JAMES M MEYERS , Univ. of California, Berkeley

JOHN A MILES, Univ. of California, Davis

JULIA FAUCETT, Univ. of California San Francisco

IRA JANOWITZ, Univ. of California San Francisco

DIANA G TEJEDA, Univ. of California, Davis

EDWARD WEBER, Univ. of California Cooperative Extension, Napa

RHONDA SMITH, Univ. of California Cooperative Extension, Sonoma

LINDA GARCIA, Univ. of California Cooperative Extension, Sonoma

Work-related musculoskeletal disorders are rising in incidence and account for a majority of workers' compensation dollars. They are increasing in incidence and concern in California, which has just implemented the first occupational health standard for ergonomics in the U.S.

Review of California worker's compensation system reports suggests that 43% of all reported injuries in California agriculture were sprains and strains. Overexertion as a cause of injury for this area was cited for 25% of reported injuries. These data suggest a high proportion of musculoskeletal disorder incidence and ergonomic risk factors.

With support of a NIOSH Community Partners grant, the authors reviewed data from three cooperating vineyard companies in Napa and Sonoma Counties finding both high rates of evidence of MSDs and identifying priority MSD hazards. Data from OSHA 200 injury report logs identified 29 reported MSDs and 435 lost work days in a working population of 194 in a 30 month period. The majority of these (20) involved backstrain.

High risk job tasks were identified including: employer-identified tasks, analysis of injury reports, and ergonomics risk factor checklist survey of task work. Triangulating across these three data groups resulted in identification of high priority tasks including: hand harvest work, hand pruning, and weeding using shovels.

This work was supported by NIOSH Agreement PHS-CCU912911-01.

MUSCULOSKELETAL DISORDERS

Occupational musculoskeletal disorders (MSDs) may affect muscles, tendons, joints, nerves and related soft tissues anywhere in the body. The lower back and upper extremities, including the neck and shoulders, are the most common sites. Because repeated risk factor exposure of the same muscle, tendon, or region may result in injury and inflammation to the affected area, names such as cumulative trauma disorder, repetitive motion injury, repetition strain injury, and occupational overuse syndrome have been applied to these disorders.

Work-related musculoskeletal disorders (MSDs) are rising in incidence and account for a majority of workers' compensation costs (Guo et al., 1995). They are increasing in incidence in California, which has consistently experienced injury rates higher than the national average in all industries (Robinson, 1988). Of greatest concern are back injuries which are the most frequently cited cause of disability in persons aged 45 or less (Andersson, 1981), account for most lost time from work (Clemmer et al., 1991), and account for a significant proportion of workers' compensation costs (Nagi et al., 1973; Spengler et al., 1986; Robinson, 1988, Webster and Snook, 1990; Glisan, 1993).

Concern is also growing about cumulative injuries to upper extremity nerves and soft tissues resulting from repetitive motions. The number of work-related cases of cumulative trauma disorders (CTDs) have significantly increased in the past several years and in 1989 accounted for more than half of all work-related illness cases. According to the 1993 National Ambulatory Medical Care Survey (CDC, 1998) more than 60% of all injury visits were to orthopedists, with "sprains and strains of joints and adjacent muscles" comprising the most frequent diagnosis category for all ages except for persons under 15 years old. Despite surveillance gaps MSD cases appear to be increasing faster than any other occupational illness category (BNA, 1991). In California, "cumulative injuries" claims comprise a share that is twice the size of any other specific injury category (California Department of Insurance et al., 1993).

ERGONOMIC RISK FACTORS

ERGONOMIC RISK FACTORS IN AGRICULTURE

Studies of agricultural safety and health (Murphy, 1992) document that agricultural work involves those risk factors associated with musculoskeletal disorders. Despite ongoing changes in the scale of farming operations and types of machinery involved, very little change has occurred in tasks performed by most farm workers, or with those tasks most likely to generate back injuries or MSDs. Field jobs (harvesting, weeding, irrigating, cultural practices, etc.) remain demanding physical tasks, involving stooped postures, lifting and carrying, and repetitive hand work. Meyers, et al (1996) suggested these three priority risk ergonomic factors as of general concern in California agricultural work. Research has shown that many important risk factors can be successfully addressed in agricultural work using ergonomic approaches (Lundqvist, 1992; Lundqvist et al., 1992; Wick, 1992; Miles and Steinke, 1993, Meyers, et al, 1996, 1997).

