouch/squat, balance, crawl, climb, taste, smell, speech, hear, feel/tactile, vision/read, data entry, driving, foot action, handling of odd objects.

Grip types

Power grip, precision grip

Essential job tasks

Tasks of duties that are deemed to be very important, necessary, or vital to the job or service.

Non-essential job tasks

Tasks or duties that are not an integral part of the job or service; they may be shared by other workers within the organization.

Musculoskeletal Disorders (MSDs)

Injuries and disorders of the musculoskeletal system that are caused or aggravated by various hazards or risk factors in the workplace.

Idiopathic MSD

Build up, damage accumulates over time, not enough time to rest & recover. Not one specific act/incident.