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Copyright © 1998, by Paul M. Morneau
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Abstract
Paramedics in Ontario are required to sit in their ambulance for extended periods of time. The increasing use of "Stand-bys" and "Roaming" has lead to increased back injuries amongst paramedics. A survey of paramedics in the Ottawa/Carleton area indicates that there is a reason for concern. A significant health and Safety issue exists and needs to be corrected. The wealth of literature on the subject would suggest that Paramedics should limit their time positioned in the seated posture. The literature also suggests that paramedics should have more supportive vehicle seats with a larger front cab area.
The Ontario Ministry of Health (M.O.H.) has been deploying ambulances in this province in a way to maintain "balanced emergency coverage." This has historically involved placing an ambulance on "stand-by" between two areas when one areas' ambulance(s) have/has been sent on a call. In addition to this long standing practice of stand-bys, a new policy has been recently implemented in regards to deploying ambulances and paramedics in the Ottawa/Carleton region. This new system is referred to as "Roaming."
In the recent past, ambulances would normally respond to emergency calls from various stations across the region or from a stand-by location. Paramedics would remain at their respective stations or at the designated stand-by location between calls. This was changed after a study on "call volume" in Ottawa/Carleton was completed by the Ottawa General Hospital-"Base Hospital Program" (BHP). The BHP determined statistically dominant zones within the region. These zones are numerically marked and indicate which areas contain the most critical calls (code 4's) most often. For instance, "Zone 1" indicates the geographical area (downtown Ottawa) which has the most code 4's, most often . Zone 2 has the next highest volume of code four calls and so on. The result of the BHP study showed that many of the ambulance stations were not necessarily well positioned to respond to these zones and therefore the response times to code 4 calls were longer than they needed to be. Also, the BHP suggested that a mobile ambulance is more likely to have a quicker response time than an ambulance crew that has to leave from a station. They suggested that the time between crew notification (time 2) and the crew being mobile (time 3) is decreased, if not eliminated, when the crew is mobile. This assumption seemed to prove itself during the 1996 Ontario Public Service Employee's Union (OPSEU) strike (Ambulance Response Information System: Monthly Statistics, 1996). During the strike, paramedics were "locked out" of their stations. However, the "Emergency Services Agreement" (ESA) between OPSEU and the Ontario government required that a minimal number of ambulances and Paramedics would remain staffed in order to respond to emergency calls. This led to the situation where all paramedics working under the ESA would report to a central Fleet Centre to pick up an ambulance and then remain mobile for the duration of their shift. Many union leaders and "Health and Safety" representatives have questioned the validity of the assumptions made by the BHP and the Ontario Ministry of Health during the Strike. Union officials argue that the statistics during the strike are not valid due to the very different staffing patterns and the response to emergency calls only. These assumptions have led to the addition of "Roaming" to the current daily practices of a paramedics duties.
The new system that has been implemented requires that paramedics remain mobile in their ambulances between calls for at least half of their shift (shifts are usually twelve hours long). Along with the "Roaming" policy paramedics have always had to respond to "code 8's" (stand-by's). When an ambulance crew from one station leaves on a call an ambulance crew from a neighboring station is positioned on "stand-by" somewhere between the two stations. The ambulance crew that is placed on "stand-by" are required to leave their station to drive to a particular intersection and wait for a call. Stand-bys are usually located at an intersection that is relatively equidistant between two stations.
The combination of "Roaming" and "stand-bys" have resulted in Paramedics sitting in either an idling or moving ambulance for long periods of time resulting in a static posture with increased exposure to vehicular vibrations.
The major concern of the newly implemented "roaming" procedures and the long standing policy of "stand-bys" is the potentially deleterious effects on paramedics. Paramedics sit for long periods of time, in an idling or moving ambulance. Does this result in an increased incidence of back discomfort, back pain or back injuries?
Back injuries are more likely to occur in paramedics in Ottawa/Carleton due to the new MOH policy requiring them to "roam" for at least half of there shift between calls. The long standing policy that requires paramedics in Ottawa/Carleton, across Ontario and in many other places throughout North America, to sit on "stand-by" for long periods of time will also result in more back injuries to them. Research in the area of vibration and static seated posture support this hypothesis. (Pope & Wilder 1996)
The purpose of this paper is to determine whether exposing paramedics to long lengths of vibration and static seated posture will lead to an increased incidence of back injuries. Furthermore, it is hoped that the Ontario Ministry of Health and the Ottawa General Hospital-Base Hospital Program will adjust their policies on "roaming" and on "stand-bys". These administrators must be made aware of the deleterious effects that "roaming" and excessive "stand-bys" can have on paramedics. Administrative controls need to be implemented to reduce paramedics' exposure to vibration and long periods of sitting. Engineering controls are also needed to ensure proper seating design in ambulances.
