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EVALUATION OF FOOT-TRANSMITTED VIBRATION AND TRANSMISSIBILITY CHARACTERISTICS OF MINING BOOTS AND INSOLES
byPULKIT SINGH
Thesis submitted in partial fulfillment of the requirements for the degree of Master of Human Kinetics (MHK)
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Canada
Ill
Abstract
Vibration can enter the body of mobile equipment operators, the hands of workers using
power-tools or the feet of workers standing on vibrating platforms (Eger et al, 2006).
Epidemiologically, 4-7% of workers in Canada, the United States and the European
Union are exposed to potentially harmful vibrations (Bovenzi, 1996). Mine workers
drilling from stationary platforms are exposed to whole-body vibration above the eight
hour health guidance caution zone set-out in ISO 2631-1 (Leduc et al, 2010). Literature
suggests that the health effects typically observed in the hands have been reproduced in
the feet when exposed to similar vibration frequencies and accelerations (Griffin, 2008).
However, research associated with foot transmitted vibration (FTV) is limited despite
evidence of negative health effects of vibration at the foot, either with direct segmental
exposure (Thompson et al, 2010) or indirectly with hand-arm vibration exposure
(Sakakibara and Yamada, 1995). Improved understanding of FTV is warranted, to deal
with potentially harmful vibrations, which lead to injury, and to identify interventions
capable of attenuating harmful vibrations at the foot.
The primary objective of study one (Chapter 2) was to determine the vibration
transmissibility between the floor and the ankle when exposed to FTV. The
transmissibility between the floor and ankle was compared between males and females
and between different foot arch types to determine if there was a significant difference in
floor-to-ankle vibration transmissibility. The second objective was to determine if there is
correlation between floor-to-ankle transmissibility and participant reported discomfort
scores. Sixteen university aged participants (eight males and eight females) participated in
the study. The participants were exposed to two levels of vibration, while standing on a
low frequency (3.15-lOHz) and a high frequency (40Hz) vibration platform. Vibration
was recorded at the floor and the ankle with two tri-axial accelerometers in accordance
with the ISO 2631-1 guidelines. Participants reported body discomfort on a 9-point
discomfort scale following each vibration trial. Vibration recorded in the z-axis (vertical
axis) entering the foot (Fawz) was compared to vibration recorded in the z-axis at the
ankle (Aawz). The percentage difference between Aawz and Fawz was taken as a measure
of vibration transmissibility from the floor through the foot to the ankle. There was a
significant difference in floor-to-ankle vibration transmissibility (p= 0.001; F= 3.27) by
vibration exposure frequency. The participants attenuated FTV when exposed to high
frequency vibration; however, there was no significant attenuation of vibration during low
frequency vibration exposure. There was no significant difference in the floor-to-ankle
vibration transmissibility or discomfort by gender (p= 0.715), or foot arch type (p=
0.515).
Despite evidence to support their efficacy, many industries use mats and insoles believing
they are capable of attenuating FTV (Leduc et al, 2011). Therefore, the primary objective
of the second study (Chapter 3) was to determine the transmissibility of commercially
available insoles and mining boots. Sixteen participants (eight males and eight females)
experienced four insoles and two mining boot conditions at two vibration levels, while
standing on a low frequency vibration platform (3.15-10Hz) and a high frequency
vibration platform (40Hz). Vibration was recorded at the floor and above the insole/boot
at the ankle with two tri-axial accelerometers in accordance with the ISO 2631-1
standard. The percentage difference between the vibration recorded at the ankle (Aawz)
and the vibration recorded at the floor (Fawz) was used to determine vibration
transmissibility of the insole/mining boot. A paired comparison of the insoles/mining
boots was also done to identify the preferred insole/mining boot based on participant
comfort reports (9-point scale) provided after each insole/mining boot condition. There
was a significant difference in vibration transmitted from the floor through the insole (p=
0.00; F= 17.91) and boot (p= 0.014; F= 6.31) to the ankle by exposure frequency. All the
insoles and mining boots attenuated vibration during high frequency vibration exposure;
however, with the exception of mining boot 1 none of the insoles or mining boot 2 were
effective in attenuating vibration during low frequency FTV. There was no significant
difference in vibration transmissibility or reported discomfort between genders. The
participants identified insole-3 and mining boot-2 as most comfortable when exposed to
low frequency and high frequency FTV. Future studies should identify an effective boot-
insole combination capable of attenuating vibration frequencies believed to contribute to
potential health risks at the feet.
VI
Acknowledgement
“I can no other answer make, but, thanks, and thanks” - William Shakespeare
Finally I am taking this privilege to thank all the wonderful people who helped me from
the beginning to the completion of this project. Believe me it wouldn’t have been such a
smooth and pleasant journey without having all of you around. Every one of you fills a
space of deep respect in my heart.
I am very thankful to my family for providing me this great opportunity while staying
away from everyone. At last, I followed the tradition of success and your belief and love
was always a source of inspiration whenever I was down. Thank you Papa, Mummy and
Bhai, I love you all.
Especially I would like to thank my mentor, Dr. Tammy Eger who always stood by me
throughout the project and for being a great source of inspiration. Tammy, the way you
managed all the situations and your brilliant ideas were key to the successful completion
of the project. In one word, you are the best and I feel fortunate to have worked under
your supervision. Thank you Dr. Eger.
I would also like to thank Dr. Sylvain Grenier and Dr. Alison Godwin. It was impossible
to complete the project without your valuable time and suggestions. Thanks to Dr.
Michelle Oliver, Dr. Jim Dickey and Dr. Ron House for their collaboration and valuable
input to the project.
VII
Thanks to Sulabh Singh, Mallorie Leduc, Ashish Dhall, Jason Chevrier and Matthew
Felton for helping me in the data collection and with my pilot studies.
I would like to acknowledge the continuous help and support from the Centre for
Research Expertise in the Prevention of Musculoskeletal Disorders, Workplace Safety
and Insurance Board of Ontario, Ontario Mining Industry and Workplace Safety North
for financially supporting the project.
At last, my deepest gratitude to all the participants who voluntarily stepped on the
vibration platform for this project.
Thank you everyone.
VIII
Co-Authorship and Author Contributions
Chapters 2 and 3 have been presented as draft manuscripts intended for submission to a
peer-review journal.
Chapter 2:
EVALUATION OF GENDER DIFFERENCES AND FOOT ARCH TYPE IN FOOT TRANSMITTED VIBRATION
Chapter 3:
EVALUATION OF VIBRATION TRANSMISSIBILITY PROPERTIES AND COMFORT OF INSOLES AND BOOTS WORN BY MINE WORKERS
The research work completed in Chapter 2 and Chapter 3 was financially supported by
the Workplace Safety and Insurance Board of Ontario and the Centre of Research
Expertise for the Prevention of Musculoskeletal Disorders (CRE-MSD). The Ontario
mining industry and Workplace Safety North also provided continued support for the
research work.
IX
TABLE OF CONTENTS
1. Review of Literature 1
1.1 Introduction 2
1.2 Understanding Vibration 4
1.3 Epidemiology and Health Effects 5
1.4 Hand-Arm Vibration Exposure 9
1.5 Whole-Body Vibration Exposure 14
1.6 Effect of Vibration in Standing 15
1.7 Biodynamic Response and Transmissibility 19
1.8 Comparison Between Hand-Arm and Foot-Ankle Response to Vibration 23
1.8.1 Anatomy of Hand and Foot 23
1.8.2 Arches of the Foot 24
1.8.3 Assessment of the Foot Arch 25
1.8.4 Bio-dynamics and Vibration Transmissibility of the Hand 26
1.9 Strategies to Reduce Vibration 29
1.9.1 Reduction Strategies for WBV Exposure 29
1.9.2 Reduction Strategies for HAV Exposure 31
1.9.3 Reduction Strategies for FTV Exposure 33
1.10 Thesis Outline 33
References 36
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2. Examination of Floor to Ankle Vibration Transmissibility and Subjective Discomfort of Males and Females with Different Foot Arch Classification when Exposed to Foot Transmitted Vibration
Abstract
2.1 Introduction
2.2 Methodology
2.2.1 Participants
2.2.2 Vibration Exposure
2.2.3 Vibration Measurement
2.2.3.1 Vibration Measurement at Platform
2.2.3.2 Vibration Measurement at Ankle
2.2.4 Foot Arch Assessment
2.2.5 Discomfort Measurement
2.2.6 Floor to Ankle Vibration Transmissibility Measurement
2.2.7 Data Collection Procedure
2.2.8 Data Analysis
2.2.9 Statistical Analysis
2.3 Results
2.3.1 Floor to Ankle Vibration
2.3.2 Discomfort Score
2.4 Discussion
2.4. ITransmissibility
2.4.2 Discomfort
2.5 Limitations
2.6 Conclusion
References
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3. Evaluation of Vibration Transmissibility Property and Comfort of Insoles and Boots Worn by Mine Workers
Abstract
3.1 Introduction
3.2 Methodology
3.2.1 Participants
3.2.2 Insoles and Boots Evaluated
3.2.3 Vibration Exposure
3.2.4 Vibration Measurement
3.2.4.1 Vibration Recording at Floor
3.2.4.2Vibration Recording at Ankle
3.2.5 Transmissibility Measurement
3.2.5.1 Effective Amplitude Transmissibility of Insoles and Boots
3.2.6 Discomfort Score
3.2.7 Paired Comparisons
3.2.8 Data Analysis
3.2.9 Statistical Analysis
3.3 Results
3.3.1 Insole Transmissibility
3.3.2 Discomfort Score Associated with Insole Transmissibility
3.3.3 Mining Boot Transmissibility
3.3.4 Discomfort Score Associated with Boots
3.4 Discussion
3.4.1 Transmissibility
3.4.2 Discomfort
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3.5 Limitations 124
3.6 Conclusion 125
Reference 126
4. General Discussion 134
4.1 Linking of the Previous Chapters 134
4.2 Relevance to the Mining Industry 135
4.3 Relevance to the Medical Industry 135
4.4 Relevance to the Insoles/Mining Boot manufacturing Industries 136
4.5 Conclusion 136
References 138
Appendix 1 141
Appendix 2 147
Appendix 3 153
Appendix 4 159
Appendix 5 168
Appendix 6 174
Appendix 7 207
XIII
List of Figures
Chapter 1
1.1 Pictorial Demonstration of Arches of Foot 25
Chapter 2
2.1 Placement of Accelerometers 60
2.2 Accelerometer placed on lateral malleolus of the ankle and secured by taping 61
2.3 Foot Print for Measurement of Arch Index 63
2.4 Axis Orientation of the Ankle Accelerometer 66
2.5 Main Effect Plot for the Percentage Vibration Transmissibility Versus Gender, Frequency and Mass
2.6 Interaction Plot for the Percentage Vibration Transmissibility Versus Gender, Frequency and Mass
Chapter 3
3.1 The Commercially Available Insoles Tested
3.2 Two Types of Commercially Available Mining Boots that were Tested
3.3 Accelerometer Mounted Over the Lateral Malleolus of the Left Ankle Above the Cut off Boot
3.4 Placement of Accelerometers
3.5 Axis Orientation of the Ankle Accelerometer
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70
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3.6 Accelerometer Placed on the Lateral Malleolus of the Ankle and Secured by Pro-Wrap Taping 106
3.7 Main Effect Plots for the Percentage Vibration Transmissibility Versus Gender, Frequency, Insole and Mass
3.8 Interaction Plot for the Percentage Vibration Transmissibility Versus jjj Gender, Frequency, Insole and Mass
3.9 Main Effect Plots for LB Discomfort Versus Gender, Frequency, Insole and Mass 114