Because of increasing MSD incidence and growing concern California OSHA, in July of 1997, implemented the first occupational health standard for ergonomics in the U.S. Additionally, California OSHA has noted comparatively high injury rates in agriculture and designated it a targeted high risk industry.

WINE GRAPE PRODUCTION IN CALIFORNIA

California is home to over half of the wineries in the nation, and grapes rank as the second largest cash crop in California agriculture with a 1994 total value of over $2.3 billion. Wine grapes constitute a significant portion of that total and occupy more than 400,000 acres. The California vineyard industry employs more than 31,000 workers per year.

According to AgSafe (1992) it experienced an average of 9 fatalities and 3654 reported non-fatal disabling injuries per year in the 1981-1990 period. This incidence of fatal injury is among the highest of all agricultural commodities analyzed and was largely attributed to vehicles (38%) and struck by hazards (16%). The rate for non-fatal injuries of about 4.3 per 100 workers, puts vineyard work well above the average reported for other workers in California (3.5 per 100 workers). In the absence of a reliable surveillance system, these data are most likely incomplete.

AgSafe (1992), which studied the largest data base, estimated that 42% of all reported non-fatal disabling injuries in vineyard work were sprains and strains, of which 41% were said to be back injuries. Reported causes emphasized overexertion at about 23% and being stuck by something at about 27%. An analysis of five years of injury data (1985-1990) from California vineyards (Meyers and Steinke, unpublished) reveals a similar pattern. This analysis also suggested that 30% of all reported injuries occurred within an employees first 6 months and 59% occurred in an employee’s first two years.

This project is taking place in northern California, with cooperating winegrape vineyard operations in Napa and Sonoma Counties. While the winegrape industry is expanding rapidly both along the central coast and in San Joaquin Valley, this area remains the state's premier wine production center and it constitutes the largest and most productive premier winegrape area in the state. Many of the state's and the world's largest and best known wine producers are located in this area. Producers in this area account for nearly half of all winegrape acreage in the state. There are over 110 wineries represented in the Napa Valley Vintners Association alone.

RISK FACTOR IDENTIFICATION METHODS

The larger objective of this study is to assess the efficacy of engineering interventions to significantly or reduce targeted ergonomics risk factors and resulting MSDs. A first step in the project’s work is to identify ergonomics risk factors present and any evidence of MSDs. A three-part strategy is employed to accomplish this, as follows: 1) all jobs were defined and described and then screened for ergonomic risk factors using a checksheet method; 2) cooperators injury and first aid records were reviewed; and 3) workers and supervisors were asked to identify job tasks that they find especially difficult or hazardous.

Ergonomic analysis of jobs and tasks was accomplished through employment of a simple worksite screening checklist as described by Keyserling (Keyserling, et al, 1992). An unpublished checksheet we have titled "quickcheck" was used. Three trained ergonomics evaluators used the checklist to evaluate identified job tasks on each of the cooperating worksites. Evaluators practiced with the checklists using videotapes of other agricultural jobs to improve inter-rater reliability with the checklists. As a result of the first checklist survey, the highest scoring job tasks were selected, and submitted to a more detailed checklist modified from validated checklists previously published by Keyserling (Keyserling, et al, 1988) and developed for use in manufacturing.

The assessment of health outcomes related to ergonomic interventions is made difficult by the chronic nature of the injury, taking years to develop. Descriptive data (OSHA log 200's for pre- and post-intervention periods) are reported to illustrate changes in injury rates. However the number of workers who file injury claims is a small fraction of the study population and given the chronic nature of injury development further information was sought. A review of employer’s separate first aid records (i.e., those not referred to medical care and returning to work) was added to the review. These records were analyzed by Dr. Faucett of UCSF for symptoms of probable MSDs.

