Risk Factors of Low Back Pain Among Filipino Male Air-conditioned Bus Drivers

Risk Factors of Low Back Pain Among Filipino Male Air-conditioned Bus Drivers

A Research Presented to The Special Studies Committee of the College of Public Health University of the Philippines, Manila In Partial Fulfillment of the Requirements In PH 199

Submitted by Group 8 Gail M. Culla Felicidad Clare S. Martinez Jay Patrick R. Santiago Mia Marie M. Tad-y

Adviser Benjamin C. Vitasa, MD, MPH, PhD

23 February 2004

Abstract The general objective of the study is to determine the risk factors associated with low back pain among Filipino male air-conditioned bus drivers. It specifically aims to describe the distribution of bus drivers according to age, long driving time, vibration exposure, long distance driving, duration of employment, driving posture, seat/workplace design and psychological factors; describe the distribution of bus drivers with low back pain by age, long driving time, vibration exposure, long distance driving, driving posture, seat/workplace design, and psychological factors; and determine the association of different risk factors with low back pain adjusting for the effects of confounders and other independent variables. An analytical cross-sectional design was used. Three hundred seventy-eight drivers of air-conditioned buses from eight bus companies located in an urban cluster of bus stations were included as subjects. A self-administered questionnaire was given to each subject to obtain data on independent variables such as demography, long distance driving, driving posture, seat design, vibration exposure, duration of employment as a bus driver, psychological factors and long driving time. Anthropometric data were gathered using a tape measure. The outcome variable, low back pain was assessed based on questions asked in the questionnaire, using as inclusion criteria, chronicity of at least 6 months, recurring at least twice a week and 30 minutes duration per experience of pain. Using logistic regression, the association of risk factors with low back pain was determined. The identified risk factors included age, insufficient work space, abnormal vibration, uncomfortable sitting posture, constrained posture, rough roads, boredom, depression, frequent movement of back, frequent movement of shoulders, long distance driving, long driving time, vibration exposure, employee satisfaction with management and height. Results showed that constrained posture, long distance driving and employee satisfaction with management were significantly associated with low back pain. Drivers with any one of these characteristics have greater odds of having low back pain of 3, 2.2 and 2, respectively.

2

1.0 Introduction Transportation through a vehicle allows movement from an origin to its destination. Through driving, the course of a vehicle is controlled. For commuters, traveling by land would not be possible without the vehicle and the driver himself. Drivers are people who consider driving as their profession and source of income. It is of great importance for them to know that aside from the benefits they can get from this job, their life can still be at risk. Aside from possible accidents due to work, their health can also be at risk. Low back pain is a form of occupation-related disease which may cause increased cases of absenteeism and lesser productivity for the working population. Drivers, as part of this population, should be aware that this health issue is not a minor problem and should be taken seriously because it can affect them directly and even their employers. All over the world, several studies on low back pain have been conducted but only few have established its association with driving a bus. No known Philippine study on low back pain among bus drivers exists. Bus driving is only one of many jobs that persons with a driver’s license can go into. Having little knowledge on the possible occurrence of low back pain due to driving and its prevention can adversely affect the health and productivity of bus drivers. For these reasons, a study to establish the association between long driving time and low back pain is important and timely. Recommendations on the prevention of low back pain can be formulated based on the study.

3

2.0 Review of Related Literature Low back pain (LBP) is chronic pain localized in the lumbo-sacral spine with acute and sudden onset lasting for about thirty minutes and is intermittent and recurring for at least twice a week for six months. It is the most common cause of occupational disability in the industrialized societies and together with headache, is the most frequent variety of pain which workers have to contend with. However, physicians diagnose low back pain as acute if it lasts less than a month and is not caused by serious medical conditions. Most cases clear up in a few days without medical attention although recurrence after a first attack is common (1). 2.1. Epidemiology of Low Back Pain Between 60% and 90% of the general population experience back pain at one time or another during their lifetimes. In a study done in Denmark, it was noted that 40% of the general population had recurrent LBP in 5 years (2). A cross-sectional study done in Nigeria among office workers revealed that 38% suffer from episodes of LBP in a 12-month period (3). Another cross-sectional study showed that 60% of women in a textile factory in Vietnam suffer the same condition (4). Greater in magnitude is the 73%-76% prevalence of LBP among nurses in Switzerland shown in an eight-year cohort study (5). Every year, nearly 15% of American adults visit their doctors because of low back pain episodes (6). These data were gathered through questionnaires, observations, interviews and health records. Men and women are equally at risk. Low back pain is second to upper respiratory infection as the reason for seeing a doctor. In the US, its cost is second to cancer and heart disease. The Center for Disease Control reported that in 1995, 4

over 20 million visits to physicians and clinics were related to back symptoms. Low back pain occurred in 25% of the working population and the economic impact in the United States has been estimated to be over $75 billion per year (6). According to the National Research Council and the Institute of Medicine of the National Academies, it affects about 1 million workers and costs the nation between $45 billion and $54 billion in compensation expenditures, lost wages and decreased productivity annually (7). The majority of patients with low back pain state that they have increased pain while sitting or upon arising from sitting. It is believed that almost all LBP is aggravated and perpetuated by poor sitting posture in both sedentary and manual workers. 2.2. Low Back Pain and Driving Several studies have shown the statistically significant relationship between LBP and driving. In a cross-sectional study done in Denmark, the prevalence of frequent low back pain among urban bus drivers was 57% (2). This figure is not far from the 56.62% LBP prevalence seen among bus drivers in Lithuania (8). However, the figure is slightly lower in a study done among Japanese truck drivers. From 153 respondents, the prevalence of LBP in one month was 50.3% (9). 2.3. Anatomy and Pathophysiology of Low Back Pain The important functions that the lower back or lumbar area serves for the human body include structural support, movement and protection of certain body tissues. It holds most of the body’s weight and is involved in bending, extending or rotating at the waist. The lumbar spine and muscles protect the soft tissues of the

5

nervous system and spinal cord as well as adjacent organs of the pelvis and abdomen (10). The lumbar spine is composed of vertebrae “stacked” together that forms a movable support structure and protects the spinal cord from injury. Each vertebra possesses a spinous process, a bony prominence behind the spinal cord, which shields the cord's nervous tissue. There is also a strong bony "body" in front of the spinal cord to provide a platform suitable for weight-bearing. The lumbar vertebrae stack immediately atop the sacrum bone in between the buttocks. On each side, the sacrum meets the iliac bone of the pelvis to form the sacroiliac joint of the buttocks (10). The discs are pads that serve as "cushions" between each vertebral body which minimize the impact on the spinal column. Each disc is designed like a jelly doughnut with a central softer component, the nucleus pulposus, which is capable of rupturing or herniating through the surrounding outer ring, the annulus fibrosus, and, thereby, irritating adjacent nervous tissue (10). Ligaments are strong fibrous soft tissues that firmly attach bone to bone. Ligaments attach each of the vertebrae and surround each of the discs (10). The nerves that provide sensation and stimulate the muscles of the low back as well as the lower extremities (the thighs, legs, feet, and toes) exit the spinal column through bony portals called "foramen" (10).

6

Many muscle groups which are responsible for flexing, extending, and rotating the waist, as well as moving the lower extremities attach to the lumbar spine through tendon insertions (10). The aorta and blood vessels that transport blood to and from the lower extremities pass in front of the lumbar spine into the abdomen and pelvis. Surrounding these blood vessels are lymph glands and involuntary nervous system tissues which are important in maintaining bladder and bowel control (10). The uterus and ovaries are important pelvic structures in front of the lumbar area of women. The prostate gland is a significant pelvic structure in men. The kidneys are on either side of the back of the lower abdomen in front of the lumbar spine (10). The skin over the lumbar area is supplied by nerves that come from the roots of the lumbar spine (10). A back strain usually occurs when the muscles surrounding the spine are forced to stretch too far, lift too much weight or move in such a way that they sustain very small tears. A microscopic amount of bleeding into the muscle usually results from the tearing of the muscles and ligaments, followed by swelling and muscle spasms (10). The actual damage that is done when someone suffers a strained back can be quite variable. The muscles that support and move the spinal column may be injured, the ligaments that connect the vertebral bodies together or form strong capsules around the facet joints might be partially torn or a mild case of a slipped

7

intervertebral disc may be the source of the pain. In each of these situations, the human body is usually able to heal itself and will do so without surgery if given the proper treatment. There are many sources of low back pain involving the vertebrae, intervertebral disks, and nerves. Low back pain caused by soft tissue problems is likely to originate in one or more of three different locations: 1) Quadratus lumborum and its adjacent structures. Quadratus lumborum is the muscle between the bottom rib and the top of the pelvis. It is a key muscle in coordinating upper and lower body movements. It is a deep muscle, situated underneath the lumbar paraspinal muscles. Muscle problems are invariably accompanied by connective tissue problems. This area, unprotected as it is by any skeletal structures, is thick with connective tissue: the thoracolumbar fascia, the gluteal aponeurosis, and other tough connective tissue cover and surround these muscles. 2) The buttock muscles. These include the three gluteal muscles—gluteus maximus, medius and minimus— and the deep lateral rotators of the hip, especially pyriformis. 3) Iliopsoas. This is the primary hip flexor—its chief assistant being rectus femoris—running down through the abdominal cavity and the groin to the lesser trochanter. But its origins are the inner surface of the ilium (iliacus muscle) and the transverse processes of the lumbar vertebrae, which mean that every lifting of the leg pulls on the pelvis and the lumbar spine (11). 2.4. Risk Factors of Low Back Pain Body measurements and overall posture of the driver, seat/workstation design, long driving time, long distance driving, duration of employment, social and

8

psychological factors and long term whole body and hand-arm vibration exposure contribute to the development of low back pain. Anthropometry is the study of human body dimensions.