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3.10 Main Effect Plots for UB Discomfort Versus Gender, Frequency, Insole and Mass
3.11 Main Effect Plots for the Percentage Vibration Transmissibility Versus Gender, Frequency, Boots and Mass
3.13 Main Effect Plots for UB Discomfort Versus Gender, Frequency, Boot and Mass
3.14 Main Effect Plots for LB Discomfort Versus Gender, Frequency, Boots and Mass
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3.12 Interaction Plot for the Percentage Vibration Transmissibility Versus Gender, Frequency, Boots and Mass 119
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XV
List of Tables
Chapter 1
1.1 Different Body Areas and there Reported Resonant Frequency Range 7
1.2 Reported Cases with Raynaud’s Phenomenon of Toes in Vibration Exposed 17 Workers
Chapter 2
2.1 Demographic Data and Pre-test Discomfort Rating
2.2 Summary of the Vibration Characteristics
2.3 Multivariate Analysis: GLM ANOVA Transmissibility Versus Gender, Frequency,Mass, Discomfort and Foot Arch Type
3.2 Paired Insole Comparisons for Vibration Testing
3.3 Paired Boot Comparisons for Vibration Testing
3.4 Multivariate Analysis: GLM ANOVA Transmissibility Versus Gender, Frequency, Insole, Mass and Discomfort
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59
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2.4 Mean Vibration Transmissibility in the Males and Females with Different Foot Arch Types at LF and HF Vibration Exposure ^
Chapter 3
3.1 Demographic Data and Pre-test Whole Body Musculoskeletal Discomfort Reported by the Participants on a Nine Point Scale
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3.5 Transmissibility and Discomfort Score During Three Different Insole Condition in 110 Males following HF and LF Vibration Exposure
1123.6 Transmissibility and Discomfort Score During Three Different Insole Condition in Females following HF and LF Vibration Exposure
3.7 Transmissibility and Discomfort Score for Boot Conditions in Males following HF and LF Vibration Exposure
3.8 Transmissibility and Discomfort Score for Boot Conditions in Females following HF and LF Vibration Exposure
1173.9 Multivariate Analysis: GLM ANOVA-Transmissibility Versus Gender, Frequency,Boots, Mass and Discomfort 118
Glossary
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Abbreviation Long FormA(8) 8-hour energy equivalent vibration total valueANOVA analysis of variance&wx frequency-weighted r.m.s. acceleration in the x-axis
frequency-weighted r.m.s. acceleration in the y-axisaWz frequency-weighted r.m.s. acceleration in the z-axisDF dominant frequencyFTV foot-transmitted-vibrationHAV hand arm vibrationHAVS hand arm vibration syndromeHGCZ health guidance caution zone
HF high frequencyISO International Organization for StandardizationIN 1 insole 1IN 2 insole 2IN 3 insole 3LB lower bodyLF low frequencyNIN no insoler.m.s. root-mean-squareSD standard deviationUB upper bodyVATS vibration analysis tool-setVDV vibration dose valueVWF vibration white fingerVWFt vibration white footWBV whole-body vibrationwd weighting factor, applied to the x & y axes, as described in ISO 2631-1Wk weighting factor, applied to the z-axis, as described in ISO 2631-1
XVII
Vibration Terminology and Definitions
Listed below are the vibration related terms, along with a basic definition, that have been
used throughout the thesis document. However, for a detailed understanding of
terminologies related to mechanical vibration and shock, the reader should refer to the
1997, ISO 5805 (mechanical vibration and shock - human exposure - vocabulary)
document and the 1990, ISO 2041 (vibration and shock - vocabulary) document.
,4(8) - The 8-hour energy equivalent vibration total value for a worker in meters per
second squared (m/s2), including all whole-body vibration exposures during the day.
Acceleration: A vector quantity that specifies the time-derivative of velocity.
Accelerometer: A pick-up that converts an input acceleration to an output (usually
electrical) that is proportional to the input acceleration.
Amplitude: The maximum value of a sinusoidal vibration.
Amplification: A signal is said to be amplified if it increases in amplitude and intensity
Attenuation: Attenuation is the reduction in amplitude and intensity of a signal. For
example, a vibration signal may be attenuated as it is transmitted through the body.
Biodynamics: The science of the physical, biological and mechanical properties and
responses of the human body (tissues, organs, parts and systems) to an external force
(vibration) or in relation to the internal forces, produced by an interplay of external forces
and the body’s mechanical activity.
Comfort: Subjective state of well-being or absence o f mechanical disturbance in relation
to the induced environment (mechanical vibration or repetitive shock).
XVIII
Damping: The dissipation of energy with time or distance (i.e. the amplitude of the
vibration signal decreases).
Directional vibration: Translational or rotational mechanical vibration [shock] acting
upon a human as a whole or upon parts of a human (e.g. hand, head or limbs).
Dominant frequency: A frequency at which a maximum value occurs in a spectral
density curve.
Frequency weighted: A term indicating that a wave-form has been modified according
to some defined frequency weighting.
Frequency weighting: A transfer function used to modify a signal according to a
required dependence on vibration frequency. For whole-body vibration, the frequencies
thought to be most important range from 0.5-80Hz. However, because the risk of damage
to different body parts is not equal at all frequencies a frequency weighting is used to
represent the likelihood of damage from the different frequencies.
Hand arm vibration/hand transmitted vibration: Mechanical vibration directly applied
or transmitted to the hand-arm system, commonly through the palm of the hand or
through the fingers gripping a tool or work piece.
ISO 5349-1: The International Standard for the measurement and assessment of human
exposure to hand-transmitted vibration.
ISO 2631-1: The International Standard used to describe the effects of whole body
vibration exposure on human health.
Peak value: The maximum value of a vibration (maximum deviation from the mean
value) during a given interval.
XIX
Resonance: A resonance of a system in forced oscillation exists when any change,
however small, in the frequency of excitation, causes a decrease in a response of the
system.
Resonant frequency: The frequency at which resonance occurs. At the resonant
frequency of a system, peak oscillation will occur.
r.m.s. value: For a set of numbers, the square root of the average of their squared values.
Shock absorber: A device for the dissipation of energy in order to reduce the response of
a mechanical system to applied shock.
Segmental vibration: Mechanical vibration applied or transmitted to a particular
segment, area or region of the human body.
Transmissibility: The unit-less ratio of the response amplitude of a system, in steady-
state forced vibration, to the excitation amplitude. A value greater than one would
indicate the vibration was amplified as it travelled from the “input location” to the
“output” locations, whereas a value less than one would indicate attenuation.
Transfer function: A mathematical relationship between the output and the input of the
system.
Transient vibration: The vibratory motion of a system other than steady-state or
random.
Vibration: The variation with time of the magnitude of a quantity which is descriptive of
the motion or position of a mechanical system, when the magnitude is alternately greater
and smaller than some average value or reference.
XX
Weighted acceleration: Weighted vibration level value or set of values of vibrational or
repetitive shock acceleration affecting human that has been subjected to a computational
or signal conditioning operation to reflect human response characteristics as a function of
vibration frequency or exposure time.
VATS: The Vibration Analysis Toolkit. A software application used to derive the
various measures required by the ISO 2631-1 standard for assessing the health effects of
whole-body vibration exposure.
Whole Body Vibration: Mechanical vibration transmitted to the body as a whole,
usually through areas of the body (e.g. buttocks, soles of the feet, back) in contact with a
supporting contact surface that is vibrating.
x-axis vibration: Translational mechanical vibration in the direction of the x-axis of the
anatomical coordinate system of the human body or of a part of the body.
y-axis vibration: Translational mechanical vibration in the direction of the y-axis of the
anatomical coordinate system of the human body or of a part of the body.
z-axis vibration: Translational mechanical vibration in the direction of the z-axis of the
anatomical coordinate system of the human body or of a part of the body.
CHAPTER 1
REVIEW OF LITERATURE
1.1 Introduction
People can be exposed to vibration in the workplace and/or during activities of their daily
life. Automobiles, different equipment and industrial activities expose people to periodic,
random and transient mechanical vibration, which can interfere with comfort, activities
and health (ISO 2631-1, 1997). In the workplace, people can be exposed to vibration
when standing, sitting, and in some cases, when lying while in contact with a vibration
source. Vibration exposure has been one of the latent causes for occupational health
injury/disease in many industries. The harmful effects of vibration on health usually
appear after several years of vibration exposure (Fritz, 2000). Knowledge of how
vibration is transmitted to and through the human body can provide an important input to
our understanding of the bio-dynamic response of the body to vibration exposure. Also an
improved understanding of vibration transmissibility is also necessary for proper design
and application of protective measures to attenuate harmful vibrations.
The International Organization for Standardization (ISO) provides guidelines for
vibration exposure and measurement in ISO 2631-1: Mechanical vibration and shock -
Evaluation of human exposure to whole-body vibration - Part 1: General requirements.
The guidelines are applicable to situations where the individual is exposed to whole-body
vibration when sitting, standing, or lying on a vibrating surface. Similarly, The ISO
provides further guidelines for measuring segmental vibration transmitted through the
hand-arm system; ISO 5349-1: Mechanical vibration - Guidelines for the measurement
and the assessment of human exposure to hand-transmitted vibration. However, an
analogous standard to assess health risks associated with segmental vibration transmitted
through the feet does not exist. Currently, exposure to foot-transmitted vibration (FTV),
3
whether of a whole-body or segmental nature, is evaluated according to ISO-2631-1
guidelines. Recent work by Leduc et al. (2011) and Thompson et al. (2010) suggests this
may not be the best approach.
Exposure to whole-body vibration (WBV) from a seated position and techniques to
attenuate vibration that enters the body when seated has been widely studied (Paddan et
al, 2001; Niekerk et al, 2003). Similarly hand arm vibration (HAV) exposure associated
with gripping tools that vibrate rapidly has been studied in more depth (ISO 5349-1,
1986) and attention is turning to the development of anti-vibration tools and gloves to
reduce HAV exposure (Jetzer et al, 2003). However, health effects associated with
exposure to FTV and the bio-dynamic response of the feet to FTV are less understood.
Workers can be exposed directly or indirectly to FTV. For example, indirect exposure can
occur from hand-held drills attached to the standing platform (Hirata et al, 2004; Leduc et
al, 2011). On the other hand, direct vibration exposure occurs when the workers stand to
operate mobile equipment such as locomotives (Eger et al, 2006; Leduc et al, 2011).