As a third method, workers and field supervisors were interviewed by Spanish-speaking project staff and asked to identify specific tasks that they found to be especially difficult to perform or found to be particularly hazardous with respect to potential for injury.

RESULTS

Dr. Faucett found significant evidence of MSDs in reviewing cooperators health records. She reviewed records for 3 cooperators representing 194 permanent workers. Records were available for 2 1/2 years for two vineyards and for 1 1/2 years for one. As Table 1 below shows, 29 MSDs were defined for 28 employees. These MSDs represented 435 lost workdays. This suggests an incidence rate of 149.5 per 1000 workers. As the breakdown below shows, back injuries predominate and lifting during harvest and tractor/equipment predominate reported causes.

TABLE 1

REPORTED MSDs AMONG VINEYARD COOPERATORS

BODY PART # REPORTED CAUSE_________#__

Back 20 Lifting (harvest) 6

Neck/Shoulder 3 Tractor/Equipment 6

Hand/Arm 3 Staking 3

Lower Ext. 3 Pruning 3

Suckering 2

All Other 8____

Ergonomics job screening by Mr. Janowitz and Ms. Tejeda also provided substantial evidence of risk factors in vineyard work. All jobs defined by D. Tejeda in step 1 above were screened using the "quickcheck" checksheet (adapted from ANSI Z-365). Results are displayed in Table 2 and clearly show harvest jobs as demonstrating the most severe ergonomic risk factors.

TABLE 2

ERGONOMIC RISK FACTORS IN VINEYARD JOBS

JOB CHECKLIST SCORE

Harvest 25

Hoeing/Weeding 19

Cutting Heads 17.6

Pruning 17.3

Pre-Pruning 16.6

Staking 15.2

Planting 15

Vine Training 14

Shoot Positioning 11

Leaf Removal 10

Tying 9.4

Fruit Thinning 8

Shoot Thinning 7.5

Suckering 7.5________

Workers’ and field supervisors’ identification of jobs perceived as contributing to MSDs, stressful, or especially tiring are displayed in Table 3 by vineyard.

TABLE 3

WORKER PERCEPTION OF RISKY JOBS

VINEYARD 1 VINEYARD 2 VINEYARD 3

Harvest Shoveling Pruning

Pruning Planting Planting (shoveling)

Irrigation Emitter Installation Harvest Harvest_____

In order to better understand workers’ exposures to these risk factors, we asked supervisors to estimate the numbers of workers performing specific jobs and the duration of the job task in the vineyard. Results are shown on Table 4.

TABLE 4

VINEYARD JOB RISK EXPOSURE

TASK # WORKERS DURATION____

Harvest 90+% 6-8 weeks

Pruning 50-90% 8-10 weeks

Shovel Work 50% Season

Tractor Drivers 18% Season

Staking 10-20% Occasional

Emitter Punch 10-20% Occasional_____

Because our long-term project is interested in selecting a few jobs for intervention, we triangulated across the three primary measures above to identify jobs that appeared and scored high on all three lists. The jobs identified as having the greatest potential risk for MSD incidence were: harvest work, pruning, and weeding with shovels. These jobs were re-observed based on samples of at least 4 different workers performing each for 5-10 minutes each. The following descriptions delineate the most common risk factors for the development of work-related musculoskeletal problems in these selected tasks for intervention planning:

1. Harvest

The worker stands facing the vine, reaches in with the non-dominant hand, grasps a grape cluster, and cuts it free with a curved knife held in the dominant hand. As each cluster is cut, it is dropped towards a plastic bin lying on the ground at the worker's feet. The worker must frequently alter his/her body position to see, reach, cut, and dispose of the grape clusters.