M.H. Pope, Ph.D., of the Orthopedic Biomechanics Laboratory at the University of Iowa has done extensive research on the effects of vibration on the seated human. His research would suggest that exposure to vibration does have a deleterious effect on humans. (Pope & Wilder 1996) Other research on exposure to vibration in the workplace supports Pope's research (Brinckmann et al. 1994). Stothart and McGill, in their work on Stadiometry, have identified "static work posture" and "exposure to vibration" as known risk factors leading to back injuries (Stothart & McGill, 1996)
This chapter will cover several studies and background literature which detail the effects of vibration and posture on the human being. Some of the literature deals with the effects of vibration on the human body, while other literature makes direct reference to the effects of vibration in driving. Postural effects on intervertebral disc (disc) pressure is also discussed.
Anderson (1986) shows that the lumbar spine in the seated human flattens as compared to standing. The lumbar lordosis is decreased when sitting due to backward rotation of the pelvis. This results in a 65% increase in disc pressure as compared to standing. Anderson did an earlier study in 1974 on disc pressures specifically with those sitting in a car seat. The study used three female subjects and one male subject. All subjects were healthy and without a history of back problems. Anderson found that lumbar disc pressure was increased in the sitting position. He also determined that certain angles of the seat and backrest resulted in varying disc pressures.
Klingenstierna and Pope (1986) completed a study that showed how disc "creep" or compression is faster when exposed to vibration. They quoted studies by Wilder which relate lower back pain in drivers with exposure to vibration. In their study they exposed eight men, between the ages of twenty-two and forty-four, to thirty minutes of vibration. They then compared pre and post spinal heights as an indication of creep. Those subjects exposed to vibration showed statistically significant spinal height decreases. They concluded that creep increases with exposure to vibration.
A study done by Pope in 1980 surveyed 3500 subjects. The surveys confirmed that those people with lower back pain had greater exposure to vibration. The study also showed that drivers were subjected to higher levels of vibrations and therefore displayed a higher level of incidents of lower back pain. They also determined that the vertical vibration produced by a truck was in the 2-15 Hz range.
Pope (1996) explains how lower back pain amongst workers is at epidemic proportions. He explains how the incidence of lower back pain increases with those workers who have to sit for long lengths of time. He quotes Kelsey as saying "men who spend more than half their workday in a car have a threefold increased risk of disk herniation." He continues to mention that vibrations of 6 Hz can be obtained from driving speeds as low as 50 mph on good highway surfaces. Pope also suggests that there is a "symbiotic effect of vibration and posture." "A further epidemiological study by Kelsey et al. (1984), conducted in Connecticut from 1979-1981, found that the greater the number of hours spent in a motor vehicle, the higher the risk for an acute prolapsed lumbar intervertegral disc." (Zacharkow, 1988)
Pope did a study in 1987 in which he exposed five females and five males (that were in good health and free of any back pain) between the ages of fifteen and forty-five to vibration and impact while seated. He used a "Sinusoidal Excitation Apparatus" that could change the resonant frequency from between 2-15 Hz (the typical vibration frequency range when driving). He also quotes Heliovaara (1987) as saying that he "found vibration to be the greatest occupational risk factor" in herniated nucleus pulposus. Heliovaara suggests that occupational drivers have twice as many disk herniations as compared to non-occupational drivers. Other studies and authors found that the incidences of disk injuries can be as much as five times more frequent in occupational drivers. (Zacharkow, 1988)
Rasmussen (1982) explain the effects of vibration on the human body. He identified various sources of occupational vibration and explained its harmful effects. He stated that feelings of discomfort are noticed with as little as 4 Hz of vibration. The literature suggests that occupational driving results in greater incidents of back injury. First of all, the seated position (as in driving) results in greater intervertebral disk pressure. Secondly, vibration (as is caused by driving) results in a increased rate of creep resulting in decreased disk size which leads to pain from accelerated facet wear and nerve root compression due to narrowed vertebrae spacing. Studies also suggest that exposure to the combination of vibration and sitting is particularly injurious to the spine.