It includes body

volumes, masses of body segments, center of gravity and inertial properties (12). Engineering anthropometry deals with the application of scientific physical measurement methods to human subjects for the development of engineering design standards (13). It includes static and functional measurements of dimensions and physical characteristics of the body as they occupy space, move and apply energy to physical objects. Static or structural body dimensions are taken with the body of the subjects in fixed, standardized positions. Functional or dynamic body dimensions are taken when the body of the subject is involved in some physical movement (14). Anthropometric measurements, such as leg length and weight, are factors to be included in determining causation of low back pain among bus drivers. Unequal lengths of both legs might contribute to posture, which if improper might significantly lead to low back pain. Weight, on the other hand would influence how the spine would support the body especially the upper back. Anthropometers, tapes and scales are used to obtain measurement (14). Another risk factor for LBP is height. It has been suggested that tall people are at higher risk of having low back pain than short people (15). The average heights for Filipino adults are as follows: those aged 60 and over, 153 centimeters or five feet; those aged 40 to 59, 156.2 cm or 5 feet 1 inch; and those aged 20 to 39, 157.6 cm or 5 feet 2 inches. There were significant differences in the average

9

heights by sex. Among those aged 20 to 39, the average height for men was 163.3 cm or 5 feet 4 inches (16). Posture may be a factor causing LBP. It is a position or attitude of the body, the relative arrangement of body parts for a specific activity, or a characteristic manner of bearing one’s body (1). Sitting posture also contributes to the development of low back pain. Prolonged sitting may result in excessive loading and tissue deformation of the lumbar spine (17). The type of sitting posture also plays a role in reducing excessive stresses on the spine which may lead to LBP. Flexed postures are advantageous, as flexion results in increased fluid flow and improved transport of nutrients into the intervertebral discs (18). This may decrease the likelihood of degenerative changes, which have been associated with decreased metabolic transport in the disc (19). A similar study also concluded that flexed postures are favorable when sitting and when lifting heavy materials (20). In a population study on primitive cultures who squat while sitting in a flexed position, it was found that there was decreased incidence of degenerative changes in their lumbar spines (21). On the other hand, a recent study supports the lordotic or extended position for sitting as beneficial since this posture helps to balance the loads on various spinal structures and prevents stressing the posterior ligaments (22, 25). Sitting with the back slouched for as little as 20 minutes can result in increased laxity of the posterior spinal ligaments. It may take 30 minutes or more for these ligaments to regain their previous level of stiffness (22). Also, sitting with the

10

spine in extension reduces the intradiscal pressure. Extension helps to cause the nucleus to move anteriorly, thus helping to prevent and reduce the tendency for posterior disc bulging and protruding (23). Research has also shown that lumbar disc herniation may result from prolonged sitting in the typical flexed posture (24). Lordotic, extended position should be preferred for sitting over the flattened or flexed posture. However, given that any sitting posture results in increased spinal loading, frequent changes in posture from sitting to standing, etc., over the course of a day is to be preferred for protecting the spine (17). There are several sources of pain in postural problems. The ligaments, facet capsules, periosteum of the vertebrae, muscles, anterior dura mater, dural sleeves, epidural areolor adipose tissue and walls of blood vessels are innervated and responsive in nociceptive stimuli. Also, mechanical stress to pain-sensitive structures, such as sustained stretch to ligaments or joint capsules or compression of blood vessels, causes distention or compression of the nerve endings that leads to the experience of pain. This type of stimulus occurs in the absence of an inflammation reaction. It is not a pathologic problem but a mechanical one. Relieving the stress to the pain-sensitive structure relieves the pain stimulus and the person no longer experiences pain. If the mechanical stresses exceed the supporting capabilities of the tissues, breakdown will occur. If this continues without adequate healing, overuse syndromes with inflammation and pain will affect function without an apparent injury. Relieving the mechanical stress along with decreasing the inflammation is important (23).

11

Pain can come from muscles, ligaments, nerves, discs, or bones. People who lead a sedentary lifestyle are especially at risk, because their bodies are not conditioned. They are prone to strains when they use their backs. Other risk factors include advancing age, frequent or heavy lifting, obesity, poor posture and repetitive movements including twisting (26). Seat/workstation design and posture may also be factors in the development of low back pain. Driving is different from ordinary sitting in that the body is subject to different forces such as accelerations and decelerations, lateral swaying from side to side and whole body up and down vibrations while the vehicle is in motion (27). Prolonged periods of driving in a constrained posture on a seat with poor ergonomic design during a trip may result in de-conditioning, which is the weakening of the muscles supporting the spine and trunk due to inactivity, less exercise, and lack of balance. These muscles cannot fully withstand pressure or even support the spinal cord to its normal position. Thus, the entire back becomes sore and tired (28). There is growing evidence that the combination of these factors, coupled with the design of the seat itself, may increase the risk and occurrence of back problems for some people. Ergonomics is an approach, which puts human needs and capabilities at the focus of designing technological systems. The aim is to ensure that humans and technology work in complete harmony, with the equipment and tasks aligned to human characteristics. The term originated from the Greek words “ergon” which means work and “nomos” which means natural laws (29).

12

Ergonomics, also called human factors, is based on biological or natural sciences. Its main components are anatomy, physiology, psychology, medicine, and engineering. The contribution of basic anatomy lies in improving the physical fit between people and the things they use. Anthropometry provides data on the structure of human body, in various postures. On the other hand, biomechanics considers body responses, particularly the operation of muscles and limbs, when subjected to various internal and external forces. It ensures that working postures are beneficial and excessive forces are avoided (29). Human physiology supports two technical areas. Work physiology focuses on how the body functions when performing work.

It addresses the energy

requirements of the body and sets standards for acceptable physical work rate and workload and for nutrition requirements. Environmental physiology focuses on how the body functions when subjected to climatological factors. It also includes analysis of the impact of physical working conditions, such as thermal, noise and vibration, and lighting, and sets the optimum requirements for these (29). Psychology is concerned on the behavioral responses of human to work and environment, particularly human information processing and decision-making capabilities. It aids in the cognitive fit between people and the things they use (29). Medicine is directed towards diagnosis of injuries, which can either be acute or chronic. Lastly, engineering provides information on machinery and assists in its adaptation for human use (30).

13

Ergonomic stressors result from poor workplace designs. These stressors may include the following: repetition, the number of motions or movements that are performed per cycle or per shift; force, the power of the muscles used to produce motion in order to perform necessary activities; and extreme postures, wherein muscles are required to work at a level near or at their maximum capacity. Before setting standard measurements and providing necessary seat adjustments, ergonomic stressors and occurrence of possible health conditions should be considered (31). Musculoskeletal disorders are injuries of the soft tissues of the upper extremities, shoulders and neck, lower back, and lower extremities that are primarily caused or exacerbated by workplace risk factors, such as sustained and repeated exertions or awkward postures and manipulations. Repetitive motion injury (RMI), also known as repetitive stress injury, is a type of stress injury that results from repetitive motions such as frequent bending or sustained awkward positioning performed over extended periods of time without allowing for sufficient rest. RMI includes medical conditions resulting from repeated use of a body part (31). Ergonomics has a wide application to everyday situations with its significant implications for efficiency, productivity, safety and health in work settings (29). The different aspects of the workstation are then evaluated to determine if it fits the person who works in it. Workspace is the area within which a person performs the tasks that add up to one’s job. Its physical design includes working out how much space is needed

14

and positioning of furniture, tools, equipment and other items needed to perform tasks, in respect with posture, access, clearance, reach and vision of the user (32). The evaluation of the seating of Qantas flight deck crew showed that there is a widespread postural discomfort due to insufficient room space and LBP during flying among middle- and long-distance Qantas pilots (33). It was also found that an unsuitable workspace that prevents employees from sitting in a balanced position can cause poor body positions. The physical arrangement of work space elements such as work surfaces, tools and equipment may not correspond with the reaches and clearances of seated employees. The workstation may also be unsuitable because the seats are too high or low for an employee's body size and shape. These changes may ultimately lead to low back pain (34). The ergonomic design of the driver’s workstation is a necessary component of driver safety and health protection. The relative comfort and functional utility of the driver’s seat is a consequence of their physical design in relation to the physical structure and biomechanics of the human body (35). The driver’s seat should be vertically and horizontally adjustable and have adjustable lower back support and springs (36). The height of the seat should be such as to avoid excessive pressure on the thigh. The front edge of the seat should be a bit lower than the distance from the floor to the thigh, when seated. It was recommended that the front edge be at least 2 inches below the popliteal crease, which is the crease at the back of the hollow knee (37). The length and width of the seat would partly depend on the type of seat. In general, the length should be set to be suitable for small persons in order to

15

provide clearance for the calf of the leg and to minimize thigh pressure, and the width should be set to be suitable for large persons (14). The steering wheel should be adjustable along the axis of the steering column. Possible adjustments in its angle of inclination can provide more comfort. The pedals should have equal angles and be within easy reach for both short and tall drivers (36). The measurements of the workstation and the adjustments that can be made should fall within a range that is applicable to all drivers. The adjustability and the ways of adjusting the driver’s seat and steering wheel should be coordinated so drivers within the design range can find positions for their arms and legs that are comfortable and ergonomically healthy. Seats should provide for correct curvature of the lumbo-sacral section of the spine in order to keep the spinal column in a state of balance. Seats without or with inadequate backrest may cause kyphosis, a forward-leaning posture produced by excessive pressure between the vertebrae.