Exposure to FTV can affect neurological, vascular and musculoskeletal systems of the
exposed worker, which occurs either due to direct exposure or as a secondary
complication to HAV syndrome (Sakakibara, 1995). Despite evidence of negative health
effects associated with FTV, little is known about the bio-dynamic response of the feet
and lower body to vibration. Even though awareness to prevent health hazards associated
with FTV has been employed by many industries with the use of anti-vibration mats,
insoles and mining boots, the efficacy of these materials in reducing vibration
transmissibility is yet to be proved.
In the following sections, vibration will be discussed in general terms and
epidemiological evidence for health effects associated with WBV, HAV and FTV will be
presented. The importance of an improved understanding of the structures exposed to
vibration will also be discussed before attention is given to interventions aimed at
decreasing the health risks associated with exposure to vibration. Lastly, the objectives of
the research project will be outlined.
1.2 Understanding Vibration
Vibration is a mechanical movement that oscillates about a fixed (often a reference) point.
Oscillatory displacement involves alternating velocity in one direction with a velocity in
the opposite direction. This change of velocity means that the object is constantly
accelerating, first in one direction and then in the opposite direction (Griffin, 1998). The
oscillations produced are characterized as a simple harmonic sine wave or a multiple
wave complex differing in frequency and acceleration, or a random non-repeating series
of complex waves (Palmear, 1998). Vibration needs a medium to propagate the energy
through a system (Mansfield, 2005). When an individual is exposed to vibration, the
vibration energy is transmitted into the body through compressions and rarefactions of
tissues and fluids in the body (wave-propagation).
In order to describe the characteristics of a vibration signal, frequency and acceleration
are generally reported. Acceleration is a measure of the magnitude or amplitude of signal
oscillation and is typically reported in m/s2 (meters per second squared). Frequency is a
measure of the number of oscillatory motions completed in one second and is measured in
cycles/second or Hertz (Hz). Vibration can occur along three principal axes: vertical
vibrations are measured along the z-axis, fore-aft vibrations are measured along the x-
axis, and side-side (lateral) vibrations are measured along the y-axis.
1.3 Epidemiology and Health Effects
International Labor Office in 1977 identified vibration exposure as being one of the latent
causes for occupational injury/disease in many industries (Mandal, 2006). Studies have
reported that approximately 4-7% of workers in Canada, the United States and European
countries are exposed to vibration that may potentially cause negative health effects
while exposed to FTV in standing. Leduc et al. (2010) also reported that two of seven
17
miners exposed to FTV were diagnosed with Vibration White Feet (VWFt) in her
research study at Northern Ontario mine sites. Reportedly, both of the workers were
exposed to standing vibration through their feet and were also diagnosed with HAVS.
Table 1.2 shows various cases with Raynaud’s phenomenon of the toes reported in
previous research.
Table 1.2: Reported cases with Raynaud’s phenomenon of toes in vibration exposed
workers
Mills ( 1942)l) one pneumatic hammer operatorSuzuki et al. (1966)2> one rock drillerGomibuchi and Ohi one chain-saw and wood collecting machine operator(1967)1)Hashiguchi et al. ( 1988)4) three cases: a chain-saw operator,
a rock driller, a stone crusher operatorHedlund (1989)*> six cases of twenty-seven minersToibana and Ishikawa ten cases: three chain-saw operators, three rock(1990)6) drillers, and others
(Table taken from: Sakakibara H; Sympathetic responses to hand-arm vibration and
symptoms o f the foot; 1994)
Furthermore, in a case report presented by Thompson et al. (2010), the authors reported
VWFt in a mine worker (54 year old male with 18 years o f vibration exposure while
working with rock drills and roof bolters) solely from exposure to FTV (i.e. independent
of exposure to HAV). The subject was diagnosed with bilateral and symmetric
vasospastic disease (Raynaud's phenomenon) in the feet but not in the hands. Due to the
central sympathetic vasoconstrictor reflex induced vasospasm in the extremities, House et
al. (2010) recommended screening of workers exposed to HAV for any vascular
18
abnormalities in the feet. In another study, whose purpose was to rule out the
vasoconstrictive changes in the foot as being solely dependent on the sympathetic
pathway mediated by HAV exposure, researchers found that miners exposed to segmental
foot vibration had severe vasospasm of the feet than hands. This led to the conclusion that
the changes in the feet were not necessarily sympathetically induced from HAVS and
could be the direct result of segmental vibration exposure at the feet while standing. Choy
et al. (2008) has also reported white toes in a 58 year old male subject with 30 years of
vibration exposure as a rock drill operator. In the same study, researchers suggested that
symptoms of the feet must be assessed by the occupational and environmental medicine
physicians when diagnosing HAVS due to the high incidence of vasoconstrictive changes
in the feet following HAV exposure. Structural changes like thickening of the tunica
media in the foot vessels and perivascular fibrosis have also been reported in the
individuals with long-term direct vibration exposure of the foot while standing
(Hashiguchi et al, 1994). Direct exposure to FTV in the experimental animal models has
also reported sciatic nerve damage (Lundborg et al, 1987) and atrophy of the muscles of
the legs and sole (Shanskaya, 1965).
Adverse health effects during HAV exposure are associated with vibration exposure with
a frequency range of 20-50 Hz, and more than 80Hz for the fingers; whereas the risks to
the whole body are greatest in the frequency range of 4-8Hz (Griffin, 1990). The
symptoms of the feet during vibration exposure were noted when exposed to the critical
HAV frequency levels. Moreover, ISO 2631-1 places the greatest emphasis on the lower
frequency ranges (0-20 Hz), which may not adequately address the health risks at the feet.
Therefore, it might be more appropriate to determine the health risks associated with
vibration exposures at the feet by referring to the guidance in ISO 5349-1, hand-arm
19
vibration standards. However, since ISO 5349-1 standard does not contain information on
standing vibration measurement, which are well demonstrated by ISO 2631-1 standards;
the current study adapted ISO 2631-1-Mechanical vibration and shock - Evaluation of
human exposure to whole-body vibration - Part 1: General requirements; guidelines for
vibration measurement at the feet in the individuals exposed to FTV while standing.
1.7 Biodynamic Response and Transmissibility
Some understanding of the manner in which vibration is transmitted to and through the
body is necessary to understand how vibration influences human comfort, performance
and health. It is also necessary for the proper consideration of protective measures that
prevent direct contact with the vibration source (e.g. seat cushions, anti-vibration gloves
etc.) or reduces vibration transmission in the body (e.g. postural changes). Measures of
the dynamic responses of the body are represented by transfer functions, which are
categorized into two groups: those where two measures are obtained at different points
(i.e. at the driving point of vibration and a location remote from the driving point) and
those where two different measurements are obtained at the same point. The first method
is used to calculate vibration transmissibility through the body, in which the ratio of
motion at one point to motion at another point is determined. The latter case most often
involves the determination of the ratio of the force and acceleration to determine the
driving point mechanical impedance (Mansfield, 2005).
The transfer function at any frequency can be expressed as either two numbers
(magnitude and phase) or as a single complex number. The combination of the magnitude
and phase is commonly referred as the “transfer function” and the magnitude alone as the
“transmissibility” (Mansfield, 2005).
20
The equation if transmission of vibration from the floor (vibration platform) to the ankle
is considered will be:
T (f) = a gnk!e(f)/anoor(f) (Equation 1)
Where, aankie(0= acceleration measured at the ankle at frequency (f)
a n o o r ( f ) = acceleration measured at the floor at frequency (f)
Thus, if the aankie(f)/ a f l o o r ( f ) ratio is less than 1 it indicates attenuation of the vibration and
if it is more than 1, it indicates amplification of the vibration during its course through the
heel to the ankle (Mansfield, 2005).
The peak in the vibration transmissibility occurs at the resonant frequency of the tissue,
and then vibration at that frequency is amplified by a buildup of stored energy due to
repeated stretching and compression of tissue (Mansfield, 2005). As mentioned earlier,
all mechanical systems have its typical resonant frequency at which there is maximum
shear force at the tissue level. Bio-dynamic studies have identified critical frequencies for
some of the body segments and it has been reported that some type of detrimental effects
are closely related to vibration exposure, resulting in resonant behavior of the exposed
body part (Holmlund et el, 2000).
In the past, whole-body vibration transmissibility has typically been determined between
the seat surface (input) and the head (output) (Griffin, 1990). Other studies have
discussed vibration transmissibility to other body parts like the hip (Guignard, 1959),
shoulder (Rowlands, 1977), thorax (Donati and Banthoux, 1983) and cervical vertebrae
21
(Cooper, 1986; Griffin, 1990). Differences in the transmissibility from the seat to the head
have been attributed to changes in the posture of the body, head and limbs (Griffin, 1990).
The effect of neck and pelvic postures on vibration transmissibility has been reported by
Messenger and Griffin (1989). It was concluded that an anatomically erect sitting posture
would tend to increase the transmission of vibration to the head at higher frequencies but
minimize transmissibility at low vibration frequencies. Also, there is some evidence that
changes in the foot position alter seat-to-head vibration transmissibility (Rowlands and
Maslen, 1973; Rowlands, 1977 and Griffin et al, 1979; Griffin, 1990; Jack et al, 2008).
Muscle tension along the body during vibration exposure has also been identified as the
possible cause of alterations in vibration transmissibility (Guignard, 1959 and Griffin et
al, 1979; Griffin, 1990).
There are limited resources on gender differences in vibration transmissibility. Griffin and
colleagues (1982) exposed 18 male and 18 female subjects to WBV between 1-100 Hz
and found that, although the median transmissibility had the same general form, women
had significantly less vertical head motion at 2.5 Hz and significantly more vertical head
motion at 40, 50 and 63 Hz than men. In a separate study, researchers found that females
tend to absorb more vibration power per kilogram of sitting weight. However, researchers
attributed this finding to the higher body fat mass to muscle mass ratio in female
compared to their male counterparts. It was reported that fat, being viscous and inelastic,
implies a high degree of damping, and thus leads to greater vibration absorption in
females (Lundstrom and Holmlund, 1998).
Studies on the transmission of vertical floor vibration to the heads of subjects standing
erect generally suggest that vertical head vibration is similar to that when seated in an
erect posture. Paddan (1987) showed that transmissibility to all six axes of the head is
22
broadly similar whether standing or sitting erect, with the greatest motion occurring in the
mid-sagittal plane (i.e. x-axis, z-axis and pitch axis) (Griffin, 1990; Matsumoto and
Griffin, 2000). However, there was greater transmission of vertical vibration to the pelvis
and the lower spine in the standing posture than in the sitting posture at the principal
resonance (5-6 Hz) and at higher frequencies (Matsumoto, Griffin, 2000). Also, it was
found that “unlocking and slightly bending the knees” results in a small reduction in the
vibration transmissibility at any frequency below 25 Hz. Bending the knees so that they
were vertically over the toes reduced vertical transmissibility of the vibration at all
frequencies above 5 Hz (Griffin, 1990). A recent study by Caryn and Dickey (2010)
reported that the axial skeleton is exposed to large amounts of mechanical energy with
full knee extension.
