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The Human Body
The Human Body
The Human BodyIntroductionHuman body
– Nervous system– Musculoskeletal system
n Muscular forcesn Muscle extension and contractionn Complex system of muscles and bones
– Produces movements– Cardiovascular system
n Heartn Blood vesselsn Respiratory system
FreivaldsA.,(2009)Niebel’sMethods,Standards,andWorkDesign.McGraw-Hill
n Central Nervous System– Brain– Spinal Cord
n Peripheral nerves– Efferent nerves: Motor nerves– Afferent nerves: Sensory nerves
SomaticNervousSystem– Connectsorganismwithoutsideworld
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
The Human BodyThe Nervous System
The Human BodyThe Nervous SystemNeuron
The structural and functional unit of all nervous tissue (nerve cell)Function
Nerve impulses transmitted through nerve cells
Structure• Soma – Cell body• Axon – Conduct nerve impulses away
from cell bodies• Dendrites – Mediate impulses from other
neurons to the somaKroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
The Human BodyThe Nervous System
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
Function of nerves– Control system– Regulates external and internal activities– Monitors a variety of sensations– Factors influencing the working of a neuron
n Sensitivity of stimulin Ability to transmit a stimulus
– Stimulation of nervesn Impulse travels along nerve fiber
The Human BodyThe Nervous System
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
Muscle innervationn Every muscle is connected to the brain
– Efferent nerves or motor nervesn Motor nerves carry impulses to skeletal muscles
– Afferent nerves or sensory nervesn Sensory nerves conduct impulses back to the brain as signals
n Each nerve fiber serves to innervate several muscle fibers
n Motor unit– Includes motor neuron and the muscle fibers that it
innervates
The Human BodyThe Nervous System
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
Motor Unit§ Group of muscle fibers innervated by branches
of same motoneuron§ Size depends on function of muscle
- May vary between and within muscles- Small in size where precision movement is
required§ Eye muscle à10 fiber in each motor unit
- Larger in coarse acting muscles§ Limb muscleà single motoneuron can supply
more than 1900 fibers
The Human BodyThe Nervous System
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
Reflexes– Controls movement and activity
n Reflex consists of three parts1. An impulse travelling along sensory nerve2. Intermediate neurons, passing impulse to motor nerves3. Final impulse to activate muscle
n Blinking is a reflex used to protect the eye– Stimulus: Unexpected movement– Impulse travels to the brain
n Message passed to motor nerve– Motor nerve operates muscles of the eyelids
The Human BodyThe Nervous System
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
Skilled WorkGrasping Operation
1. Use of visual information to direct movement toward object to be grasped
2. Information from eye is transferred to brain
3. On basis of visual information- Brain decides the next move
4. When object is grasped- Pressure sensitive nerves send new signals to the brain- Operator can adjust finger pressure
The Human BodyThe Nervous System
Kroemer,K.H.E..,Grandjean,E.(1997)FittingtheTasktotheHuman.Taylor&Francis
Conditional Reflexes§ Practice of movements for a long time§ Complete movement pattern becomes engraved in
the brain§ Coordination and delicate adjustment of muscular
movements- Continuous stream of sensory information reaches
motor coordination centers§ Skilled work
- Learning eliminated conscious control - Movements are automatic
The Human BodyThe Musculoskeletal System
Types of muscles– Cardiac Muscle
n Heart muscle– Skeletal Muscles
n Attached to the bone– Smooth Muscles
n Internal organs and walls of blood vessels
FreivaldsA.,(2009)Niebel’sMethods,Standards,andWorkDesign.McGraw-Hill
The Human BodyThe Musculoskeletal System
FreivaldsA.,(2009)Niebel’sMethods,Standards,andWorkDesign.McGraw-Hill
Skeletal Muscles• 400 muscles within the body• Constitute approximately 50% of total body
weight• Attached to the bone by tendons and crosses one
or more joints• Controlled by the voluntary nervous system or
somatic nervous system
FunctionGenerate movement around a joint
The Human BodyThe Musculoskeletal System
FreivaldsA.,(2009)Niebel’sMethods,Standards,andWorkDesign.McGraw-Hill
Structure of muscles• Constitutes of large number of muscle fibers
- Number of fibers depends on muscle size• Connective tissues bind fibers to form bundles• Attached to the bone by tendons and crosses one
or more joints• Controlled by the voluntary nervous system
FunctionGenerate movement around a joint
The Human BodyThe Musculoskeletal System
Structure of Muscle – Group of muscle fibers constitute a muscle– Muscle fibers subdivided into components that
provide the contractile mechanismsn Myofibrilsn Protein filaments
– Filamentsn Allows muscles to contractn Types
– Thick filaments– Thin filaments
n Sliding filament theory– Filaments slide over each other– Allows muscle length to change during contraction
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
The Human BodyThe Musculoskeletal System
The Human BodyThe Musculoskeletal System
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
