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CHAPTER 1.0

INTRODUCTION

Electromyography is a technique for recording the electro-physiological properties

of muscles during contraction and rest. The result that is obtained is termed as an

electromyogram, which is often either graphical or numerical in nature. The device is

termed as an electromyograph. The electromyograph records the electrical potentials

which are generated in the muscles during both contraction and rest. (Tan , n.d). The

possibility of the electromyograph to record the electrical activity enables the

investigator to determine the integrity of muscular contractions. This methodology has

also ergonomic applications as in the case of this study.

Movements of the limbs , heart and other parts of the body are made possible by

muscle cells that act as tiny motors consuming energy and causing the contractions

necessary to make the muscles move. Nerves responsible for muscular contraction are

called motor neurons. That muscle which one particular nerve innervates is termed as

a motor unit. When a motor unit is activated via an action potential, it triggers a

sequence of stages that cause the muscular fibres to contract (Seeley. et al, 2000). The

electromyograph records this electrical activity.

Rubber tapping is the process of extracting the rubber from the rubber tree. This is

a highly manual process that involves the usage of a tool that resembles a sickle. Due

to financial constraints even in this modern era rubber tapping has been confined to

the manual process. The average number of trees that the rubber tapper will tap ranges

from 300 to 400 on a usual working day (Tapping Management of Rubber, 2007).

Due to the manual nature of this process the rubber tapper workers are exposed to

cumulative traumatic disorders also referred to as repetitive stress injuries. Such

complications are only aggravated due to improper handling of the rubber tapper tools

and/or lack of ergonomic design in the tools itself.

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1.1 ELECTROMYOGRAPHY

1.1.1 Physiology of EMG

Electromyography (EMG), also referred to as myoelectric activity, measures the

electrical impulses of muscles at rest and during contraction. As with other

electrophysiological signals, an EMG signal is small and needs to be amplified with

an amplifier that is specifically designed to measure physiological signals. This signal

can be recorded or measured with an electrode, and is then displayed on an

oscilloscope, which would then provide information about the ability of the muscle to

respond to nerve stimuli based upon the presence, size and shape of the wave – the

resulting action potential. While the electrode could be inserted invasively into the

muscle (needle electrodes), a skin surface electrode is often the preferred instrument,

because it is placed directly on the skin surface above the muscle without employing

the method of pinch insertion into the test subject. When EMG is measured from

electrodes, the electrical signal is composed of all the action potentials occurring in

the muscles underlying the electrode. This signal could either be of positive or

negative voltage since it is generated before muscle force is produced and occurs at

random intervals (Tan , n.d) .

The EMG signal is first picked up by electrode and amplified. Frequently more

than one amplification stages are needed, since before the signal could be displayed or

recorded, it must be processed to eliminate low or high frequency noise, or any other

factors that may affect the outcome of the data. The point of interest of the signal is

the amplitude, which can range between 0 to 10 millivolts (peak-to-peak) or 0 to 1.5

millivolts (rms). The frequency of an EMG signal is between 0 to 500 Hz. However,

the usable energy of EMG signal is dominant between 50-150 Hz (Tan , n.d).

In order to obtain a signal that yields the maximum information, the method

employed and the implementation device has to be considered. There are many

dependent factors that could affect a surface EMG since the signal is susceptible to

noise interference such as hum, signal acquisition such as clipping and baseline drift,

skin artefacts, processing errors, and interpretation problems. For example, the contact

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of electrode to the skin could distort a recording signal. The inadequate amplification

of the signal could cause a recorder detection problem. A wrong filter could efface

some of desirable information of a signal. Moreover, there are other factors such as

the distance between electrodes as well as the recording times used in the experiment.

The device utilized in the measuring of the signal must also be considered since low-

level input into a recording device could also affect data and yield inaccurate results

(Tan , n.d).

1.1.2 Excitable Tissue and Action Potential

There are two main types of tissue in the nervous system: excitable tissue and

nonexcitable tissue. The excitable tissue, which is composed of neurons, responds to

and transmits nerve stimuli. The non-excitable tissue, composed of glial cells, does

not response to voltage or any other conventional stimulus, since glial cells are non-

conducting, and function only as support cells in the nervous system (Seeley. et al,

2000).

Excitable tissue can be divided into four components: sensory receptors, neuron

cell bodies, axons, and muscle fibres. In a situation involving a harmful stimulus such

as contact with a sharp pebble or a hot surface, the resulting pain and pressure are

transmitted by sensory receptors. The pain is by a receptor potential, which is the

transmembrane potential difference of a sensory cell. Produced by sensory

transduction, a receptor potential results from inward current flow, which will bring

the membrane potential of the sensory receptor toward the threshold to trigger the

neuron into generating a rapid burst of voltage pulses called the action potential (APs)

(Seeley. et al, 2000).

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Figure 1.1: Typical time variations associated with a sudden, steady stimulus.

(Adapted from Seeley. et al, 2000)

As shown in Figure 1.1, triggered by a constant high-pressured stimulus, the

sensory receptor generates an initially high receptor potential that rapidly decreases to

a much lower, steady level. This decrease in the receptor potential is called

adaptation. The action potential produced by the neuron has a magnitude of 0.1 volts ,

which is a value that is shared by every animal, from a squid to a human (Seeley. et al,

2000).

To step off that pebble, the neuron sends a message along a nerve axon to the base

of the spinal cord. The axon, or nerve fibre, is the slender projection of a neuron that

conducts electrical impulses away from the soma, or the nerve cell body. There are

two types of axons: the afferent axon and efferent axon. The afferent axon, or sensory

axon, leads to the central nervous system, and carries messages from sensory receptors

at the peripheral endings to the spinal cord or brain. The efferent axon, or motor axon,

originates at the spinal cord and carries information through the body parts, synapse

with muscle fibres to stimulate muscular contraction as well as the muscle spindles to

alter proprioceptive sensitivity, which is a key factor in muscle memory and hand-eye

coordination. Because these two types of axons are designed to relay high-speed

messages, their diameter is between 0.001 and 0.022 millimetres, which is longer than

ordinary axons, which have a diameter between 0.0003 and 0.0013 millimetres. When

compared with the ordinary axons, the efferent and afferent axons also have a thicker

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layer of myelin, an electrically insulating fatty layer that increases the speed of

impulses by means of saltatory conduction. Therefore, by inhibiting charge leakage,

myelinated axons propagate action potentials that recur at successive nodes rather than

waves, and thus “hop” along the axon, thereby increasing the speed of the impulse.

With a large diameter and thick of myelin sheaths, all signals can thus travel through

the afferent and efferent axons at speeds as high as 120 meters per second, or 270

miles per hour. On the other hand, the ordinary axons, which are solely responsible for

simple activities such as reporting pain and temperature changes, have small diameters

and unmyelinated fibres, which are adequate to carry slow-speed signals (Seeley. et

al, 2000).

Figure 1.2: Excitable tissue called into play when a person steps on a sharp pebble

(Adapted from Seeley. et al, 2000).

As shown in Figure 1.2, the afferent axon carries the action potential burst from

the neuron to the interneuron, a neuron that communicates only to other neurons, or to

the motor neuron. This causes a chemical transmitter to be released across a narrow

fluid gap called synapses. The latter are specialized junctions that allow neurons to

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signal to their target cell, which could be another neuron or a non-neuronal cell such

as a muscle or gland. The action potential crosses this junction to either another

interneuron or a motorneuron, triggering another action potential burst as the process

repeats until the message reaches the efferent axon, which then carries the action

signal back down to the leg muscle. Once the signal reaches the muscle tissue, the

message instructs the muscle to contract, resulting in lifting the foot off the pebble

(Seeley. et al, 2000).

1.1.3 Generation of Action Potentials

As stated earlier, after a sensory receptor generates information, this electric signal

is transmitted to its intended target by travelling through an axon. However, an axon is

a relatively poor conductor because it rapidly attenuates the electrical signal. The

potential can decrease to 37 % of its original value after travelling a distance of only

0.15 millimetres along an axon, resulting in an unusable potential value. This distance

in which the potential becomes unusable is called the length constant. The length

constant is dependent upon the size of the axon, as it is proportional to the square root

of an axon diameter (Seeley. et al, 2000).

To overcome this tendency of signal attenuation, the nervous system uses a

method to increase the strength of the electric signal. When the potential decreases to

a threshold level, such as eight millivolts, the neuron will fire another 100 millivolts

action potential. However, the action potential will keep decreasing after travel

through the axon, which in effect will stimulate the neuron to fire one burst of action

potential after action potential, a process that is referred to as frequency modulation.

For example, in order to make a potential increase to 10 millivolts, the neuron might

fire ten times per second, although the neuron is also able to extinguish voltage in

order to end action potential (Seeley. et al, 2000).

To get more insight in this process, one must understand the structure of the axon.

There are ions arranged in constant random thermal motion inside an axon, with

protein molecules being one of the main components of the axon membrane. Under

normal conditions, sodium (Na+) and calcium (Ca2+) are more concentrated in the

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extracellular fluid, while potassium (K+) is more concentrated within the cell. In

effect, K+ is the key determinant of the resting membrane potential, since the resting

cell membrane is more permeable to K+ than to the Ca2+ and Na+ molecules.

However, while it plays a small part in the resting membrane potential, Na+ is a key

player in the generation of electric signals. When a cell goes from a resting to an

excited state, or firing level, the cell increases its Na+ permeability. This causes Na+

molecules to enter the cell through voltage-gated channels, thus moving down its

chemical gradient. This addition of the positive charge of Na+ to the intracellular fluid

causes the cell to become depolarized and initiates an action potential. The

extinguishing level that marks the falling phase of the action potential is the result of

an increase in K+ permeability in the cell. However, the closing and opening of the

voltage-gated channels is regulated by the jostling of the atoms within the cell, which

results in randomness in the train of the generated action potentials. Consequently, any

undesired departure from a perfectly ordered system may give rise to so called noise.

Higher receptor potential will initiate less noisy action potentials. However, a noisy

system is not always bad, as it enables living things to be able to adjust themselves to

changing environment (Seeley. et al, 2000).