The lordosis type of posture with

adequate lumbo-sacral back support represents a more desirable posture. An angle of 90 degrees or less between the seat pan and backrest may cause pressure on the lower lumbar discs and back muscles. The resultant forces contribute to LBP and degeneration of the lumbar spine (14). Loss of rigidity and sagging of the seat pan due to wear and tear results in elevation of the knee to a higher level which causes gravity forces of the upper body to concentrate at the lower lumbar spine. The seat surface should be more or less plane rather than shaped, although a rounded front edge is highly desirable. Upholstery should be firm rather than soft.

16

The covering materials should also be porous for ventilation and rough to aid stability (38). In order to establish a desirable posture, the angle of the seat and back should be considered. The seat should be at a moderate angle and the back should have an angle of from about 95 to 105 degrees or more with the seat.

With

inclination of the backrest to at least 20 degrees, the amount of support needed to balance the trunk is minimized and body weight is transferred to the backrest. Adequate support for the lumbar area should also be taken into consideration. It is important in preventing spinal complications and discomfort caused by angles between the vertebrae (14). A probable solution to LBP due to poor posture is the use of a lumbar pad support. A study in the Philippines showed that use of lumbar pad support significantly decreased the occurrence of LBP among taxi drivers. Thirty taxi drivers with LBP due to poor posture were asked to use the pad support. The occurrence of LBP among them was compared with a similar sample size not using lumbar pad support (39). Lumbar pad supports can compensate for an ineffective postural seat design which may contribute to tension and fatigue of driver. Foot posture contributes to development of low back pain in that poor foot posture can affect the ligaments of the lower limb and put more stress on the back and knees. Driving involves active use of the feet—the right foot on the accelerator pedal, the left on the brake and also on the clutch in a stick shift. When the feet are active, they cannot be used to support and stabilize the lower body unlike ordinary

17

sitting wherein the feet are rested on the floor. Poor quality or worn footwear do not properly support the feet as well (40). Long driving time refers to the length of time the driver spends at the wheel while traveling. Continuous driving for four hours or more can increase the risk of having low back pain. Driving with limited movements for a prolonged period or sitting in one position for hours can aggravate back pain and even damage one’s health because of fatigue and lack of exercise (41).

A study found that after

accounting for all the possible psychological causes of back injury, drivers with the San Francisco Municipal Railway (Muni) still have an elevated risk for injury that can be attributed solely to their physical working conditions, particularly the number of hours on the job. Drivers who worked full-time had more than twice as many back injuries as those who worked part time (42). Driving distance pertains to the interval, in kilometers, between the origin and destination. Men drive an average of 71 kilometers and women 55 kilometers each day (27). Long driving distance is applicable to buses, which travel from urban to rural areas, and vice versa. The duration of employment is the span of time or number of years a person has been engaging his services as a driver of a company. This factor usually goes with age. Young drivers have more acute episodes of back pain while older people have more cases of chronic pain (43). High-risk occupations such as those with exposure to whole body vibration caused by long distance driving, place workers at risk for low back pain. The longer a person is on the job, the higher the risk (41).

18

Epidemiologic studies on low back pain consistently show a strong correlation with whole body vibration from motor vehicle driving (44). Other sources of vibration may include rocky and bumpy roads, worn out shock absorbers and bus engines that are not well-maintained. Vehicle vibration enters the driver's body through the seat. The structural properties of automobile seats may be a source of LBP for the driver. Because of the strong coupling between the seat backrest and the vehicle floor, a differential motion between backrest and seat cushion occurs when driving. It inevitably induces continuous strains in the lower lumbar spine of the seat occupant and is therefore a possible source of low back pain (45). Two general categories of vibration impinging on humans are whole body vibration or WBV (vibration transmitted to the entire body through some support such as a vehicular seat or building floor); and segmental (e.g. hand-arm) vibration (vibration locally applied to specific body parts such as hands and arms from a vibrating hand tool). Bus drivers, among others, are exposed to both types of vibration. The vehicle moving and hand-arm vibration cause whole body vibration by contact with the gear stick when shifting gears (46). A British study found exposure to hand-transmitted vibration and finger blanching and sensory symptoms to be significantly associated.

There was no

marked excess of LBP complaints in workers exposed to WBV, with only moderate excesses in men exposed above the British Standard and male riders of heavy industrial vehicles (47). Whole body vibration exposure is another risk factor for low back pain. In a questionnaire survey of back pain symptoms in professional truck drivers, three

19

factors were found to be related significantly to the prevalence of LBP. These were irregular duty time, short resting time and long driving time in a day (9). Evidence also shows that while LBP is age-related, it is also occurring earlier than expected for workers exposed to whole body vibration (48). Whole body vibration is related to prolonged sitting posture, poor working posture and inadequate working conditions in contributing to low back pain (49). A number of studies have been conducted on the association of vibration exposure and low back pain.

It was found that the occurrence of low back

symptoms increased with increasing whole body vibration exposure in terms of total or lifetime vibration dose, equivalent vibration magnitude and duration of exposure from years of service. Frequent awkward exposures are also related to some types of low back symptoms. Moreover, risk may be due to both whole body vibration exposure and prolonged sitting in a constrained posture (50).

However, it was

determined that in many working situations with a daily exposure of eight hours or more, suspension seats—conventional or air—will not protect drivers from harmful exposure to whole body vibration (51). To measure the level of exposure quantitatively, a vibration signal is first collected using vibration pickup devices, which are usually placed on machinery bearing caps. The caps are an ideal place for pick-ups because of their accessibility and because they are the points through which vibration transmits the most readily. For each point, the vibration signal picked up is then recorded in a vibration meter or vibration analyzer. A vibration meter will allow defect determination, but to analyze the cause, a vibration analyzer is needed (52).

20

Psychological factors play a role in the three phases of LBP—onset of pain, perception of pain and chronic pain. Recent research shows that in many people, preexisting depression and the inability to cope may be more likely to predict the onset of pain than physical abnormalities.

Moreover, social and psychological

factors play a part in the severity of pain a person experiences. Depressed people are more likely to experience vague physical symptoms, including LBP. In a study of truck and bus drivers, almost all the truck drivers liked their work and their bosses while bus drivers stated much lower job satisfaction. 50% of the truck drivers reported LBP but only 24% lost time at work. Bus drivers with LBP had a significantly higher absentee rate in spite of less stress on their backs. A related study found that pilots who generally reported high job satisfaction reported much fewer back problems than their flight crews. Another study stated that low rank, low social support and high stress in soldiers were associated with a higher risk for disabling back pain. Also, the way a patient perceives and copes with pain at the beginning of an acute attack may in fact condition the patient to either recover or develop a chronic condition. Those who over-respond to pain tends to feel out of control and discouraged, increasing their risk for long-term problems. A study found that among patients with back problems, the fear of pain was actually more disabling than the pain itself (53). Depression, low activity or high pain behavior, negative beliefs or fear of pain are three psychological-behavioral factors that consistently show a significant relationship with LBP. However, it has not been determined which of these factors is greatly involved in predicting disabling LBP (54).

21

Emotional factors which increase experienced pain include anxiety, anger and depression. Specific psychological factors that can increase pain are degree of focus on the pain, boredom, beliefs about the meaning of the pain and a sense of poor control over pain (55). Psychological factors are important in people with chronic low back pain. Dissatisfaction with a work situation, the management, or a job and boredom contribute significantly to the onset and persistence of LBP (56). The research on Muni drivers, led by Niklas Krause, showed that physical and psychosocial conditions in the workplace play a role in causing back injury. The research also found that after accounting for physical work load, a stressful job with high psychological demands, low satisfaction and low supervisor support can cause spinal injury (42). There are many other factors not related to driving which should also be considered in LBP. For ages 20-60, a herniated disc may be the cause of LBP. Other possible causes are myofascial pain, spondylolysis, fracture, facet syndrome, stenosis, fibromyalgia, infection, spondyloarthropathy, and tumor (57). LBP can also be caused by referred pain. Referred pain is pain caused by one part of the body and is also perceived in another distant part of the body not directly involved with the cause. Most common sources of referred pain to the low back are the organs in the abdomen, pelvis and retroperitoneal space, such as stomach, intestines, uterus and ovaries and kidneys. For example, pain of peptic ulcer, diverticulitis of the colon, pelvic inflammatory disease, acute prostates and

22

trochanteric bursitis (inflammation of the bursa of the hip area) can refer pain to the low back (58). Low back pain is a persistent global problem and everyone is susceptible. Its prevalence is consistently similar across countries. It has been studied extensively and has been shown to be possibly be prevented with the right measures. Still, the problem remains unsolved. In the Philippines, no studies have been done on LBP among bus drivers. Several studies have been done on LBP, but of different population other than bus drivers. This study would contribute to the pool of knowledge already available regarding LBP status in the Philippines and possibly that of Southeast Asia. Preventive measures may be designed in order to address the current situation of the LBP among Filipino male bus drivers.

3.0 Objectives of the Study General Objective: To identify risk factors associated with low back pain among bus drivers. Specific Objectives: 1.

Describe the distribution of bus drivers according to age, long driving time, vibration exposure, long distance driving, driving posture, seat/workplace design and psychological factors.

2.

Describe the distribution of bus drivers with low back pain by age, long driving time,

vibration

exposure,

long

distance

seat/workplace design and psychosocial aspects.

23

driving,

driving

posture,

3.

Determine the risk factors of low back pain adjusting for the effects of confounders.

