Transcript Muscular –Skeletal System

Chapter 3:Physical Ergonomics
Dept. of Biomedical, Industrial, & Human Factors Engineering
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Human Activity Continuum
As a result of activity, the body undergoes various
changes:
Physiological
Psychological
Cognitive
Etc.
Stress and strain
Stress – some undesirable condition, circumstance, task, or other factor
that impinges upon the individual (outside effector)
Examples – heavy work, immobilization, heat and cold, sleep loss, etc.
Strain – refers to the effects of stress on the individual
Examples – blood chemistry, oxygen consumption, electrical activity of the
muscles or the brain, heart rate, work rate, errors, attitudes
People vary on what creates their stress and the level of stain associated
with stress
Dept. of Biomedical, Industrial, & Human Factors Engineering
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Human Activity Continuum
Physical
Dynamic
activity
Psychomotor
Cognitive
Static
loading
Sensory
functions
Thinking
calculating
EMG
EOG
Strain measures
HR
O2 consumption
HR recovery
HRV
EEG
Dual-task
Subjective ratings
ex: NASA TLX
Abbreviations:
EMG - electromyogram
EOG – electroculogram
HRV – heart rate variability
EEG - electroencephalogram
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Stress and Performance
Performance
Peak Performance
Overload
Boredom
Stress
Stress does not always lead to
ill effects
Sources of job stress
Workplace arrangement
(dimensions, relative location,
etc.)
Work content (speed and
accuracy requirements, etc.)
Work organization (work-rest
cycles, start-stop times, work
control, etc.)
Work environment (coworkers, supervisor, heat, cold,
fear of job loss, etc.)
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Muscular-Skeletal System
Movement Terminology
Flexion – decreasing joint angle
Extension – increasing joint angle
Abduction – away from the body
Adduction – towards the body
Pronation – inward rotation
Supination – outward rotation
Sagittal
Horizontal
(traverse)
Lateral
(frontal)
YZ
XZ
XY
Planes of Reference
Sagittal – vertical plane dividing
left and right half of body
Lateral (frontal) – vertical plane
dividing front and back of body
Horizontal (traverse) – horizontal
plane dividing top and bottom of
body
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Muscular-Skeletal System
Skeletal System
206 bones establish framework
Give body structure
Provide protection to vital organs (e.g., skull, ribs)
Basis for activity such as bones in arms, legs, etc.; Levers that
produce movement
Bones are connected to each other via ligaments
Bones connected to muscles via tendons
Produce elements of blood within bone marrow
Store calcium and phosphorus
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Muscular-Skeletal System
Bones - specialized form of connective tissue
Composition
Calcium carbonate/calcium phosphate (60-70%)
Stiffness (stress/strain)
Compressive strength
Collagen (protein)
Flexibility, tensile strength
Decrease with age
Water (25-30%)
Contributes to strength
Connective Tissue in Skeletal System
Cartilage – firm yet elastic and flexible, rapid growth and handles
moderate stress
End of ribs (expansion)
Spinal disks (cushion)
Accounts for bone growth at ends
Hardens when fully developed
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Muscular-Skeletal System
Bones connected to each other at joints
Hinge joints (wrist)
Pivot joints (elbow)
Ball and socket joints (shoulder, hip)
Joints
Fibrous – no movement (e.g., skull)
Cartilaginous – limited range of movement (e.g., spinal
column)
Synovial – large range of movement
Fluid cavity to lubricate (e.g., knee)
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Muscular-Skeletal System
Type of Movement (joints)
Gliding or angular (elbow, knee)
One dimensional
flexion/extension, abduction/adduction
Circumdunction (shoulder, hip, wrist)
Two dimensional, no rotation
Rotation (shoulder, hip, forearm)
Two dimensional about longitudinal axis
Limiting Factors for Range of Motion
Tension of ligaments – elbow or knee extension
Tension of antagonistic muscles – flex/stretch with extended knee
Contact of soft tissue – flex hip with knee relaxed, elbow or knee
flex
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Muscular-Skeletal System
Mobility study by Staff (1983)
32 major body joints
Electric bubble goniometer used to measure range of motion
Females exhibited significantly greater mobility except in ankle