Thus the muscles have an important role in adding to the effect of vibration. The fatigue that was found in muscles after vehicular vibration is indicative of the loads in the muscles. Thus it would seem reasonable to recommend the avoidance of heavy lifting after vibration exposure (i.e.: lifting patients). It would also be advisable to take frequent rests. (Pope, 1991)
Several studies have indicated how the static seated
posture and vehicular vibration lead to fatigue in those who are
exposed to it. Fatigue occurs as a result of increased postural
muscle use. Seat design can play a big role in how much postural
musculature is recruited. Seats that lack proper design will necessitate
the recruitment of the erector spinae and lateral flexor muscles
to name a few. Continuous recruitment of these muscle is required
when a vehicles seat offer little or no support (See Chapter 6).
(Zacharkow, 1988) Paramedics forced to "roam," or sit
on stand-by for long periods of time, are being exposed to excessive
amounts of vibration while sitting in poorly designed seats.
The major concern of the long standing policy of placing ambulances on "stand-by" and the newly implemented "roaming" procedures are the potentially adverse effects on paramedics sitting, for long periods of time, in an idling, a moving, or a stationary (idling or not) ambulance. Does this result in an increased incidence of back injuries/pain? In order to try and determine this, several steps have been taken. A survey of ninety-two paramedics, mostly from the Ottawa/Carleton area, was completed. Currently there are approximately 220 paramedics employed in Ottawa/Carleton. Some of the questions addressed in the survey attempted to determine if: a) the amount of time spent in the ambulance by paramedics has increased since roaming has been implemented, b) to determine if there has been an increase in back injuries and, c) to determine what factors might make the situation worse.
Ninety-two surveys (Appendix A) were returned by Ontario Paramedics (mostly from the Ottawa/Carleton area). All of the respondents work regularly on ambulances, not on transfer cars.
The first part of the study involves survey research of paramedics. The survey research will attempt to develop a relationship between the increased amount of time being spent in an ambulance (roaming & stand-bys) and an increased incidence of back pain/injury. An initial pretest of the survey was given to a subgroup of paramedics and managers to determine if any flaws existed in its structure. The survey was then refined. The refined surveys were then distributed to as many paramedics in Ottawa/Carleton as possible. (See Appendix A for sample surveys) A cover letter (Appendix A) accompanied the surveys to explain: that the surveys were of a voluntary nature, who was doing the survey, what was being surveyed and how to contact the survey administrators. This survey measured the impact of "roaming" and long stand-bys on paramedics. Such questions as the length of time spent roaming or sitting on stand-by were analyzed.
The literature on sitting for extended periods of
time in a vehicle and exposure to vehicular vibrations is clear.
Both are harmful to the back and combined they intensify the problems.
In order to see whether, in fact, there was a problem in this
regard, a survey was distributed to Paramedics from various ambulance
stations across Eastern Ontario, most from within the Regional
Municipality of Ottawa/Carleton (which currently has 220 paramedics
employed within its boundaries) (Appendix A). Ninety-two surveys
were returned. The subjects that responded consisted of 80 males
and 12 females between the ages of twenty and fifty-five. (Figures
4.1 & 4.2)
The average shift length worked by the paramedics was 11.7 hours. Most paramedics regularly work a twelve hour shift. During their shift, paramedics estimated that they spend 23% of their shift "roaming," 32% of their shift on stand-by, and 31% of their shift driving. This equates to a significant amount of their shifts in which they are exposed to the seated posture and vibration of one kind or another. Some respondents may have confused the time spent driving with the time spent roaming. Figure 4.3 illustrates the amount of time spent by paramedics on different tasks, with 56% being spent on "roaming" and stand-bys.
Seventy-one percent of respondents reported suffering
from back pain or back discomfort more often now than before "roaming"
was initiated. Ninety-three percent of the paramedics said that
they suffer from back pain or discomfort while simply sitting
in the ambulances (this was pain/discomfort not due to a lifting
injury). When they were asked to rate how often this pain/discomfort
from just sitting occurred, 62% stated that it occurred at least
once a week or more often (Figure 4.4).