4.0 Significance of the Study Studies in the Western countries have shown that vehicle drivers—trucks, buses, taxis—are at an increased risk of developing low back pain, with contributing factors such as long driving time, whole body vibration exposure, long distance driving, ergonomics, age, duration of employment and psychological factors. However, there are no known studies conducted in the Philippines to look into the effects of these factors to the development of low back pain among Filipino bus drivers. This study will determine if an association exists between the risk factors and low back pain among Filipino bus drivers. Driving would expose the drivers to long periods of experiencing vibration, poor ergonomic conditions, long distance travel and long driving time, causing low back pain. Necessary measures can then be recommended that will alleviate and/or prevent low back pain, which would benefit the bus drivers in terms of better health as well as the companies in terms of increased productivity.

24

25

6.0 Materials and Methods

6.1 Study Design An analytical cross-sectional study was done in 8 bus companies located along Gil Puyat Avenue and Epifanio delos Santos Avenue at Pasay City.

Preliminary visits and discussion with managers were performed in

order to gather preliminary data on the feasibility of the study and to ask initial permission to be able to implement the study.

6.2 Study Population The study included as its subjects Filipino male air-conditioned bus drivers from 8 bus stations. Non-airconditioned bus drivers were not included in order to maintain the homogeneity of the subjects. Also, according to the bus company managers, air-conditioned bus drivers more often complain about low back pain (LBP) than non-airconditioned bus drivers and therefore, it is expected to have more cases of LBP. Several studies in other countries have shown a low back pain prevalence of about 50% (9).

Initial interviews with the bus drivers and

supervisors also showed that LBP is a common medical complaint of drivers. Based on these, the sample size was computed as follows: P = 0.5662 α or d = 0.05 Z α = 1.96 Q = 1- P n = PQZ2 d2

P = proportion of bus drivers with chronic low back pain Q=1–P Z = normal variate Z α = 1.96 where α = 0.05 α = maximum allowable error

26

n = 0.5662 x 0.4338 x (1.96) 2 (0.05) 2 n = 377.4 = 378 subjects Proportional allocation was done to assure proper presentation of each bus company in the study. Using the formula Pax = ( n1 / T) x n, the number of subjects per bus station was computed as follows: where: Pax = proportionally allocated sample size per bus (x1, x2,…,xn) company n1 = total number of drivers per company T = total number of bus drivers from all the companies n = computed sample size n = Pax1 + Pax2 + … + Pax10 The following were the computed proportionally allocated sample size per bus station: •

Tritran Bus Company – 31

•

Grand Star Coach Bus Company – 8

•

Green Star Bus Company – 51

•

JAC Liner – 4

•

BBL Transportation Systems Inc. – 16

•

Victory Liner – 75

•

Pangasinan Five Star Bus Company, Inc. – 118

•

Philtranco – 74 27

6.3 Data Collection The group sent a letter to each bus company management, which stated the objectives of the study and asked for their permission to allow their company to be included in the study. The group also verified the initial data about the number of drivers employed in each company. The researchers went to the bus stations everyday for three weeks, depending on a schedule, which was prepared, based on the availability of drivers. Drivers were approached while they were taking a break or waiting for their buses to get full. The information and consent form was given for signature and a self-administered questionnaire was given to each driver afterwards. A group member (S1) provided assistance and answered queries from drivers when necessary. In addition, the same student quickly edited accomplished questionnaires.

While the questionnaires were being

answered, the corresponding bus and bus seat/workplace dimensions were measured by two other members (S3 and S4) of the group. The subjects were also asked to show their usual driving posture by sitting on the bus driver’s seat. Leg reach to the pedal, arm reach to the steering wheel and reclining angle were measured. Anthropometric measurements (leg length, arm length and weight) were measured by another member of the group (S2) after the subjects have finished answering the questionnaires assisted by S1. Exposure of the drivers to vibration was measured qualitatively using the questionnaire.

28

6.4 Data Collection Tools Assisted Self-Administered Questionnaire This was used to determine demographic data and information about driving time, driving distance, driving posture, duration of employment as a driver and psychosocial factors. Measuring Tape Leg length, arm length and seat / workstation dimensions were taken using a measuring tape. This data was important to relate body posture and seat design in relation to LBP. Protractor This was used to measure the reclining angle of the seat. Weighing Scale This was used to estimate the subject’s weight. This data was important since it had an effect on the force exerted on the lower back when the person is sitting or standing.

6.5 Data Processing From the data gathered, a coding manual was prepared. Data was encoded using Epi-Info Software version 6.0 and Statistical Package for Social Sciences (SPSS) version 10.0 available in the group’s personal computer.

These data were processed into tables and graphs for better

visual analysis.

29

6.6 Data Analysis The risk factors included were vibration exposure, rough roads, long driving time, long distance driving, uncomfortable sitting posture, insufficient room space, constrained driving posture, seat design and psychological factors. The prevalence of LBP among the subjects was also computed. Chi square test and logistic regression were used to test for the association of risk factors and low back pain. Finally, multivariate analysis was performed with the use of SPSS using backward-Wald method.

6.7 Operational Definition of Variables Dependent variable: 1. Low Back Pain – chronic pain localized in the lumbo-sacral spine with an acute and sudden onset lasting for about thirty minutes and is intermittent and recurring for at least six months.

Independent variables: 1. Long Distance Driving – driving distances wherein low back pain is felt 2. Long Driving Time – driving for more than four hours everyday according to a study on bus drivers in Lithuania

30

3. Duration of employment – this is the span of time (number of months and years) a person has been engaging his services as a bus driver. 4. Posture – a position of attitude of the body, the relative arrangement of body parts while driving which includes reclining angle, sitting, arm, and leg position 5. Psychological Factors – depression, low activity or high pain behavior, negative belief, or fear of pain 6. Depression – feeling down or unhappy with working conditions or family problems related to mental stress 7. Boredom – state of being uninterested because of frequent exposure to long hours of driving 8. Constrained posture – inability to maintain a comfortable sitting position while driving 9. Abnormal vibration – unusual vibration due to poorly maintained buses 10. Vibration exposure – exposure to vibration for more than 4 hours a day, abnormal vibration complaint, with at least 20% rough roads experienced Confounding variables: 1. Seat / workstation Design – the overall make-up of the drivers’ seat in relation to easing low back pain and other injuries which include the reclining angle of back seat and overall adjustability 2. Age – number of years lived of subject since last birthday.

31

Other definitions: 1. Pain – unpleasant sensory experience associated with actual negative potential tissue damage or described in terms of such damage. 2. Anthropometry – dealing with measurement of leg length, arm length, and weight 3. Work – an activity in which one exerts strength or faculties to do or perform a labor, task, or duty that affords ones accustomed means of livelihood

7.0 Ethical Considerations An informed consent form was prepared which explained all the information about the study and was signed by each participant. Any information obtained from the drivers employed in the different bus companies were kept confidential. The study is not obliged to provide treatment for identified cases of low back pain (LBP).

Instead, any form of intervention will remain as the bus companies’

responsibility upon giving them the results of the study.

8.0 Assumptions, Strengths and Limitations This study presupposed that all answers to the questions provided to bus drivers are truthful and reliable. The strength of this study is related to the fact that no similar studies locally have been done in the past. The results of the study can serve as basis for future researches among bus drivers in a larger scale. In addition, aside from

32

presenting low back pain among bus drivers, companies will also benefit in terms of less worker absence and improved productivity once low back pain complaints are reduced. Only air-conditioned bus drivers were included in the study.

Simple

random sampling was not done in the selection of the bus drivers for reasons that their schedules are not fixed and they usually are on a rotation basis. Drivers also come at different times and based on the limited time available for data collection, waiting for the driver based on the selection by random sampling will not allow fulfillment of the sample size required. The subject’s availability during the scheduled visits of the researchers and willingness to participate were instead used as criteria for participation. A great degree of selection bias was not expected since the bus drivers were informed that no treatment would be provided if found with low back pain. Thus, drivers with low back pain were not expected to volunteer which will unduly increase the number of LBP cases. In addition, personal characteristics and risk factors were elicited which were controlled for in the data analysis using logistic regression. Vibration exposure was measured qualitatively using a questionnaire due to the unavailability of a vibration meter for a quantitative measurement. However, the study attempted to put together several risk factors affecting exposure to vibration such as seat design and exposure to rough roads. Based on the recommendation of the study’s ergonomics adviser, quantitative analysis of anthropometric and ergonomic data cannot be performed

33

due to limitations of time and data gathered.

However, these data will be kept

for future use in related studies.

9.0 Results and Discussion After data collection, the data were presented based on univariate, bivariate and multivariate analysis. 9.1 Univariate Analysis Figure 1. Civil Status of Subjects Single

1% 95%

Married

0%

Separated

4%

Widowed

95% of the drivers are married. Table 1. Insufficient workspace experience Insufficient workspace No Yes

Frequency 143 235

Percentage 37.8 62.2

A little over 60% of the drivers complained of experiencing insufficient workspace. Figure 2. Abnormal vibration 19% Yes No 81%

81% of the drivers experienced abnormal vibration due to their current job. Table 2. Uncomfortable sitting posture Uncomfortable sitting posture No Yes

Frequency 145 233

Percentage 38.4 61.6

A little over 60% of the drivers experienced uncomfortable sitting posture at their workstation.