The worker moves along the vine to reach new clusters. When moving, the worker must either stoop to lift and place the bin or push it with a foot to slide it along with a sideways leg movement. Prior to moving the bin, workers stoop to gather up clusters which missed the bin. When the bin is full (approx.80#) the worker stoops to lift it and carries it to the tractor/trailer and dumps the grapes in over a 4 ft. high container lip. Workers often carry bins overhead and do run with bins, so that they are often lowering the bins from overhead or shoulder height positions to dump them in the trailer. Alternatively, workers may lift the bins to the trailer from knuckle height. Workers are paid on a group incentive basis and move as fast as possible.

The harvest job cycle consists of:

TASK TIME (SECONDS)

Cutting 25

Stooping to gather fallen grapes, slide bin to next position 5

Carry to trailer, dump in 10

Walk/run to new cutting area 3-7

Total job cycle 43-47

When cutting, the dominant hand is engaged in very repetitive gripping, and averages some 25-50 cuts per minute depending on grape variety and yield density. There is impact imparted to the hand as the vine gives way at the end of each cut.

When moving the bin there is mild to moderate twisting of the trunk and either a full body stoop to reach the bin with the hands followed by a heavy lift & toss motion, or a heavy lateral force exerted by the leg to move the bin.

High force is required when lifting and carrying the 80 lb. bin when it is full. The loaded bin is accelerated rapidly to carry it and to empty it in the trailer.

Awkward postures in the harvest task include moderate shoulder flexion (up to 80 degrees) and mild shoulder abduction (up to 30 degrees); frequently severe forearm pronation (up to 90 degrees) and occasionally severe forearm supination (up to 90 degrees); moderate-to-severe ulnar deviation (up to 30 degrees)and virtually no radial deviation of the wrist. Trunk flexion ranges from mild during cutting (20-45 degrees) to severe during stooping to gather fallen grapes, (up to 90 degrees sustained for about 5 secs). Neck flexion is occasionally severe (up to 45 degrees), but often the neck is in extension of more than 5 degrees. This is related to the visual demands of the task, needing to see through foliage to make a safe and appropriate cut. Workers were often observed to be in a forward head position of trunk flexion with simultaneous neck extension. Depending on the height of the vine, some harvesting may be performed in a squatting, crouching, or kneeling position.

Additional risk factors include:

Constant ulnar deviation of dominant hand;

Very high energy cost;

Pressure on hand from poorly-designed knife handle;

Cuts on non-dominant hand from knife; and

Long carries with bins held overhead for some work methods.

2. Pruning

The worker stands facing the vine, reaches in with the dominant hand gripping shears, and cuts vine to be pruned. the non-dominant hand may be used to stabilize branch to be pruned and may sweep cut branches into the space between vines. The worker must constantly alter body position with respect to the vine in order to reach appropriate branches. Shears must be oriented with cutting blade against the cordon in order to avoid splintering. This means that the cutting hand must be frequently realigned to match branch growth angle. Grip force on the shears is estimated at 30#. Workers make between 36 and 46 cuts per minute.

Because the cutting activity is virtually constant, no clear work cycle can be seen other than completion of a vine section. The job cycle may be described as:

TASK TIME (SECONDS)

Pruning one vine 60

Subcycle (each cut with shears) 1.4-1.5 secs/cut

The cutting shoulder demonstrates moderate to severe flexion (up to 130 degrees) and mild to severe abduction (up to 130 degrees). The cutting forearm demonstrates pronation and supination (up to 90 degrees). The cutting wrist demonstrates severe ulnar deviation (up to 50 degrees) and occasional radial deviation (up to 15 degrees). The non-cutting hand is generally held in more neutral position, but often holds cuttings with a pinch grip, which is an awkward posture of the hand, and then removes the cutting from the vine, applying high grip forces to free it from the surrounding wires, branches and foliage.

Trunk flexion is typically sustained in a moderate range (30-75 degrees) for 30-60 secs. while cutting, with brief severe flexion during stooping to gather fallen cuttings (up to 90 degrees); and with moderate to severe neck flexion (up to 45 degrees).

Additional risk factors include:

Impact imparted to the hand as the handles of the pruners close at the end of each cut;

Pressure on the dominant hand from pruner handles; and

Pressure on non-dominant hand from branches being gripped and cut.