Figure 1.3 : Model of action potential (Adapted from Seeley. et al, 2000)

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From Figure 1.3, the ‘sodium in’ curve is negative because the current that flows

into the axonplasm is defined as negative. On the other hand, the current that flows

out of the axonplasm is defined as positive. The sodium carrier proteins convey Na+

ions into the axon in accordance with the ‘sodium in’ curve. When crossing the

membrane, there is only low voltage left to drive the sodium ions into the bridges of

the transport proteins. Consequently, the dip of the sodium curve exists at the peak of

action potential curve. On the opposite side of the sodium curve, the potassium carrier

proteins convey K+ ions out of the axon in accordance with the “potassium out”

curve. To the left of the sodium dip, the Na+ current in is much greater than the K+

current. As a result, the voltage rapidly rises to 100 millivolts above the resting

potential. To the right of the dip, the potassium ions are small excess to the sodium

ions, which marks the slow drop in voltage (Seeley. et al, 2000).

1.1.4 Propagation of Action Potentials

In this section, the focus will be on how unmyelinated and myelinated axons

generate their action potentials. Regenerating nerve fibres could either be

unmyelinated or myelinated. As stated earlier, unmyelinated fibres have thin

membranes to carry slow-speed signals. On the other hand, myelinated axons have

thick membrane allowing them to carry highspeed signals (Seeley. et al, 2000).

In unmyelinated fibres, the AP propagates in the form of an ocean wave. When the

voltage across the membrane rises above the threshold level of eight millivolts, a

regenerating axon starts to generate an action potential. The thin membrane of the

unmyelinated axon allows ions to easily move across the membrane. Figure 1.4 shows

the AP waveform initiated by an unmyelinated axon (Seeley. et al, 2000).

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Figure 1.4: Net ion current curve and action potential of an unmyelinated axon

(Adapted from Seeley. et al, 2000)

Figure 1.4 (a) depicts the net ion current that generates the action potential. The

voltage rises to its peak at 100 millivolts before decreasing in value. Figure 1.4 (b)

shows the curve of voltage and current versus distance. It is interesting to see the

distance and time curve are mirror image of each other. While generally the distance

curve can differ from the time curve, the myelinated axon can generate the distance

curve and time curve of the action potential that has the same shape and amplitude

(Seeley. et al, 2000).

In comparison to unmyelinated axons, myelinated axons have a thicker wall. This

makes it impossible for sodium and potassium ions to move across the axon

membrane. As a result, regeneration of the action potential cannot occur. However,

the thick membrane also enables the axon to carry high voltage messages without

breaking down (Seeley. et al, 2000).

The thick, non-regenerating myelin membrane is offset by periodic nodes, which

are also known as nodes of Ranvier. The nodes are 100 outside diameter apart, as

illustrated at the top of Figure 1.5 (Seeley. et al, 2000).

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Figure 1.5: Nodes in the myelinated axon and action potential that is generated

(Adapted from Seeley. et al, 2000)

1.1.5 Electrodes that are used in electromyography

The EMG electrode could be explained by a receiving antenna concept. A

receiving antenna is an electrical device that detects oscillating magnetic fields, which

are generated from various sources. Then the signal is transmitted through the air from

source to the receiving antenna, a concept that is used to engineer the design of

electrode. In terms of recording the EMG signal, the muscle fibre is a biological signal

generator, spreading out over voltage fields to the volume-conductivity surrounded by

fluid. This fluid serves to convey an EMG signal to an electrode, like air carry signals

to an antenna (Tan , n.d)

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Figure 1.6 : The Series of Bio Electric Events (Adapted from Tan , n.d)

The EMG recording starts from the beginning of the bioelectrical events as shown

in Figure 1.6. The changing conductivities in the membranes will make action currents

flow across the membranes as well as into the extracellular fluids around active cells.

The extracellular currents will then generate potential gradients as they flow through

the resistive extracellular fluids. The changing potential gradients, subsequently, will

produce electrical currents in the electrode leads by capacitive conductance across the

metal/electrolyte interface of the electrode contacts. These weak currents will then

flow through the high impedance circuits of the amplifier input stages, which will then

convert these currents into large output voltages (Tan , n.d).

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The EMG electrodes can be classified by using its geometry. There are six classes

of EMG electrodes: monopolar electrode, bipolar electrode, tripolar electrode,

multipolar electrode, barrier or patch electrode, and belly tendon electrode (Tan , n.d).

A monopolar electrode takes potential from electrode and ground as the inputs to

the differential amplifier. When measuring, only a bare electrode is placed, without

utilizing other electrical connection. Because the ground yields a negative input to

differential amplifier, the potential from electrode is always based on ground (Tan ,

n.d).

A bipolar electrode is used to measure the voltage different between two specific

points. It generally must be used with a differential amplifier. A bipolar electrode has

two contacts that are not connected to each other. Therefore, one node will be used for

positive input, and the other will be used for a negative input for the differential

amplifier. Because the differential amplifier treats both inputs equally, it will yield an

accurate output. However the distance between the electrodes could affect the

measurement result. Placing the electrodes too far from one another could yield a

weak signal. On the other hand, placing them too close may also result in unusable

data, since the amplifier pre-processes each inputs signal separately before subtracting

those signals for output. In addition, there must be another contact used as a reference

point for these two inputs (Tan , n.d).

A tripolar electrode has three electrodes that are placed at equal intervals along a

straight line. The central electrode is usually connected to the positive input of a

differential amplifier, while the electrodes on the sides are usually connected to the

negative input of a differential amplifier. This configuration also requires another

electrode to serve as a reference. The tripolar electrode is often used to record nerve

potentials, as its configuration holds the advantage of being able to reject some forms

of biological noise (Tan , n.d).

A multipolar electrode consists of rows of bipolar electrodes where an equal lead

is connected each side of bipolar electrodes to serve as a positive and negative input

for a differential amplifier. Besides, another electrode must be applied as a reference

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point. The multipolar electrode is often used to record the activity of certain motor

units based on idiosyncrasies in their fibre locations (Tan , n.d).

The barrier or patch electrodes are typical bipolar electrodes that are closely

connected to a dielectrical barrier. The dielectrical is a non conductive substance that

is placed between the electrodes. This configuration redirects currents in extracellular

flowing around the tissue nearby. The patch also keeps the currents that are generated

from tissues on each side to prevent them from spreading into each other.

Consequently, the potential gradient of a desired action is larger, and the potential

gradient of an undesired action is smaller (Tan , n.d).

A belly tendon electrode is one of the fields of interest in the clinical EMG. Its

geometry is an interesting hybrid of the monopolar and bipolar approaches. In this

technique, the first electrode is placed in or over the middle point of the muscle of the

belly, which serves as the positive input to the amplifier. The second electrode is

placed over the tendon of the same muscle, which is usually about the end of

contractile elements, and serves as the negative input to the amplifier. This

arrangement gives a clean leading negative waveform, since there is no virtual active

contribution from tendon electrode. A belly tendon electrode is employed specifically

for tendon applications although it is not used for measuring a selective muscle EMG

recording during physiological activity (Tan , n.d).

All of electrode geometries discussed above could be considered as a dipole

antenna in term of electrical behaviour. Monopolar electrodes are used to measure the

EMG signal of very small muscle. This is a good approach for sampling a signal that

occurs near the surface of an active single fibre. On the other hand, tripolar electrodes

and multipolar electrodes are used for sampling some large muscles (Tan , n.d).

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1.1.6 Amplifier of EMG Signals

The amplifier is an electronic device that serves to boost low power signal to

higher power signal that is usable to perform work. There are two reasons to amplify

the signal. First, amplification increases the level of signal enough to protect an

electrical interference during transmission. Second, the signal is amplified so that it

could be stored in a storage device, or displayed by a measurement device like

oscilloscope. In case of an EMG signal, an amplifier is necessary. There are no such

devices that can measure EMG signal without amplification (Tan , n.d).

A differential amplifier is used to amplify an EMG signal, as it has the ability to

eliminate the noise from the signal. As shown in Figure 1.7 the differential amplifier

takes two inputs, subtracts them and amplifies the different. In this case, if there is

noise interference through the input wires, the noise could be circuitry cancelled out

so long the transmission of the two inputs is completely symmetrical manner (Tan,

n.d).

Figure 1.7 : A Schematic representation of the differential amplifier configuration.

The EMG Signal is represented by ‘m’ and the noise signal by ‘n’ (Tan , n.d.)

It is difficult to make an amplifier with perfect subtraction. The Common Mode

Rejection Ratio (CMRR) could measure the accuracy of subtraction in each amplifier.

It is suggested to have a CMRR value at 90dB in order to sufficiently discard a

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contaminated noise. Yet with modern technology, the differential amplifier could

make a CMRR value of 120dB. However, even though a differential amplifier has the

ability to reduce unwanted noise signals that occur from both sides of the input wires,

contaminated noises could still exist. This noise could have been injected into the

signal by a stray capacitance that has been amplified, and thus, degrading the signal

(Tan , n.d).

Every electronic component or even an amplifier itself behaves as an effective

filter, since there are no such electronic devices that can transfer all frequency range.

The electrode itself tends to have lower impedance for a higher frequency and have

higher impedance for a lower frequency. The connection of electrode, cable and

amplifier creates an implicit filter effect. The electrode contacts are connected in

series to an amplifier; they function similar to that of a capacitor, while an impedance

of amplifier is similar to that of a resistor. This connection visualizes a High-Pass

filter circuit. The low frequency voltage tends to be attenuated and drop the highest

voltage across the electrode contacts rather than the amplifier. On the other hand, the

cables that connect electrodes to an amplifier have a stray capacitor behaviour. It is

considered that this capacitor is connected to ground, which simulates a Low-Pass

filter circuit. The stray capacitor will provide low impedance, at which the high

frequency picked up by electrodes tend to drop their voltage here. Therefore an

amplifier will see an attenuation of high frequency (Tan, n.d).

The implicit filter could cause signal problems if it is not considered carefully in

the design of an amplifier. The explicit filter with real components (resistor and

capacitor) functions by using the same concept of an implicit filter, and could help in

increasing the signal-to-noise ratio. Since a signal is desired to be within in some

frequency range, it is good idea to have an explicit filter for that particular band.

Therefore, noise with the frequency outside a desired frequency band will be distorted

as shown in Figure 1.8 (Tan, n.d).

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Figure 1.8 : Implicit Signal Filter Circuit Diagram (Adapted from Tan, n.d)

The implicit filter is important in designing a differential amplifier. To reduce an

implicit capacitance effect, the electrode contact should be placed close to an

amplifier. In other words, an amplifier should be located as close to the signal source

as possible (Tan , n.d).