34

Figure 3. Constrained posture 32% Yes No 68%

Nearly 70% of the drivers had constrained posture at the workstation. Table 3. Rough roads Rough roads No Yes

Frequency 20 358

Percentage 5.3 94.7

Almost 95% of the drivers experienced rough roads while driving. Figure 4. Boredom 26% Yes No 74%

74% of the drivers experienced boredom while driving. Table 4. Depression Depression No Yes

Frequency 154 224

Percentage 40.7 59.3

Nearly 60% of the drivers had experienced depression. Figure 5. Frequent movement of back

8%

Yes No

92%

A little over 90% of the drivers move their backs frequently while driving. Table 5. Frequent movement of arms Frequent movement of arms No Yes

Frequency 36 342

Percentage 9.5 90.5

Almost 91% of the drivers frequently move their arms while driving. 35

Figure 6. Frequent movement of shoulders 4%

Yes No

96%

96% of the drivers frequently move their shoulders while driving. Table 6. Frequent movement of feet Frequent movement of feet No Yes

Frequency 31 347

Percentage 8.2 91.8

92% of the drivers frequently move their feet while driving. Figure 7. Back pain experience 14% 86%

Yes No

86% of the drivers experienced back pain. Table 7. Upper back pain experience Upper back pain No Yes

Frequency 256 122

Percentage 67.7 32.3

32% of the drivers experienced upper back pain. This comprises about 37% of all back pain complaints. Table 8. Mid back pain experience Mid back pain No Yes

Frequency 318 60

Percentage 84.1 15.9

16% of the drivers experienced mid back pain. This comprises almost 20% of all back pain complaints. Table 9. Low back pain experience Low back pain No Yes

Frequency 120 258

Percentage 31.7 68.3

68% of the subjects experienced low back pain. This comprises almost 80% of all back pain complaints.

36

Figure 8. Rest period

Yes No

1%

99%

Almost all of the drivers have rest periods in between trips. Table 18. Work Satisfaction Work Satisfaction Level I like my job Just right I don’t like my job Others

Number 334 44 0 0

Percentage 88.4 11.6 0 0

All of the drivers are satisfied with their work. Figure 9. Employee satisfaction with management 13%

I Am Happy I Like I Don't Like I Am not Happy

10%

50%

27%

A little over 75% of the drivers are satisfied with management. Table 11. Relationship with co-workers Relationship Good Just right Difficult Others

Number 313 63 1 1

Percentage 82.8 16.7 0.3 0.3

Almost all have good relationship with co-workers. Figure 10. Salary satisfaction 20% 10%

Happy Enough Not Enough

54%

16%

70% of the drivers are satisfied with their salaries.

37

Not Happy

Table 12. Seat design Type of Seat Design With cushion and with lumbar pad support With cushion but without lumbar pad support Without cushion but with lumbar pad support Without cushion and without lumbar pad support Others

Frequency 292 83 0 0 3

Percentage 77.2 22 0 0 0.8

Almost 80% of the driver seats are cushioned and have lumbar pad supports. Figure 11. Driving posture

47% 8%

Reclined Straight Stooped

45%

45% of the drivers have reclined driving posture. 47% have straight posture while driving. Only about 10% have stooped driving posture. Table 13. Seat reclinability Reclinability No yes

Frequency 175 203

Percentage 36.3 53.7

Almost 55% of the driver seats can be reclined. Figure 12. BMI Underweight (< 18.5)

52% 11% 1% 36%

Healthy Weight (18.5-24.9) Overweight (25-30) Obese (>30)

A little over 60% of the drivers exceeded the normal BMI. Only 36% met the normal BMI.

38

Table 14. Age Group Age group 20-24 25-29 30-34 35-39 40-44 45-49 50-54 ≥ 55

Frequency 49 60 45 70 70 58 20 6

Percentage 13 15.9 11.9 18.5 18.5 15.3 5.3 1.6

A little over 90% of the drivers are aged 20-49. The age group 35-44 comprises almost 40% of the drivers. Table 15. Number of years employed Number of years 0-4 5-9 10-14 15-19 20-24 25-29 > 30

Frequency 32 62 172 29 30 21 12

Percentage 8.5 21.7 45.5 7.7 7.9 5.6 3.2

45% of the drivers have been employed for 10-14 years as bus drivers. Figure 13. Long distance driving 24%

100-199

200-299

300-399

400-499

500-599

600-699

3% 2%

41%

4% 7%

> 700

19%

42% of the drivers drive from 400-499 kilometers per day. Figure 14. Vibration Exposure 35% Yes No 65%

65% of the drivers are exposed to vibration while driving. 39

Table 16. Long driving time Hours 10

Frequency 126 195 26 31

Percentage 33.3 51.6 6.9 8.2

A little over 50% of the drivers experience LBP from 30 minutes to 5 hours a

day. Table 18. Frequency of LBP in a week Frequency of Low Back Pain in days per week 1-2 3-4 5-7

Number

Percentage

249 54 75

65.9 14.3 19.8

About 65% of the drivers experience LBP once to twice a week. Figure 15. Duration of LBP experience in years 10% 13%

6%

0

>0- 12

36% of the drivers have experienced LBP from one to less than six years. A little over 30% did not experience LBP at all. Table 19. LBP cases Cases of LBP No Yes

Number 144 234

A little over 60% of drivers have LBP.

40

Percentage 38.1 61.9

Figure 16. Rough roads experienced

18%

< 20

20-39

40-59

60-79

9% 12%

34% 27%

> 80

A little over 60% of the drivers experience less than or equal to 39% of rough roads. Table 20. Weight Kilograms 45-54 55-64 65-74 75-84 85-94 > 95

Frequency 8 59 138 120 38 15

Percentage 2.1 15.6 36.5 31.7 10.1 4

Almost 70% of the drivers weigh from 65-84 kilograms. Table 21. Height Centimeters < 159 160-160.9 161-161.9 162-162.9 163-163.9 164-164.9 165-165.9 166-166.9 167-167.9 168-168.9 169-169.9 170-170.9 171-171.9 172-172.9 173-173.9 174-174.9 > 175

Frequency 27 18 16 16 28 15 23 15 28 34 17 26 21 12 23 11 48

Percentage 7.1 4.8 4.2 4.2 7.4 4 6.1 4 7.4 9 4.5 6.9 5.6 3.2 5.1 2.9 12.7

Almost 30% of the drivers have heights from 167 to less than 171 centimeters.

41

Figure 17. Seat reclining degree

6%

16%

< 95

95-97

98-100

101-103

104-106

107-109

7% 6% 31%

3%

> 110

31%

About 60% of the seats are reclined from 95 to 100 degrees. Table 22. Number of buses driven out of 10 buses with adjustable seats toward and away from the wheel Number of buses 0-1 2-3 4-5 6-7 8-9 10

Frequency 32 18 19 9 36 264

Percentage 8.5 4.8 5 2.4 9.5 69.8

Almost 10% of the drivers have driven buses without adjustable seats. Table 23. Number of buses driven out of 10 buses with reclinable seats Number of buses 0-1 2-3 4-5 6-7 8-9 10

Frequency 126 17 20 10 31 174

Percentage 33.3 4.5 5.9 2.6 8.2 46

A little over 33% of the drivers have driven buses without reclinable seats.

42

9.2 Bivariate Analysis A. Results Pearson chi square test was used to determine the association of risk factors with low back pain. Significant associations were based on a 5% level. A p-value cut off of ≤ 0.2 was used for all independent variables which will subsequently be included in the multivariate analysis. A summary of the results of the Pearson chi square test for association is shown below. Table 24-A. Summary of Variables Cross-Tabulated with LBP Using Chi Square Test for Association with P value of ≤ 0.2 Association between Independent variable Dependent Variable 1. Constrained posture LBP 2. Uncomfortable sitting posture LBP 3. Frequent movement of LBP shoulders 4. Long distance driving LBP 5. Boredom LBP 6. Depression LBP 7. Insufficient work space LBP 8. Long driving time LBP 9. Abnormal vibration LBP 10. Frequent movement of LBP back 11. Employee satisfaction with LBP management 12. Height LBP 13. Percent of rough roads LBP 14. Vibration exposure LBP 15. Rough roads LBP

Chi square

P value

Remarks

24.89 11.05 8.08

0.000 0.001 0.004

Significant Association Significant Association Significant Association

16.59 6.04 5.45 5.18 4.229 4.08 3.95

0.011 0.014 0.020 0.023 0.040 0.043 0.047

Significant Association Significant Association Significant Association Significant Association Significant association Significant Association Significant Association

6.02

0.110

No Significant Association

21.80 6.67 1.91 1.86

0.150 0.154 0.167 0.173

No Significant Association No Significant Association No Significant Association No Significant Association

Table 24-B. Summary of Variables Cross-Tabulated with LBP Using Chi Square Test for Association with P value of > 0.2 Association between Independent Variable Dependent Variable 1. Years of education LBP 2. Consultation with doctor LBP after injury

Chi square

P value

Remarks

0.93 2.18

0.335 0.337

No Significant Association No Significant Association

43

3. Injury to right shoulder 4. Injury to both arms 5. Seat base length 6. Duration of employment 7. Injury to right foot 8. Accident experienced 9. Salary satisfaction 10. Accident injury 11. Frequent movement of arm 12. Injury to left leg 13. Sprain 14. Civil status 15. Seat adjustability towards and away from the steering wheel 16. Job training 17. Length of training for current job 18. Type of seat 19. Self training 20. Injury to chest 21. Injury to back 22. Injury to right thigh 23. Reclining degree of seat 24. Weight 25. Relationship with coworkers 26. Training from current job 27. Body mass index 28. Frequent movement of feet 29. Work satisfaction 30. Inclination of seat 31. Training from previous job 32. Driving position 33. Injury to left arm 34. Injury to both shoulders 35. Injury to left thigh 36. Injury to both thighs 37. Injury to right knee 38. Injury to left knee 39. Injury to both knees 40. Injury to right leg 41. Injury to both legs 42. Injury to left foot 43. Injury to both feet 44. Dislocation 45. Muscle strain 46. Fracture 47. Injury to right arm 48. Age 49. Number of buses out of 10 buses with reclining seats

LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP

2.18 2.18 10.05 6.44 1.88 0.65 2.67 1.47 0.42 1.24 1.24 2.06 0.34

0.337 0.337 0.346 0.375 0.391 0.419 0.445 0.479 0.519 0.537 0.537 0.559 0.559

No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association

LBP LBP

0.32 3.76

0.570 0.585

No Significant Association No Significant Association

LBP LBP LBP LBP LBP LBP LBP LBP

0.22 0.89 0.68 0.68 0.68 3.68 2.86 1.3

0.63 0.641 0.712 0.712 0.712 0.720 0.721 0.729

No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association

LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP LBP

0.6 1.08 0.07 0.06 0.06 0.41 0.37 0.33 0.03 0.03 0.33 0.03 0.03 0.33 0.03 0.03 0.33 0.03 0.03 0.03 0.29 0.18 1.97 0.61

0.742 0.783 0.790 0.800 0.804 0.815 0.830 0.847 0.859 0.859 0.859 0.859 0.859 0.859 0.859 0.859 0.859 0.859 0.859 0.859 0.864 0.913 0.962 0.988

No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association No Significant Association

44

Fifteen independent variables cross-tabulated with LBP were found to have a p-value of ≤ 0.2 using Chi square test for association. These were, constrained posture, abnormal vibration, vibration exposure, uncomfortable sitting posture, boredom, depression, frequent movement of back, frequent movement of shoulders, long distance driving, long driving time, insufficient workspace, employee satisfaction with management, percent of rough roads, rough road experience and height. Variables with a p-value of ≤ 0.2 were included for purposes of logistic regression analysis. The following are the cross tabulations of the independent variables with LBP. Table 25. Relationship of Insufficient Work Space and LBP Insufficient Work Space

Low Back Pain No

No Yes

Yes

Frequency 65 79

Percentage 45.8 33.5

Frequency 77 157

Percentage 54.2 66.8

Chi square = 5.18 P value = 0.02287480 There is a significant relationship between insufficient room space and LBP. Table 26. Relationship of Abnormal Vibration and LBP Abnormal Vibration

Low Back Pain No

No Yes

Frequency 35 109

Yes Percentage 49.3 35.5

Frequency 36 198

Percentage 50.7 64.5

Chi square = 4.08 P value = 0.04328993 There is a significant relationship between abnormal vibration and LBP. Table 27. Relationship of Uncomfortable Sitting Posture and LBP Uncomfortable Sitting Posture

Low Back Pain No

No Yes

Yes

Frequency

Percentage

Frequency

Percentage

71 73

49.0 31.3

74 160

51 68.7

Chi square = 11.05 P value = 0.00088653 There is a significant relationship between uncomfortable sitting posture and LBP. 45

Table 28. Relationship of Constrained Posture and LBP Constrained Posture

Low Back Pain No

No Yes

Yes

Frequency

Percentage

Frequency

Percentage

69 75

56.6.0 29.3

53 181

43.4 70.7

Chi square = 24.89 P value = 0.00000061 There is a significant relationship between constrained posture and LBP. Table 29. Relationship of Rough Roads and LBP Rough Roads

Low Back Pain No

No Yes

Frequency 11 133

Yes Percentage 55.0 37.2

Frequency 9 225

Percentage 45 62.8

Chi square = 1.86 P value = 0.17285062 There is no significant relationship between rough roads and LBP. Table 30. Relationship of Percent of Rough Roads and LBP Percent

Low Back Pain No Frequency 45 45 24 17 13

175

3 7 7 13 8 5 14 11 5 10 1 23

20 30.4 46.7 46.4 23.5 29.4 53.8 52.4 41.7 43.5 9.1 47.9

12 16 8 15 26 12 12 10 7 13 10 25

80 69.6 53.3 53.6 76.5 70.6 46.2 47.6 58.3 56.5 90.9 52.1

Chi square = 21.80 P value = 0.14962400 There is no significant relationship between height and LBP. B. Discussion Factors such as employee satisfaction with management, height, rough roads, vibration exposure and rough road complaints were found not to be significantly associated with LBP in the bivariate analysis. However, the p values of these variables were within 0.06 – 0.20. Review of related literature showed strong correlation of these variables with low back pain. Thus, they were included in the multivariate analysis. 1. Insufficient Work Space Results show that insufficient room space is associated with low back pain. This is consistent with a study evaluating the seating of Qantas flight deck crew which showed that postural discomfort due to insufficient room space and low back pain during flying among middle- and long-distance Qantas pilots were widespread (33). An unsuitable workspace that prevents employees from sitting in a balanced position can cause poor body position. The physical arrangement of workspace elements such as work surfaces, tools and equipment may not correspond with the

49

reaches and clearances of seated employees. The workstation may also be unsuitable because the seats are too high or low for an employee's body size and shape. These changes may ultimately lead to low back pain (34). 2. Abnormal Vibration (Whole Body Vibration) A significant association was also observed between abnormal vibration and low back pain. Although reports of low back pain were found to be age-related, there was evidence that low back pain occurs earlier than expected for workers exposed to whole body vibration (WBV).

WBV is also related to poor working posture,

prolonged sitting posture and inadequate working conditions and contribute to the occurrence of low back pain (48). In a related study, a significant relationship was also found between exposure to hand-transmitted vibration and sensory symptoms. There was no marked excess of low back pain complaints in workers exposed to WBV, with only moderate excesses in men exposed above the British Standard and male riders of heavy industrial vehicles (47). 3. Uncomfortable Sitting Posture Uncomfortable sitting posture was also observed to be associated with low back pain. The type of sitting posture also plays a role in reducing excessive stresses on the spine, which may lead to LBP (18). Sitting with the back slouched for as little as 20 minutes can result in increased laxity of the posterior spinal ligaments (22).

50

4. Constrained Posture Results show that there is a significant relationship between LBP and constrained posture. Posture is the relative arrangement of body parts for a specific activity (1). Thus, it is important to know and maintain proper posture to avoid stresses which may cause pain and discomfort.

Poor working posture or constrained posture

requires muscles to work at a level near or at their maximum capacity (31). As a result, there is de-conditioning of the muscles and the entire back becomes sore and tired, causing low back pain (28). 5. Rough Roads Rough roads, i.e. rough roads driven and rough road complaints, were found to be not significantly associated with low back pain. This is not consistent with the fact that rough roads may result in whole-body vibration, which occurs while riding vehicles over rough terrain. A related study also observed a strong correlation between whole body vibration and motor vehicle driving (44). This may be due to the fact that the bus drivers gave only an estimate of rough roads experienced while driving. 6. Boredom Results show that a significant relationship exists between boredom and low back pain. Psychological factors are even more important in people with low back pain. Dissatisfaction with a work situation, a supervisor, or a dead end job and boredom contribute greatly to the onset and persistence of low back pain (56). Other factors

51

which increase the risk of low back pain together with boredom include degree of focus on the pain, beliefs about the meaning of the pain and a sense of poor control over the pain (55). In this study, about 66% of the bus drivers who experience boredom at work have low back pain. 7. Depression There is a significant relationship between depression and low back pain. Recent research indicates that in many people, preexisting depression and the inability to cope may be more likely to predict the onset of pain than physical abnormalities. People who are depressed are more likely to have vague physical symptoms, including low back pain. Depression, low activity or high pain behavior, negative beliefs or fear of pain are the three psychological-behavioral factors that have continued to show consistent, empirically supported predictive capabilities. However, it has not been determined which of these factors are greatly involved in predicting disabling low back pain (53). 8. Frequent Movement of Back A significant relationship was observed between frequent movement of back and low back pain. About 64% of the subjects with low back pain move their backs frequently. The exact cause of low back pain may be hard to find. Pain can come from muscles, ligaments, nerves, discs, or bones. People who are inactive are especially at risk of LBP, are not conditioned, and prone to strains when they move their back frequently. Repetitive motion injury (RMI), also known as repetitive stress injuries, is a type of stress injury that results from repetitive motions such as frequent bending or

52

sustained awkward positioning performed over extended periods of time without allowing for sufficient rest (31). 9. Frequent Movement of Shoulders Results show that frequent movement of shoulders is significantly associated with low back pain. Repetitive manipulation of body parts particularly the shoulders while driving may result in injury or illness of its soft tissues, thus contributing to the development of low back pain (31). 10. Long Driving Time Results show that long driving time was significantly associated with low back pain. This finding is consistent with a study which showed that driving for eight hours or more may not protect drivers from harmful vibration exposure leading to low back pain (51). A related publication also showed that drivers have an elevated risk for injury that can be attributed solely to their physical working conditions, particularly the number of hours on the job (42). 11. Long Distance Driving Results show that long distance driving is significantly associated with low back pain. A little over 40% of the subjects drove at a range of 400 to 499 km every day. Findings from a related study showed that people who drove long distances were at significantly increased risk of having neck and low back pain. A recent Swedish

53

study found significantly increased risks of low back pain among those who drove long distances and spent a long time each day in their car (41). 12. Vibration Exposure No significant association was observed between vibration exposure and low back pain. Vibration exposure included whole-body vibration and at least 20% rough roads experienced by the drivers while driving. This finding is contrary to previous studies conducted on the subject matter (48, 49, 50, 51). There was sufficient evidence that vibration exposure to drivers could be a health hazard particularly with regard to back problems. The relatively high vibration exposure levels combined with long exposure duration and prolonged sitting are likely to contribute to low back pain. From a study on the association of whole body vibration and low back pain, it was found that the average WBV level experienced by drivers of heavy transport vehicles exceeded health, fatigue and comfort limits of the Australian Standard and most exposures were within the Caution zone for health according to the current International Standard on whole body vibration (49). A possible explanation to the negative finding in our study is that vibration was assessed qualitatively. 13. Employee Satisfaction with Management Results show that employee satisfaction with the company management is not significantly associated with low back pain. This finding is contradictory to previous studies which state that employer policies, attitudes, and actions determine the satisfaction level of employees, which

54

in turn, affects health-related conditions. Social and psychological factors play a role in how severely someone experiences pain and even vague symptoms. People who are depressed are more likely to have vague physical symptoms, including low back pain (53). A related article stated that after accounting for physical work load, a stressful job with high physiological demands, low satisfaction, and low supervisor support can cause spinal injury, particularly low back pain (42). A possible explanation to the negative finding in our study is that information bias may have occurred.