The human body has a complex response to vibration that varies greatly within and
between individuals. Although there are some data showing the transmission of vibration
to the body (impedance) and also through the body (transmissibility), the complexity of
the phenomenon and the factors which influence vibration in the body is not well
understood and needs more work. Also, there is a lack of knowledge on the vibration
transmissibility through the feet and the lower body while standing on a vibration source.
Considering the increase in the reported cases with VWFt, this justifies the need for
further research in this context to prevent health hazards.
1.8 Comparison Between Hand-Arm and Foot-Ankle Response to Vibration
1.8.1 Anatomy of the Hand and Foot
(Paraphrased from Gray’s Anatomy o f the Human Body, 1918; Nor kins and Levangie,
2001)
23
The ‘wrist and hand’ in the upper extremity and ‘ankle and foot’ in the lower extremity of
the human body appears to be structurally constructed on similar principles. The
interdependence of the ankle and foot with the more proximal joints of the lower
extremities and the great weight bearing stresses to which these joints are subjected have
resulted in higher frequency of lower extremity disorders (Norkin and Levangie, 2001).
The hand and wrist consists of proximal carpal bones, middle metacarpal bones and the
terminal free mobile segment, phalanges. Similarly, in the lower extremity, the hind foot
consists of tarsal bones, mid-foot has tarsal and metatarsal bones, and the forefoot
consists of metatarsals and phalanges. The proximal row of carpal and tarsal bones
consists of cubical bones, which are chiefly concerned in distributing forces transmitted
to or from the long, weight bearing bones of the upper or lower extremities. The middle
part of the metatarsals and metacarpals provides greater surface area for the efficient
force distribution and transmission. The terminal portion of the hand and foot or
phalanges are the most movable part, to allow a large range of movement, particularly
flexion/extension.
The vascular and nerve distribution in the foot and hand are very similar. The ulnar and
radial artery supply blood to the hands whereas the medial and lateral plantar artery
supply blood to the feet. The muscles of the hand are innervated by the median and ulnar
nerves and the intrinsic muscles of the foot are innervated by the medial and lateral
plantar nerves.
However, functionally, the hand and foot have different roles. The foot forms a firm basis
of support for the body in the erect posture and helps in the propulsion of the body. In
comparison, the hand is used for functional activities and has great dexterity. Another
very marked difference lies between the metacarpal bone of the thumb and the metatarsal
24
bone of the great toe. The metacarpal bone of the thumb is constructed to permit great
mobility, is directed at an acute angle from that of the index finger, and is capable of a
considerable range of movements at its articulation with the trapezium carpal bone. On
the other hand, the metatarsal bone of the great toe is more massive and assists in
supporting the weight of the body, lies parallel with the other metatarsals, and provides
push off during the terminal stance phase of the gait cycle. (Gray’s Anatomy of the
Human Body, 1918; Norkins and Levangie, 2001).
1.8.2 Arches of the Foot and Hand
The foot consists of plantar arches to support the body weight, provide smooth propulsion
by acting as a rigid lever, shock absorption and adjust to ground contours. Although the
arch-like structure of the foot is similar to the structure of the palmar arches of the hand,
the arches of the hand serve to facilitate grasp and manipulation of objects (Norkins and
Levangie, 2001). The foot is constructed of a series of arches formed by the tarsal and
metatarsal bones, and is strengthened by the ligaments and tendons of the foot. The
main/functional arches are the transverse arch and the medial longitudinal arch (MLA).
The medial longitudinal arch is made up by the calcaneus, the talus, the navicular, the
three cuneiforms, and the first, second, and third metatarsals. The chief characteristic of
this arch is its elasticity, due to its height and to the number of small joints between its
component parts (Figure 1.1). The transverse arch is present along the medial-lateral
border o f the foot. This is formed by the curvature of the five metatarsal bones.
25
Medial longitudinal arch
lateral longitudinal arch
Figure 1.1: Pictorial Demonstration of the Arches of the Foot (Arthur’s Medical
Clipart, 2009)
The medial longitudinal arch of the foot demonstrates two extremes of anatomical
structural position, the high arch foot and the flat foot. Although all types of arches of the
foot help to support the erect body posture during weight bearing and dynamic activities,
the MLA has been found clinically significant in these arch-related pathologies. Muscular
imbalances, structural malalignments of the joints, gait abnormalities, impaired joint
mechanics and repetitive stress injuries are caused by either high arch or flat arch foot
(Franco, 1986; Kisner and Colby, 2002).
1.8.3 Assessment of the Foot Arch
The human foot can have a range of structural variations, more so than any other part of
the body. Its functional mechanics are influenced by its structure, particularly the height
of the MLA (Cavanagh et al, 1987; Shiang et al, 1998; McCrory et al, 1997). Several
methods have been used in the past to evaluate the MLA of the foot including foot-prints
(Hawes et al, 1992), direct observation (Giladi et al, 1985), radiographs (McCrory et al,
1997; Cavanagh et al, 1997), photographs (Cowan et al, 1993), and ultrasound (Honning
26
et al, 1985). In 1987, Cavanagh and Rodgers put forth an arch index measure, which is
the ratio of the area of the middle third of the toeless footprint (truncated foot) to the total
footprint area. The arch index has been recognized as a useful tool in assessing the
structural characteristics of the foot. An arch index of less than 0.21 is indicative of a high
arch foot and an arch index of greater than 0.26 indicates a low arch foot. The arch index
has also been shown to be a valid predictor of arch height and showed strong association
to navicular height measured by the radiographic technique (McCrory et al, 1997).
Moreover, the arch index has been used as a reliable technique to determine the incidence
and prevalence of flat footedness in the population (Rose et al, 1985; Igbigbi et al, 2002).
1.8.4 Bio-dynamics and Vibration Transmissibility of the Hand
Although magnitude, frequency, duration and direction of the vibration are considered
prime factors that determine the vibration transmissibility and its effects, there are also
some other important factors associated with HAVS. Vibration transmissibility in the
hand-arm system is defined as the ratio of the vibration measured on the hand-arm system
and the input vibration on the hand-tool interface (Dong et al, 2005). As defined by Dong
et al, the bio-dynamic force is the vibration energy transmitted from the handle of the
equipment to the hand-arm system, and the internal body dynamics which lead to the
further transmission of this vibration energy to the other locations of the hand-arm
system, are defined as bio-dynamic stresses (Dong et al, 2005). It was stated that the
stresses caused by the vibration energy are responsible for the damage caused to the tissue
following vibration exposure (Dong et al, 2005).
Vibration transmissibility through the hand-arm system is largely determined by the bio
dynamic response of the hand to vibration exposure, which depends on the physical
characteristics of the hand, hand grip, tool-operating technique, area of hand in contact
with the tool, push force, and elbow posture (Griffin, 1990). Dong et al. stated that the
surface area of the hand in contact with the vibration source plays a significant role in the
vibration transmissibility, which is estimated through the apparent mass or mechanical
impedance of the hand-arm surface in contact with the vibrating tool (Dong et al, 2005).
It has been reported that increased coupling between the hand and the handle of the
equipment tends to increase the impedance at the hand. Griffin (1990) reported that a
moderate grip force is associated with greater impedance than a light grip over the handle
of the tool in use. Researchers also reported that variations in the angle at the elbow joint
while operating a hand held device also altered the impedance measured at the hand. The
greatest transmission of vibration was reported while working in a closed biomechanical
chain with the extended elbow (Griffin, 1990).
The vibration-induced stresses and strains on the fingers are different from the palm-
wrist-arm system, as the fingers are structurally different and offer lower impedance
(Griffin, 1990). In another study, Dong et al, (2010) reported that the impedance
distributed at the fingers is less than at the palm at frequencies below 100 Hz because the
effective mass of the fingers at lower frequencies is less than that of the palm. There is a
difference in the response and mechanism of injury of the hand and fingers to the
vibration exposure at different frequencies (Dong et al, 2010). Vibration power or
vibration exposure measured at the finger tip may be more closely associated with VWF,
whereas vibration power measured at the palm-wrist level may have a better correlation
with disorders of the wrist and arm. Thus, devices that are effective in attenuating
28
vibration at the palm level may not attenuate vibration as efficiently at the fingers (Dong
et al, 2005). Further, it was reported that the efficiency of the anti-vibration gloves was
dependent on the apparent mass of the exposed area of the hand or finger. It was stated
that the higher the apparent mass of the exposed area of the hand-arm system the more
effective the gloves were at attenuating the vibration (Dong et al, 2005).
Since the physiological and pathological response of the feet to vibration is comparable to
the hand-arm system, as represented in various studies (Hedlund, 1989; Sakakibara et al,
1991; Hirata et al, 1995; Sakakibara et al, 1994; Thompson et al, 2010; Choy et al, 2008),
a similar approach can be used to evaluate the bio-dynamic response of the foot. Based on
the difference in impedance distributed at the fingers and hand (Dong et al, 2010), it is
hypothesized that there could be differences in the vibration impedance distributed at the
toes and the sole of the feet. Also, with reference to HAV, FTV may also depend upon the
apparent mass of the foot and toes, which may be dependent on physical factors like the
surface area of the feet in contact with the vibrating surface, body weight, angle of the
hip-knee-ankle, etc. There is limited knowledge on the bio-dynamic response of the foot
to FTV. Future research can be done to understand the of the foot to vibration exposure,
which will be helpful in devising measures to attenuate vibration that enters the body
through the feet.
1.9 Strategies to Reduce Vibration
Several strategies can be adopted to reduce harmful vibration from entering the body.
Ergonomic measures like decreased tool vibration, reduced exposure times, regular
29
maintenance of equipment, and the use of personal protective equipment are often
recommended to limit exposure to vibration. Proper training with respect to driving and
equipment use and regular health monitoring could also help to limit negative health
outcomes associated with HAV and WBV exposure (Mansfield, 2005). Strategies
suggested to reduce HAV and WBV might also be helpful to reduce FTV.
1.9.1 Reduction Strategies for WBV Exposure
Ergonomics best practices suggest interventions should focus on either reducing the
magnitude of vibration exposure or reducing the duration of the vibration exposure to
minimize the overall health effect o f the vibration exposure (Mansfield, 2005).
Engineering solutions like improved axle suspension, engine mounting or suspension
seats can be implemented in heavy vehicles to minimize vibration transmission to the
operator (Mansfield, 2005). Maintenance of the road has reportedly helped in reducing
shocks and harmful vibrations experienced by heavy equipment operators (Mansfield,
2005). A reduction in vibration dose can also be achieved by monitoring the speed of
vehicles, as several operators have reported lower speeds result in less vibration
transmitted to the vehicle operator (Mansfield, 2005; Eger et al, 2011). Also, multi
cylinder engines have been reported to have higher dominant frequencies than single
cylinder engines. Considering the fact that WBV effects are multifold at frequencies less
than 20Hz, multi-cylinder engines can be an ideal solution for reducing whole body
vibration effects (Mansfield, 2005). Studies have also suggested that isolating the
vibration source from the body of the equipment to minimize the vibration transmission
into the body of the equipment, as an effective measure. Thus, mounting the engine of the
30
vehicle on a resilient mounting to isolate engine vibration from the chassis vibration has
been found as an effective measure in reducing vibration (Mansfield, 2005).
