Work Physiology & Workload Assessment Agenda Work Physiology - - PowerPoint PPT Presentation

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Work Physiology & Workload Assessment Agenda Work Physiology - - PowerPoint PPT Presentation

Dec 15, 2023 155 likes •511 views

Work Physiology & Workload Assessment Agenda Work Physiology Workload Assessment Human Physiology Definition The science of normal functions and phenomena of living things. The study of the mechanical, physical, and

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Agenda

  • Work Physiology
  • Workload Assessment

Work Physiology & Workload Assessment

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Definition

  • The science of normal functions and phenomena of living things.
  • The study of the mechanical, physical, and biochemical

functions of living organisms.

Components of interest

  • Respiratory system
  • Circulatory system
  • Metabolic system

Human Physiology

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Function

  • Provides O2 for energy metabolism
  • Moves air in and out of lungs.
  • Dissipates metabolic byproducts.
  • Removes CO2, water, and heat from blood into air to be exhaled.

Respiratory System

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Function

  • Carries O2 from lungs to cells

(where metabolic processes

  • ccur)
  • Carries nutritional material from

small intestines to cells

  • Removes byproducts of

metabolism (CO2, heat, water)

Circulatory System

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Collection of processes that converts nutrients to chemical energy, then to mechanical energy and heat. Metabolic rate is divided into three parts:

  • Basal metabolism
  • Maintains body temperature, body functions, and blood circulation.
  • Activity metabolism
  • Provides the energy for activities.
  • Digest metabolism
  • Accounts for transformation of food within the body.

Metabolic System

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Range of joint motion

  • Rotational capacity of joint

Muscular strength

  • Localized, e.g. bicep, or whole body
  • Posture-specific or motion-specific

Physiological capacity

  • Musculoskeletal
  • Metabolic
  • Circulatory

Capacity for Physical Work

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Joint ROM

  • Explains joint mobility
  • Affected by flexibility (e.g. tissue stiffness) and environment (e.g.

clothing, temperature)

  • Active ROM: Individual moves the joint.
  • Passive ROM: Another person moves the joint.

Joint Range of Motion (ROM)

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Measurement of a maximum voluntary exertion Affected by types of muscle contractions

  • Isometric: muscle does not change length
  • Isotonic: constant muscle force
  • Isokinetic: constant velocity exertion
  • Isoinertial: work against a constant load

Muscular Strength

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What do we measure?

  • Maximum torque or force that a group of muscles can

develop under prescribed conditions.

  • Posture specific or motion specific
  • e.g. Maximum elbow flexion torque at 90 deg flexion angle (concentric

isometric exertion)

  • e.g. Maximum elbow extension force throughout its range of motion

(eccentric isokinetic exertion)

Strength Measurement

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Testing factors affecting strength

  • Posture: muscle length, moment arm
  • Motion: velocity, acceleration
  • Time to build-up the max; Length of exertion
  • Amount of rest time between consecutive exertions
  • Hand-load coupling
  • Instructions
  • Environment

Strength Measurement

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Personal factors affecting strength

  • Gender
  • Age
  • Anthropometry
  • Health

Strength Measurement

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Definition: Any reduction in the ability to exert force in response to voluntary effort Contributory factors

  • Metabolic
  • Include chemical changes, reduction in blood flow resulting in ischemia.
  • Activation impairment
  • Central drive-related fatigue
  • Peripheral fatigue
  • Excitation-contraction coupling failure

 Excitation-contraction coupling: A process by which a muscular action potential in the muscle fiber causes the myofibrils to contract

Muscle Fatigue

Sandow A (1952). "Excitation-Contraction Coupling in Muscular Response". Yale J Biol Med 25 (3): 176–201. PMC 2599245.PMID 13015950.

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Endurance time

  • The time taken for a muscle to lose its volitional,

sustained force-producing capability.

  • A function of…
  • Contraction force
  • Exercise-rest cycle
  • Muscle fiber composition

Muscle Fatigue

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Design strategies

  • Quantify strength requirements of task, and, identify

individuals who can meet the requirements.

  • Quantify workers’ strength capabilities and, design tasks

with them in mind.

Occupational Application of Strength Data

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Use to assess physiologic capacity of individual or requirements of a task Typical rates

  • At rest: about or less than 0.5 liter/min
  • For heavy work: about 5 liter/min

Oxygen Consumption (VO2)

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Maximum rate of oxygen consumption (VO2 max) Capacity of an individual; a description of efficiency of cardiovascular system Affected by:

  • Gender, age, physical training.

