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

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 biochemical functions of living organisms.  Components of interest  Respiratory system  Circulatory system  Metabolic system

Respiratory System  Function  Provides O 2 for energy metabolism o Moves air in and out of lungs.  Dissipates metabolic byproducts. o Removes CO 2 , water, and heat from blood into air to be exhaled. 3

Circulatory System  Function  Carries O 2 from lungs to cells (where metabolic processes occur)  Carries nutritional material from small intestines to cells  Removes byproducts of metabolism (CO 2 , heat, water)

Metabolic System  Collection of processes that converts nutrients to chemical energy , then to mechanical energy and heat .  Metabolic rate is divided into three parts:  Basal metabolism o Maintains body temperature, body functions, and blood circulation.  Activity metabolism o Provides the energy for activities.  Digest metabolism o Accounts for transformation of food within the body. 5

Capacity for Physical Work  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

Joint Range of Motion (ROM)  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. 7

Muscular Strength  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

Strength Measurement  What do we measure?  Maximum torque or force that a group of muscles can develop under prescribed conditions.  Posture specific or motion specific o e.g. Maximum elbow flexion torque at 90 deg flexion angle (concentric isometric exertion) o e.g. Maximum elbow extension force throughout its range of motion (eccentric isokinetic exertion)

Strength Measurement  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  Personal factors affecting strength  Gender  Age  Anthropometry  Health

Muscle Fatigue  Definition: Any reduction in the ability to exert force in response to voluntary effort  Contributory factors  Metabolic o Include chemical changes, reduction in blood flow resulting in ischemia.  Activation impairment o Central drive-related fatigue o Peripheral fatigue o Excitation-contraction coupling failure  Excitation-contraction coupling: A process by which a muscular action potential in the muscle fiber causes the myofibrils to contract Sandow A (1952). "Excitation-Contraction Coupling in Muscular Response". Yale J Biol Med 25 (3): 176–201. PMC 2599245.PMID 13015950.

Muscle Fatigue  Endurance time  The time taken for a muscle to lose its volitional, sustained force-producing capability.  A function of… o Contraction force o Exercise-rest cycle o Muscle fiber composition

Occupational Application of Strength Data  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.

• Oxygen Consumption (VO 2 )  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 15

Maximum Aerobic Power (MAP)  Maximum rate of oxygen consumption (VO 2 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 http://www.carefusion.com/our-products/respiratory-care/metabolic-carts/masterscreen-cpx-metabolic

Heart Rate (HR)  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 Terminologies  Resting pulse: average rate before work  Working pulse: average rate during work  Work pulse: working – resting pulse

Workload Classification  Energy Cost of Work (Activity  Grades of Physical Work Standards) (Activity Standards)

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

How to Minimize Fatigue  Quick administrative controls  More people on job  Limit exposure  Job rotation; work-rest cycle  Engineering Controls  Automate  Reduce load

Bioinstrumentation  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  Motion (posture) Analysis  3D linear and angular coordinates  Velocity  Acceleration  Force Analysis  Ground reaction forces  Joint reaction forces  Muscle contraction force

Motion Analysis  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  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  Optical system  Each camera captures 2D coordinates of reflective markers.  Synchronize multiple cameras to get 3D coordinates.  3D Linear coordinates output from each marker. http://www.med.nyu.edu/rehabengineering/res  Highly accurate (up to 0.1 mm earch/locomotion.html resolution) but usually the most expensive.  Widely used in film industry. o https://www.youtube.com/watch?v=ZnrKKjaVxCA

Motion Analysis  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  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. o https://www.youtube.com/watch?v=6TWrcZ84fR4

Force Analysis  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  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. o https://www.youtube.com/watch?v=jyAXnnuxFOw  Usually electric powered.

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

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Force Analysis  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. o http://www.youtube.com/watch?v= rSN9OU08XUU&feature=related

Force Analysis (internal)  Electromyography (EMG)  Measures electric potential generated by muscles  Can estimate muscle contraction force level and fatigue development o Force level: Magnitude of the potential o Fatigue: Median frequency of EMG signal  Uses needle electrodes or surface electrodes

Capacity for Physical Work  Example  Electromyography (EMG)  Optical System