Preventing Musculoskeletal Disorders in the Workplace

Transcription

1 Protecting Workers Heath Series No 5 Preventing Muscuoskeeta Disorders in the Workpace Prof. Dr. rer. nat. Awin Luttmann PD Dr.-Ing. Matthias Jäger Prof. Dr. med. Barbara Griefahn Institute for Occupationa Physioogy at the University of Dortmund Institut für Arbeitsphysioogie an der Universität Dortmund Ardeystrasse 67 D Dortmund Germany and Dr. med. sc. Gustav Caffier Dr. med. Fak Liebers Dip.-Ing. Uf Steinberg Federa Institute for Occupationa Safety and Heath/ Bundesanstat für Arbeitsschutz und Arbeitsmedizin Nödnerstrassie D Berin Germany

2 Cover page ayout Tuua Soasaari-Pekki Finnish Institute of Occupationa Heath Design and ayout M/s Safire Graphix, New Dehi, India Other bookets from the Protecting Workers Heath Series: No.1 : Preventing heath risks from the use of pesticides in agricuture No.2 : Understanding and performing economic assessments at the company eve No. 3 : Work organization and stress at work No. 4 : Raising awareness of Psychoogica Harassment at Work

3 WHO Library Cataoguing-in-Pubication Data Preventing muscuoskeeta disorders in the workpace/awin Luttmann... [et a.] Protecting workers heath series ; no Muscuoskeeta diseases - prevention and contro 2. Workpace 3. Risk factors 4. Guideines I. Luttmann, Awin. II. Series ISBN X (LC/NLM cassification: WA 440) Word Heath Organization 2003 A rights reserved. Pubications of the Word Heath Organization can be obtained from Marketing and Dissemination, Word Heath Organization, 20 Avenue Appia, 1211 Geneva 27, Switzerand (te: ; fax: ; emai: bookorders@who.int). Requests for permission to reproduce or transate WHO pubications whether for sae or for noncommercia distribution shoud be addressed to Pubications, at the above address (fax: ; emai: permissions@who.int). The designations empoyed and the presentation of the materia in this pubication do not impy the expression of any opinion whatsoever on the part of the Word Heath Organization concerning the ega status of any country, territory, city or area or of its authorities, or concerning the deimitation of its frontiers or boundaries. The Word Heath Organization does not warrant that the information contained in this pubication is compete and correct and sha not be iabe for any damages incurred as a resut of its use. Printed in India A iustrations are copyright protected, therefore when using any of them the copyright owner has to be named: Lang/Metze Ateier f:50, Berin

4 Preface Disorders of the muscuoskeeta system represent a main cause for absence from occupationa work. Muscuoskeeta disorders ead to considerabe costs for the pubic heath system. Specific disorders of the muscuoskeeta system may reate to different body regions and occupationa work. For exampe, disorders in the ower back are often correated to ifting and carrying of oads or to the appication of vibration. Upper-imb disorders (at fingers, hands, wrists, arms, ebows, shouders, neck) may resut from repetitive or ong-asting static force exertion or may be intensified by such activities. The severity of these disorders may vary between occasiona aches or pain to exacty diagnosed specific diseases. Occurrence of pain may be interpreted as the resut of a reversibe acute overoading or may be a pre-symptom for the beginning of a serious disease. The purpose of this document on the prevention of muscuoskeeta disorders is to inform about risk factors and to infuence the actions of empoyers and the behaviour of workers in such a way that risks of physica oadings, dangerous to heath or unnecessary fatiguing, are avoided or diminished. The document has been prepared in such a way that it can be used by empoyers, supervisors, and occupationa heath trainers when designing work and work environment or for preparing information materias and training programs. In consequence, appication of the guide shoud be hepfu to reduce harm to individuas, to infuence the efficiency of work positivey, and to reduce costs on the pubic heath system. It is intended that this booket be used by empoyers, supervisors and occupationa heath trainers to hep them recognise risks that may ead to muscuoskeeta disorders, as we as to design work itsef and the work environment in a way which is safe for the empoyee. Acknowedgement is expressed to the foowing reviewers: Thomas R. Waters, Ph. D., Nationa Institute for Occupationa Safety and Heath, Cincinnati; Dr. Hisashi Ogawa, Word Heath Organization, Regiona Adviser for Occupationa Heath, Regiona Office for the Western Pacific, Mania; and Eveyn Kortum-Margot, Occupationa Heath Programme, Word Heath Organization, Geneva, Switzerand.