Muscle contraction– The ability of a muscle to shorten to about half its
normal resting length– Work done by a muscle in a complete contraction
increases with its length– Each muscle fiber contracts with a certain force
n Strength of entire muscle depends on sum of muscle fiber forces
The Human BodyThe Musculoskeletal SystemMuscle contraction
– Maximum strength of human musclen Muscle cross section of 100 mm2 can develop a force
of 30 to 40 Newtons– Inherent muscle strength depends on the muscle
cross-sections– Maximum muscle strength
n At the midrange of the motion
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
The Human BodyThe Musculoskeletal System
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
Regulation of muscular effort– Muscle fiber made to contract by incoming nervous
impulses– Amount of muscle strength depends on number of
nervous impulsesn Excitation of the number of motor nerve cells
– Speed of muscle contractionn Speed at which force is developed during a given
interval of time
The Human BodyThe Cardiovascular System
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
Heavy work§ Activity that requires physical exertion§ Characteristics
- High energy consumption- Severe stresses on the cardiovascular system
§ Energy consumption and cardiac effort- Set limits to performance of heavy work- Used to assess severity of physical task
The Human BodyThe Cardiovascular System
Physiological MeasuresHeart rate
- Normal 72 - 80 beats per minute (bpm)Body temperature
- Normal 98.6º F
Oxygen consumption- Average resting 0.25 - 0.3 liters per
min (L/min)
Blood pressure- Normal 120/80 mm Hg
(systolic/diastolic)
Respiration (ventilation) rate Blood
Metabolites concentration in saliva Urine
The Human BodyThe Cardiovascular System
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
Metabolismn Conversion of chemical energy (food energy) to mechanical
energy and heat
The Human BodyThe Cardiovascular System
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
Basal Metabolism– The rate of metabolic activity of a subject after 12 h fasting and
8 h resting is called Basal Metabolic Rate (BMR)– Energy consumed at rest– Steady energy consumption– All chemical energy from nutrients is converted into heat– Factors influencing basal metabolism
n Gendern Size n Weight
BMR maintains 1) Body Temperature2) Body Functions3) Blood circulation
The Human BodyThe Cardiovascular System
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
Energy expendituren Energy expenditure is required for the muscle contraction
processn Unit of measurement: Kilojoules (kJ)n Assessment
– Direct method§ Measurement of heat (energy) generated by a person in a
calorimeter– Indirect method
n Recording oxygen uptake required for oxidation of nutrients– 1 liter of oxygen consumed = 20 kJ (5kcal) energy released
The Human BodyThe Cardiovascular System
Kroemer,K.H.E.,andGrandjean,E.,(1999).FittingthetasktotheHuman.TaylorandFrancis.
Energy Expenditure– Two basic types of metabolism
n Aerobic– More efficient, but very slow
– Sustained for a long duration
Example: Distance Running
n Anaerobic– Very inefficient, but is much quicker– Work performed for no more than few minutes
Example: Sprinting
The Human BodyThe Cardiovascular System
Energy Expenditure
Sub Maximal - Oxygen Consumption Vs. Time
0
1
2
3
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
minut e s
The Human BodyThe Cardiovascular System
Heart Rating Guidelines– Measurement of oxygen consumption and energy expenditure is very
expensive– An alternate and indirect method of measuring energy expenditure is
heart rate– The heart pumps the blood carrying oxygen to the working muscles, thus
the higher the level of energy expenditure, the higher the heart rate level– Instrumentation: heart rate monitor, $100, easy to use
%HRmax = (HRave - RHR) / (Est. HRmax - RHR) * 100%– Est. Hrmax = 220 - age for females– Est. Hrmax = 205 - age/2 for males
Guideline: Never exceed 1/3 of an individuals max HR or max oxygen consumption!!
FreivaldsA.,(2009)Niebel’sMethods,Standards,andWorkDesign.McGraw-Hill
The Human BodySubjective Ratings
FreivaldsA.,(2009)Niebel’sMethods,Standards,andWorkDesign.McGraw-Hill
Subjective Ratings of Perceived Exertion (RPE)– An even easier way of rating workload,
replacing the expensive machinery– Borg 10 & 20 Scales
Borg’s 1967 RPE Scale with
Verbal Anchors (20 Scale)
Rating Verbal Anchor6 No exertion at all7 extremely light89 very light
1011 light1213 somewhat hard1415 hard1617 very hard1819 extremely hard20 maximal exertion
The Human BodyMeasure Equipment
Heart rate - Heart rate monitor
Blood pressure - Blood pressure monitor
O2 consumption
- Beckman Metabolic Cart (MMC)
CO2 production
Respiratory quotient (RQ)
Tidal volume
Minute ventilation (Ve)
Breath/min
Electromyogram (EMG) - Physiograph- Preamplified surface electrodes connected to a PC (via hardware and software)
Electrocardiogram (ECG/EKG) - Electrocardiograph (5 lead, 9 lead)Lung capacities - FEV1.0, FVC - SpirometerStatic strength - Grip strength- Pinch strength- Back, composite strength
- Hand grip dynamometer- Pinch gauge- Load cell
Dynamic strength - Isokinetic- Isoinertial
- Cybex, LIDO- Air Force 6 ft incremental lift
Range of motion - Goniometer - FlexometerTemperature (oral, skin) - Thermometer, temp probes