A raw EMG signal is an AC signal. Its bandwidth could occur anywhere from a

few tens of cycles per second to 3000 cycles per second. Therefore, sometime a large

amount of DC voltage appeared at the output of preamplifier. A DC offset can be

removed by adding a series capacitor to the output, which also allows the AC signal to

pass through. The DC offset can also happen between the recording electrodes

themselves, especially if they are made from different materials. A battery-powered

source sometime could overpower a sensitive preamplifier, which could also disgrace

the contact of electrodes or damage surrounding tissue. Placing a capacitor between

inputs of AC coupling could prevent this problem (Tan , n.d).

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A DC-offset-adjust potentiometer is often added to sensitive equipment, since it is

easy to adjust the DC-offset. However, the DC offset also dependents on temperature

Therefore, it is better to power up the equipment for sometime before adjusting the

DC offset (Tan , n.d).

1.1.7 Problems caused by noise and artefacts

In the process of recording an EMG signal, the source of the generated signal is

not only from bioelectrical generator or active cell, but also from any electrical fields

that occur around an electrode and lead cables. These electrical fields produce some

signals that could also be added to an EMG signal, causing a form of interference that

is called noise. Interference noise can be produced from anything that has an electrical

field such as power lines, computer monitors, transformers, or EMG amplifier itself.

Once noise has occurred, it could cause problem in recording an EMG signal.

Therefore while planning out the design of the amplifier device and recording the

EMG signal, noise factors should be taken into consideration, since noise could come

from a variety of sources such as electronic components, recording devices, ambient

noise, motion artefacts, or inherent instability of the signal (Tan , n.d).

Any electronic devices can produce noise. The noise frequency is range between 0

Hz to a 1000 Hz. This kind of noise cannot be eliminated. Using an intelligent circuit

design and a good quality of electronic components to construct the device can only

reduce the noise (Tan , n.d).

Ambient noise could be generated from any electronic device that created an

electromagnetic field such as televisions, computer monitors, motors, electrical power

lines, fluorescent lamps or light bulbs. In fact there are radio waves and magnetic

fields floating all over our body. It is virtually impossible to drain these radiators to

ground (earth surface). The ambient noise also cannot be avoided. The ambient noise

frequency occurs primarily within the range 50 Hz or 60 Hz, while the amplitude of an

ambient noise is about one to three times greater than that of an EMG signal (Tan,

n.d).

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Motor artefacts come from two sources ; first, from the contact of an electrode to

skin; second, from the connection of cable from electrode to the amplifier. When

performing a grasping experiment, a movement of the wire alone could cause a noise

problem. This electrical noise from both sources has the frequency range between zero

to twenty hertz. However, a proper design of circuitry with a good connector and

stable electrode contact could reduce this motion artefact problem (Tan, n.d).

Inherent instability of the signal is caused by a nature of EMG signal. The

amplitude of the EMG signal frequency range between zero hertz to twenty hertz is

particularly unstable due to the quasi-random nature of the firing rate of motor units. It

is suggested to consider an EMG signal frequency in this range as an unwanted noise

signal (Tan, n.d).

There is no boundary in what amplitude of an EMG signal is good for yielding

accurate recordings. While a certain amount of noise could be tolerated, the question

is exactly how much noise could be allowed. In other words, there is a question about

the tolerable levels of the signal-to-noise ratio. The signal-to-noise ratio is determined

by taking the ratio of the amplitude of desire signal over the amplitude of added noise

signal. The main concern now is in the lever of the signal-to-noise ratio that could

degrade an analysis result. If the noise is produced from thermal motion, then twice of

desired signal amplitude over the noise amplitude is good enough. However, if the

noise occurred periodically (pause like) and forms a pattern similar to the desired

signal, it is suggested that ten times grater of the desire signal amplitude than the noise

amplitude would be clarified a confusing event. In order to determine signal-to-noise

ratio, the study of noise behaviour alone may be required to see how noise could affect

the real signal (Tan, n.d).

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1.1.8 Interpretation of an Electromyogram

Figure 1.9 :- Interpretation of an Electromyograph ( Image generated using Adobe

Illustrator CS3)

As shown in Figure 1.9 the various waves that are generated are also indicative of

the recruitment patterns of the muscle i.e., The number of motor units that have been

activated as a result of the stimulus.

Figure 1.10:- Actual EMG recordings (Adapted from Mills 2007)

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As shown in Figure 1.10 , This is an actual EMG recording with 3 subjects with

different pathological conditions :-

1. A – Recruitment patterns during maximum voluntary contractions of the

deltoid muscle in a healthy subject.

2. B – Recruitment patterns of the muscle fibres during maximum voluntary

contractions of the deltoid muscle with spinal muscular atrophy.

3. C – Recruitment patterns of the muscle fibres during maximum voluntary

contractions of the deltoid muscle with polyositis

4. Note the difference in the different amplitude calibrations.

Maximal Voluntary Contraction or MVC refers to a condition in which a person

attempts to recruit as many fibres in a muscle as possible for the purpose of

developing force (Seeley. et al, 2000).

1.1.9 Uses of Electromyography :

In essence an EMG gives us a visual depiction of electrical activity of muscles. An

EMG is usually an extension of clinical examination when trying to diagnose and

differentiate between various nervous disorders. The electromyographer will analyze

the electrical activity of the muscles which is either a graphical depiction and/or is

heard as popping noises through a loud speaker. Any discrepancy in the firing

behaviour of the action potentials is a significant indicator of a pathological condition.

(Mills 2007).

The EMG study is also essential in trying to distinguish between the neurogenic

disorders ( pathological dysfunction involving the nervous system) or myogenic

disorders supplementing and appropriate diagnosis. This process involves needle

electrodes which are directly inserted into the muscle when a much focused

measurement is required or with the use of surface electrodes that determine the

activity of groups of muscles instead of individual muscle fibres. These electrodes are

attached to an EMG which will display the recordings as a graph using chart software

on a computer monitor (Mills 2007).

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Since the EMG is able to give us a graphical depiction of muscular activity this

technique can be employed in this experiment in order to determine which muscles are

most active when performing the rubber tapping process. This information will assist

us in determining which tool is more ergonomically designed hence being safe for the

usage by the rubber tapper workers.

1.2 Rubber Tapping :

1.2.1 Process of Rubber Tapping :

Tapping begins once trees reach maturity; that is at about seven years, although

this may be latter in unfavourable areas. Tapping involves periodically cutting the

bark on the trunk, and hence severing latex vessels. It is best done at a 25-30° angle

from the horizontal, from high on the left of the tree to low on its right, in an action

exposing the maximum number of latex vessels per length of incision. Tapping

productivity is a critical issue in maintaining sustainable supplies of natural rubber

(Rubber Tapping , n.d).

One of the main reasons for the successful establishment of Hevea brasiliensis on

a plantation scale was the discovery of the excision method of tapping for harvesting

rubber: the same cut is regularly reopened by the removal at each tapping of a thin

shaving of bark from the sloping cut. This principle is in general use today: Ridley

was the pioneer of this method. Each time a tree is tapped (with a suitable knife) a

channel is prepared along which the latex flows. This method avoids wounding trees

(Rubber Tapping , n.d).

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Figure 1.11 : The most common rubber tapping technique used today ( Adapted from

Google Image search keyword “Rubber Tapping”

As illustrated in Figure 1.10 , The cut penetrates to within 1 mm of the cambium;

the precise depth varying with the skill of the tapper. The same cut is regularly

reopened by the removal at each tapping of a thin shaving of bark. The object of

tapping should be to get as much latex as possible from the trees with the smallest

excision of bark convenient, and minimize damage to the health of the trees and their

capacity for continuing to yield latex (Rubber Tapping , n.d).

The cut is made either with a notched knife which is drawn down the incision, or

with a chisel which is pushed along it. In both cases thin slivers of bark are excised,

and latex flows immediately along the cut and into a cup attached to the trunk. The

flow progressively diminishes, and stops in 1 to 3 hours as severed vessel ends

become plugged by caps of coagulum. Once begun, tapping is normally continued for

10-20 years, depending on how quickly the accessible bark is consumed.

Consumption is determined by the degree to which new or 'virgin' bark is cut away,

and to which cut bark is renewed after tapping. In conventional approaches tapping

moves along successive panels, first traversing easily accessible virgin bark and then

returning to cover renewed bark 6-7 years later. It may also utilize virgin bark at

higher levels of the tree, and even extend to bark of third renewal (Rubber Tapping ,

n.d).

Much depends on the standard of tapping, however. Bark consumption is higher,

yield per cm of cut is less, and renewal is poor if there is a lack of skill, but under

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skilled operations tapping may continue for 25 or more years. Some unskilled

smallholders use 2-3 times as much bark per cm as skilled tappers, and the damage

may reduce the total period to 15 years or less (Rubber Tapping , n.d).

The commonest tapping system with budgrafts involves a 'half spiral' cut half way

around the tree. This is executed on alternate days, provided there is no substantial

rain which prevents tapping by diluting latex flows and washing them down the trunk.

Rainguards greatly reduce the effects of rainfall. Tapping with selected seedlings is

only done every third day, since more intensive systems usually lead to a permanent

drying up of latex or tapping panel dryness (Rubber Tapping , n.d).

It is advantageous to begin tapping early in the day, when the turgor pressure of

the latex and its consequent rate of flow is higher. Thus it is usual for the tapper to

carry a light source (often a torch like a miner's lamp) to help in seeing before dawn-

breaks (Rubber Tapping , n.d).

The usual procedure in tapping is for one person to first tap as much as can be

managed; depending on conditions, this is normally a 'task' of 500-600 trees which

takes 3-4 hours. Younger trees are simpler to tap. The same person then returns to

collect the still-liquid latex from the cups, emptying it into a bigger container. There is

then a residual flow of latex which coagulates on the cut and in the cup; this is secured

at the next tapping as 'scrap' and 'cup lump' (Rubber Tapping , n.d).