5 Exampes of physica oadings at work which may be dangerous to heath: Kneeing for ong duration Manipuation of heavy oads Whoe-body vibration Static work and awkward posture Sitting for ong duration

6 Contents Part 1: Objectives 1.1 Work-reated muscuoskeeta disorders - a definition Characteristic heath probems Basic risk factors for the deveopment of 3 muscuoskeeta disorders 1.4 Factors to be considered in prevention 12 Part 2: Guidance 2 Guidance on main risk factors Risk factor: Manipuation of heavy oads Risk factor: Work with high force exertion Risk factor: Working in unfavourabe body postures Risk factor: Monotonous repetitive tasks Risk factor: Long-asting oadings Risk factor: Physica environmenta conditions 25 Appendix: Basic rues for preventive actions in practice 27 Summary 29 Concusion 30 Further reading and references 31

7 1 Part 1 Objectives 1.1 Work-reated muscuoskeeta disorders - a definition The term muscuoskeeta disorders denotes heath probems of the ocomotor apparatus, i.e. of musces, tendons, the skeeton, cartiage, igaments and nerves. Muscuoskeeta disorders incude a forms of i-heath ranging from ight, transitory disorders to irreversibe, disabing injuries. This booket focuses on muscuoskeeta disorders, which are induced or aggravated by work and the circumstances of its performance. Such work-reated muscuoskeeta disorders are supposed to be caused or intensified by work, though often activities such as housework or sports may aso be invoved. Most important ocaization of work-reated muscuoskeeta disorders Upper extremities (shouder arm hand) Main articuations (e.g. knee)

8 2 1.2 Characteristic heath probems Heath probems occur, in particuar, if the mechanica workoad is higher than the oad-bearing capacity of the components of the muscuoskeeta system. Injuries of musces and tendons (e.g. strains, ruptures), Lower back igaments (e.g. strains, ruptures), and bones (e.g. fractures, unnoticed microfractures, degenerative changes) are typica consequences. In addition, irritations at the insertion points of musces and tendons and of tendon sheaths, as we as functiona restrictions and eary degeneration of bones and cartiages (e.g. menisci, vertebrae, intervertebra discs, articuations) may occur. There are two fundamenta types of injuries, one is acute and painfu, the other chronic and ingering. The first type is caused by a strong and short-term heavy oad, eading to a sudden faiure in structure and function (e.g. tearing of a musce due to a heavy ift, or a bone fracture due to a punge, or bocking of a vertebra joint due to To prevent muscuoskeeta disorders, a baance between mechanica oad at work and oad-bearing capacity of the muscuoskeeta system is most important. a vehement movement). The second resuts from a permanent overoad, eading to continuousy increasing pain and dysfunction (e.g. wear and tear of igaments, tendovaginitis, musce spasm and hardening). Chronic injuries resuting from ong-term oading may be disregarded and ignored by the worker because the injury may seemingy hea quicky and it may not resut in an actua significant impairment.

9 The number of such injuries is substantia. In industriaized countries, about one-third of a heath-reated absences from work are due to muscuoskeeta disorders. Back injuries (e.g. ower back pain, ischiadics, disc degeneration, herniation) have the highest proportion (approximatey 60%). The second position is taken by injuries of the neck and the upper extremities (e.g. pain syndromes of the neck, shouders, arms, tennis ebow, tendinitis and tendovaginitis, carpa tunne syndrome, syndromes reated to cumuative traumata, the so-caed cumuative trauma disorders (CTDs) or repetitive strain injuries (RSIs)), foowed by injuries of knees (for exampe, degeneration of menisci, arthrosis) and hips (e.g. arthrosis). It is generay accepted that working conditions and workoad are important factors for the deveopment and continuance of these disorders Basic risk factors for the deveopment of muscuoskeeta disorders Mechanica overoad, repetition frequency, exposure time, posture and accidents Work-reated muscuoskeeta disorders are supposed to be causay inked to physica oad resuting from occupationa activities. Disorders or injuries affecting musces, tendons, joints, igaments and bones are mainy caused by mechanica overoad of the respective bioogica structures. Potentia overoad of tissues resuts from high intensity forces or torques acting on and inside the body. Exampes of occupationa activities coinciding with high mechanica requirements are handing of objects, as in transportation jobs, or the appication of pushing or puing forces to toos or machines. The detrimenta effect of mechanica overoad depends mainy on the magnitude of the force. Furthermore, the duration of exposure is an important factor in the deveopment of muscuoskeeta disorders. It is mainy determined by the number of repetitions per unit time (e.g. per day) as we as by the tota exposure time (e.g. hrs per day or days per month). Regarding the character of exposure, occasiona vocationa oading

10 4 events can be discriminated from ong-asting activities occurring over many years during the entire occupationa ife. Short-term oadings may primariy ead to acute heath disturbances whereas ong-asting exposure may, in a fina stage, cause chronic disorders. The risk for the muscuoskeeta system depends to a great extent on the posture of the operator. Especiay, twisting or bending the trunk can resut in an increased risk for the deveopment of diseases at the ower back. Postura demands pay an important roe, particuary, when working in confined spaces. Besides such types of occupationa oading resuting from usua work-site conditions, muscuoskeeta disorders can aso be caused by unique, unforeseen and unpanned situations, e.g. by accidents. The origin of disorders due to accidents is characterized by a sudden overstrain of the organs of ocomotion Tota mechanica oading Accident due to an unpanned situation The tota oad affecting the muscuoskeeta system depends on the eve of the different oad factors, mentioned before, such as the eve and direction of forces, the duration of exposure, the number of times an exertion is performed per unit of time, postura demands Risk quaities According to the factors mentioned before, different risk categories can be derived using different combinations or quaities thereof, such as high intensity forces, ong exposure duration,