Tools and Methods

  • Metabolic cart and treadmill

Maximum Aerobic Power (MAP)

http://www.carefusion.com/our-products/respiratory-care/metabolic-carts/masterscreen-cpx-metabolic

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Can assess energy expenditure Primary indicator of circulatory function Indicator of workload Function of:

  • Consumed energy
  • Specific muscles involved
  • Extent of static loading
  • Environmental stressors

Heart Rate (HR)

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Resting pulse: average rate before work Working pulse: average rate during work Work pulse: working – resting pulse

Heart Rate Terminologies

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  • Energy Cost of Work (Activity

Standards)

Workload Classification

  • Grades of Physical Work

(Activity Standards)

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Operational definition: reduced ability to continue existing effort. Proper work-rest cycle can counteract the fatigue and provide opportunity to repay oxygen debt.

Fatigue

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Quick administrative controls

  • More people on job
  • Limit exposure
  • Job rotation; work-rest cycle

Engineering Controls

  • Automate
  • Reduce load

How to Minimize Fatigue

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Tools that can be used to characterize, assess, or quantify work Type of measures

  • Externals: posture, motion, force
  • Internal responses: muscle activity, HR, etc

Bioinstrumentation

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Motion (posture) Analysis

  • 3D linear and angular coordinates
  • Velocity
  • Acceleration

Force Analysis

  • Ground reaction forces
  • Joint reaction forces
  • Muscle contraction force

Bioinstrumentation

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Goniometer

  • Manual goniometer: measurement of angles using simple

scale (static angle only)

  • Electrogoniometer: use variable resistor to measure voltage

and convert to angle

Motion Analysis

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Electromagnetic-based system

  • Multiple sensors in an electromagnetic field.
  • 6 degrees of freedom output from each sensor.
  • Very accurate but expensive.
  • Susceptible to metal interference.

Motion Analysis

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Optical system

  • Each camera captures 2D coordinates
  • f reflective markers.
  • Synchronize multiple cameras to get

3D coordinates.

  • 3D Linear coordinates output from each

marker.

  • Highly accurate (up to 0.1 mm

resolution) but usually the most expensive.

  • Widely used in film industry.
  • https://www.youtube.com/watch?v=ZnrKKjaVxCA

Motion Analysis

http://www.med.nyu.edu/rehabengineering/res earch/locomotion.html

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Video Record Analysis

  • At least two cameras placed perpendicular to each other
  • Less accurate compared to electrogoniometer, electromagnetic-based

system and optical system

Motion Analysis

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Orientation Tracker

  • One of the newest techniques in motion capturing.
  • 3D orientation (roll, pitch, yaw) output from each sensor.
  • Use earth-magnetic field.
  • No camera or reference point is required.
  • Minimal environmental interference.
  • Very accurate and portable.
  • Very expensive for a full body capture

system.

  • https://www.youtube.com/watch?v=6TWrcZ84fR4

Motion Analysis

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Dynamometer

  • Hand dynamometer: measures isometric hand grip force
  • Push-pull dynamometer: measures isometric push or pull force

exerted or supported by two hands

  • Hydraulic or electric

Force Analysis

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Full body dynamometer

  • Measures isometric and isokinetic forces and torque of extremities and

trunk

  • Provide dynamic resistance as well as static resistance.
  • Can simulate various work postures.
  • https://www.youtube.com/watch?v=jyAXnnuxFOw
  • Usually electric powered.

Force Analysis

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Force plate or force platform

  • Measures ground reaction forces and moments
  • Integrates data from four tri-axial load cells
  • Often used to study gait pattern, slip potential, and body balance

Force Analysis

http://www.youtube.com/ watch?v=30bEa_mJqGY&f eature=related

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Force Analysis

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Pressure sensors

  • Glove

pressure mapping system: measures pressure on palm and figures in hand grip motion.

  • Seat

pressure mapping system: measures pressure distribution of a seat pan.

  • Foot

pressure mapping system: measures foot pressure distribution while walking, jumping, or standing.

  • http://www.youtube.com/watch?v=

rSN9OU08XUU&feature=related

Force Analysis

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Electromyography (EMG)

  • Measures electric potential

generated by muscles

  • Can estimate muscle contraction

force level and fatigue development

  • Force level: Magnitude of the potential
  • Fatigue: Median frequency of EMG

signal

  • Uses needle electrodes or

surface electrodes

Force Analysis (internal)

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Example

  • Electromyography (EMG)
  • Optical System

Capacity for Physical Work