In 2008, Mayton tested ergonomically modified suspension seats in newer trucks and
reported that the improved seat quality provided better overall isolation to drivers from
WBV exposure compared to older seats. In another study, a new car seat design which
reduced contact between the seat and the ischial tuberosities, helped in reducing both the
contact pressure and amplitude of vibration transmitted through the body (Makhsous et al,
2005).
Canadian Institute of Mining, Edmonton in 2004 proposed an onboard warning system
based on ISO 2631-1 to help operators monitor the vibration levels experienced in a
heavy hauler. The onboard system consists of light signals to determine the level of
vibration exposure where, green represents a safe zone, yellow a caution zone, and red-a
danger zone. The onboard system also estimates the overall vibration exposure for the
entire shift and warns the worker when he/she is over a recommended daily exposure
limit.
If engineering solutions cannot be achieved then reducing the duration of vibration
exposure should be considered as the ideal measure to reduce vibration exposure
(Mansfield, 2005). Training to ensure an ergonomically sound posture to operate heavy
equipment should also be considered as an important measure to reduce the health effects
associated with vibration exposure. For example, improved seat designs may be helpful
in the maintenance of a good posture in the vibration environment (Griffin, 1990).
Training on the proper technique to use the equipment is also very important in reducing
31
the amount of vibration that enters the body (Mansfield, 2005). Lastly, all workers
should undergo routine medical check-ups at regular intervals to monitor their vibration
exposure and health status (Griffin, 1990).
1.9.2 Reduction Strategies for HAV Exposure
There are some general techniques that can be adapted to reduce hand-arm vibration
exposure. Vibration can be transmitted to the hands and arms of operators from vibrating
tools, vibrating machinery or vibrating work pieces. Depending on the nature of the work,
vibration can enter one arm only or both arms simultaneously and travel up to the
shoulder (ISO 5349-1, 1986). In order to reduce hand-arm vibration, strategies are
employed to reduce vibration at the source and/or to reduce vibration transmitted to the
worker. Engineering controls focus on manufacturing low emission vibration tools which
have features such as vibration-reducing handles (Mansfield, 2005). Hand tools should
be ergonomically designed to minimize the need for high grip forces and hand and finger
exposure. Tools should also avoid the emission of cold gases on worker’s hands as it
reduces the vascular supply to the localized tissue and increases the risk of vibration
induced white finger (Griffin, 1990). Medical management is also important. Workers
who are regularly exposed to vibration should be advised on the adverse effects of long
term vibration exposure and a routine health check-up should be conducted to screen
workers for HA VS. Appropriate warnings, such as trigger times, should be tagged to tools
known to emit harmful vibrations (Mansfield, 2005).
Individual training in the proper handling and knowledge of the equipment is also
important to differentiate any unwanted change in the equipment behaviour (Mansfield,
2005). Unwanted vibration exposure must be avoided and tools should not be held when
32
not in use. Wearing adequate clothing, use of appropriate personal protective equipment
(PPE) and keeping the hands dry and warm are also very important while working with
hand held vibration tools. The severity of HAVS has been reported to be higher in
smokers and it is highly recommended that workers avoid smoking if their work involves
vibrating tools (Griffin, 1990).
The use of personal protective equipment such as anti-vibration gloves is also
recommended to operators working with vibration tools. ISO approved (ISO-10819) anti
vibration gloves have been found to attenuate harmful vibrations from entering the hand-
arm system during vibration exposure (Jetzer et al, 2003). However, the effectiveness of
anti-vibration gloves depends on the exposed area of the hand. It was reported by Dong et
al. (2005) that the higher the apparent mass of the exposed area of the hand the better the
gloves were at attenuating vibration. Also, the grip force was reported to affect the
transmissibility of these anti-vibration gloves. Different gloves have different material
properties and it was found that the stiffness of some of the material increased with the
application of force, which led to an increase in vibration transmissibility (Dong et al,
2005). As mentioned earlier, it is also important to note that the same anti-vibration glove
cannot be effective at attenuating hand and finger vibration because of differences in the
physiological and bio-mechanical properties of the hand and fingers (Dong et al, 2005).
1.9.3 Reduction Strategies for FTV Exposure
Some of the general measures like engineering controls, ergonomic modifications and
manufacturing tools with the main aim to minimize vibration emission, are the key
measures for reducing vibration exposure to any body part. Isolated standing areas on
drilling platforms have been reportedly used to reduce vibration that enters through the
33
feet (Leduc et al, 2011). Personal protective equipment like anti-vibration mats, boots
and insoles has also been introduced to the workers to help attenuate FTV. However the
ability of these PPE to attenuate vibration has yet to be proved. A recent study by Leduc
et al. (2011) identified mats that were effective in attenuating some vibration at the feet.
However, there is no reported literature on the efficacy o f insoles and boots used by
operators exposed to FTV in reducing vibration magnitude at the feet. Therefore, future
research to determine the effectiveness o f mining boots and insoles should be conducted.
1.10 Thesis Outline
Long-term segmental vibration exposure at the feet can lead to vibration induced white
feet (VWFt) (Thompson et al, 2010; Choy et al, 2008; Hedlund, 1989). Other
pathological findings related to neurovascular structures, musculoskeletal structures,
sympathetic nervous system etc., have also been reported following vibration exposure at
the feet (Choy et al, 2008; Takeuchi et al, 1986; Hirata et al, 1995; Hashiguchi et al,
1994). However, there is limited knowledge on the bio-dynamic response of the feet to
FTV and less is known about appropriate interventions to attenuate FTV. Therefore, the
objectives of this study are four fold: 1) to measure vibration transmissibility through the
foot (between the floor and ankle); 2) to determine if floor-to-ankle transmissibility is
significantly different between males and females; 3) to determine the influence of arch
types (foot surface area in contact with the vibration platform) on floor-to-ankle vibration
transmissibility; and 4) to evaluate the efficacy of mining boots and “anti-vibration”
insoles in FTV attenuation.
Chapter 1: Literature Review: This chapter includes background knowledge on work
that has been done in the field of vibration, including vibration terminologies and
nomenclature, types of vibration exposure, international standards that comment on
vibration measurement techniques, reported occupational health hazards due to vibration
exposure and necessary steps to combat harmful vibrations. At each step in the literature
an attempt has been made to relate the importance of previous research in the study of
FTV. Also the chapter includes information on reported cases of foot ailments due to
vibration exposure and the patho-physiology behind it. The basic intent of this chapter is
to justify the present research work, which deals with health effects associated with FTV
and interventions to reduce its harmful effects.
Chapters 2 and 3 are written as papers ready for journal submission. Specific objectives
of Chapter 2 are as follows.:
a) to determine vibration transmissibility between the floor and the ankle in standing
individuals exposed to two levels of FTV
b) to determine if there is a significant difference in floor-to-ankle vibration
transmissibility between males and females when exposed to FTV
c) to determine if there is a significant difference in floor-to-ankle vibration
transmissibility with the surface area of the foot in contact with the vibration
surface
d) to determine if there are any differences in floor-to-ankle vibration transmissibility
with participant body mass.
e) to determine if there is a significant difference in subjective discomfort reported
by males and females when exposed to FTV
35
Specific objectives of Chapter 3 are:
a) to measure and document the vibration transmissibility properties of three
commercially available anti-vibration insoles when exposed to low frequency and
high frequency vibration.
b) to measure and document the vibration transmissibility properties o f two
commercially available mining boots when exposed to low frequency and high
frequency vibration
c) to determine if there is a significant difference in the subjective discomfort scores
when participants are exposed to FTV while wearing different insoles and mining
boots.
In the final chapter. Chapter 4. conclusions derived from Chapter 2 and 3 are discussed
along with limitations and future directions. The relevance of the work to the mining
industry and workers exposed to FTV is also discussed.
Examination of floor-to-ankle vibration transmissibility and subjective discomfort of males and females with different foot arch classifications when exposed to foot-
transmitted vibration
49
Abstract
Research concerning foot-transmitted vibration (FTV) is limited despite evidence of
vibration induced white feet. There has been extensive research on the bio-dynamic
response and on adverse health effects resulting from exposure to vibration when seated
or vibration when gripping power tools. However, research associated with FTV is
limited despite evidence of vibration induced white feet. Therefore the main objective of
the study was to determine vibration transmissibility between the floor and the ankle
while standing. Specific objectives were 1) to determine if there were any significant
differences in floor-to-ankle vibration transmissibility between males and females; 2) to
determine if there were any significant differences in floor-to-ankle vibration
transmissibility by foot arch type; 3) to determine if there were any significant differences
in floor-to-ankle vibration transmissibility by body weight; and 4) to determine if there
were any significant differences in reported discomfort by gender or vibration exposure
frequency. Sixteen participants (eight male and eight female) were exposed to two-levels
of vibration, while standing on a low frequency (3.15-lOHz) and a high frequency (40Hz)
vibration platform. The vibration was recorded at the floor and the ankle with two tri-
axial accelerometers in accordance with the ISO 2631-1 standard. Participants reported
body discomfort on a 9-point discomfort scale following each vibration trial. Frequency-
weighted acceleration in the z-axis (vertical axis) entering the foot (Fawz) was compared
to frequency-weighted acceleration in the z-axis at the ankle (Aawz). The percentage
difference between Aawz and Fawz was taken as a measure of vibration transmissibility
between the floor and the ankle. Multivariate analysis was performed with a selected
alpha level of 0.05 and six degree of freedom to analyze the vibration transmissibility (y-
axis) against frequency, gender, mass and foot arch type (x-axis). There was a significant
50
difference in vibration transmissibility at two frequencies (F = 3.27, p= 0.001) with less
vibration transmitted to the ankle at high frequency (72.61+/-33.99) than low frequency
(106.27+/-9.53) vibration exposure. There was no significant difference in floor-to-ankle
transmissibility by gender (F=3.27, p=0.715) or participant body weight (F=3.27, p=
0.849). Also there was no significant difference in vibration transmissibility with
differences in foot arch type (F=3.27, p= 0.515).
51
2.1 Introduction
People can be exposed to vibration in the workplace and during leisure activities.
Vehicles, machinery and industrial activities can expose people to different forms of
mechanical vibration, which can interfere with comfort, activities and health (ISO 2631 -
1; 1997). In the workplace, people can be exposed to vibration when standing, sitting and
in some cases lying while in contact with a vibration source. Vibration exposure is
becoming one of the latent causes for occupational health hazard in many industries.