11 5 highy repetitive exertions, strong postura demands, strong or ong-asting muscuar strain, disadvantageous environmenta or psychosocia conditions Factors contributing to the deveopment of muscuoskeeta disorders In the foowing, muscuoskeeta oad is characterized with respect to the main infuences, such as the eve of force, repetition and duration of execution, postura and muscuar effort as we as environmenta and psychosocia factors. 1. Exertion of high-intensity forces may resut in acute overoading of the oaded tissues. High-intensity forces are active within the body tissues particuary during ifting or carrying heavy objects. Furthermore, pushing, puing, hoding or supporting an object or a iving being are a matter of high-intensity forces. 2. Handing oads over ong periods of time may ead to muscuoskeeta faiures if the work is continued for a considerabe part of the working day and is performed for severa month or years. An exampe is performing manua materiashanding activities over many years, which may resut in degenerative diseases, especiay of the umbar spine. A cumuative dose can be regarded as an adequate measure for the quantification of such types of oadings. Reevant factors for the description of the dose are duration, frequency and oad eve of the performed activities. 3. Muscuoskeeta disorders may aso resut from frequentyrepeated manipuation of objects, even if the weight of the objects handed or the forces produced are ow. Such jobs (e.g. assembing sma workpieces for a ong time, ong-time typing, supermarket checkout work) may induce

12 6 disadvantages for the muscuature, even if the forces appied to the handed objects are ow. Under such conditions, the same parts and fibres of a musce are activated for ong periods of time or with a high frequency and may be subject to overoad. Eary fatigue, pain, and possibe injuries are the consequences. Repeated manipuation of objects 4. In a we-designed workstation, work can be performed most of the time in an upright posture with the shouders unraised and the arms cose to the trunk. Working with a heaviy bent, extended or twisted trunk can resut in an overoad of spina structures and increased activity of entire musces. If the trunk is simutaneousy bent and twisted the risk of spina injury is consideraby increased. If movements or postures with the hands above shouder height, beow knee eve or outstretched are performed over proonged periods or recurrenty, working conditions shoud be changed. Working in a kneeing, crouching or squatting position augments Continuous sitting in a fixed posture: disadvantageous for muscuature the risk of overoading muscuoskeeta eements. Aso, ong-time sitting in a fixed posture is accompanied by ongasting muscuar activity which may ead to an overoad within muscuar structures. Such working positions shoud be avoided and the time for working in such positions shoud be kept to a minimum, if such work is not competey avoidabe.

13 5. Static muscuar oad is found under conditions where musces are tensed over ong periods of time in order to keep a certain body posture (e.g. during work with the hands overhead in driing hoes into the ceiing, hoding the arms abducted in hair dressing, hoding the arms in typing position above the keyboard, working in a confined space). A characteristic of static muscuar oad is that a musce or a group of musces is contracted without the movement of the corresponding joints. If the musce has no opportunity to reax during such a task, muscuar fatigue may occur even at ow-force eves, and the function of musces may be impaired and it may hurt. In addition, static oad eads to a deficiency in bood circuation in musces. Under norma conditions, the permanent change between contraction and reaxation acts as a circuationsupporting pump. Continuous 7 contraction restricts the fow of bood from and to the contracted musce. Sweing of egs, for exampe, is an indicator of such a ack in bood circuation. Static work with hoding the hands overhead 6. Muscuar inactivity represents an additiona factor for the deveopment of muscuoskeeta disorders. Musces need activation to maintain their functiona capacity, and the same is true of tendons and bones. If activation is acking, a deconditioning wi Deconditioning due to ow deveop, which eads to muscuar demand and ongasting physica inactivity functiona and structura deficits. As a resut, a musce is no onger abe to stabiize joints and igamenta structures

14 8 adequatey. Joint instabiities and faiures, incoordination connected with pain, movement abnormaities and overoading of joints may be the consequences. 7. Monotonous repetitive manipuations with or without an object over ong periods of time may ead to muscuoskeeta faiures. Repetitive work occurs when the same body parts are repeatedy activated and there is no possibiity of at east Monotonous repetitive manipuations Continuous keyboard and mouse use during data entry a short period of reaxation, or a variation in movement is not possibe. Reevant determining factors are the duration of the working cyces, their frequency and the oad-eve of the performed activity. Exampes of repetitive work are keyboard use whie typing, data entry, cicking or drawing a computer mouse, meat cutting, etc. Unspecific compaints due to repetitive movements of the upper extremities are often summarized in the term repetitive strain injury - RSI. 8. Strain on the ocomotor system may aso occur due to the appication of vibration. Vibration may resut from hand-hed toos (e.g. rock dri) and, therefore, exert vibration strain on the hand-arm system. Hand-arm vibration may resut in the dysfunction of nerves, reduced bood circuation, especiay in the fingers (white finger syndrome) and degenerative disorders of bones and joints of the arms. Another risk concerns