Drivers may not have answered honestly for fear of

dismissal from the company despite assurances of confidentiality. 14. Height No significant association exists between height and low back pain. This finding is contrary to previous studies which showed that height is a risk factor to low back pain. Tall people are at a higher risk of having low back pain than short people (15). A possible explanation to this finding is that the average Filipino male height is between 162 and 164 cm (16).

9.3 Multivariate Analysis The Statistical Package for the Social Sciences (SPSS) version 10 was used to perform logistic regression. The relationship of risk factors with low back pain was determined while controlling for the effects of confounders and other independent variables. The risk factors included age, rough roads experienced, percent of rough roads, abnormal vibration, vibration exposure, uncomfortable sitting posture, constrained posture, boredom, depression, frequent movement of back, frequent

55

movement of shoulders, long distance driving, long driving time, height, employee satisfaction with management and insufficient work space. The confidence level used was 95% with an α equal to 0.05. Using the backward Wald method, the independent variables were analyzed. The study claims that the independent variables from the bivariate analysis would increase the probability that a driver will develop low back pain. A step-by-step elimination using the backward-Wald method is shown in Appendix A (Table 42-A and 42-B).

A. Results Results showed that three independent variables significantly contribute to the probability of LBP occurrence among bus drivers. These are constrained posture, employee satisfaction with management and long distance driving. Table 40. Risk Factors to Low Back Pain Variable Constrained Posture Long Distance Driving Employee Satisfaction to Management

Odds Ratio and Confidence Interval 3.013 (1.961,4.880) 2.185 (1.111, 4.299) 1.989 (1.153,3.429)

B. Discussion 1. Constrained Posture Drivers who experience constrained posture while driving have 3 times greater risk of having low back pain compared to those who do not.

56

De-conditioning, which is the weakening of the muscles supporting the spine and trunk, occurs due to poor working posture or constrained posture. The former can cause the entire back to become sore and tired, leading to low back pain. 2. Long Distance Driving Drivers who drove for at least 300 km per day have 2.1 times higher risk of developing low back pain than those who drive for less than 300 km in a day. According to a study, increased risk of having neck and low back pain was found among those who drive long distances. 3. Employee Satisfaction with Management Drivers who experienced dissatisfaction with the management are 2.1 times more at risk of having low back pain than those who are satisfied. Vague symptoms, including low back pain, are more likely to occur among depressed individuals. A related article stated that after accounting for physical workload, a stressful job with high physiological demands, low satisfaction, and low supervisor support can cause spinal injury, which may lead to low back pain.

57

10.0 Conclusion 1. Constrained posture is significantly associated with low back pain. Drivers with constrained posture while driving have 3 times greater odds of having low back pain. This finding suggests that maintaining proper posture will reduce the risk of low back pain. 2. Long distance driving is significantly associated with low back pain. Drivers who drive for at least 300 km per day have 2.2 times higher risk of developing low back pain. This finding suggests that management should look into the possibility of modifying work shifts of bus drivers based on a 300 km-maximum distance per day. Hence, this should not generally affect income of drivers on one hand and company productivity on the other hand. 3. Employee satisfaction with management is significantly associated with low back pain. Drivers who show dissatisfaction to management are 2.1 at risk of having low back pain. This finding emphasizes the importance of good management-worker relationship in improving the drivers’ well being. Thus, better work performance, less absenteeism and increased productivity will be achieved.

58

11.0 Recommendations 1. Health education should be conducted in order to inform the drivers about the effects of long driving time and low back pain. The causes of low back pain will be discussed. Posters, fliers and multimedia showing the latest concepts and preventive measures on low back pain should be provided. Measures to alleviate and prevent LBP can then be made. 2. Regular medical check-ups should be provided by the company to identify and address health problems of bus drivers, particularly low back pain. Low back pain which lasts for less than 6 months is acute.

However, it is

considered chronic if it occurs for more than 6 months. Early detection of low back pain in its acute stage is crucial in the prevention of its progression to chronicity. Therapy for identified low back pain cases is helpful in improving worker performance. At present, no health professionals in companies with 300 or more employees were observed. As a possible solution, bus companies proximate to each other may employ a part-time health professional which will provide service to the cluster of bus companies. 3. The company should provide health fitness training for their employees. Exercise is important in preventing repeat episodes of low back pain and avoiding it in the first place. The bus company is recommended to have a resident physical therapist when teaching its employees on how to exercise safely. A complete exercise program should include aerobic activity as well as

59

stretching and strength training. Aerobic exercise has been reported to improve or prevent low back pain. Exercises such as abdominal bracing, neutral spine and basic and advanced curl ups, side bridge and bird dog exercise are recommended by Joy M. Beatty, MSPT in order to prevent occurrence of low back pain. (See Appendix B for detailed exercise descriptions.) 4. The companies should have regular maintenance of their buses. Previous studies have found that bus engines and seats kept in good condition reduce whole body vibration exposure due to rough roads and poorly maintained engines. Also, adjustable seats should be maintained in order to assure sufficient workspace and comfortable sitting posture of the bus driver. 5. Regular meetings should be conducted by the management in order to assess the working condition of their employees and immediately address problems. It has been proven that dissatisfaction with a work condition, a supervisor and boredom can greatly contribute to the onset and persistence of low back pain. It is therefore important to address these problems in order to assure worker satisfaction to management. 6. Drivers with special needs, e.g. older employees, those with serious health complaints and those recovering from an illness should be given some degree of flexibility in their work schedule. However, individual adjustments in schedule should not affect the performance of the whole workforce. Recent research shows that in many people, pre-existing depression and inability to cope may be

60

more likely to predict the onset of pain than physical abnormalities. As a result, there is a significantly higher absentee rate in spite of less stress in their backs. 7. Bus companies should include health programs to be carried out by medical professionals such as stress management, lecture/demonstration on proper driving posture and stretching exercises. 8. Bus companies should consider developing a working schedule that would allow driving shifts every 300 km. This would minimize the risk of having low back pain. If driving is extended, drivers should be given enough rest periods of at least 30 minutes.

61

12.0 References 1. Kisner, Carolyn and Lynn Allen. Therapeutic Exercise: Foundations and Techniques. 1990. 2. Netterstrom, B. and K. Juel. “Low back trouble among urban bus drivers in Denmark.” Scand J Society Medicine 17.2. (1989): 203-206. 3. Omokhodion, F.O. and A.O. Sanya. “Risk factors for low back pain among office workers in Ibadan, Southwest Nigeria.” Occupational Medicine 53.4. (June 2003): 287-289. 4. Nguyen, Tran Nhu and Thi Thu Nguyen. “Case Study on Improving OSH service for female workers: Working conditions and health of female workers in the fibre textile industry in Viet Nam.” (21 November, 2000). 6 September, 2003: http://www-ilomirror.cornell.edu/public/english/region/asro/bangkok/asiaosh/country/vietnam/ca sestud/thu.htm. 5. Maul I., T. Laubli, A. Klipstein and H. Krueger. “Course of low back pain among nurses: A longitudinal study across 8 years.” Occupational and Environmental Medicine 60.7. (July 2003): 497-503. 6. “Low Back Pain.” (2003). 10 September, 2003: http://www.neurometrix.com/company.htm. 7. Vines, Vanee and Mark Chesnek. “Some Jobs Increase Risk for Musculoskeletal Disorders: Intervention Programs Can Be Effective.” (17 January, 2001). 7 September, 2003: http://www4.nas.edu/news.nsf/isbn/0309072840?OpenDocument. 8. Maciulyte, Nijole. “Bus Drivers’ Health and Conditions of Work.” 6 September, 2003: http://www.gla.ac.uk/ecohse/2000papers/maciulyte.pdf. 9. Miyamoto, M., Y. Shirai, Y. Nakayama, Y. Gembun and K. Kaneda. “An Epidemiologic Study of Occupational Low Back Pain in Truck Drivers.” 30 August, 2003: http://www.nms.ac.ip/jnms/2000/06703186e.pdf. 10. “Lower Back Pain.” 7 September, 2003: http://www.medicinenet.com/Low_Back_Pain/page1.htm. 11. The Pain and Posture Clinic. “An Illustrated Guide to Muscles and Clinical Massage Clinic.” 10 September 2003: http://www.danke.com/Orthodoc/lowback.htm.