Interestingly, 88% of paramedics within their first six years of employment complained of suffering from this back pain/discomfort at least once a week of more often. Even more significant was the fact that 90% of all respondents thirty years of age or younger complained of this pain/discomfort at least every other shift or more often.
Ninety-five (95) percent of respondents were unhappy with the way that "roaming" and/or stand-bys have been implemented. They had several different concerns of which the most common will be discussed here. The most common complaint was that stand-bys are too long. Many subjects suggested that the application of stand-bys were very inconsistent. In some areas stand-bys are not maintained after certain hours while in other areas they are maintained 24 hours a day. Some stand-bys are only a few kilometers from the paramedics' stations, leading them to wonder why bother placing them there for such long periods of time in the first place. Others suggested that they worked in a significantly busier area than their neighboring area. While on stand-by they would end up doing calls back towards their own area the majority of the times. They suggested that this resulted in longer response times to more calls, more often. Others wondered why they would often be placed on stand-by so far away from their station to only end up leaving their own area without balanced emergency coverage.
Many paramedics suggested that stand-bys were used excessively as a result of a lack of sufficient numbers of ambulances staffed in the area. They said that more ambulances should be placed on the road instead of continually compromising two areas with one ambulance placed on stand-by between them. They went on to discuss how the ever increasing use of stand-bys was an obvious indication of a serious lack of ambulances in the area(s). They felt that stand-bys should be a rare occurrence and that if they become too prevalent then more ambulances should be staffed in those areas. Some suggested that if this could not be done then the human cost involved with maintaining too many standbys, too often was too high. Others thought that it was ironic that more ambulances were not being staffed on the road when, in reality, the taxpayers ended up paying so much money in increased vehicle maintenance costs, fuel costs and "Workers Compensation" (WCB) costs due to the prevalence of stand-bys. They said that if that money would be used towards more staffed ambulances, then there would be less of a need to put ambulances on stand-by in the first place and also less incidences of WCB claims.
Some other issues that were mentioned dealt with
the lack of comfort within the current ambulance designs. Eighty-nine
percent of paramedics felt that the seats in the front of the
ambulances were not comfortable (Figure 4.5).
They commented about a lack of ability to get out of the vehicle and move around while on stand-by. Reasons for this were such things as: poor radio systems that have unreliable portable communications thereby forcing the crew to stay in the vehicle in order not to miss a call; being forced to park at remote intersections late into the night or early into the morning where walking around might be hazardous (i.e.: dark, risk of violence); severely cold or hot weather conditions forcing them to remain in the ambulance with it running the entire time while on standby; lack of proper facilities to stretch or exercise "If we are lucky there maybe a donut shop open at 3am but that is hardly a place to walk around in circles or to do stretching exercises" (Survey respondent, 1998). The paramedics also complained about the constant inhalation of vehicular exhaust fumes while on stand-by.
More specifically, in regards to the vehicle design, Figure 4.6 shows that 80% of the paramedics were either unsatisfied or very unsatisfied with the leg room in the front cab of the ambulance. It's important to note that the average height of those "very satisfied" with the leg room in the front cab of the ambulances was 166cm (5'5") compared to the average height of those "very unsatisfied" being 179cm (5'11").
Eighty-seven percent of respondents were either unsatisfied
or very unsatisfied with the ability to recline the driver's seat
of the ambulances. Ninety-nine percent of respondents noticed
at least some vibration while sitting in the ambulances (Figure
4.7).
Finally, figure 4.8 clearly illustrates that 100% of all paramedics that returned surveys would prefer
to have armrests installed in the ambulances.
All of the recent vehicle models in Ontario ambulances
have had armrests discontinued, including the latest ambulance
conversion-(Demers, 1998 Ford). A few older Dodge van ambulances
have armrest, but they represent only a small percentage of the
front-line fleet and are quickly being phased out. (Figure 5.4)
After having looked at the literature on the effects of sitting in vibrating (moving or idling) vehicles, the consensus of studies indicates a strong relationship with a higher incidence of back injuries to those people who work under these conditions. Paramedics work under these conditions in Ontario. They are required to "roam" or be on stand-bys for excessive periods of time in addition to all the regular lifting and driving duties that they normally perform. In a study on injuries among emergency services workers it was determined that the most commonly injured area was the lower back. This has been found to be true in several other American studies of ambulance personnel. (Gershon, 1995) In a large part this is probably due to lifting injuries, however, these lifting injuries are more likely to happen more often when exposing this known, high risk group for back injuries to excessive vehicular sitting and vehicular vibrations.