15 Exposure to vibration: Use of vibrating toos 9 whoe body vibration generated by vibrating vehices and patforms such as earth-moving machines, ow-ift patform trucks or tractors and trucks driving off-road. The vibration is transferred to the driver via the seat. Whoe-body vibration can cause degenerative disorders, especiay in the area of the umbar spine. The effect of vibration may be intensified if the vehice is driven in a twisted body posture. A vibration-attenuating driving seat may hep to reduce the effect of vibration. 9. Physica environmenta factors such as unsuitabe cimatic conditions can interact with mechanica oad and aggravate the risk of muscuoskeeta disorders. In particuar, the risk of vibrationinduced disorders of the hands is consideraby enhanced if ow temperature coincides with the use of hand-hed vibrating toos. Another exampe of environmenta factors infuencing the muscuoskeeta strain is the ighting conditions: If ighting and Physica environmenta factors:work at heat visua conditions are deficient, musces are strained more intensivey, particuary in the shouder and neck region. 10. Besides the mechanicay-induced strain affecting the ocomotor organs directy, additiona factors can contribute to the beginning or aggravation of muscuoskeeta disorders. Psychosocia factors can intensify the infuence of mechanica

16 10 strain or may induce muscuoskeeta disorders by themseves due to increasing musce tension and by affecting motor coordination. Furthermore, psychosocia infuences such as time pressure, ow job decision atitude or insufficient socia support can augment the infuence of physica strain. A summary of the main factors contributing to the risk of deveoping work-reated muscuoskeeta disorders is provided in the tabe.

17 11 Tabe : Main factors contributing to muscuoskeeta disorders Factor Possibe resut Exampe Good practice or consequence exampe or soution Exertion of high- Acute overoading Lifting, carrying, Avoid manua intensity forces of the tissues pushing, puing handing of heavy heavy objects objects Handing heavy Degenerative Manua materias- Reduce mass of oads over ong diseases especiay handing objects or number periods of time of the umbar spine of handings per day Frequenty Fatigue and Assemby work Reduce repitition repeated overoad of ong time typing, frequency manipuation muscuar structures check-out work of objects Working in Overoad of Working with Working with an unfavourabe skeeta and heaviy bent or upright trunk and posture muscuar eements twisted trunk, or the arms cose to hands and arms the body above shouders Static muscuar Long-asting Working overhead, Repeated change oad muscuar activity working in a between activation and possibe confined space and reaxation of overoad musces Muscuar Loss of functiona Long-term sitting Repeated standing inactivity capacity of musces, with ow muscuar up, stretching of tendons and bones demands musces, remedia gymnastics, sports activities Monotonous Unspecific com- Repeated activation Repeated interruption repetitive paints in the upper of the same musces of activity and pauses manipuations extremities (RSI) without reaxation aternating tasks Appication of Dysfunction of Use of vibrating Use of vibrationvibration nerves reduced hand-toos, sitting attenuating toos bood fow, degene- on vibrating and seats rative disorders vehices Physica Interaction with Use of hand-hed Use goves and environmenta mechanica oad toos at ow heated toos at ow factors and aggravation temperatures temperatures of risks Psychosocia Augmentation of High time pressure, Job rotation, job factors physica strain, ow job decision enrichment, increase in atitude, ow socia reduction of negative absence from work support socia factors

18 Factors to be considered in prevention The idea baance With regard to maintenance and promotion of heath, a weighed baance between activity and rest is necessary. Rest pauses are a prerequisite for recovery from oad-induced strain and for preventing accumuation of fatigue. Movement shoud be preferred to static hoding, the aim shoud be a combination of active periods with oading and inactive periods of reaxation. The individua favourabe oad can vary from subject to subject depending on functiona abiities and individua resources. Overoad as we as inactivity shoud be avoided. Appropriate oad effects training of musces eading to adaptation and thus an increase in the capacity of musces, tendons and bones. This is essentia for heath and we-being. CAVEAT: This genera view, however, needs refinement in specia cases, since parts of the muscuoskeeta system may not adapt to oads in the same way. For exampe, repetitive ifting of heavy oads probaby does increase musce capacity, but probaby does not increase the capacity of the spina discs to withstand mechanica oading. As a consequence, strength training coud misead individuas to beieve they coud safey ift greater oads and thus risk back probems. Jobs shoud, therefore, be so designed that most peope are abe to carry them out, rather than ony a few strong individuas The principe of ergonomics A risk for disorders of the muscuoskeeta system appears if the oad and the functiona capacity of the working person are not baanced. The basic principe of ergonomics is to create an appropriate baance between the requirements of the work and the capacity of the working person, by either adapting the work to the person by design of the respective work, or by deveoping the