flexion and wrist abduction
Bone development
Change shape, size, and structure depending on mechanical
demands
Wolff’s law – bone deposited where needed and resorbed where
not needed
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Muscular-Skeletal System
Muscles – major prerequisite for human activity
600 muscles in the body; 80 account for most vigorous activity
3 types of muscles
Striated (skeletal)
Cardiac (heart)
Smooth (walls of blood vessels and internal organs)
Skeletal is the most concern to ergonomists
Composed of bundled muscle fibers (length range from 0.2 to 5.5 inches,
but some are as large as 12 inches
Mechanical leverage – muscle applies forces on the bone(s) to which it is
attached
Maximum force in extended state; little force in contracted state
Muscle generates mechanical work by converting chemical energy into
mechanical energy
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Muscular-Skeletal System
Muscles (con’t)
Three thin filaments
Actin (primary filament)
Troponin
Tropomyosin B proteins
Myosin (thick filament) slides over to bring about contraction
Figure 3.3 Pulat
Antogonist Pairs
Can only contract and pull, cannot push
For each motion, there is a muscle to perform opposite motion
Act as break to slow motion and prevent damage
Precise motor movement
Example: Bicep
flexion (bicep contract; tricep inhibit)
extension (tricep contract; bicep inhibit)
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Muscular-Skeletal System
Physiological Characteristics
Irritability (excitability): react to stimuli (electrical stimulation)
Chemical reaction creates muscle contraction
Contractility: increase tension
Shorter and thicker
Extensibility: stretched beyond resting length
Requires antagonist or gravity force
Elasticity: return to resting length
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Muscular –Skeletal System
Classification of muscle contraction
Isometric: no change in muscle length
No physical work performed
Tension usually constant
Concentric: decreasing muscle length
Positive work
Acceleration of limb during movement
Tension decreases
Eccentric: increasing muscle length
Negative work
Deceleration of limb
Tension increases
Isotonic: applied force is constant
Rare in practice
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Muscular Tension
Length of muscle
Maximum tension occurs at resting length (or slightly longer)
All active myosin sites lined up with actin attachment sites
Joint angle changes length
1.5
% max tension
100
1
50
0.5
0
60
0
-0.5
1002
180
4
6
8
% resting length
-1
-1.5
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Muscles
Velocity of Contraction
Maximum velocity at zero tension
Maximum force at zero velocity
Cross sectional area
Max force (0.3-0.4 N/mm2)
Only gender difference is cross-sectional area
Women narrower muscle
Women 2/3 force of men
Electrical Process of muscle
Resting potential of muscle fiber
90 mV with inside negatively charge relative to exterior
Due to imbalance of ions
Action Potential is reversal of resting potential
Positive charge applied (depolarization)
Lasts 2-4 msec, speed 5 m/s
Refractory period is where muscle has decreased ion permeability
1-3 msec after action potential
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Physiological Strain-Basic Physics
Concepts
Force – a unit of force is a newton (N) = 1 kg-m/s2
1 N = 0.225 lbf (pounds force)
Work or Energy – work is done or energy is consumed when a force is applied
over a distance
Measures:
1 N x 1 m = 1 J (joule)
Kilocalorie (kcal) = amount of heat required to raise the temperature of 1 kg of water
from 15 degrees Celsius to 16 degrees Celsius
The Calorie which is used for energy content of food is actually a kilocalorie
1 kcal = 1000 cal = 1 Cal (food)
1 kJ = 1000 J
1 kcal = 4.1868 kJ
1 kcal = 3087.4 ft lbs
Power = work per unit time
Measures
Watt (W) = 1 J/s
Horsepower (hp) = 736 W
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Muscular Activity
Metabolism
Supplies the energy needed to slide the actin filaments over the
myosin filaments. It is a chemical process of converting food into
mechanical work and heat.
Some mechanical work is consumed by the body while other is
consumed by physical activity
Basic source of energy for contraction of the muscle is glycogen or
glucose which is abundant in the blood
Sources of energy (next time)
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