62

12. Sanders, M.S. and E.J. McCormick. Human Factors in Engineering and Design. 7th ed. New York: McGraw-Hill, Inc., 1993. 13. Kroemer, K.H.E. “Functional Anthropometry.” Proceedings of the Human Factors Society, October 16-19, 1978. 680-683. 14. McCormick, Ernest J. and Mark S. Sanders. Human Factors in Engineering and Design. New York: McGraw-Hill, Inc., 1982. 15. “Low Back Pain and Sciatica” (September 1999). 11 December, 2003: http://wellness.ucdavis.edu/medical_conditions_az/backpain54.html. 16. Tan, Michael L. “Weights and Waists.” (5 August, 2003). 12 December, 2003: http://www.inq7.net/opi/2003/aug/05/opi_mltan-1.htm. 17. Weitz, L.H.B. “Sitting and Low Back Pain.” 11 December, 2003: http://www.drweitz.com/scientific/sitting.htm. 18. Adams M.A. and W.C. Hutton. “The effect of posture on the lumbar spine.” Journal of Bone Joint Surgery 67B. (1985): 625-629. 19. Holm S. and A. Nachemson. “Nutritional changes in the canine intervertebral disc after spinal fusion.” Clinical Orthopedics 169. (1982): 243-258. 20. Cox J.M. Low Back Pain. 5th ed. Baltimore: Williams & Wilkins, 1990. p.125. 21. Fahrni W.H. and G.E. Trueman. “Comparative radiological study of the spine of a primitive population with North Americans and Northern Europeans.” Journal of Bone Joint Surgery 47B (1965): 552-555. 22. McGill S.M. and S. Brown. “Creep response of the lumbar spine to prolonged full flexion.” Clinical Biomechanics 7 (1992): 43-46. 23. Mc Kenzie, R. The Lumbar Spine: Mechanisms, Diagnosis, and Therapy. New Zealand: Spinal Publications Limited, 1981. 24. Wilder D.G., M.H. Pope and J.W. Frymoyer. “The biomechanics of lumbar disc herniation and the effect of overload and instability.” Journal of Spine Disorders.1 (1988): 16-32. 25. Hedman T.P. and G.R. Fernie. “Mechanical response of the lumbar spine to seated postural loads.” Spine 22 (1997): 734-743. 26. Mason, Terry. “Nonspecific Back Pain.” (30 May, 2001). 20 December, 2003: http://health.discovery.com/diseasesandcond/encyclopedia/1656.html.

63

27. “The Road Less Traveled… because it hurts? Part 1: Why does driving hurt so much.” 24 August, 2003: http://backandneck.about.com/library/weekly/aa050101a.htm. 28. “Chicken Noodle Soup for Low Back Pain.” 30 August, 2003: http://www.back.com/articles-chicken.html. 29. “Ergonomics”. 7 November, 2003: http://www.ergonomics.org.uk/ergonomics/definition.htm. 30. Weimer, Jon. Research Techniques in Human Engineering. New Jersey: Prentice Hall PTR, 1994. 31. Manalac, Belinda. “Ergonomics Program” (July 2003). 11 December, 2003: http://www.ehs.uci.edu/programs/safety/ergo.html. 32. “What is workspace?” 7 November, 2003: http://www.ergonomics4schools.com/lzone/workspace.htm. 33. Lusted, M., S. Healey and J.A. Mandrijk. “Evaluation of the seating of the Qantas flight deck crew.” Applied Ergonomics 25. (1994): 275-282. 34. Canadian Center for Occupational Health and Safety. “OSH Answers: Working in a Sitting Position – Overview.“ (19 June, 1998). 22 December, 2003: http://www.hse.gov.uk/research/abs_9899/phy_abs.htm. 35. Grosbrink, Alfons and Andreas Mahr. “Ergonomics of Bus Driving”. (1998). 7 November, 2003: http://www.oshforeveryone.org/wsib/files/ilo/tra10ae.html?noframe. 36. “Bus Drivers’ Alert”. 7 November, 2003: http://www.itf.org.uk/Sections/it/road/bus%20alert1.htm. 37. Tichauer, E.R. The Industrial environment: Its evaluation and control. Washington, D.C.: Department of Health, Education and Welfare, National Institute for Occupational Health, 1973. 38. “Ergonomics and Driving.” 22 August, 2003: http://ergoboy.com/ergo_for/driving.php. 39. Parangalan, Von Anthony and Gener Jimenez. “Effectivity of Lumbar Pad Support in Decreasing Low Back Pain Secondary to Poor Posture among Taxi Drivers.” Thesis. University of the Philippines, 1994. 40. “Foot Posture and Low Back Pain.” 23 August, 2003: http://www.backsunlimited.com.

64

41. Hedge, Allan. “Driving and Back Care.” 23 August, 2003: http://www.spineuniverse.com. 42. McBroom, Patricia. “Back Pain Sufferers Vindicated.” (9 December, 1998). 22 December 2003: http://www.berkeley.edu/newa/berkeleyan/1998/muni.html. 43. Drivers.com staff. “Back Pain when Driving?” (14 June, 2000). 30 August, 2003: http://www.drivers.com/cgi-bin/go.cgi?type=ART&id=000000295&static=1. 44. Johnson, D.A. and M. Neve. “Analysis of possible lower lumbar strains caused by the structural properties of automobile seats: A review of some recent technical literature.” Journal of Manipulative and Physiological Therapeutics 24.9. (November-December 2001): 520-528. 45. Wilder, D.G., M.H. Pope and M. Magnusson. “Mechanical Stress reduction during seated jolt/vibration exposure.” Semin Perinatol 20.1. (February 1996): 54-60. 46. Salvendy, Gavriel. Handbook of Human Factors. 1987. 47. Palmer, Keith. “Hand-arm vibration: Whole-body vibration: Number and distribution of workers exposed.” Research. Medical Research Council, 1999. 48. Boshuizen H.C. P.M. Bongers and C.T.J. Hulshof. ”Self-reported back pain in fork-lift truck and freight-container tractor drivers exposed to whole body vibration.” Spine 17:1. (17 January, 1992): 59-65. 49. Mistrot, P., P. Donati, J.P. Galmiche and D. Florentin. “Assessing the discomfort of the whole-body multi-axis vibration: laboratory and field experiments.” Ergonomics 33:12. (1990): 1523-1536. 50. Bovenzi, M. and A. Zadini. “Self-reported Low Back Symptoms in Urban Bus Drivers Exposed to Whole Body Vibration.” Spine 17.9. (September 1992): 10481059. 51. Burdorf, A. and P. Swuste. “The effect of seat suspension on exposure to wholebody vibration of professional drivers.” Annual Occupational Hygiene 37:1. (February 1993):45-55. 52. “Noise and Vibration: Measurement Procedure.” 10 September, 2003: http://www.menlh.go.id/apec_vc/osaka/eastjava/noise_en/vib/page10.html. 53. “What Conditions Make People Susceptible to Low Back Pain?” 24 August, 2003: http://www.ucdmc.ucdavis.edu/ecdhc/health/a-z/54Backpain/doc54medical.html.

65

54. “Risk Factors for Chronic, Disabling Low-Back Pain: An Update for 2000.” American Pain Society Bulletin 10.2. (March-April 2000). 55. Aboussafy, David. “Managing Chronic Pain.” 11 December, 2003: http://www.wilsonbanwell.com/articles/health/managing_chronic_pain.htm. 56. Ehrlich, George E. “Low Back Pain.” Bulletin of the World Health Organization 81. (2003): 671-676. 57. Carron, Harold and Robert E. Mc Laughlin. Management of Low Back Pain. Great Britain: John Wright and Sons, 1982. 58. Benja-athon, A. “Low Back Pain.” 24 August, 2003: http://musclejointnerve.com/lowback.html. 59. Beatty, Joy M. “Preventing Back Pain with Exercise.” (6 June 2003). 13 December 2003: http://www.orthop.washington.edu/sports_medicine/backpain/01. 60. Gaba, A., R. Hipolito, C.M. Melendres, P.A. Pena, C.A. Sayo and H.D. Singson. “Illumination and its Relationship with Worker Performance as Defined by the Company Under Study.” Thesis. University of the Philippines, 2003.

66

13.0 Acknowledgements We would like to express our deepest gratitude and appreciation to the following individuals without whose contribution we could not have completed this research: Dr. Benjamin C. Vitasa, our beloved adviser, for the “lessons learned” which have taught us to go deep into the heart of our research and for bringing out the best in each of us. Dr. Ethel M. Estanislao, our statistics adviser, whose knowledge has enlightened our path towards the fulfillment of our research. Prof. Jingky Lozano, for so graciously sharing her precious time and giving us advice when we needed it most. Prof. Rosebelle Azcuna, for lifting up our spirits with her insights during moments of confusion. Rowena Yra, Shelly La Rosa and Ricky Hipolito, the fun-loving and everdependable research assistants, who have supported us through thick and thin. The management of the bus companies for their cooperation in the conduct of our study: Mr. Jun Belen, station master, Tritran Bus Co. Mr. Ruben Locegro, dispatcher, BBL Trans System Mr. Armando Mendoza, station master, Victory Liner Mr. Ricardo Mercado, Jr., traffic operation staff, Grand Star Bus Co. Ms. Jennifer Bañaga, vice president, administration, Philtranco Ms. Pepita Iraya, inspector, JAC Liner, Inc. Ms. Lucita Limosnero, special trip coordinator, Green Star Bus Co. Ms. Josephine Solomon, head, personnel dept, Pangasinan Five Star The three hundred seventy eight bus drivers who participated in this study, for their time and cooperation. Classmates and friends, especially Emmanuel Paragas, Jr., Joseph Eufemio Martinez and Dennis Pascual for their help and encouragement which has taught us to move on. Mrs. Felicidad Serafico and Jollibee for providing food which gave strength to both our minds and bodies. The CPH guards for giving us help and protection whenever we need one. The song “Maybe” for serving as our inspiration and relaxation in the middle of difficulties. Our parents who has shown much love through their unfailing support and understanding: Mr. Teodoro P. Culla and Mrs. Lourdes M. Culla Mr. Edmar O. Martinez and Mrs. Maura S. Martinez Mr. Joselito S. Santiago and Mrs. Precy R. Santiago Mr. Leroy J. Tad-y and Mrs. Josie M. Tad-y And above all, God Almighty, our light and our protection amidst the challenges of life.

67