The survey of paramedics validates the academic research in regards to vehicular sitting exposure and vehicular vibration exposure in that it does show that paramedics, in the population studied, demonstrate significant back problems. Lower back pain can result from several factors, however, the greatest risk is the combination of long-term exposure to vibrations and frequent lifting. (Magnusson, 1996) "Prolonged exposure to vibration when seated has been shown to lead to muscle fatigue, particularly of the erector spinae and oblique abdominal musculature" (Wilder et al., 1982) "Individuals involved in lifting activities directly after prolonged driving in a flexed sitting posture would therefore be at a very high risk for developing low back pain" (Adams & Hutton, 1982) The results of the survey show that this is true.
Does the vehicle design help or hinder the problems faced by paramedics? The ambulance vehicle designs worsens the problems faced by paramedics. The two areas of vehicle design that exacerbates the problems associated with back injuries are: front cab space and seat design.
The front cab space in ambulances is very confined-so much so that many paramedics cannot recline the backrest of the seat and drive at the same time. (figure 5.1) In fact, many of the Dodge ambulance conversions do not provide a backrest that will recline at all. (figure 5.2)
As mentioned earlier, 80% of respondents to the survey felt unsatisfied or very unsatisfied with the amount of leg room in the front cab of the ambulances. Of those that were satisfied, their average height was 166cm (5"5") as compared to the average height of the "very unsatisfied" being 179cm (5'11"). So, in general, the very few "satisfied" respondents tended to be significantly shorter people. These people would be able to move the seat more forward, thereby enabling them to recline the backrest to a more ergonomically correct position.
The degrees of quality of seats in the ambulances vary between make, model and year. The seats that are currently installed in the front cabs of Ontario ambulances are of very poor quality. (Figures 5.3 & 5.4) The goal of a good vehicle seat should be to limit the amount of postural stress caused by static muscular contractions. (Zacharkow, 1988) In general, the following problems exist with the seats in Ontario's ambulances:
The general quality of seats (in regards to limiting back pain/discomfort) in Ontario ambulances is poor. This statement is made based on the fact that paramedics are required to drive and sit on stand-bys in these seats for extended periods of time every shift they work. These seats, along with the limited front cab space, do very little to limit the amount of postural stresses caused by sitting in them for prolonged periods. Also, the trend in Ontario's ambulance seat designs is worsening. The Ford truck is the base model being used in ambulance conversions. The current brand of seats that are being purchased from Ford by the Ontario Ministry of Health continue are insufficient. The need for engineering controls is obvious.
Recommendations which will help ensure the health and safety of paramedics in regards to vehicular vibration exposure and vehicular sitting exposure can be made in two general categories. The first category involves initiating administrative controls in regards to policies and procedures for the use of roaming and stand-bys. The second category involves initiating engineering controls to ensure the best possible vehicular environment so to maximally reduce the risks to the paramedics' health and safety.
Both the literature and the survey suggest that the current policies and procedures practiced by ambulance dispatch centers (authorized by the Ontario Ministry of Health), in regards to stand-bys and roaming, pose a significant risk to the health and safety of paramedics. Paramedics are forced to increase their normal vehicular vibration and vehicular sitting times to a significant extent by the overuse of stand-bys and roaming. The use of stand-bys and roaming should be limited in the following ways:
Engineering controls to limit the amount of exposure to vibration and to limit the effects of the static seated posture involve changes to the front cab of the ambulances and primarily to the seat design (Table 6.1).