19 13 capacity of the humans to the work by training and vocationa adjustment. The primary aim shoud be the adaptation of working conditions to the capacity of the working persons, whereby it is of particuar importance to consider the dependency of individua capacity on age and gender. The adaptation of human beings to work shoud not be preferred, as here the work cannot be performed by a persons, but ony by seected and specificay trained groups. Additionay, the possibiity of deveoping human abiities during work execution shoud not be misused as a pretence for maintaining poory designed conditions of work or work environment Work performance strategies A risk factor for overoading the muscuoskeeta system resuts from the method of performing the work by the worker. There are risky and ess risky strategies to execute the task. An exampe is ifting heavy objects having the centre of gravity near the body. To fufi this demand, heavy objects shoud be ifted, whenever possibe, by bending the knees instead of bending the back. Further measures to reduce overoading risk are avoiding twisted and ateray bent postures, working continuousy at a moderate pace and not during short time-periods with high time-pressure. The worker must be informed about those possibiities and shoud be motivated to use them Avoid accidents and injuries The avoidance of accidents is another important fied for the prevention of muscuoskeeta disorders. Hazardous situations, in particuar for punges, can occur during work at greater height, for exampe on a adder, a scaffod or a construction site. The risk for punges can be reduced by securing the standing position and by stabiizing the equipment on which the worker cimbs. In particuar, the use of steady adders and fixing the adders to the foor or on

20 14 stabe objects is indispensabe. Ony sufficienty stabe and steady scaffods shoud be used and these shoud be fixed to the buiding. Furthermore, securing the position of the worker by roping to the cimbing aid (adder; scaffod) or buiding is an important measure for preventing punges. Injuries to head, hand and foot can be avoided by using protective hemets, goves or shoes, respectivey. Another important measure is to avoid objects from faing down by fastening or covering them in an appropriate manner. In particuar, during the transportation of goods with cranes or other hoisting devices, goods shoud be fixed by covering them or by spreading a pane underneath.

21 15 Part 2 Guidance 2 Guidance on main risk factors In this part, some of the main risk factors for the deveopment of muscuoskeeta disorders are isted, and exampes of tasks and working conditions are provided. Additionay, potentia causes for heath disturbances and injuries as we as suggestions as to how to avoid these are made. Risk frequenty resuts from exposure to mechanica oading. The main infuencing factors are high forces resuting from ifting and pushing or puing heavy objects, high repetition frequency, ong duration of force execution, unfavourabe posture, uninterrupted musce force exertion or working on or with vibrating machines. In some cases, the degree of handing precision, rather than the actua force exerted, constitutes an additiona hazardous factor. 2.1 Risk factor: Manipuation of heavy oads Where are heavy oads manipuated? Exampes are: ifting and carrying of heavy objects in transportation jobs, construction sites, etc., Manipuation of heavy oads: Transportation job at construction sites

22 16 transferring persons in heath professions, in od-age care and hospita care Why are heavy oads harmfu? Hoding and moving of heavy oads requires high muscuar force; this may ead to acute overoad and/or fatigue of musces. Exampes: Repeated manipuation of heavy bricks in construction work, oading of coffee sacks, cement bags or other oads in ships, containers or orries. During hoding and moving of heavy oads, high forces occur in the skeeta system, too. Risk of acute overoading and The risk for muscuoskeeta disorders depends on the reation between the oad-weight and the functiona capacity of the working person damage may resut. Loadings being incurred over a ong period of time may cause or promote degenerative disorders, especiay in the ow-back area (e.g. when handing oads with a bent back). For the individua risk of manua materias-handing activities, the functiona capacity of the working person pays an important roe How can heavy oads be handed with ow risk for harm? The most important factors concerning the risk are the weight of the object to be manipuated, the horizonta distance between the oad and the body and the duration and repetition frequency of task execution. This eads to some important measures for handing objects.

23 Advice to the empoyee: Lift oads cose to the body. 17 Lift with both hands, symmetricay to the mid-sagitta pane, bring the oad as cose as possibe to the body. Lift heavy oads with an upright trunk by extending the initiay fexed egs and avoid manipuation of oads in unfavourabe postures (e.g. atera bending or twisting). Use cranes, ifters, doies, hoists, paet jacks, mobie eevators, or simiar devices, if avaiabe, for ifting and transporting heavy oads. Carry heavy and/or unwiedy oads with two persons. Advice to the empoyer: Avoid manua handing tasks, especiay of heavy oads. If manua handing is sti necessary, introduce ergonomic measures to minimize the resuting risk. Avoid moving oads over obstaces. Avoid carrying over uneven or sippery routes, over steps or stairs. Avoid high or frequent handing procedures. Avoid arge masses (e.g. instead of one heavy sack use two sacks of smaer weight). Provide aids (hoists, or simiar devices). Mark heavy oads. Mark non-symmetrica oad distribution within the object. Mark containers or barres with movabe content (fuids, granues, etc). Suggest and carry out training on handing.