A major tapping advance was the introduction, in Malaysia, in the early 1970s, of

the 'stimulant' ethephon or 2-chloroethyl phosphonic acid. This is applied at intervals

to bark of first, or later renewal, either close to or in the tapping cut. It dissolves

slowly in the presence of water, releasing the gas ethylene in the bark and delaying

plugging with consequently greater latex flow. While ethephon increases yield in the

short term, however, that effect is not maintained, and the stimulant is most usefully

employed in 'substituting' for labour and getting similar yields with less frequent

tapping. Subsequently, the Rubber Research Institute of Malaysia has applied ethylene

directly to rubber trees to stimulate latex flow using systems known as RRIMFLOW

and REACTORRIM (Rubber Tapping , n.d).

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Stimulation introduces flexibility into tapping as labour use in this labour-

intensive activity may thereby be reduced. Thus, although most tapping is still done

on alternate or third- daily systems, it is possible through skilful stimulant application

combined with once-a-week excision to secure perhaps 80 per cent of the yield on

alternate daily; this produces crops at lower cost. It is hoped that weekly tapping may

eventually be achieved (Rubber Tapping , n.d).

A further significant advance has been the introduction, again in Malaysia, and

following three decades of research including that on stimulation, of the puncture

system of tapping. This as currently applied involves making one puncture each week

on a scraped area of bark treated with stimulant. Latex flows directly into a closed

receptacle, which protects it from natural coagulants. It is then collected 2-3 days later

while still in liquid form, after a prolonged period of flow. Puncture tapping again

saves much labour compared to conventional methods, but is capital-intensive in

equipment and chemicals and requires good management. It seems more promising

than the previous avenue in this research of battery-driven mechanical tapping

machines; these worked well, but were far too expensive for normal use (Rubber

Tapping , n.d).

Better conventional tapping systems have also been initiated, and include the

'upward' tapping of virgin bark high up on the tree, using a knife attached to a long

stick. This system, which may be accompanied by stimulation, is based on earlier

Indonesian methods and enables yields to be maintained once lower virgin bark has

been tapped away and poor renewal threatens a drop in output. It is thus especially

pertinent to smallholding conditions (Rubber Tapping , n.d).

Rainguards assist in increasing both tapper and tree productivity during periods of

heavy rainfall. Tapping cups are essential implements of the industry. Earthenware

cups are widely used. They are cheap, but heavy. Glass cups are used in a few

plantations. Plastic cups have been introduced to the industry. Glass cups are lighter

and easy to clean but are more expensive and easily broken. Further, they are easily

stolen from the field. Plastic cups are lighter and easy to transport. However, rubber

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tends to stick to the cups permanently making cleaning difficult. The cup is placed in a

wire hanger attached to two pieces of wire and an extensible spring attached to the

rubber trees. A spout is fixed to the rubber trees to enable the latex to flow from the

tapping cut into the cup (Rubber Tapping , n.d).

In areas where cuts are opened higher than the tapper can reach, one-step or two-

step ladders are used to enable the tappers to tap comfort ably. Such ladders are

specially made with a platform so that when it is placed against the rubber trees, the

tapper can stand on the platform to tap the tree with a good degree of stability. The

ladder should be light to make carrying it from tree to tree feasible (Rubber Tapping ,

n.d).

1.2.2 Common Rubber Tapping techniques :

The rubber tapping process is a very labour intensive process which involves both

and skill and endurance. The rubber tappers make their rounds during the early

morning hours of the day, since the latex production is maximal before the sun comes

out. There are various methods which are employed to extract the latex namely :-

1. Half Spiral Method (Also Called Excision method) – As shown in Figure 1.12

& Figure 1.13 , In this method a half spiral is cut on one side of the bark. This

angle of slope is roughly 30°. The cut is usually made about 150cms from the

ground of young rubber trees. The cut is usually 1mm which is deep enough to

just reach the cambium ( that part of the rubber tree responsible for the

growth). Once the cut is made a small collecting cup which is usually an

earthen pot is attached to the tree. It takes roughly 3 hours for the latex to run

down. Once the latex ducts are plugged by drying the tapper comes and

removes the dried latex wire and collects the latex in a cup. In modern

methods a stimulant is applied to the tree which was developed in Malaysia

during the 1970’s , this stimulant which is ‘ethephon’ or 2-chlorothyl

phosphoric acid is applied to the tree in order to prolong the latex oozing. This

is the most common method which is used till this day. (FAO Document

Repository,n.d).

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Figure 1.12: Latex oozing as a result of

the cut source (Adapted from Google Image search Keyword “Rubber Tapping”)

Figure 1.13: Half Spiral Method

source (Adapted from Google Image Search Keyword “Rubber Tapping”

2. Upward Sloping Cut – This method is employed for those rubber trees which

are older and have been tapped several times , the cut is made in an upward

fashion at an angle of 45°. The cut is made just above the previous cut on the

bark so that both the channels meet. This excision is also made much higher on

the tree , for this purpose the rubber tapping tool is attached to an extension

handle to that the higher part of the tree can be reached (Tapping Management

of Rubber 2007) .

3. Triangular Tapping Method – As illustrated in Figure 1.14 This alternative

method involves making a triangular incision on the bark of the tree , the

triangle is pointed downwards towards the end of the triangle a container is set

to collect the rubber. However the yield gained by this method is not as high as

compared to other most common methods (Tapping Management of Rubber

2007).

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Figure 1.14 : Triangular Cut Method of collection ( Adapted from Google Image search Keyword “Rubber Tapping”

4. Malaysian Puncture System – This method was developed in the Rubber

Research Institute in Malaysia which is a more modern way of tapping the

rubber trees , which involves making a punch directly on the tree using a tool

to make a small hole on the bark of the tree. However this method is capital

intensive and requires good management of equipment and chemicals (Rubber

Tapping , n.d) .

5. Mechanized Rubber Tapping System – this method was also developed by

Rubber Research Institute in Malaysia which involves the usage of small

battery operated devices that make the excisions on the trees. However this

method is not used because of it extremely high cost of application (Rubber

Tapping , n.d).

1.2.3 Common Rubber Tapping Tools :

The process of rubber tapping has been around for quite some time and the tools have

subsequently also evolved according to their usage.

1. Traditional Knife – One of the most common tools which are used to make the

excisions is a sharp knife. An extension is also added to the knife so that it will

be able to reach higher part of the older rubber trees (Tapping Management of

Rubber 2007).

2. Curved Knife (Sickle Knife) – As illustrated in Figure 1.15 This involves the

usage of a curved knife which almost resembles a sickle being very sharp

(Armstrong,n.d).

Figure 1.15 : Curved Sickle Shaped Knife (Adapted from Google Image Search

Keywords “Rubber Tapping Tool Sickle Knife”)

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3. Modern Tools – The more modern tools as illustrated in Figure 1.16 and

Figure 1.17 ,which are used for the rubber tapping are more ergonomically

designed with a more comfortable grip .

Figure 1.16 – Type 1 - Rubber tapping

tool for the upward motion cuts (Adapted from

http://www.alibaba.com/catalog/11680623/Rubber_Tapping_Knife/showimg.html)

Figure 1.17 – Type 2 Rubber tapping tool for the downward motion cuts (Adapted

from http://www.alibaba.com/catalog/11680623/Rubber_Tapping_Knife/showimg.html)

The muscles which are involved in the process of rubber tapping are usually the

muscles of the hands arm, fore arm and shoulders and the back. Since the process

involves the bending of the tappers while performing the excisions upper and lower

back involvement should be present. Muscular aches are to be expected in the rubber

tapper tools especially when the tools which are used are either not effective or the

process which is being performed is not according to the procedures of the process

(Strength & Conditioning Terminology, n.d).

During this process the muscles involved undergo maximum voluntary contraction

and the contractions are both isokinetic (contraction in which muscles are of constant

velocity) & isotonic (contraction in which constant force is being generated). This

rhythm is to be maintained by the rubber tappers in order to ensure that the excisions

made are the same in every tree during the rounds (Strength & Conditioning

Terminology, n.d).

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1.2.4 Malaysian Rubber Industry:

In 1876, Sir Henry Wickham, at the request of the India Office, collected and

shipped from Brazil 70,000 seeds from the wild rubber tree. These were rushed to

Kew Gardens in London and planted in specially prepared hot-houses. The small

number, which survived, were taken in 1877 to Ceylon and later to Malaysia and other

countries of South-east Asia (The Story of Malaysian Natural Rubber 2002).

The rubber tree quickly flourished in Malaysia; large areas of jungle were cut

down and planted with rubber trees. Henry Nicholas Ridley, who was appointed

Director of the Singapore botanic gardens in 1888, was one of the pioneers of those

times and did perhaps more than anybody to encourage planting of this new crop (The

Story of Malaysian Natural Rubber 2002).

By the end of the nineteenth century there were 2500 hectares of rubber in Asia.

Shortly afterwards Henry Ford started making his famous motorcar and the demand

for rubber – to make tyres – rocketed. The trees in the South American jungle could

not possibly produce enough rubber and so the new plantations of Asia found that the

world wanted all the rubber they could produce, and more. By 1910 there were ½

million hectares of rubber planted and the countries of Asia had now become the main

suppliers of rubber (The Story of Malaysian Natural Rubber 2002).

With the spread of motoring to every country in the world, even today’s enormous

acreage of rubber (about 6 million hectares in all) cannot supply enough. There is not

enough natural rubber to go around. Scientists have developed man-made rubbers

from petroleum. These are often mixed with natural rubber. For some products,

however, only natural rubber can be used (The Story of Malaysian Natural Rubber

2002).

Peninsular Malaysia – comprising 12 of the 14 states in the Malaysian federation –

is among the world’s most important rubber growing areas. Rubber is also grown in

Sabah (formerly North Borneo) and Sarawak, which, known together as East Malaysia

make up Malaysia (The Story of Malaysian Natural Rubber 2002).

Altogether Malaysia produces almost 20% of the world’s natural rubber. A good

deal of Malaysia’s rubber (over half) comes from thousands of privately owned plots

of land called smallholdings, which are usually about 2 hectares. The rest is grown on

big estates owned by various companies; each can cover over a thousand hectares.

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Altogether, Malaysia has 1.7 million hectares of rubber (The Story of Malaysian

Natural Rubber 2002).

In recent years most of the older trees have been replaced by newer varieties

which yield up to ten times as much rubber, thanks to scientific cross-breeding and

careful cultivation (The Story of Malaysian Natural Rubber 2002).