3. Shovel Weeding

The worker works along a vine row, reaching towards and under the vines with a shovel to cut weeds away with the front edge of the shovel blade. During the cutting movements, moderate to severe trunk flexion (forward bending of 30-90 degrees); and mild to moderate body twisting (20-30 degrees) were observed

Moderate shoulder and arm forces are applied by swinging the shovel with the arms so that the blade impacts and cuts the root of the weed. High static grip forces are sustained by both hands on the shovel handle for periods of 12-33 seconds during the weeding. Workers typically make 50-60 cutting motions per minute. Mild to moderate wrist extension is present throughout the activity. Shoulder extension is moderate (up to 60 degrees). Neck position is technically close to neutral, but since the trunk is in prolonged flexion of 30-90 degrees, the neck is in a posture that is difficult to maintain for long periods due to muscle fatigue.

Mild grip forces are needed to hold the shovel during the 10-11 seconds of walking to the next area to be weeded.

TASK TIME (SECONDS)

Swinging the shovel to cut 12-33

Walking to next position 10-11

Total Job Cycle 22-44

DISCUSSION

Field measurement of ergonomics risk factors is fraught with difficulties. At minimum, neither workers nor employers want work disrupted. In agricultural settings, job tasks often change quickly and sometimes unpredictably. Finally, in a complex work setting there are any number of complicating or intervening elements or occurrences (e.g. weather, staffing changes)with potential for affecting data collection.

In this instance we have sought to control variability in checksheet job evaluation by using three trained evaluators whose results were averaged for the data reported here. Still, checksheet job screening for ergonomics risk factors is neither as detailed nor as standardizable as would be data from validated instruments such as the NIOSH Lifting Equation (Waters, Putz-Anderson, Garg, 1994), Greenleaf WristSystem or the Lumbar Motion Monitor (Marras, Sudhakar, Lavender, 1989). These and other approaches will be employed in the next phase of this project.

Similarly, estimation of MSDs and MSD symptoms from written reports suffers from inherent imprecision. Where possible, safety coordinators and workers were interviewed about reported injuries or symptoms in question. In the next phase of this study, detailed pain and symptom interviews will be conducted in Spanish with participating workers. Based on our experience in plant nurseries, we do expect this more detailed data to support the findings reported here.

As Slovic (1986) and others have demonstrated, individual estimation of risk involved in any given event is both complex inexact. Still, there was a high degree of agreement between workers and supervisors at each site and across groups at multiple sites about jobs perceived as risky.

The triangulation method employed does add further strength to the summary observations. The fact that three different methods were employed without shared communication about results does much to increase confidence in the identification of high risk jobs and tasks.

Finally, while it must be noted that the rate of MSD incidence reported is only an indicated rate from a small and non-randomly selected sample, the magnitude of the result should do much to

inspire confidence that a measurable effect is occurring.

CONCLUSIONS

These results should generate new concern for the full group of heavy manual labor agricultural field jobs and the contribution that identifiable ergonomics risk factors make to overall reported injury rates. There is substantial evidence here of both MSDs and MSD symptom incidence among winegrape vineyard workers. There is also very strong evidence of significant ergonomics risk factors associated with MSD development in jobs identified and analyzed. While this sample of vineyards was not randomized and is not fully generalizable to the wine grape industry, still a suggested rate of incidence of MSDs of 149.5 per 1000 workers should be taken as an indication of priority need. This is well above the rates targeted by the US Public Health Service in Healthy People 2000 (Healthy People 2000, 1991; objective 10.2) of an incidence of no more than 60 per 100,000 workers. It also more than double the indicated rate observed in our previous work in plant nurseries of 66 per 1000 workers.

These results confirm years of anecdotal evidence that field agricultural jobs are physically demanding and take a physical toll. They also confirm our belief that the large proportion of sprain/strain reported injury types and overexertion reported as injury cause are evidence of relatively high incidence of MSDs.

Moreover, they help explain why we see so few workers performing these jobs beyond age 35. They help explain the apparent age-related migration out of field agricultural work by older workers. They also raise our concern that we will find similar MSD rates in other agricultural field jobs.