24 Risk factor: Work with high force exertion Where is high force exertion found? Exampes are: pushing or puing of heavy objects puing of troeys and other means of transportation positioning of packages in a transportation vehice manipuation of scaffod parts transfer of patients. High force exertion: Pushing of heavy objects Why is high force exertion harmfu? The exertion of force requires high musce forces. This may ead to an acute overoading and/or fatigue of musces. During such work high forces aso occur in the skeeta system. This may ead to an acute overoading and injury of the skeeta structures. Force exertion, where the force acts distanty from the body, bears a high risk of damage to the umbar spine tissues. For tasks with ong-asting or frequenty repeated high force exertion, there is risk of degenerative diseases especiay of the umbar spine. This is true, in particuar, if force exertion is carried out in unfavourabe body postures How can high force exertion be avoided? Advice to the empoyee: Carry out pushing and puing in such a way that the force acts cose to the body.

25 19 Avoid pushing or puing with ony one hand. Avoid pushing or puing with strong atera bending and/or twisted trunk. Advice to the empoyer: Provide conditions for secure standing. Provide wheeed vehices, troeys, doies, or simiar devices. Avoid pushing or puing in confined rooms because of constrained postures. Avoid obstaces and uneven ground. 2.3 Risk factor: Working in unfavourabe body postures Where do unfavourabe postures occur? Exampes are: work overhead work in constrained positions work in confined rooms work in extremey bent, twisted or extended postures work in a continuousy incined posture (e.g. construction work, concrete reinforcement work) work out of reach work in a kneeing, ying, crouching or squatting position Why are unfavourabe postures harmfu? The keeping up of a certain body posture demands high musce force; acute overoad and/or fatigue of musces can, therefore, be the resut.

26 20 Exampes are: Construction work far from the body demands high activation of muscuature for hoding the arms Twisted or extended body postures demand high muscuar strain and tension of trunk musces. During unfavourabe body postures, high forces occur aso in the skeeta system. This may ead to acute overoading and damage of skeeta structures. For ong-asting activities with an incined trunk, degenerative disorders, especiay in the umbar region, can arise if such work is executed over a period of many years. Body posture: Avoid unfavourabe postures Maintaining unfavourabe body postures for ong periods of time is connected with ong-term activation of certain musces which may ead to muscuar fatigue and considerabe reduction in bood circuation. Such partia decrease in the functiona abiity of the muscuature eads to a reduced abiity to react on sudden impacts and may therefore resut in increased accident risk How can unfavourabe postures be avoided? Advice to the empoyee: Bring body cose to the position where the object must be handed, or where force appication is performed. Avoid strong atera bending or twisting of the trunk. Approach the working area and body cose enough to enabe carrying out the task within reach; use aids such as scaffods and adders, if suitabe.

27 21 Change posture often to activate different musces aternatey whie carrying out tasks; consider aternating between standing and sitting postures. Use of adjustabe equipment: Patform Use of adjustabe tabe Advice to the empoyer: Offer adjustabe equipment: chairs, tabes, scaffods, etc. Suppy rooms of sufficient size to avoid constrained postures. Arrange toos within reach. Set time-imits when constrained postures are unavoidabe and/or aternate tasks of different nature. Avoid giving tasks that require a kneeing, ying, crouching, or squatting position.

28 Risk factor: Monotonous repetitive tasks Where do monotonous repetitive tasks occur? Execution of simiar or identica movements during a arge part of the working time with a high rate of repetition (i.e. severa times per minute). During the course of work the working person has often itte infuence on the working pace, speed, task sequence and work and break schedue. Commony, the working person cannot abandon the workpace without being repaced by another person. Exampes are: assemby ine cash registration oading of packing machines. Monotonous repetitive task: Assemby ine Why are monotonous repetitive tasks harmfu? Long-asting repetitive musce oad eads to musce fatigue, which - if sufficient recovery is not guaranteed - may ead to irreversibe changes in the muscuar structure. Not ony high-eve forces but aso ow-eve forces may cause such an effect. Repetitive movements are often superimposed with static oading, in particuar postura oad How can monotonous repetitive tasks be avoided? Advice to the empoyee: Avoid continuous oading of the same musces for onger periods of time. Strive for changes in motion in order to avoid identica muscuar activation patterns. For strongy monotonous work, changes in the execution of movements may be imited.

29 23 Change body posture frequenty in order to reduce static oading. Use rest pauses. Advice to the empoyer: Provide for organizationa changes, such as job rotation, job diversification or job enrichment, to reduce the extent of task repetition for individuas. Enabe autonomous decisions about the timing of breaks. Mechanize unavoidabe monotonous tasks with high oad. 2.5 Risk factor: Long-asting oadings Where do ong-asting oadings occur? Exampes are: maintaining a static posture (e.g. during brickaying at foor eve; concrete reinforcement work; picking of fruits and vegetabes at foor eve; writing; typing; work with computer mouse). Long-asting oading: Picking up vegetabes at foor eve hoding of objects or toos (e.g. driing in a ceiing; overhead painting; hoding of operation instruments in surgery, carrying a tray uninterruptedy). Long-asting oading: Hawker s tray