The plantation industry in Malaysia is on the way out. Once the largest exporter of

natural rubber in the world, today Malaysia has become an importer of rubber. It is

said that by the year 2005, there will be less than 10,000 acres planted with rubber

trees for research purposes only while the rest will be devoted to palm. The current

work force in the rubber plantations is also expected to drop to 5,000 workers from

more than 100,000 workers. Palm plantations will continue to employ workers but

they will mostly be contract or migrant workers (Arutchelvan 2002).

1.3 Ergonomics

1.3.1 What is Ergonomics

Ergonomics is the process of fitting the job to the worker — instead of the worker

to the job. Ergonomics matches the design of tools, controls, & equipment to fit the

safety needs of the operator. Since each of us has different needs, ergonomic design of

tools, equipment and workspaces must be adjustable enough to accommodate a varied

range of body types. For example, tools such as scissors must be designed in order to

accommodate individuals who are right-handed or left-handed. Organizations that

overlook the safety of workers in their workplace often specifically addresses the field

of workplace ergonomics, which examines the impact that tools, positions, repetitive

movements, and the tasks of workers have on workers’ health and safety (Ergonomics,

n.d)

The mission of ergonomics is to provide solutions to work related pain and

discomfort. Ergonomics training and awareness may save money. Yearly, workers

across America file worker's compensation claims due to workplace injuries. Second,

ergonomics prevents injuries, including back injuries, carpal tunnel syndrome, work

related musculoskeletal disorders (WRMSD) and other injuries that can occur as a

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result of highly repetitive and physically demanding job tasks. Third, when workers

and employers prioritize health and safety and are aware of ergonomic principles,

productivity is enhanced. Workers learn to analyze their work as well as listen to red

flags such as slouching in chair, dry eyes, loss of concentration, or tingling sensations.

In a win-win situation for the employer and employee where money is saved, injuries

are prevented, and productivity is increased, the altruistic objective is that workers

will experience job satisfaction (Ergonomics, n.d).

Depending on what is entailed in your job, ergonomics may be for you.

Ergonomics trainings, awareness, and programs should especially be considered if

workers are engaged in (Ergonomics, n.d):

• Repetitive work; such as sweeping in Custodial work; typing in clerical work,

lifting in childcare & adult care for those that work as nurse’s aides for

example.

• Reaching; such as stretching arms above head to pick fruit in farm work.

• Bending, twisting; such as stocking shelves in grocery and retail stores.

Common risk factors or work place elements that could cause pain and injury to an

employee and which are considered by organizations that are in charge of workers

safety are (Ergonomics, n.d) :-

• Vibrations; as may be experienced by bus drivers.

• Chemical hazards; such as refinery workers who may be exposed to hazardous

fumes, spills.

• Biological hazards; such as home health care aides who are exposed to human

blood or other body fluids.

• Heat / Cold Stress; such as for construction workers.

• Noise and Hearing Conservation; such as for construction workers.

1.3.2 Ergonomics in Hand tools:

The process of selecting and or modifying tools, especially hand tools, to provide

a better fit for the user is something everyone at one time or another has attempted to

do in daily life. Whether that tool is a computer keyboard used at work or a small

Phillips screwdriver used for a woodworking hobby in the garage, no one tool works

for all jobs and no one tool fits all users in the most efficient or comfortable fashion.

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Fit, in terms of comfort and efficiency of use, is particularly important for tools used

for long-term projects or for occupational activities (Cacha , 1999).

It is easy to find research that documents the association of hand tools and the

problems that result if the wrong tool is used for a task, or if the correct tool is used

improperly. Much of the desire to create a better hand tool has always been driven by

the parallel desire to create a more efficient work process and an improved product at

a lower cost. In the mid-1800s, Wojciech Jastrzebowski coined the word ergonomics,

which means the study or science of work. Many pioneers in the ergonomics field

have since refined this study of the science of work, especially after World War II.Â

Today, the science of ergonomics is now more often referred to as "fitting the task to

the person". The ergonomics task is not limited to work only, but may refer to work,

recreational, sports, etc. Ergonomics, also known as human factors, also attempts to

look at the cognitive or decision making performance of humans (Cacha , 1999).

In the last decade, tremendous strides have been made in design and development

of hand tools in an attempt to reduce the problems, including potential injuries to the

worker, while also increasing tool efficiency. These improved hand tools are often

sold or labelled as "ergonomic" hand tools. It is important to remember that no one

hand tool is perfect for every job, and no one hand tool is perfect for every user

(Cacha , 1999).

Developing a "single standard" for ergonomic hand tool design is difficult because

of the variation in human anthropometry (i.e., branch of human science that deals with

body measurements, human performance, work environments, and tasks). Therefore,

investigation of appropriate tool design and of using hand tools while utilizing proper

ergonomic principles continues to evolve. There are guidelines and methods,

however, by which tools can be tested to effectively evaluate specific ergonomic

features. In general, ergonomic hand tool features can be classified by the following

design goals (Ergonomics Hand Tools , 2003) :

• Decrease the force or grip strength required to use the tool.

• Decrease repetitive motion associated with using the tool.

• Decrease awkward body postures or wrist positions when using the tool.

• Decrease vibration transmitted to the hand and wrist.

1.3.3 Cumulative Traumatic Disorders and Carpal Tunnel Syndrome

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Due to the highly manual nature of the rubber tapping process, the rubber tapper

workers are exposed to what is termed as RSI’s or repetitive strain injuries. These are

a group of disorders that originate in those muscles which are repetitively used for

action. They are also known as Cumulative Traumatic Disorders or CTD’s. Since the

trauma or injury sustained over a period of time develops into a more severe form of

the injury.

One of the most notorious CTD’s that afflict the modern age is Carpel Tunnel

Syndrome or CTS for short. This disorder affects those individuals who have to use

their forearms and wrists specifically. However the risk of developing is low in people

who take appropriate measures while performing a task. These disorders are also

developed in those individuals whose professions involve the extensive use of hand

tools. The lack of knowledge of the proper use of these tools coupled with the bad

design of the tool itself contributes to the development of the CTS (CTS , n.d).

Carpal tunnel syndrome is a painful condition caused by pressure on the nerve that

serves the fingers and palm. The carpal tunnel is a passage in each wrist that is formed

by the carpal bones and the volar carpal ligament (Figure 1.18). Carpal tunnel

syndrome occurs when the median nerve, which travels from the arm to the fingers,

becomes compressed within the carpal tunnel. Although the tunnel usually protects the

median nerve, tissues within the tunnel can become inflamed or swollen. This

inflammation results in pressure on the nerve. Carpal tunnel syndrome occurs when

the median nerve becomes compressed, causing numbness, tingling, and pain in the

hands. The pain can also extend to the arm and shoulder (Kao 2003).

Figure 1.18: Illustration of Carpal Tunnel

Syndrome (Adapted from Google Image Search key words “Carpal Tunnel Syndrome”)

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Carpal tunnel syndrome is usually characterized by pain or tingling. Other

symptoms may include numbness or weakness in the hands that may cause the person

to drop objects. If this weakness continues for long periods of time, it may result in

permanently atrophied muscles. Some people with carpal tunnel syndrome experience

intense pain that shoots up the arm to the shoulder (Kao 2003).

Although some medical conditions such as diabetes can increase a person's risk for

carpal tunnel syndrome, most cases are caused by repetitive motions of the hands or

wrists. Carpal tunnel syndrome is most common in middle-aged people, but is rare in

young people who have not yet had long-term exposure to the repetitive motions that

most often cause the condition (Kao 2003).

Treatment varies from wearing a brace to drug therapy or surgery. Mild carpal

tunnel syndrome may be effectively treated with a brace, which is usually worn

overnight. This gives the wrist a chance to rest so that the swollen tissues inside the

carpal tunnel can shrink, reducing pressure on the median nerve. As symptoms

become more severe, drugs or surgery may be recommended (Kao 2003).

Although carpal tunnel syndrome can be caused by several medical conditions, the

most common cause is overuse of the wrists due to repetitive tasks. Any condition that

causes the tissues within the carpal tunnel to swell can lead to carpal tunnel syndrome.

Some examples are broken or dislocated wrist bones, arthritis, thyroid imbalance,

diabetes, menopausal hormone changes, and pregnancy. However, the most frequent

cause is repetitive tasks that require bending of the wrists or grasping with the hands.

Tasks that carry a recognized risk for carpal tunnel syndrome include typing, cutting,

sewing, or playing a musical instrument. Overuse of small hand tools is often

associated with this condition. Use of vibrating tools, such as a jackhammer, is also

considered to be a contributor (CTS, n.d).

Tingling in the hands is an early sign of carpal tunnel syndrome. The tingling may

be followed by a feeling of weakness or numbness in the hands and intense shooting

pain that travels up the arm. The symptoms of carpal tunnel syndrome often first

appear at night and may be pronounced enough to cause sleeplessness. One or both

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hands may tingle painfully. This tingling may become more frequent and often

involves the thumb, index, and ring fingers (CTS, n.d).

CTS can be diagnosed confidently with patient history alone, however one of the

techniques which are employed to detect the presence of CTS is the use of the EMG

technique (Bernardo 2004). The EMG tests reveal the following important diagnostic

information :

• Shows delay in the latency of the motor unit action potential for the abductor

pollicis brevis.

• False negative rates for neurophysiological examination of the median nerve

have been estimated in several trials to be between 7 and 13%.3

• EMG testing is the standard diagnostic test of choice, but if a questionnaire is

employed (see below) EMG testing can be reserved for atypical cases or to

rule out more diffuse neuropathy, as in diabetics, when the response to

treatment may be reduced.

Once the diagnosis is made we will determine the best possible treatment for the

patient trying to prevent further nerve damage and trying to reverse the process. The

different treatment options include bracing, physical therapy, and surgical correction.

One of the common physiotherapy methods of treating CTS is the use of a splint

which would keep the wrist straight and reduce pressure from the carpal tunnel, which

is useful in the early stages of the condition (1.19) The treatment option that is chosen

depends on the severity of nerve damage shown on the EMG/nerve conduction study,

making this test very crucial. The earlier in the disease process that we see the patient

the better chances of recovery. The later in the course the patient comes to our

attention the chances of recovery are less, the patient could develop permanent

paralysis, and surgical procedures might be required even though they could have

been avoided early in the disease course. Patients could have full recovery with

minimal intervention if they seek medical attention early (CTS , n.d).