Regular and long-term exposure to vibration can lead to vascular, musculoskeletal,
neurological and other systemic disorders (Sakakibara et al, 1994; Abercromby et al,
2007). Acute health effects reported from whole-body vibration (WBV) exposure include
loss of visual acuity, postural stability and manual control; whereas chronic health effects
include low back pain, early degeneration of the spine, herniated discs, neurological,
digestive and circulatory disorders (Mayton et al, 2008). Similarly, workers exposed to
hand-arm vibration (HAV) have reported episodes of blanching of the fingers; tingling,
numbness and reduced tactile sensation in the hand and fingers; and also reduction in
muscular strength and dexterity (EU Guide to good practice on HAV, 2006; Cohen et al,
1995; Bovenzi, 1998). Associated changes with hand-arm vibration syndrome (HAVS)
include thickening of the tunica media of the blood vessels, demyelination of the neural
tissues and collagen deposition in the connective tissues of the exposed part (Takeuchi et
al, 1986).
Vibration exposure during standing and the resulting health effects to the feet have
received little attention and the impact of vibration frequency on the feet is not clearly
understood. Workers are exposed to foot transmitted vibration (FTV) when working with
52
equipment that requires them to stand on a surface that vibrates (Eger et al, 2006). Health
effects like neurological symptoms typically observed in the hands after occupational
exposure to HAV have been reproduced in the feet of workers exposed to similar
vibration frequencies and accelerations (Griffin, 2008). Other studies have also reported a
reduction in the nerve conduction velocities in the lower extremity (Juntunen et al, 1983;
Hirata et al, 1995); Raynaud’s phenomenon of the toes (Hedlund, 1989; Choy et al, 2008;
Thompson et al, 2010; Leduc et al, 2010); thickening of the blood vessel walls and
increased collagen deposits in the connective tissue (Hashiguchi et al, 1994); and
reduction in the lower extremity skin temperature (Sakakibara et al, 1991).
Vibration exposure via the feet has also been found to cause muscle and nerve fiber
degeneration in animal models (Shanskaya et al, 1965 and Lundborg et al, 1989). It has
been reported that changes in the feet are induced by stimulation of sympathetic nervous
system in the workers with HA VS when exposed to HAV (Sakakibara H, 1994; House et
al, 2010). However, some of the studies have also identified vibration white foot (VWFt)
independent of HAVS in individuals exposed to segmental FTV (Thompson et al, 2010;
Hedlund, 1989). These findings throw light on the occurrence of VWFt in workers who
are exposed to segmental lower extremity vibration in standing, independent of HAV
exposure. The vibration frequency in both the case reports that led to the development of
VWFt was reported to be 40Hz (Thompson et al, 2010; Hedlund, 1989).
Different parts of the body have their own resonant frequency and it has been reported
that some types of detrimental health effects are associated with exposure at resonant
vibration frequencies (Holmlund et al, 2001). The hand-arm system is reported to have a
resonant frequency between 20-50Hz and frequencies above 80Hz are believed to be
more harmful for the fingers (Dong et al, 2004; Dong et al, 2010). On the other hand,
frequencies in the range of 4-8Hz are associated with seated spinal resonance (Griffin,
1990). The resonant frequency of the foot and toes has not been documented. During an
underground mine study by Leduc et al, (2011), workers were exposed to FTV between
3.15-6.3Hz (WBV range) and 31.5-40Hz (HAV range). Moreover, workers consistently
exposed to vibration between 31.5-40Hz had an increased diagnosis of VWFt (Leduc et
al, 2011).
Evidence from the hand-arm vibration literature indicates factors other than vibration
exposure frequency also influence vibration transmissibility. Vibration transmissibility in
the hand-arm system is defined as the ratio of the vibration measured on the hand-arm
system and the input vibration on the hand-tool interface (Dong et al, 2005). Vibration
transmissibility through the hand-arm system is largely determined by the bio-dynamic
response of the hand which depends on the physical characteristics of the hand, hand grip,
tool-operating technique and area of hand in contact with the tool, push force, elbow
posture etc. (Griffin, 1990). For example, a moderate grip force is associated with greater
impedance (and transmissibility) than a light grip over the handle of the tool in use
(Griffin, 1990). There is also greater vibration transmissibility to the arm and shoulder
when operating vibration tools with extended elbow (Adewusi et al. 2011). Similarly,
greater vertical transmission of FTV has been reported while working with fully extended
knees compared to slightly flexed knees (Caryn and Dickey, 2010; Griffin, 1990).
However, the influence of mass (force) or surface area in contact with the vibration
source, on foot transmitted vibration has yet to be documented.
Researchers have also used comfort (discomfort) as a measure to understand the effect of
vibration exposure. A comfortable stimulus is defined as the one where the subjects do
not have to change their activity or reduce vibration exposure magnitude (Mansfield,
2005). Depending on the intensity and characteristics of vibration, a vibration stimulus
might not be painful but produce a sense of discomfort (Mansfield, 2005). Furthermore,
several researchers have exposed participants to short periods of vibration and accurately
obtained discomfort reports (Dickey et al, 2006). For example, Dickey et al. (2006)
reported that there was no significant difference in the reported discomfort between a 15
or 20 second vibration exposure, or a 5 or 10 second rest duration when participants were
exposed to single axis, planar or six degree of freedom vibration in a lab setting.
Given the limited research documenting the transmission of FTV through the foot, but
evidence of VIWFt (Thompson et al, 2010; Leduc et al, 2011), the objectives of the
present study were;
1) to determine if there are any significant differences in floor-to-ankle vibration
transmissibility when participants were exposed to low-frequency FTV and high-
frequency FTV;
2) to determine if there are any significant differences in floor-to-ankle vibration
transmissibility between males and females;
3) to determine if there are any differences in floor-to-ankle vibration transmissibility for
different foot arch types;
4) to determine if there are any differences in floor-to-ankle vibration transmissibility
with participant body mass.
55
5) to determine if there are any significant differences in participant reported discomfort
by gender or FTV exposure frequency
Based on the literature review it was hypothesized that:
1. there will be greater vibration transmissibility through the foot during high
frequency vibration exposure, since there has been greater incidences of VWFt
reported at higher vibration exposure frequencies (Thompson et al, 2010; Leduc et
al, 2010; Hedlund, 1989).
2. there will be less vibration transmissibility in females compared to males as
females typically have a higher body fat to muscle mass ratio (Lundstrom and
Holmlund, 1998).
3. there will be less vibration transmissibility in individuals with a high foot arch due
to the reduced surface area of the foot in contact with the vibration surface
(Griffin, 1990).
4. female participants will report less discomfort than the male participants because
the overall vibration transmissibility will be lower in females.
5. there will be a greater floor-to-ankle vibration transmissibility for heavier
participants based on evidence from HAV exposure that found an increase in
HAV transmissibility with increased grip force (Griffin, 1990).
56
2.2 Methodology
The research study was approved by Laurentian University’s Research Ethics Board and
informed consent was provided.
2.2.1 Participants
Sixteen participants (eight males and eight females) with a mean age of 26 years (males)
and 20 years (females), mean height of 171 cm (males) and 165.7 cm (females), and a
mean mass of 75 kg (males) and 67.1 kg (females) were recruited by convenient
sampling. The demographic data are presented along with baseline musculoskeletal
discomfort reports in Table 2.1. Participants were ruled out for past history of concussion,
any fracture in the previous six months, diabetes, neurological disorders, peripheral
vascular disorders, back pain, or motion sickness before being cleared to participate in the
study.
2.2.2 Vibration Exposure
Two vibration profiles were generated to expose participants to FTV with a dominant
frequency below 10Hz and FTV with a dominant frequency between 30-40Hz. A custom
made vibration simulator in the Biomechanics Lab at Laurentian University generated the
lower frequency profile and an exercise vibration platform (Power Plate North American,
Inc., Irvine, CA) was used to generate the higher frequency vibration. The equipment was
previously used in a laboratory study by Leduc et al. 2011 to evaluate FTV and the author
adapted similar methods during data collection.
57
Table 2.1: Demographic Data and Pre-test Discomfort Rating
Participants Gender Mass (kg) Height (cm) Age(Years)
Initial Discomfort (0-9)
1 Male 63.6 167.5 27 0
2 Male 95.5 177.5 38 0
3 Male 82.3 171 23 0
4 Male 66.4 175.5 24 0
5 Male 86.4 173 26 0
6 Male 69.1 164 25 0
7 Male 70.9 170 23 0
8 Male 65.9 170 23 0
9 Female 62.5 164 21 0
10 Female 61.8 166 20 0
11 Female 57.3 163 19 0
12 Female 102.3 175 19 0
13 Female 50.9 161 20 0
14 Female 77.3 161 20 0
15 Female 72.7 171 20 0
16 Female 52.3 165 23 0
The lower frequency profile was selected to replicate the dominant frequency associated
with operating a locomotive in an underground mine, while the higher frequency was
selected to simulate FTV experienced when standing on a drilling platform or
underground raise platform (Leduc et al, 2010; Leduc et al, 2011). Refer to Table 2.2 for
details on the vibration profiles used in the experiment.
58
Table 2.2: Summary of the vibration characteristics
Vibration
Profile
Profile Details
Dominant Frequency Frequency-weighted r.m.s.
acceleration
1 3.15-10 Hz l.lm /s2-2 m/s2
2 40 Hz 22.1m/s2
2.2.3 Vibration Measurement
Two Series 2 10G MF tri-axial accelerometers (NexGen Ergonomics, Montreal, QC)
were used to record vibration at the platform and vibration transmitted from the floor to
the ankle (Figure 2.1). Vibration data were collected with a 500Hz sampling frequency, in
accordance with ISO 2631-1 standards and stored on two portable dataloggers, DataLOG
II P3X8 (Biometrics, Gwent, UK) (Figure 2.1).
2.2.3.1 Vibration Measurement at the Platform
A tri-axial accelerometer was mounted in a wooden foot-board which was a replica of a
Brannock device with cut out space at the heel to secure the accelerometer (Figure 2.1).
The wooden foot-board was placed on top of the vibration platform so that the
accelerometers were in contact with the vibrating surface. The participants were
instructed to stand on the wooden foot-board so that the lateral malleolus of the ankle
(where the ankle accelerometer was secured) stayed in line with the floor accelerometer.
Figure 2.1: Placement of accelerometers: a) Recording at the ankle; b) Recording at
the floor. Picture shows replication of the Brannock device with a cut out at the end
for the accelerometer. The participant stood on this apparatus with his/her heel
aligned over the accelerometer, c) Data logger used to record vibration.
2.2.3.2 Vibration Measurement at the Ankle
The tri-axial accelerometer was mounted on the lateral malleolus of each participant’s left
ankle (Fig 2.1). The accelerometer was secured over the bony prominence with double
sided common stationary velcro and a stretchable wrapping tape (Fig 2.2). The
participants were provided with a pair of typical athletic socks, which they wore over the
ankle accelerometer while standing on the vibration platform. The accelerometer was
aligned with the vertical axis and calibrated each time prior to recording vibration. The
angular deviation of the accelerometer was maintained well within 15 degrees from the
vertical axis as suggested in the ISO 2631-1 standard guidelines. The participants did not
wear any other footwear during data collection.
Figure 2.2: Accelerometer placed on the lateral malleolus of the ankle and secured
by elastic taping.