Finally, these results confirm our growing belief that a triumvirate of extreme ergonomics risk factors must be given priority in agricultural injury prevention work. Those are: full body stooped posture, highly repetitive hand work; and the manual lifting and carrying of heavy loads.

These risk factors are surmountable with often low cost, non-labor displacing interventions as we have found in prior work in plant nurseries. It is time to take another look at many of the jobs and tasks which are routine in agriculture and which are largely taken for granted as immutable and give ergonomics risk factor reduction new priority.

AgSafe (1992). "Occupational injuries in California agriculture 1981-1990". UCDANR, Oakland.

Andersson, A. (1981). Epidemiologic aspects on low-back pain in industry. Spine 6(1):53-60.

Armstrong, T. J. (1986). Ergonomics and cumulative trauma disorders. Hand Clinics 2(3):553- 565.

Armstrong, T. J., and D. B. Chaffin (1979). Carpal tunnel syndrome and selected personal attributes. J. Occup. Med. 21(7):481-486.

Bureau of National Affairs. (1991) References. Occupational Health and Safety Reporter. 11/18: 2.

California Department of Industrial Relations, Department of Labor Statistics (1992). California Work Injuries and Illnesses-1991.

California Department of Insurance, Research and Special Projects (1993). Lowering Workers' Compensation Insurance Costs by Reducing Injuries and Illnesses at Work.

Centers for Disease Control and Prevention, National Center for Health Statistics. (1998). National Ambulatory Medical Care Survey: 1993 Summary. Vital and Health Statistics. series 13, No. 136. US Department of Health and Human Services.

Clemmer, D., Mohr, D. (1991). "Low-back injuries in heavy industry II: Labor Market Forces." Spine. 16(7): 831.

Erdil, M., O. B. Dickerson, and E. Glackin (1994). Cumulative trauma disorders of the upper extremity. In Occupational Medicine, 3rd ed. C. Zenz, O. B. Dickerson, and E. P. Horvath (eds.), Mosby, St. Louis.

Frederick, L.J. (1992). Cumulative trauma disorders--an overview. AAOHNJ. 40(3):113-116

Frymoyer, J. W. (1988). Back pain and sciatica. N. Eng. J. Med. 318:291.

Garg, A., and J. S. Moore (1992). Prevention strategies and the low back in industry. Occupational Medicine: State of the Art Reviews 7(4):629-640.

Gerr, F., Letz, R., Landrigan, P.J. (1991). Upper-extremity musculoskeletal disorders of occupational origin. Annu Rev Public Health. 12: 543-566.

Glisan, B. (1993). Customized prevention programs play vital role in back protection process. Occup. Health and Safety 62(12):21-26.

Guo, H., S. Tanaka, et al. (1995). Back pain among workers in the United States: National estimates and workers at risk. Am. J. Indus. Med. 28:591-602.

Keyserling, W., et al. (1988) Postural risk factors associated with back pain: Findings of a case- referent study. Applied Industrial Hygiene. 3(3): 89.

Healthy people 2000 : national health promotion and disease prevention objectives. (1991)

Washington, D.C. : U.S. Department of Health and Human Services, Public Health Service.

Kelsey, J. (1982) Epidemiology of musculoskeletal disorders. NY. Oxford University Press

Keyserling, W., Brouwer, M., Silverstein, B. (1992) A checklist for evaluating ergonomic risk factors resulting from awkward postures of the legs, trunk and neck. International Journal of Ergonomics, 9:283-301.

Keyserling, W., et al. (1988) Postural risk factors associated with back pain: Findings of a case- referent study. Applied Industrial Hygiene. 3(3): 89.

Leamon, T. (1994) Research to reality: A critical review of the validity of various criteria for the prevention of occupationally induced low back pain disability. Ergonomics. 37(12): 1959-1974.

Lundqvist, P. (1992) Ergonomics and accident risks in a new type of poultry house. Proceedings of International Ergonomics and Safety Conference, Denver, CO.