30 Why are ong-asting oadings harmfu? Long-asting musce oad eads to musce fatigue. Fatigue without sufficient recovery can ead to irreversibe changes in the muscuar structure. Even the exertion of ow-eve forces (for exampe, ongasting fixed posture) can ead to over-exertion and fatigue of sma musces or musce groups. Long-asting contraction of musces may resut in insufficient bood circuation. In the skeeta system ong-asting oading (e.g. due to ong-asting work in an incined posture) can ead to deficient nutrition of the spina discs How can ong-asting oading be avoided? Advice to the empoyee: Move instead of hoding a static position. Use toos for hoding objects. Strive for frequent change in body position. Strive for frequent upright positions from incined positions. Stand up from time to time when working in a sitting position, for exampe, whie making a teephone ca. Advice to the empoyer: Provide toos for hoding (e.g. screw-camps; handes, which enabe hoding with ow musce force). Provide scaffods, adders, or simiar devices. Suppy arm supports at computer workpaces. Suppy handes or grips which can be used with right as we as eft hand. Pace handes/grips to enabe use in a neutra position of wrist and arm.

31 Risk factor: Physica environmenta conditions Where is the risk on account of physica environmenta conditions? Vibration: Hand-arm vibration encountered through hand-hed toos may ead to degenerative disorders or to bood circuation probems in the hand (especiay the fingers - white finger syndrome). Whoe-body vibration in vehices may ead to degenerative disorders, in particuar, of the umbar and thoracic spine. Cimate: High temperatures during the manipuation of heavy oads may ead to bood pressure probems and to an increase in body temperature. At ow temperatures, a decrease in dexterity may occur. Lighting: Insufficient ighting or dazzing may induce constraint postures. Furthermore, it may increase the danger of stumbing or faing. Sips and fas: Physica environmenta conditions: Lighting Unsuitabe, uneven, unsteady or sippery working surfaces and foors can cause tense, strenuous working postures and movements, in particuar, in tasks entaiing the handing of oads.

32 How can the risk of physica environmenta conditions be reduced? Vibration: The effect of hand-arm vibration can be reduced by using toos with ow vibration, reducing the time of usage of vibrating equipment, wearing goves and avoiding coinciding infuence of ow temperatures. The effect of whoe-body vibration can be reduced by using vibration-absorbing seats and reducing the time during which vibration is appied to the body. Cimate: Wearing of appropriate garments, reguar change of stay in rooms with high and ow temperatures, imited stay in rooms with high or ow temperature. Lighting: Physica environmenta conditions: Cimate Suppying sufficient and undazzing ighting equipment. Sips and fas: Avoid unsuitabe, uneven, unsteady or sippery working surfaces, foors and transportation routes whenever it is possibe.

33 27 Appendix Basic rues for preventive actions in practice A risk for disorders of the muscuoskeeta system appears if the oad and the functiona capacity of the worker are not in baance. With regard to maintenance and promotion of heath, the foowing points have to be considered: There is a need for a weighed baance between physica activity and recovery. Movement shoud be preferred to static hoding. The aim shoud be a combination of active periods with higher oad and periods of reaxation. Overoad shoud be avoided. Effective measures for preventing overoad are reducing the required forces and repetitions. Manua handing shoud be avoided. If avoidance is not competey possibe, it shoud be restricted by appying ergonomic and organizationa measures; the empoyees shoud be educated and trained so that they can hep to minimize the overa risks. Too ow oad shoud be avoided. An appropriate oad for the organs of ocomotion is essentia in order to keep up their functiona abiity. The individua favourabe oad can vary from person to person depending on functiona abiities and individua resources. The primary aim of ergonomics is the adaptation of working conditions to the capacity of the worker. High human capabiities of the empoyees shoud not be misused as a pretence for maintaining poory designed conditions of work or work environment. Thus it is important to take into account infuencing factors such as age, gender, the eve of training, and the state of knowedge in an occupation. The working conditions shoud be

34 28 arranged in such a way that there is no risk from physica oad for anyone at the workpace. Fundamenta points infuencing the physica oad functions of an empoyee at worksite are: requirements of work with respect to body positions and postures of the empoyee design of working area configuration of body supports ight and visua requirements arrangement of contros and dispays movement sequences of operations design of work-rest regimen type of energetic oads with respect to force, repetition and duration of work magnitude of menta oads by increasing the atitude and contro of work or job enrichment. A secondary way is to deveop the capacity of the humans to the work by training and vocationa adjustment. The possibiity of deveopment of human abiities whie executing work shoud not be the pretence for keeping a poory designed condition of work or the work environment. The seection of workers according to individua capacity shoud be imited to exceptiona situations. Successfu prevention of work-reated heath risks requires a schedued and stepwise procedure: anaysis of the working conditions assessment of the professiona risk factors consideration/provision of measures for diminishing the risk factors by ergonomic design of the workpace (prevention in the fied of working conditions)