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Figure 1.19 : A splint used to keep the wrist straight ( Adapted from Google image

search keyword – “CTS”)

1.4 Research Objectives:

Since it is clear that the Malaysian rubber industry is still a dominant player in this

sector, its workforce is in excess of 100,000 workers (Arutchelvan 2002). Most of

them still employ the manual rubber tapping technique. Determining which tool used

by the rubber tapper is the most efficient will assist those authorities who are involved

in the purchase of tools for the rubber tappers. This would ultimately increase the

productivity of the rubber tappers by reducing the amount of physical damage and

strain resulting from prolonged tapping.

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CHAPTER 2.0

MATERIALS AND METHODS

2.1 PARTICIPANTS :

22 volunteers (12 male and 10 female) without any history of musculo-skeletal

disorders participated in the research to simulate the process of rubber tapping and to

represent the workers. Each one of them had voluntarily filled out standard consent

forms and were fully informed of the experiment. In a case where there would lack of

participation from any one particular sex among the participants the distribution

would be altered so as to maintain the necessity of having 22 volunteers.

2.2 MATERIALS :

1. Standard 15L Distilled water container which would represent the bark of the tree.

2. 100% PVC Carpet 3ft X 4ft procured from a local supermarket – this would

represent the texture of the tree.

3. 3 rolls of Cloth tape procured from local supermarket - used for securing the carpet

around the tree.

4. Plastic rope – For measurement of the MVC ( Maximum Voluntary Contraction)

5. Carpet Shears procured from local supermarket for adjusting length of the rope and

the carpet if.

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2.3 Instruments and Apparatus :

1. Standard rubber tapping tools procured from a local hardware store

Figure 2.1- Upward Cutting Tool being

used for the experiment

Figure 2.2 – Downward Cutting tool

being used for the experiment

Figure 2.1a - Upward cutting tool details,

Image generated using Illustrator v10.0.

Figure 2.1b - Downward cutting tool

details, Image generated using Illustrator v10.0.

2. Powerlab ® from ADinstruments ™ - 4 channel EMG device.

Figure 2.3 : Front Panel of Powerlab/4st Device (Adapted from Powerlab/4st n.d)

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Figure 2.3a – Actual Image of the Powerlab Device

Figure 2.4 : Back Panel of Powerlab/4st Device (Adapted from Powerlab/4st n.d)

Figure 2.5 Dual Bio Amp Cable Yolk (Adapted from Powerlab/4st n.d)

Figure 2.5a – Actual Image of Dual amp Cable Yolk

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Figure 2.6 Standard surface Electrodes ( Adapted from Powerlab/4st n.d)

Figure 2.6a – Actual Image of the standard surface electrodes.

a) Supplied USB connectors , for connecting the Powerlab device with a personal

computer.

b) Chart v5.5 Software for visualizing the signals , comes standard with the

Powerlab device

c) Standard surface electrodes which has a highly conductive gel at its end for

sticking to the surface and to facilitate the movement of current into the

electrode. These electrodes will be placed on the muscles of the forearm of the

dominant hand in the individual.

d) Special Leeds which came standard with the Powerlab device, which were

colour coded for proper attachment to the double yolk bioamp cable.

e) Abrasion pad , which is used to improve the conductance of the electrical

impulses in the case where the signal detection is hampered.

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2.4 MEHTODS :

2.4.1 OVERVIEW

The MVC’s of the volunteers were recorded in the beginning of the experiment to

serve as the reference for the other tasks. Once the MVC’s were recorded each one of

the participants were asked to perform the rubber tapping process using each one of

the tools on two surfaces. The first surface was the representation of the tree and the

other was the material used for representing the texture of the tree on a flat surface.

The Powerlab instrumentation has a routine that can convert the graphical EMG

recordings into numerical outputs specifically into RMS values. Once the RMS values

of all the participants are taken they will be average out and compared to the MVC

recordings to determine which rubber tapping tool is more efficient.

2.4.2 SETUP OF THE EXPERIMENT

FIGURE 2.7 : Illustration of the Setup of the experiment ( Image generated using

Illustrator 10.0)

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Figure 2.7a – Actual Setup of the experiment

2.4.3 MUSCLES THAT WILL BE USED FOR EMG RECORDINGS

The muscles that have been identified to be responsible for the development of

carpel tunnel syndrome has been the focus of the EMG study. Since the objective of

the experiment is to determine the risk factors of the rubber tapping process. Four

muscles have been identified based on previous experiments that test for the

development of carpal tunnel syndrome. Based on a study conducted by Fagarasanu.

Et al 2004 in the measurement of angular wrist neutral zone and forearm muscular

activity the muscles which have been chosen for this experiment are :-

1. Flexor Carpi Radialis

2. Flexor Carpi ulnaris

3. Extensor Carpi radialis

4. Extensor Carpi ulnaris.

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Figure 2.7b – Position of Flexor Carpi Radialis & Flexor Carpi Ulnaris Adapted

from Google Image Search Keywords “Flexor Carpi Radialis & Ulnaris

Figure 2.7c – Position of Extensor Carpi Radialis Brevis Adapted from Google

Image Search Keywords “Extensor Carpi Radialis”

Figure 2.7d – Position of Extensor Carpi Radialis Longus Adapted from Google

Image Search keywords “Extensor Carpi Radialis”

Figure 2.7e – Position of Extensor Carpi Ulnaris Adapted from Google Image

Search keywords “Extensor Carpi Ulnaris”

Subsequently , the surface electrodes will be placed on the muscles of the dominant

hand as described in Figure 2.7f

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Figure 2.7f: Position of the surface electrodes , Image generated using Illustrator v10.0

2.4.4 CALCULATION OF THE MVC

Figure 2.8 : How the MVC will be recorded (Image generated using Illustrator 10.0)

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Figure 2.8a – Actual recording of the MVC

As described in Figure 2.8 , A piece of rope will be fixed at one end and the other

end will be attached to the rubber tapping tool. The participant will be asked to pull

the rubber tapping tool with both hands with full force for a period of 10 seconds. The

subsequent generated recordings will serve to represent the MVC values.

2.4.5 D ETERMINATION OF THE WRIST ANGLE OF DEVIATION:

Before starting the experiment the wrist neutral positions shall be determined in as

described in Figure 2.9. Subsequent angle of deviations caused when the tool is held

will be recorded as described in Figure 2.10. The difference between the wrist neutral

positions and angle of deviation when holding the tool will give us the degree of

deviation which will be essential in ascertaining the presence of any strain on the wrist

during the rubber tapping process using the specific tool.

When the subject holds the tool in the normal way, the angle of deviation shall be

recorded using a protractor on a flat surface this information will be essential in

determining whether the wrist deviation is a contributing risk factor in the

development of Carpal Tunnel Syndrome.

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Figure 2.9 - Measuring the Wrist Neutral

Zone (WNP) , Image generated using Illustrator V10.0

Figure 2.9a – Actual recording of the WNP & AOD’s while holding the tools

Figure 2.10 : Measuring the Angle of deviations using each tool, Image generated using Illustrator v10.0

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2.4.6 SURFACE DESIGN REPRESENTING THE TREE:

Figure 2.11: Construction of the surface that will represent the tree ( Image generated

using illustrator 10.0

The PVC carpet is wrapped around a 10L distilled water container which has been

filled with water to increase its weight and provide stability when the carpet around it

is excised using the rubber tapping tools. The carpet on the flat surface will also be

secured at both ends in order to keep it stable when it is excised using the rubber

tapping tools

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2.4.7 RECORDING THE RMS VALUES USING THE TOOLS :

Figure 2.12 – Using the Downward

Cutting Tool on the flat surface

Figure 2.13 – Using the Downward Cutting Tool on the Round Surface

representing the rubber tree

Figure 2.14 – Using the Upward Cutting Tool on the flat surface

Figure 2.15 – Using the Upward Cutting Tool on the Round Surface representing

the rubber tree

As illustrated in the above the surface electrodes were attached to the FCR , FCU

, ECU & ECR of the dominant hand while the actual rubber tapping process was being

simulated. The resulting graphical readings obtained from the EMG device were then

converted with an inbuilt routine to the RMS values that would be used for

subsequent data analysis. `

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Sarfraz - Recordings done for MVC using downward tool

Uln

aris

(µV

)

-500

0

500

8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15

11/14/2007 1:44:04.187 PM

Figure 2.15 – Actual EMG recordings obtained using the Downward Cutting Tool on

the round surface representing the tree

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CHAPTER 3.0

RESULTS

3.1 WNP AND DOD :

Figure 3.1 – Wrist Neutral Postions (WNP) , Degree of deviations (DOD) & Average

DOD’s

3.2 PERCENTAGE OF DEVIATION

Figure 3.2 – Percentage of deviation of the left and right wrists when using each tool

on each specific surface

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3.3 AVERAGE RMS , MVC & STANDARD DEVIATION

Figure 3.3 – Average RMS values recorded by the EMG for each tool on each surface

and their standard deviations

3.4 PERCENTAGE OF FORCE BEING USED

Figure 3.4 – Percentage of the force being used by each tool on each surface

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3.5 SUBJECTIVE ANALYSIS OF THE RUBBER TAPPING PROCESS AND

THE TOOLS :

Figure 3.5a – Upward Tool Opinions

Figure 3.5b – Downward Tool Opinions

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Figure 3.5c – Comfortability Score Distribution across ages , sex , DT Score , UT

Score and Hand Dominance for all participants

Figure 3.5d – Average and Standard Deviations of Ages of particpants , DT Score

and UT Score

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3.6 PARTICIPANT CHARACTERISTICS :

Figure 3.6 – Hand Dominance of the particpants

Figure 3.6a – Gender Distribution of Participants

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CHAPTER 4.0

DISCUSSION

4.1 CUMULATIVE TRAUMATIC DISORDERS (CTD’S) :

Rubber tapping is a highly manual process. On any typical working day the rubber

tapper will excise more than 500 – 600 trees in a span of 4 hours (Rubber Tapping,

n.d). Moreover this process is carried out on a daily basis. This exposes the rubber

tappers to various muscular skeletal injuries or MSI’s. The category of injuries that

originate from repetetive tasks are termed as repetitive strain injuries or RSI’s. The

rubber tappers are exposed to these various cumulative traumatic disorders or CTD’s.