The front cabs of the ambulances are too small. In particular the length of the cab is too short. This results in not enough room for most paramedics to correctly position their seat to be able to drive and to still be able to adjust the backrest of the seat to a more ideal angle (120 degrees from the seat pan). (Andersson, 1974) It also forces the paramedics to maintain a more hazardous static posture. Eighty percent of paramedics that responded to the survey stated that they are unsatisfied or very unsatisfied with the leg room in the ambulances. Eighty-seven percent of paramedics are either unsatisfied or very unsatisfied with the ability to recline the back rest of the seats in the ambulances. The average height of this group is 180cm (5'11") which, coincidentally is also the mean height of the males who responded to the survey. Eighty-seven percent of the population studied were males. One can make a connection then to the fact that these taller people, who make up the vast majority of the workforce, do not have the means to adjust their seats appropriately because the ambulance cab length is too short. The length of the cab must be increased in such a way to allow the back rest to recline to at least 120 degrees from the seat pan (which should be at an angle of 10-14 degrees from the horizontal) when the seat is in its farthest position back. (Zacharkow, 1988) The length of the cab should preferably allow the seats backrest to recline to an even greater degree in order to accommodate a semi-fowler or an "as close to supine" position as possible for the paramedic when they are not driving but required to be on stand-by. "When the backrest inclination increased, a larger proportion of the body weight was transmitted to the backrest and thus the stresses on the spine were reduced." (Andersson, 1974) The semi-fowler position and the supine positions allow for decreased postural muscle usage and therefore less fatigue and risk of injury.
…as a direct result of fatigue (with faulty
posture in regards to sitting) an individuals ability to perform
is reduced; his output is diminished; the quality of his production
is lowered; his mental aptitude is reduced; his susceptibility
to disease is increased…; he is much more likely to commit
errors, and his likelihood to sustain personal injuries is greatly
enhanced. (Zacharkow, 1988)
These semi-fowler to supine positions also result in less of an effect on the compression of the Intervertebral disc as is caused while sitting.
The backrest needs to be made of firm material with firm lumbar support to encourage the normal lordodic curve of the lumbar spine which will therefore be better able to distribute the vertical forces on the spine. The backrest must have firm lateral support in order to reduce the backs lateral flexor activity. (Pope, 1991) Some of the current ambulances have lateral support but it is composed of a soft "foam like" material which is insufficient. Firm, adjustable lumbar support in the backrest will assist in maintaining the lordotic curve of the lumbar spine thereby decreasing intervertebral disc pressure.
Armrests must be installed in the ambulances. These
are very basic features of a good chair and yet result in a dramatic
decrease in discomfort. Armrest assist in lowering intervertebral
disc pressures by taking much of the weight of the arms and upper
body off of the spine. Several studies have shown that both arms
make up between 9.8 to 12 percent of the total body weight. (Zacharkow,
1988) Armrests also allow for some relief for the postural muscles
of the back. Armrests act to allow the arm musculature to relieve
some of the postural stresses and also help to prevent a slumped
posture. They can also assist by providing some lateral support.
The literature is clear-exposure to a static seated position and to vehicular vibrations do result in increased back discomfort/pain/injuries. The survey of paramedics is also clear-paramedics are suffering from back discomfort/pain/injuries at an alarming rate. The seats that are currently installed in Ontario's ambulances are insufficient and of a very poor quality. The seats need to be replaced by much more supportive ones. The front cab space in the ambulances need to made larger in order to accommodate variations in drivers' sizes. Most paramedics feel that they are unable to move or recline their seats enough to reduce the impact of postural muscle fatigue.
It is clear that administrative controls are needed to limit the amount of time that paramedics are kept roaming or on stand-bys. This, along with engineering controls, to improve seat and cab space designs, will go a long way to reducing injuries to paramedics. Administrators need to reconsider the human costs involved with maintaining the current practices of roaming and stand-bys.
Adams, M..A. & Hutton, W.C. (1988) Mechanics
of the Intervertebral Disc. In P. Gosh (Ed.), The Biology of
the Intervertebral Disc. (pp. 39-71). Boca Raton: CRC
Press Inc.
Adams, M.A., Hutton, W.C. (1985) . The effects of
posture on the lumbar spine. The Journal of Bone and Joint
Surgery. 67-B (4), 625-629.
A.R.I.S. (Ambulance Response Information System).
(1997) Call statistics for Finch station. Ottawa: Ottawa
Central Ambulance Communication Center.
Andersson, G.B.J. (1974) Lumbar Disc Pressure and
Myoelectric Back Muscle Activity During Sitting. Scand J
Rehab Med 6: 128-133.
Andersson, G.B.J. (1986) Loads on the Spine During
Sitting. In Corletten et al. (Ed.) The Ergonomics of Working
Postures. London: Talyor & Francis
Andersson, G.B.J. et al. (1991). Occupational
Low Back Pain: Assessment, Treatment and Prevention. St. Louis:
Mosby-Year Book Inc.