35 29 introduction of measures for the diminution of the risk factors by infuencing the behaviour of empoyees (prevention in the fied of behaviour) coordination of the prevention measures with a subjects invoved discussion of aternative prevention approaches specific and schedued appication of the prevention approaches contro and assessment of the resuts. Summary Disorders of the muscuoskeeta system are a major cause of absence from work and ead, therefore, to considerabe cost for the pubic heath system. Heath probems arise if the mechanica workoad is higher than the oad-bearing capacity of the components of the muscuoskeeta system (bones, tendons, igaments, musces, etc). Apart from the mechanicay-induced strain affecting the ocomotor organs directy, psychosocia factors such as time-pressure, ow-job decision atitude or insufficient socia support can augment the infuence of mechanica strain or may induce muscuoskeeta disorders by increasing musce tension and affecting motor coordination. A reduction of the mechanica oading on the muscuoskeeta system during the performance of occupationa work is an important measure for the prevention of muscuoskeeta disorders. The main risk factors are high forces resuting from ifting and pushing or puing heavy objects, high repetition frequency or ong duration of force execution, unfavourabe posture, static musce forces or working on or with vibrating machines. Effective measures for the reduction of forces acting within or on the skeeta and muscuar structures incude adopting favourabe postures, reducing oad weight, imiting exposure time and reducing the number of repetitions.

36 30 Concusion Prevention of muscuoskeeta disorders can be achieved by engineering contros and appropriate organizationa arrangements. The first-mentioned aspect invoves the whoe working environment and deas with the ergonomic design of toos, workpaces and equipment. The atter concentrates upon factors such as training, instruction and work schedue. The primary aim of ergonomic work design is the adaptation of the working conditions to the capacity of the worker. It is suppemented by a secondary way, which is based on the deveopment of the persons capacity to the working requirements by training and vocationa adjustment.

37 31 Further Reading and References Bundesanstat für Arbeitsschutz und Arbeitsmedizin (ed.) (1996) Probems and Progress in Assessing Physica Load and Muscuoskeeta Disorders. Wirtschaftsverag NW, Bremerhaven (Germany). Caffier, G., Steinberg, U., Liebers, F. (1999) Praxisorientiertes Methodeninventar zur Beastungs- und Beanspruchungsbeurteiung im Zusammenhang mit arbeitsbedingten Muske- Skeett-Erkrankungen. Wirtschaftsverag NW, Bremerhaven (Germany). Chaffin, D.B., Andersson, G.B.J., Martin, B.J. (1999) Occupationa Biomechanics. John Wiey and Sons, New York (3 rd ed.). Gordon, St.L., Bair, S.J., Fine, L.J. (1994) Repetitive Motion Disorders of the Upper Extremity. American Academy of Orthopaedic Surgeons, Rosemont, IL. Hagberg, M., Siverstein, B., Wes, R., Smith, M.J., Hendrick, H.W., Carayon, P., Péruse, M. (1995) Work Reated Muscuoskeeta Disorders (WMSDs) Tayor and Francis, London (UK). Jäger, M. (2001) Beastung und Beastbarkeit der Lendenwirbesäue im Berufsatag. VDI-Verag, Düssedorf (Germany). Jäger, M., Luttmann, A. (1989) Biomechanica anaysis and assessment of umbar stress during oad ifting using a dynamic 19-segment biomechanica human mode. Ergonomics 32, Kumar, S. (ed.) (1999) Biomechanics in Ergonomics. Tayor and Francis, London (UK). Marras, W.S., Sommerich, C.M. (1991) A three-dimensiona motion mode of oads on the umbar spine. - I. Mode structure. Human Factors 33, McGi, S.M., Norman, R.W. (1985) Dynamicay and staticay determined ow back moments during ifting. J. Biomechanics 18,

38 32 Mita, A., Nicosen, A.S., Ayoub, M.M. (1997) A Guide to Manua Materias Handing. Tayor and Francis, London (UK). Mita A., Kibom, Å., Kumar, S. (2000) Ergonomics Guideines and Probems Soving. Esevier Amsterdam (NL). Nationa Research Counci (1998) Work-reated Muscuoskeeta Disorders. Nationa Academy Press, Washington D.C. NIOSH, Nationa Institute for Occupationa Safety and Heath (1981) Work Practices Guide for Manua Lifting, No Dept. Heath and Human Services, Cincinnati, OH. Seide, H., Büthner, R., Hinz, B., Schust, M. (1997) Stresses in the Lumbar Spine due to Whoe-body Vibration Containing Shocks. Bundesanstat für Arbeitsschutz und Arbeitsmedizin (ed.). Wirtschaftsverag NW, Bremerhaven (Germany). Suiter, J.K., Rest, K.M. Frings-Dresen, M.H.W. (2000) Criteria Document for Evauation of the Work-Reatedness of Upper Extremity Muscuoskeeta Disorders. Corone Institute for Occupationa and Environmenta Heath, Amsterdam (NL). Swedish Nationa Board of Occupationa Safety and Heath (1998) Ergonomics for the Prevention of Muscuoskeeta Disorders. Statute Book AFS 1998:1. Waters, Th.R., Putz-Anderson, V., Garg, A. (1994) Appication Manua for the Revised NIOSH Lifting Equation. Dept. Heath and Human Services, Cincinnati, OH.