Each year thousands of workers in the U.S. report work related musculoskeletal

problems such as tendonitis, carpal tunnel syndrome, and epicondylitis associated with

work related activities such lifting, pushing or pulling. These musculoskeletal

disorders develop over a period of weeks and are the leading cause of disability

among persons during their working years. The most common risk factors implicated

in these disorders are repetitive movements, vibration, low temperatures, mechanical

stress, posture, and inappropriate force. Although these disorders can occur anywhere

in the body, the upper extremities are most commonly affected (Kao 2003).

1. Repetitive Movements- The number of exertions per hour or shift can be

calculated from work standard and methods analysis. Some researchers have

determined that an action, which lasts greater than 50% of a cycle time or a cycle

time greater than 30 seconds, is “high repetitiveness”. This definition has proved

to be a good predictor for the development of upper extremity symptoms.

Repetitiveness also increases the forcefulness of the exertions required to

complete the task (Kao 2003).

2. Vibration- Upper extremity disorders have been associated with the use of the

hand to operate vibrating tools. Vibration may increase the force required to

complete a task by impairing sensory feedback or by the tonic vibration reflex.

Vibration exposure results from gripping power tools, holding the controls of a

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power machine, using percussion tools or using grinding machines.

Unfortunately, vibration alone cannot be isolated in order to determine its effects

from those induce by force or repetitive movement (Kao 2003).

3. Low Temperature - Cold temperatures affect manual dexterity and tactile

sensitivity. Exposing fingers to cold exhaust from pneumatic instruments or

working in a cold environment with cooling of the skin to 0-20 degrees

Centigrade has a profound effect on strength and sensitivity. Cold temperatures or

the use of poor fitting gloves affect the force required to complete a task by

impairing sensory feedback, potentially leading to muscle strains and sprains.

Well fitting gloves, on the other hand, may improve the coefficient of friction and

reduce the force of the action. The hand should be kept above 25 degrees

Centigrade to minimize these effects (Kao 2003).

4. Mechanical Stress - Localized mechanical stresses are caused by physical contact

between a part of the body and a tool or instrument. Typically this involves

contact with a hard or sharp instrument. Forceful gripping of tools with small

diameter handles has been associated with compression of the thenar branch of

the median nerve leading to atrophy and paresthesias. Use of hammers, chisels

and similar instruments has been associated with this condition. Localized

compression has also been associated with trigger fingers by the effect on tendons

or tendon sheaths (Kao 2003).

5. Inappropriate Force - The higher the force of the exertion the greater the risk for

upper extremity symptoms. The forcefulness of the task is the most significant

risk factor in upper extremity disorders. The amount of force exerted by the

fingers to hold an object is proportional to the force causing it to slip out of the

hand and inversely proportional to the slipperiness of the object. More strength is

required to exert a certain amount of force with gloves than without gloves.

6. Posture - Awkward postures affect the maximal force required/applied to a given

task. Grip force decreases to approximately 60 lbs if the wrist is flexed at 45

degrees and decreases to 75 lbs if the wrist is extended to 45 degrees. The type of

grasp is also important as it affects the magnitude of the force required to perform

a task. A pinch grasp increases the tensile loads on flexor tendons to the fingers to

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a greater extent than a power grasp. However, posture alone is not considered to

be a significant risk factor in the development of upper extremity disorders but

does affect the forcefulness required for the task. Awkward postures of the

shoulder, elbow, wrist, or hand may result in a CTD. These would include

excessive shoulder elevation, deviated wrist postures, extreme elbow postures,

and pinch type grip of working tools. One should be aware that awkward postures

might result from a poor layout of the workstation or an equipment design as well

as operator function.

The most commonly recognized work-related musculoskeletal disroders are as follows

(Ergosense, n.d):-

1. Tendinitis (tendonitis) - Irritation/inflammation of a tendon as a result of

repetitive forces or stress on a particular muscle-tendon unit (Ergosense, n.d).

2. Lateral Epicondylitis (tennis elbow) - Irritation/inflammation of tendon units over

lateral aspect of elbow resulting from impact or jerky, throwing motions

(Ergosense, n.d).

3. Medial Epicondylitis (golfer’s elbow) - Irritation/ inflammation of tendon units

over medial aspect of shoulder resulting from repeated forceful rotations of the

forearm together with bending of the wrist (Ergosense, n.d).

4. Tenosynovitis – Irritation/inflammation of a tendon or its tendon sheath resulting

from repetitive movements causing the tendon to slide along its sheath in a rapid

or frequent manner (Ergosense, n.d).

5. Synovitis - Irritation/inflammation of the inner lining of the membrane

surrounding a joint or tendon (Ergosense, n.d).

6. Stenosing Tenosynovitis of the finger (trigger finger) - Progressive constriction of

a tendon resulting from an irritation on the surface of the tendon or inflammation

of its tendon sheath leading to restriction of free movement (Ergosense, n.d).

7. De Quervain’s disease - Stenosing synovitis of the tendons of the radial side of

the wrist, leading to constriction with resultant withdrawal of the thumb away

from the hand and limited thumb movement (Ergosense, n.d).

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8. Raynaud’s Phenomenon (white finger/vibration syndrome) – Reflexive

constriction of the small arteries causing fingers to turn pale/white (intermittent

blanching), cold, numb and tingly. Condition may result from the extensive use of

vibrating tools (Ergosense, n.d).

9. Thoracic outlet syndrome - Compression of the nerves and blood vesselsbetween

the neck and shoulders causing numbness of the fingers and hands. Condition is

caused/aggravated by positional activities such as raising arms high above

shoulders or pulling shoulders back and down (Ergosense, n.d).

10. Pronator Syndrome - brought on by the compression of the median nerve in the

area between the pronator teres muscle that extends from the elbow forward

(Gehrig, 2004).

11. Ulnar or Radial Nerve Entrapment - produced by the compression of the ulnar or

radial nerves that pass through the wrist (Gehrig, 2004).

12. Extensor Wad Strain - a result of injury caused to the extensor muscles of the

thumb and fingers (Gehrig, 2004).

13. Carpal Tunnel Syndrome - Compression of the median nerve as it traverses under

a broad dorsal ligament (carpal tunnel) on the wrist causing pain tingling and

numbness of the wrist and hands. This condition is precipitated by chronic

unnatural positions of the wrists (typing), direct pressure on the median nerve by

sharp objects or hard work surface edges or tools (Ergosense, n.d).

The most common symptoms experienced by people having CTD’s are explained in

Table 4.1

Table 4.1 – Symptoms of Cumulative Traumatic disorders Adapted from (Gehrig,

2004) Disorder Symptoms

Carpal Tunnel Syndrome Pain, tingling, loss of feeling, or weakness in the thumb, index, and middle finger.

Ulnar or Radial Nerve Entrapment Weakness, loss of feeling, and/or tingling in the lower arm or wrist.

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Pronator Syndrome Closely related to those noted for carpal tunnel syndrome.

Tendinitis Pain in the wrist, mainly on the periphery or the sides of the hand and thumb. These symptoms may also be expressed in the elbow, hand, and shoulder and may lead to severe pain and weakened function of the joints.

Extensor Wad Strain Numbness, pain, and weakness in thefingers of the hand.

Thoracic Outlet Syndrome Loss of feeling, discomfort, and/ortingling in the fingers, hand, or wrist.

Prevention of work-related CTDs has become a high priority of various regulatory

bodies and government agencies concerned with workplace safety. Certain steps that

can be taken by the workers who are exposed to avoid the development of CTD’s are

(Ergosense, n.d) :

1. Reducing or elminating if possible the repetitive motions when feasible and

taking adequate rest breaks.

2. Avoiding akward postures when applying forces.

3. Using no more force than necessary to complte any given task.

4. Seeking treatment for any medical conditions that may increase personal risk such

as thyroid disorders , hypertension , diabetes and rheumatoid arthiritis.

5. Exercising and getting adequate rest.

6. Limiting the consumption of alcohol.

7. Seeking prompt medical treatment for any recurring discomfort or pain associated

with the fingers , hand , wrist , upper arm, lower arm , elbow , or shoulder that

persists for more than a few days. CTS’s can be more successfully treated and at

less cost if detected early.

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4.2 CONCERNING THE WNP , AOD , DOD, MVC & SUBJECTIVE TOOL

ANALSYSIS:

Table 4.2 – DOD , WNP , Av.DOD & Std Dev

DOD WNP Av.DOD StdDev % of Deviation

DT Rt 79º 75º 6º 2.86 9 %

DT Lt 74º 77º 5º 2.21 7 %

UT Rt 77º 75º 6º 1.41 8 %

Ut Lt 74º 77º 6º 2.46 7 %

Table 4.3 – Percentage of MVC

Tool & Surface Percentage of MVC

DTRS 72 %

DTFS 70 %

UTRS 71 %

UTFS 73 %

Table 4.4 – Averages of participant details , Standard Deviation and

both tool score Averages Std Dev

Age 23.6 1.5 Ht cm 166.5 9.1 Wt kg 67.1 22.3

Ut Score 4.54 1.53 Dt Score 5.25 1.45

The average AOD’s for both the tools in either wrists were found to be in the

range of ±6º as described in Table 4.2. The average amount of force being used as

compared to the subjects MVC’s fall in the range of ±70% as described in Table 4.3.

This indicates that the amount of force the rubber tapping process required is

signifcant enought to cause overexertion in the tappers. Moreover the AOD’s that

occur as a result of the tool design can become greater if the tappers are not familiar

with the process.

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Even though the AOD’s seem insignificant. The repetitive nature of this type of

work will definitely lead to the onset of various CTD’s more notably CTS. Even the

subjective analaysis of the design of the tools and their comfortability of use has

revealed that the tools definitely have a faulty design, the lower scores reflecting the

same are summarized in Table 4.4. The uncomfortable design of them can also be a

contributing factor to the development of CTD’s. The most common opinions about

each tool is summarized in table 4.5

Upward Tool Opinions

Downward Tool Opinions

× Needs a softer more firmer grip. × The tool itself is too short. × The design is uncomfortable. × The tool is not designed for left

handed people. × The tool is not sharp enough. × The tool is not really that useful. × The neck of the tool needs to be bent.

× Needs a softer more firmer grip. × The tool is too heavy. × The tool is not designed for left handed

people. × The tool is too long × The cuting head is not sharp enough. × The tool is uncomfortable.

