Chapter 12Chapter 12

Guidelines for Guidelines for Whole-Body Whole-Body and Segmental and Segmental VibrationVibration

DefinitionDefinition• Vibration is the oscillatory motion

of a body• rapid changes in direction of a body• high acceleration

DefinitionDefinition• Vibration is the oscillatory motion

of a body• rapid changes in direction of a body• high acceleration

DefinitionDefinition• Vibration is the oscillatory motion

of a body• rapid changes in direction of a body• high acceleration

• Any body with mass and elasticity may vibrate

• machines• structures• human body

Two Classifications of Two Classifications of Vibration:Vibration:• Free vibration

• when a system oscillates under the action of internal forces only• Ie water-balloon in the air

• Forced vibration• caused by external forces

• Opera singer and glass• external force: sound waves• glass vibrates

Quantifying VibrationQuantifying Vibration

• Rate of oscillation • Regular ==> periodic motion

• sine wave• rep time = frequency

• Hertz ==> Hz

• Magnitude of oscillation • size of the force

• Peak value• maximum stress

• Average value• absolute value

Frequency Analysis

Effects: body & segmentsEffects: body & segments• Primary determinants

• frequency• Magic fingers (1-2Hz) vs “tooth rattling”

• induce sleep

• amplitude• duration

• Secondary determinants• Point of application: buttocks, feet, hands• direction of input --fatigue• orientation of segments -- segment

mass• presence of external supports?

Mechanical & Mechanical & PsychologicalPsychological

ResponsesResponses• Mechanical effects • strain on different tissues

• energy is absorbed by tissues and organs (muscles)

• voluntary & involuntary contractions of muscles (spindles)

• cause local muscle fatigue

• Psychological effects• stress reactions

Effects on the spineEffects on the spine

• Research suggests that more low back pain occurs at an earlier age in subjects exposed to prolonged vibration• ie truck drivers, farmers, bus drivers,

pilots

Effects on segmentsEffects on segments• Vibration on segments typically

• High Hz• Low Amplitude

• Vibration Syndrome (some all, some one)

• Injured blood vessels• Nerves• Bones• Joints• Muscles

Reynaud’s Syndrome (vibration white finger)

• Cause• Vibration=> blocks finger circulation

• Symptoms• Fingers ==> white, pale, cold, & painful.• Impact on precision work.• Symptoms are intermittent.• 90% of the cases appear in women

• Etiology• Changes in blood vessel walls• Reflex contraction of blood vessel smooth

muscle

Transmission of vibration Transmission of vibration in UEin UE

• Tools = random vibration over wide Hz • 2-2000 Hz

• Transmission is linear.• Increase in tool vibration = increase

in hand vibration • Greater grip force attenuates

transmission

Vibration FactorsVibration Factors

SummarySummary

• Vibration represents high frequency of application of a relatively low force• FIT

• Best avoided• Environment or task modifications• Administrative intervention (ie

rotation)