61
2.2.4 Foot Arch Assessment
In the studies on HAV, researchers have reported that the area of the hand in contact with
the hand-held vibrating tools play an important role in the vibration transmissibility
through the hand and up to the shoulders (Dong et al, 2005; Griffin 1990). So, during the
experiment, the foot arch type of each participant was assessed as a measure of the
surface area of the foot in contact with the vibration platform while standing. The foot
print technique and Arch Index was used to measure the foot arch of each individual
(Cavanagh and Rodgers, 1987).
The Arch Index is defined as the ratio of the area of the middle third of the toeless
footprint (truncated foot) to the total footprint area (Figure 2.3) and is considered a usefiil
and reliable tool in the assessment of the medial foot arch (Rose et al, 1985; Igbigbi et al,
2002). An Arch Index of less than 0.21 is indicative of a high arch foot and an arch index
of greater than 0.26 indicates a low arch (Cavanagh and Rodgers, 1987).
The procedure, as stated by Cavanagh and Rodgers in 1987, was used to calculate the
Arch Index. Participants were asked to dip their left foot into a box containing edible
colorant and were subsequently asked to step onto graph paper of 0.36cm grid with their
full body weight to leave their foot impression on the paper. The foot impression was
allowed to dry completely and then the Arch Index was calculated using the Cavanagh
and Rodgers equation (Figure 2.3).
62
O q
L/3
L/3
L/3
Figure 2.3: Foot print for the measurement of the Arch Index. Marked areas A, B
and C show the area of the forefoot, mid foot and hind foot of the foot print,
respectively. Arch Index= B/A+B+C (Figure from the study by Stavlas et al, 2005)
2.2.5 Discomfort Measurement
A nine point unipolar continuous type verbal discomfort scale, with zero indicating an
absence of discomfort and nine indicating maximum discomfort, was used to record
participant discomfort scores (Dempsey et al, 1977). The participants were asked to
verbally report their discomfort at the start of the experiment (to serve as a baseline) and
subsequently after each 20 second vibration trial (Dickey et al, 2006). The participants
were provided with a body chart (Appendix 1) that showed different body segments and
were instructed to point out the areas of discomfort on the chart and appropriately report
the level of discomfort experienced on the nine-point scale. Discomfort in the area of the
63
head, neck, back, and/or shoulders/arms was classified as upper body (UB) discomfort,
while discomfort in the feet, knees, thighs and buttocks was classified as lower body (LB)
discomfort. The discomfort scores reported for the different body parts were summed up
on the basis of their location in either the UB or LB region and a single mean value was
calculated to represent the total UB and LB discomfort for each participant.
The frequency-weighted root mean square acceleration was calculated (aw) and expressed•n
in meters per second squared (m/s ). The frequency weightings applied, as listed in ISO
2631-1 were: x-axis=Wd, y-axis=Wd and z-axis=z'W\i (Figure 2.4). Floor-to-ankle vibration
transmissibility was calculated according to Equation 1.
65
x-axis
Figure 2.4: Axis orientation of the ankle accelerometer. The accelerometer was
aligned with the vertical axis and calibrated each time prior to recording vibration.
The angular deviation of the accelerometer was maintained well within IS degrees
from the vertical axis, as suggested in the ISO 2631-1 standard guidelines.
2.2.9 Statistical Analysis
The dependent variables were vibration transmissibility percentage and the reported
discomfort scores by the participants; whereas gender, body mass, vibration frequency,
and arch types were independent variables. To analyze the difference in the vibration
transmissibility (continuous data) and reported discomfort (continuous data) with respect
to exposed frequency, gender, body mass and foot arch type (continuous set of data), a
general linear model analysis of variance (GLM ANOVA) was performed with a selected
alpha level of 0.05.
66
2.3 Results
2.3.1 Floor-to-Ankle Vibration Transmissibility
A multivariate analysis with six degrees of freedom was performed to analyze the
transmissibility (about y-axis of the graph) against frequency, gender, mass and foot arch
type (about x-axis of the graph). We hypothesized that there would be greater floor-to-
ankle vibration transmissibility under a higher frequency FTV. There was a significant
difference in vibration transmissibility at the two vibration profiles (F = 3.27, p= 0.001),
with floor-to-ankle transmissibility being lower during exposure to high frequency
vibration (72.61+33.99) than low frequency vibration (106.27+9.53). Thus, the
hypothesis was not supported (Table 2.3; also refer to Appendix 3).
We hypothesized that females would transmit less vibration than males. However, there
was no significant difference in floor-to-ankle transmissibility by gender (F=3.27,
p=0.715).
We also hypothesized that participants with high foot arch type would attenuate more
vibration due to less surface area in contact with the vibration platform. However, there
was no significant difference in floor to ankle transmissibility with differences in foot
arch type (F=3.27, p= 0.515). Therefore, the hypothesis was rejected (Table 2.3 and 2.4;
Figure 2,5).
Also, there was no significant difference in floor to ankle vibration transmissibility by
differences in participant body mass (p= 0.849) (Table 2.4). Thus, the hypothesis was not
supported.
67
Table 2.3: Multivariate Analysis: GLM ANOVA- Transmissibility versus gender, frequency, mass, discomfort and foot arch type
Predictor Coef SE Coef T P
Constant 133.74 29.42 4.55 0.000
Gender 3.537 9.565 0.37 0.715
Frequency -46.77 11.78 -3.97 0.001
Mass -1.383 7.192 -0.19 0.849
Discom U.B -0.1596 0.5300 -0.30 0.766
Discom L.B 0.7898 0.5426 1.46 0.158
Foot Arch 4.443 6.727 0.66 0.515
68
Table 2.4: Mean vibration transmissibility in the males and females with different foot arch types at low frequency and high frequency vibration exposure
Arch Types Transmissibility
Low Frequency High Frequency
MALE High
Medium
Flat
107.9 (2.7)
107.9(11.5)
109.72 (3.8)
96.3 (44.6)
101.2(25.3}
37.58(12.6)
FEMALE High
Medium
Flat
109.68(11.9)
96.66 (10.4)
105.6 (6.9)
36.78 (12.4)
83.22 (49.3)
74.88 (22.4)
69
a
1= Male
2= Female
1= 50-68 kg
2= 69-86 Kg
3= >87 Kg
Data Means
110
100
90
80-1
g 70
{
90
80
70
Gender Frequency
* ... r " W\
1 2 1 2Mass Foot Arch
1= L.F
2= H.F
d1= Flat
2 =
Medium
3= High
Figure 2.5: Main effect plot for vibration transmissibility versus a) Gender, (b) frequency, (c) mass and (d) foot arch type
Interaction Plot for Discom L.BData Means
2 3 1 2 3. 40 Gender
-#—■ 1- m ~ 2
Frequency12
Mass12 3
Figure 2.6: Interaction plot for vibration transmissibility versus a) Gender, (b) frequency, (c) mass and (d) foot arch type
7 0
2.3.2 Discomfort Score
The mean discomfort score for the UB and LB was calculated from the verbally reported
discomfort in the UB and LB segments on a nine-point discomfort scale. The discomfort
scores reported for different body parts were summed up on the basis of their location in
the UB or LB segment and a single mean value was calculated to represent the total UB
and LB discomfort individually (Appendix 3-Table 3a and 3b).
A multivariate analysis with six degree of freedom was performed to determine if any
significant difference existed between transmissibility and reported discomfort. We
hypothesized that there would be greater subjective discomfort at high frequency
vibration exposure and that females would report lower discomfort scores than males.
There was no significant difference in reported discomfort for the UB (F= 3.27; p =
0.766) or LB discomfort (F= 3.27; p = 0.158) for either vibration profile (Table 2.3).
Also, there was no significant difference between males and females in their reported UB
discomfort (p = 0.277) or LB discomfort (p = 0.151) scores during the LF and HF
vibration exposures. (Refer Appendix 3 for detailed interaction plot).
2.4 Discussion
2.4.1 Transmissibility
The main objectives of this research were to determine floor-to-ankle vibration
transmissibility and discomfort when exposed to two levels of FTV and to determine if
gender, foot arch type, body mass or vibration exposure frequency had an effect on floor-
to-ankle vibration transmissibility. It was hypothesized that there would be greater
71
transmissibility at the higher frequency FTV. This hypothesis was not supported as there
was greater floor-to-ankle transmissibility at the 3.15Hz-10Hz vibration exposure profile
than at the 40Hz FTV profile. Our finding appears to be in contradiction to previous
theories regarding vibration induced injury as Thompson reported a case of VIWFt, when
workers were exposed to vibration at 40Hz (Thompson et al, 2010). This may hint
towards injury risk being closely linked to exposure frequency and resonance of the foot.
Although the resonant frequency of the foot has not been reported to date, there is
evidence to suggest it might be in line with reported resonant values for the hands and
fingers, since previous research has shown similar changes in the foot as the hand when
exposed to similar vibration frequencies (Hedlund, 1989; Sakakibara et al, 1991; Hirata et
al, 1995; Sakakibara et al, 1994; Thompson et al, 2010; Choy et al, 2008). The
development of HAVS is associated with vibration exposure at a frequency range of 20-
50Hz, and more than 80Hz for the fingers (Griffin, 1990). Previous research has reported
cases of VWFt in workers exposed to FTV at or above 40Hz (Leduc et al, 2010; Hedlund,
1989; Toibana and Ishikawa, 1990). For example, workers who operate drills off raised
platforms in underground mines were exposed to vibration with a dominant frequency
between 30Hz- 40Hz and several of the workers in the study had diagnosed cases of
VWFt (Leduc et al, 2010).
Vibration attenuation at the high frequency exposure (40Hz) observed in this study may
be the result of the differences in the apparent mass or impedance of the foot in contact
with the vibration surface (Dong et al, 2005). The bio-dynamic response of the foot to
FTV is still not fully understood and further studies at a greater range of frequencies and
vibration exposure magnitudes are required. Detailed information on the bio-dynamic
72
response of the foot to FTV is important to determine interventions to attenuate vibration
and reduce the incidence of VWFt in workers exposed to FTV.
Our hypothesis that females would transmit less vibration than males was not supported.
There were no significant gender differences in floor-to-ankle vibration transmissibility at
either vibration exposure profile. Gender differences in transmissibility have received
little attention in the past. In an earlier study, Griffin and colleagues (1982) exposed 18
males and 18 female subjects to WBV between l-100Hz and found that, women had
significantly less vertical head motion at 2.5Hz and significantly more vertical head
motion at 40, 50 and 63Hz. In a separate study researchers found that females tend to
absorb more vibration power per kilogram of sitting weight. This was linked to a higher
ratio of body fat to muscle mass in females. It was stated that “fat is viscous and inelastic,
implying a high degree of damping and thus more power absorption among females”
(Lundstrom and Holmlund, 1998). Future research may consider looking at differences in
vibration transmissibility between males and females with an equal body mass index
when exposed to FTV.