Lundqvist, P., Pinzke, S., Gustafsson, B. (1992) Ergonomic factors in the work situation for AI- technicians on animal farms. Proceedings of International Ergonomics and Safety Conference, Denver, CO.

Marras, W., Lavender, S., et al. (1995) Biomechanical risk factors for occupationally related low back disorders. Ergonomics. 38(2): 377-410.

Meyers, J., Bloomberg, L., Faucett, J., Janowitz, I., Miles, J. (1995). Using ergonomics in the prevention of musculoskeletal cumulative trauma injuries in agriculture: learning from the mistakes of others. Journal of Agromedicine, 2 (3): 11-24.

Meyers, J., Miles, J, et al. (1996) Small tools approach to prevention of musculoskeletal injury in nursery work. Proceedings of Nat. Inst. of Farm Safety, June, 1996. Columbia, MO.

Miles, J., Steinke, W. (1993) Identification of repetitive trauma hazards in the orchard and lumbering industry. Unpublished.

Meyers, J., Miles, J., et al. (1997) Plant nursery handtools prevent ergonomic risk factor exposure: a preliminary report. Paper presented at the 1997 meeting of the American Public Health Association, Indianapolis, IN.

Meyers, J., Steinke, W. (1992) Unpublished study of injuries in California agriculture.

Moore, J. (1992) Carpal tunnel syndrome. Occupational Medicine: State of the Art Review. 7(4): 741-763.

Murphy, D.( 1992) Safety and health for production agriculture. St. Joseph. MO. ASAE.

Nagi, Z., Riley, L., Newby, L. (1973) A social epidmiology of back pain in a general population. Journal of Chronic Diseases, 26: 769-779.

Parniapour, M., Nordin, M., et al. (1990) Environmentally induced disorders of the musculoskeletal system. Medical Clinics of North America. 74(2): 347.

Robinson, J. (1988) The rising long-term trend in occupational injury rates. Am. Journal of Public Health. 78(3): 276-281.

Silverstein, B., Fine, L., Armstrong, T. (1987) Occupational factors and carpal tunnel syndrome. Am. Journal of Industrial Medicine. 11: 343-358

Silverstein, B., Fine, L., Armstrong, T. (1986) Hand wrist cumulative trauma disorders in industry. British Journal of Industrial Medicine. 43: 779-784.

Sjoflot, L. (1984) Research programme on ergonomics in agriculture in Norway. Proceedings of the 1984 International conference on Occupational Ergonomics.

Slovic, P, (1986) Informing and educating the public about risk. Risk Analysis 6 (4): 403-415

Snook S., Campanelli, R., Hart, J. (1978). A study of three preventive approaches to low back injury. Journal Occupational Medicine, 20: 478-481.

Sommerick, C.M., McGlothlin, J.D., Marras, W.S. (1993). Occupational risk factors associated with soft tissue disorders of the shoulder: a review of recent investigations in the literature. Ergonomics. 36(6): 697-717.

Spengler, D., Bigos, S, Martin, N, Zeh, J, Fisher, L, Nachemson, A. (1986). Back injuries in industry: A retrospective study - I. Overview and cost analysis. Spine 11(3):241-245.

USDOL, Bureau of Labor Statistics. (1990) Recordkeeping guidelines for occupational injuries and illness in the United States by Industry, 1977-1988. Wash. D.C. Govt. Printing Office.

Vikari-Juntura, E.R.A. (1997) The scientific basis for making guidelines and standards to prevent work-related musculoskeletal disorders. Ergonomics. 1997. 40(10): 1097-1117.

Waters, T., Putz-Anderson, V., Garg, A. (1994) Applications Manual for the Revised NIOSH Lifting Equation. DHHS (NIOSH) Publication No. 94-110.

Webster, B., Snook, S. (1990) The cost of compensible low back pain. Journal of Occupational Medicine, 32(1): 13.

Wick, J. (1992) Ergonomic analysis and evaluation of lemon picking. Proceedings of the International Ergonomics and Safety Conference. Denver, CO.