Bovenzi, M. and Zadini, A. (1992) Self reported low
back symptoms in urban bus drivers exposed to whole-body vibration.
Spine, 17 (9), 1048-1059.
Chaffin, D.B., Andersson, G.B.J. (1991) Occupational
Biomechanics. New York: John Wiley & Sons, Inc.
Rasmussen, G., (1982) Human Body Vibration.
Denmark: Bruel & Kjaer.
Burton AK. (1996) Occupational risk factors for the
first-onset and subsequent course of low back trouble. Spine:
21, 2612-2620.
Gershon, R. et al. (1995). Review of accidents/injuries
amoung emergency medical service workers in Baltimore, Maryland.
Prehospital and Disaster Medicine. 10 (1), 33-37.
Griffen, M.J. (1990) Handbook of Human Vibration
Academic Press.
Heliovaara, M. & Knekt, P & Aromaa, A (1987)
Incidence and Risk Factors of Herniated Lumbar Intervertebral
Disc or Sciatica Leading to Hospitalization. J Chron Dis.
40, 251-258.
Hinz, B. et al. (1988). Examination of spinal column
vibrations: A non-invasive approach. European Journal of Applied
Physiology. 57, 707-713.
Kazarian, L. (?). Creep characteristics of the human
spinal column. Orthepaedic Clinics of North America. 6
(1), 3-18.
Kelsey, J. et al. (1984). Acute prolapsed lumbar
intervertebral disc: An epidemiologic study with special reference
to driving automobiles and cigarette smoking. Spine. 9
(6), 608-613.
Kelsey, J.L. & White, A.A. (1980) Epidemiology
and impact on back pain. Spine. 5 (2), 133-142.
Klingenstierna, U., Pope, M.H. (1987). Body height
changes from vibration. Spine. 12 (6), 566-568.
Magnusson, M. et al. (1996). Are occupational drivers
at an increased risk for developing musculoskeletal disorders?
Spine. 21 (6), 710-717.
Nachenson, A. (1992). Newest knowledge of low back
pain: A critical look. Clinical Orthopaedics and Related Research.
(279), 9-15.
Nachenson, A. (1975). Towards a better understanding
of low-back pain: A review of the mechanics of the lumbar disc.
Rheumatology and Rehabilitation. 14 (3), 129-141.
Pope, M. H. (1996) Occupational Hazards for Low
Back Pain, Paper presented at the symposium on: Low Back
Pain: Prevention, Control, Treatment. St. Louis.
Pope MH. & D.G. Wilder, (1996) Epidemiological
and etiological aspects of low back pain in vibration environments
- an update. Clinical Biomechanics. 11, 61-73.
Pope, M.H., Hansson, T.H. (1992). Vibration of the
spine and low back pain. Clinical Orthopaedics and Related
Research. (279), 49-59.
Pope, M.H. et al. (1991). Biomechanics of the lumbar
spine. In J.W. Frymoyer (Ed.), The adult spine:Principles and
practise (pp. 1487-1501). New York: Raven Press Ltd.
Pope, M.H. & Klingenstierna, U. (1987) Body Height
Changes from Vibration. Spine. 12, 566-568.
Pope, M.H. et al. (1985, October). Muscle fatigue
in static and vibrational seating environments. Paper presented
for the advisor group for aerospace research & development
conference, Pozzaroli, Italy.
Pope, M. H. et al. (1980) The Response of the Seated
Human to Sinusoid Vibration and Impact. Journal of Biomechanical
Engineering. 109, 279-284.
Seidel, H. et al. (1986). Effects of sinusoidal whole-body
vibration on the lumbar spine: The stress-strain relationship.
Int. Arch. Occup. Environ. Health. 57, 207-223.
Springer, J & Robinson, D. (1997) Vibration:
What's shaking? OHS Canada Magazine. 3. (1) 1-4.
Stothart, J.P. & S.M. McGill, (1996). Stadiometry:
A Method to Assess Compressive Loads on the Spine. Canada:
University of Ottawa & University of Waterloo. Proceedings
of the 9th Biannual convention of Canadian Society
of Biomechanics.
Thomson, W.T. (1981). Theory of vibration with
applications. Englewood, N.J.: Prentice-Hall.
Zacharkow, D. (Ed.) (1988). Posture: Sitting,
standing, chair design & exercise. Springfield: Thomas
Books.