Our hypothesis that there would be a significant difference in floor-to-ankle vibration
transmissibility with differences in body mass was not supported. Body mass of the
participants was thought to be important in vibration transmissibility through the foot. It
has been reported that increased coupling between the hand and the handle of hand-held
equipment during exposure to hand-arm vibration tends to increase the impedance at the
hand. Furthermore, a moderate grip force was found to be associated with greater
transmissibility than a light grip when applied on a hand held vibration tool during hand-
arm vibration exposure (Griffin, 1990). Therefore, during exposure to FTV, we
hypothesized that individuals with lower body mass would apply less contact force on the
vibration platform than individuals with greater body mass, which could lead to a
difference in vibration transmissibility. In another study by Eger et al. (2011) on the
influence of vehicle size, and haulage capacity on vibration exposure of LHD vehicle
operators, it was reported that there was significantly lower vibration exposure during
loaded haulage compared to empty haulage. Thus, there was less vibration transmitted
during the heavily loaded vehicle than when the vehicle was empty. Based on these
findings, it was assumed that there might be less vibration transmissibility in participants
with greater mass compared to lower mass participants.
We hypothesized that a high foot arch type would attenuate more vibration than the
medium and low foot arch type. This hypothesis was not supported. It has been reported
that the bio-dynamic response of the hand depends on the physical characteristics of the
hand like the hand grip and area of the hand in contact with the hand-held vibration tool
(Griffin, 1990). Health risks at the foot were believed to be associated with a similar
vibration frequency range known to lead to HAVS (Thompson et al, 2010). Similarities
between VWFt and HAVS have also been suggested from similar pathological findings in
the foot and hand when exposed to the same vibration frequency range (Hedlund, 1989;
Leduc et al, 2010; Toibana and Ishikawa, 1990; Thompson et al, 2010). Thus, foot arch
type was evaluated to determine if floor-to-ankle vibration transmissibility was dependant
on the area of the foot in contact with the vibration platform. Dong et al. has stated that
the surface area of the hand in contact with the vibration source plays a significant role in
vibration transmissibility, which is estimated through the apparent mass or mechanical
74
impedance of the hand-arm surface in contact with the vibration tool (Dong et al, 2005).
It has also been reported that increased coupling between the hand and the handle o f the
equipment tends to increase the impedance at the hand (Dong et al, 2005). This suggests
that there might be a difference in the mechanism of force distribution during composite
grip of the hand and the weight transmitted through the feet while standing. However, the
size of the anatomical structures of the hand and feet differ and might be responsible for
the differences in the impedance and vibration transmissibility in the hand and foot.
2.4.2 Discomfort
Our hypothesis regarding discomfort was not supported as there was no significant
difference between the reported discomfort and frequency of vibration exposure.
However, the participants tended to reported higher discomfort during the high frequency
vibration exposure conditions than during low frequency exposure. That being said, it is
important to note that there was a difference in the magnitude of vibration that
participants experienced during the high frequency (22.1 m/s2) and low frequency (1.1-
2m/s2) vibration conditions. Participants tended to report higher discomfort under the
higher magnitude exposure. This finding is in line with findings from Mansfield (2000)
who reported greater discomfort with higher magnitude vibration compared to lower
magnitude vibration.
Our hypothesis regarding discomfort and gender was also rejected as there was no
significant difference in reported discomfort for males or females. This finding
contradicted the results of Leduc et al. (2010) who reported lower discomfort scores for
female participants compared to male counterparts when exposed to the same level of
vibration. Furthermore, in a study to examine gender difference in subjective response to
75
WBV in different directions, while standing, it was reported that, regardless of the axis of
vibration, males reported more discomfort than females (Shibata et al, 2010).
2.5 Limitations
Earlier research has stated that a 20 second vibration exposure duration was sufficient for
participants to provide a discomfort report during seated exposure to WBV (Dickey et al,
2006). In a field study of seated WBV exposure, Grenier et al. (2010) found experienced
operators had large variability in discomfort reports and hypothesized that operators are
so habituated to high vibration levels, or biased by previous injury, that their perception
of discomfort is masked or distorted to differentiate between different stimuli, unless the
vibration is severe. Although a 20 second exposure duration was used in this study, it
might not have been long enough to enable participants to register and report discomfort
from FTV. Alternatively, participants with pervious exposure to occupational FTV or
recreational FTV (exercise platforms) might not be as sensitive to FTV. We also found
that some of the participants that had a low mass and no previous exposure to high
frequency FTV, found it more difficult to balance on the platform. Therefore, they might
have been more focused on maintaining their balance, which may have masked the
perception of vibration related discomfort. Thus, future study might consider longer
duration exposures and consider categorizing participants based on previous exposure to
FTV. Future studies might also benefit from the inclusion of experienced participants
from the mining industry for the laboratory set-up and/or a field-study in the mines.
The sample size was unequally distributed and small to determine the effect of foot arch
type on the vibration transmissibility. There were only three participants in the high foot
76
arch category, whereas six participants fell into the low and seven into the medium arch
type category. Future study with individuals equally distributed in each foot arch category
may be performed in order to determine if the area of the foot in contact with the
“Evaluation of mining boots and insoles to determine vibration transmissibility from the floor to the lower body” and “Evaluation and comparison of the Bio-dynamic response of the lower body to vibration exposure in both the genders while standing and to determine the effects of foot arch types on vibration transmissibility”
I ,_____________________________ , am interested in participating in the study on the(1) “evaluation of mining boots and insoles to determine vibration transmissibility from the floor to the lower body” and (2) “evaluation and comparison of the Bio-dynamic response of the lower body to vibration exposure in both the genders while standing and to determine the effects of foot arch types on vibration transmissibility (how vibration travels through the body)” conducted by Pulkit Singh, MHK candidate and Professor Tammy Eger, PhD, from Laurentian University (funded by the Workplace Safety and Insurance Board of Ontario & Centre for Research in Musculoskeletal Disorders). The purpose of the study is to examine the effectiveness of different types of commercially available insoles and mining boots for attenuation of the harmful vibrations that enters the body via feet. This research will also evaluate the vibration transmissibility in the lower body in both the genders by comparing vibrations recorded at the ankle and at the base of the great toe with the vibration recorded at the floor while standing on the vibration platform. Differences in the vibration transmissibility with the area of contact of the foot with the surface will also be studied during this research by prior assessment of the foot arch type.If I agree to participate, I will be randomly fitted with different pairs of mining boots and insoles. A specially designed wooden foot scale fitted with accelerometer (device to measure vibration) will be placed over the vibration platform during the standing trials. Two more accelerometers will be taped to my ankle and base of the great toe. During the study I will be asked to (I) stand on the vibration exercise platform at the University gym, and (II) stand on the vibration simulator at the School of Human Kinetics biomechanics lab. I am told that each trial will last for 20secs followed by 1 Osecs of rest period during which the mining boot and insole condition will be randomly changed. Also, I will undergo a general foot assessment session to evaluate my foot arch type and the area of my foot that is in contact with the floor. The total estimated vibration exposure during the testing will be less than 20 minutes and the testing may last approximately for two hours. I know that the vibration exposure and the duration will be in the recommended dose given by ISO standards. I will be asked few questions related to my health history and also to complete a body chart for discomfort evaluation.I have been informed that only members of the research team will have access to the data collected. My participation is strictly voluntary and I am free to withdraw from the study at any moment or refuse to participate without any penalty. I have received assurance from the researcher that all data collected will remain strictly confidential. My
142
individual results will not be reported. All collected data will be coded with a subject number and stored in a locked filing cabinet (in the Professor Eger’s office) or a password secured laptop (only members of the research team will have access to the data). After a period of 5 years paper documents collected will be shredded.I understand that I will receive no immediate benefit from my participation; however, results of the study will be used to identify an insole- boot combination capable of reducing harmful vibrations that enters the feet of workers. Also the evaluation of biodynamic response of the lower body to the vibration in both the genders will help to identify potential risks in different population types who are exposed to harmful levels of vibration on regular basis.There are two copies of this consent form; one which the researcher keeps and one that I keep.If I have any questions or concerns about the study or about being a participant, I may contact the lead researcher, Professor Tammy Eger via email [email protected]. If I have any questions or concerns surrounding the ethical conduct of the study, I may contact the Laurentian University Research Office at 705-675-1151 ext. 3213. If I would like to receive a copy of the study results I can contact Professor Tammy Eger anytime after July 1, 2011. I agree to participate in this study.
1. Have you ever sustained a head injury?________________________2. Have you had foot pain/injury or back pain/injury within the last 6 months?_______3. Do you get pain and discoloration of toes with change in temperature?________4. Do you get numbness or reduced sensations in the feet?____________5. Do you experience pins and needles sensation in the feet?___________6. Have you ever been diagnosed with diabetes?______________
If you have answered NO to the questions above, you may continue to participate in the research study. If you have answered YES to ANY of the questions; unfortunately, youwill not be able to participate in the research study due to the potential health risks causedby the vibration.
7. What is your current age? _____________
8. What is your current weight? (Lbs) _____________
9. What is your current height? (Feet/inches)__________
10. Gender:____________
11. Have you ever worked with vibration tools?__________________
12. If yes, when and for how many years?________________________
13. Did you experience any foot problems while working with vibration tools? _______
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Part B: Discomfort
The body has been divided into fourteen different regions (right). For each body region please indicate if you feel any discomfort (ache, pain, numbness) in the region at the present time. If you have discomfort in an area, please rate the severity on the 9 point scale (0 being no discomfort and 9 being maximum discomfort).
Foot Assessment Protocol
1. Objective Assessment:
2. Foot Imprint:
a) Foot Length
b) Truncated foot length
c) Dorsum Height
d) Total area in contact (i.e A+B+C)
e) Arch Index
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APPENDIX 2
The table below lists the vibration acceleration values (aRMS) for a prototype study
performed prior to the main testing. The study consisted of five male and five female
participants. The prototype study followed the same protocol and guidelines as adapted in
the main study. Participants were exposed to a high frequency and a low frequency
vibration profile. The table can also be referred to for the associated health risks for the
vibration values recorded at the floor and ankle level for the eight-hour exposure duration
based on the ISO 2631-1 eight hour HGCZ (0.45-0.9 m/s2). Based on the guidelines, for
exposures below the zone i.e. below 0.45 m/s health effects have not been clearly
documented; in the zone, i.e. 0.45 m/s2-0.9m/s2, cautions with respect to potential health-j
risks is indicated and lastly for the aRMS value above 0.9m/s , for eight hours duration,
health risks are likely (ISO 2631-1,1997).
The measurement units of the values in the chart are as follows:
•y• RMS acceleration is in meter per second squared (m/s )
• Dominant Frequency (DF) is in Hertz (Hz)
Note: P.P= Power-plate vibration exposure
Sim= Vibration simulator
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Tablet: Vibration exposure details at high frequency (P.P) and low frequency (sim) vibration condition in male participants during trial prototype
SubjectNo.
aRMS(Floor)
PEAK(Floor)
D.F(Floor)
aRMS(Ankle)
PEAK(Ankle)
D.F(Ankle)
Transmissibility(Ankle)
l a (P.P) 9.4157 14.9505 31.5 3.0896 6.6817 31.5 32.81