Table 4.5 – Tool Opinions

It was quite clear from the faulty design of the tool that the AOD’s coupled with

the constant use of roughly 70% use of the MVC will definitely lead to the onset of

CTD’s. Which will ultimately reduce the quality and efficiency of the worker and

affect the output of the industry.

4.3 COMPLICATIONS ENCOUNTERED :

One of the major complications encountered during the sampling of this research

was the instrumentation. Firstly the wrist angles have been recorded by the subject

placing the wrist on a blank piece of paper after maintaining the angle when the tools

were held. However these measurements can be measured more effectively using an

electrogoniometer.

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The muscles which have been chosen for the EMG readings are based on a

research done by Fagarasanu et al., on Measurement of angular wrist neutral zone and

forearm muscle activity. Those muscles being FCR , FCU , ECR & ECU respectively.

Since there is no existing research on the employment of the EMG methodolody in

determining the muscular activity when using rubber tapper tools the muscles that are

specifically involved in this process have not been yet identified.

During the course of this reserach the EMG device which was used was

PowerLab© from ADinstruments© with only two channels for taking human

readings. Hence muscles of only the dominant hand have been taken for the EMG

analysis. The process of rubber tapping usually involves both hands, hence a more

comprehensive reserach would involve the identification of the exact extensors and

flexors that are involved when holding and using the rubber tapping tools.

Subsequently the EMG recordings would have to be taken from the identified

muscles on both hands. The presence of more channels on the EMG device would

definitely facilitate the gathering of more data that would be more conclusive in

nature. Surface electrodes have been used to detect the action potentials originating in

the muscles , however the usage of intra muscular electrodes would assist in accurate

identification of the muscles that are involved in the rubber tapping process.

The sample size of this research stands at 24 (12 men and 12 women) who had

volunteered for this research. The participants however were not people who were

involved in the rubber tapping profession. Actual rubber tappers were not used for this

experiment since the hypertrophy of specific muscles of the wrists would produce

results that would not allow to determine wheteher the tools in itself posses any design

flaws which effect the output of the work. A larger sample size would also reveal data

that would be more conclusive in nature.

The rubber tapping process was simulated on a surface that was designed to

represent the tree addressing the portability issues of the EMG device. Sampling of

this experiment using a real rubber tree would also enhance the integrity of the results.

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CHAPTER 5.0

CONCLUSION

The data and research gathered from this experiment reveal that the current tools

used by the rubber tappers are definitely a significant contributing factor towards the

rise of any CTD’s that they may acquire. The major causative elements being the

DOD’s of the wrists while using the tool and the amount of force that is being used in

the rubber tapping process itself. Subjective analysis definitely confirms that the

rubber tapping tools themselves have been designed poorly which most probably

would be a major contributing factor affecting the output of work of the rubber

tappers.

The rubber industry is one of the most significant contributing sectors towards the

the economy of MALAYSIA. Hence any research conducted in this area to enhance

the productivity of the rubber industries would be very significant. Since the rubber

tapping industry relies heavily on the manual process of rubber tapping. Identification

of its flaws and strenghts would be an important avenue for consideration by the

associated regulatory bodies. Discovering the complications which the individual

rubber tapper workers face would also reveal an important insight which would

faciliate the maximization of their outputs.

Finally the employment of the EMG technique in identifying the muscular activity

of various types of manual processes that exist in today’s industries would be

significant in improving not in the quality of the work of the employees in general but

would contribute towards the overall improvement of the productivity of those

industries.

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CHAPTER 6.0

FUTURE DIRECTION

The following figures are the proposed concept designs which addresses the

major issues that the participants were facing when using the tools. This design

however is just a concept and its details can be altered such that it is able to be more

efficeint and comfortable for the rubber tapper workers at the same time protecting

them from the development of any RSI’s.

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Figure 6.1 – R

ubber Buddy (Im

age generated using Illustrator v10.0)

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Figure 6.2 – R

ubber Buddy B

rief Details

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Figure 6.3 – 3d View of the Rubber Buddy

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Figure 6.4 – 3d View of the Extender

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BIBLIOGRAPHY “ CTS - Carpal Tunnel Syndrome & Hand Tingling in Beverly Hills (Los Angeles County)” (n.d) , Neurology Muscular Dystrophy and Neuropathy Institute , Online Journals Database , retrieved from http://www.beverlyhillsneurology.com/peripheralneuropathy.html on 10/8/07. (CTS , n.d) “(CTS) Carpal Tunnel Syndrome” (n.d), PDR Health Website , Online Journals Database retrieved from http://www.pdrhealth.com/patient_education/Carpal Tunnel Syndrome Animations and preventive excersise.html on 10/8/07. (CTS , n.d) “Chapter 5 – Tapping Methods and Improvement”(n.d), FAO Corporate Document Repository , retrieved from http://www.fao.org/docrep/005/AC776E/ac776e00.HTM retrieved on 2/8/07. (FAO Document Repository,n.d) “Ergonomic Hand Tools and modifications for farmers and Ranchers with grasping impairments” (2003) , Agrability Project Online Journals Database , Retrieved from http://www.agrabilityproject.org/index.cfm on 10/15/07 (Ergonomics Hand Tools 2003) “Ergonomics – Labour Occupation Safety and Health Program” (n.d) , UCLA Online Journals database , UCLA-LOSH Labour Occupational Safety & Health Program retrieved from http://www.losh.ucla.edu/ergonomics/index.html on 4/8/07. (Ergonomics , n.d) “Powerlab4stog – 4 Channel Powerlab instrumentation”(n.d) , ADinstruments Website Equipment Manuals Database , retrieved from http://www.adinstruments.com on 10/8/07. “Rubber Tapping Knife” (n.d) , retrieved from http://www.alibaba.com/catalog/11680623/Rubber_Tapping_Knife/showimg.html/15 1/Rubber_Tapping_Knife_002.jpg on 4/8/07. “Rubber Tapping” (n.d) , Online journal from ‘The International Rubber Research and Development Board’ retrieved from Online Database at http://www.irrdb.com/irrdb/NaturalRubber/Tapping on 4/8/07. (Rubber Tapping , n.d) “Strength and Conditioning Terminology” (n.d), University of Connecticut Website Online Journal Database , retrieved from http://www.uconnhuskies.com/MainLinks/UConnStrength/2005/index.html on 3/8/07. (Strength & Conditioning Terminology , n.d)

For St

uden

t Refe

rence

Only

“Tapping Management of Rubber” (2007), Open Academy for Philippine Agriculture retrieved from http://www.usm.edu.ph/opapa/index.php on 3/4/07. (Tapping Management of Rubber 2007) “The Story of Malaysian Natural Rubber” (2002), The Malaysian Rubber Board , Online Journals Database retrieved from http://www.lgm.gov.my/general/aboutmrb.html on 10/8/07. (The Story of Malaysian Natural Rubber 2002) Armstrong, “Rubber Production” (n.d) , Online journal Database retrieved from http://www.bio.ilstu.edu/armstrong/course.htm 1/8/07. (Armstrong , n.d) Arutchelvan. S, “Malaysian Plantation Workers and Judicial Recorse” (2002), Hurught Osaka News Database , retrieved from http://www.hurights.or.jp/issues_e.html#7 on 9/11/07. (Arutchelvan 2002) Bernardo.J , “Carpal Tunnel Syndrome” (2004), Reports on the Rheumatic diseases series 5: Hands on , Arthritis Research Campaign , Online Journals Database retrieved from http://www.arc.org.uk/arthinfo/default.asp on 10/8/07. (Berbardo 2004) Cacha. C.A , “Ergonomics and Safety in Hand Tool Design” (1999) , CRC Press , Boca Rotan , Florida , U.S.A. (Cacha 1999) Cros. D, “Peripheral Neuropathy – A Practical approach to diagnosis and Management” (2001), Lippincott Williams & Wilkins , Philadelphia , U.S.A. (Cros 2001) Cushman.W ,“Ergosense ISSUE-9 Types of Cumulative Traumatic Disorders” (n.d), Ergonomics Consortium online journals database retrieved from http://www.ergonomics-consortium.com/ on 24/11/07. (Ergosense, n.d) Dong.H, Barr.A, Loomer.P, Rempel.D , “The effects of finger rest positions on hand muscle load and pinch force in simulated dental hygiene work” (2005), Center of Disease control , National Institute of Occupational Safety and Health, Journal of Dental Education. (Dont. et al, 2005) Fagarasanu.M , Kumar.S , Narayan.Y , “Measurement of angular wrist neutral zone and forearm muscle activity” (2004), Science Direct Clinical Biomechanics Journals , Subsidiary of Elsevier Online , Clinical Biomechanics 19 (2004) 671–677 , retrieved from http://www.sciencedirect.com/ , received via personal communication with researchers. (Fagarasanu. et al, 2004)

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rence

Only

Gehrig.J, “Fundamentals of Periodontal Instrumentation”(2004) . 5th ed. Baltimore, Md: Lippiconcott Williams and Wilkins; 12-16, 517-518 (Gehrig, 2004) Kao.S.Y, “Carpal Tunnel Syndrome as an Occupational Disease” (2003) , Department of Occupational / Environmental Medicine , Jeanes Hospital-Temple University Health System , Philladelphia , Pennsylvania , USA, Am Board Fam Pract 2003;16:533– 42 (Kao 2003) Latella. D , Meriana. C, “Occupational Therapy Manual for Evaluation of Range of Motion and Muscle Strength”(2003) , Thomson Delmar Learning , Connecticut , USA. (Latella & Meriana 2003) Mills K.R., “The Basics of Electromyography” (2007), Journal of Neurology , Neurosurgery , Psychiatry 2005;76;32-35. (Mills 2007) Purves. R, “Human Electromyography” (1998) , Ad Instruments , Online Journal from ADInstruments website retrieved from http://www.adinstruments.com on 16/9/2007. (Purves.R 1998) Seeley R. R., Stephens T. D., Tate. P., “Anatomy and Physiology” (2000) , 6th edition , McGraw-Hill Higher Education , U.S.A , p (271-275) (Seeley. et al, 2000) Tan F. C., “EMG Secrets” (n.d) , Hanley and Belfus – An Affiliate of Elsevier , Philadelphia, Pennsylvania , U.S.A. (Tan.f , n.d)

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