An electromyographic study of strength and upper extremity muscle activity in simulated meat cutting tasks.

Meat cutting has long been associated with a high incidence rate of upper extremity musculoskeletal disorders. This study examined upper extremity muscle activities and force exertion capabilities to identify postures which have potential for causing overexertion injuries. Fifteen subjects exerted force against a handle in postures similar to those observed in the meatpacking industry. Exertion level, direction of exertion, handle height, reach distance and grip type were varied. Activity in the posterior deltoid, biceps brachii, triceps brachii, extensor digitorum and flexor digitorum superficialis was monitored via surface electromyography (EMG). The ratio of normalized EMG activity to force produced during the exertion was computed for each muscle under each condition. The results showed that handle position had a significant effect on force exertion capability and the EMG/force ratio in all muscles. Force exertion capability was maximized, and the EMG/force ratio was generally minimized when participants pulled downward on a handle positioned at full arm's reach above the shoulder. For vertical cuts, force decreased and muscle activity generally increased as the handle height was lowered. For horizontal cuts, the full reach distance tended to allow greater force exertion with lower EMG/force ratios. The stab grip also tended to be associated with higher forces and lower EMG/force ratios than the slice grip. This study supports the premise that musculoskeletal stresses in meatpacking tasks can be altered through tool and workstation redesign. The data provided herein may be useful in selecting design modifications that reduce biomechanical stress on the upper extremities.

Work activities and musculoskeletal complaints among preschool workers.

The potential for musculoskeletal trauma among preschool workers has been largely unexplored in the United States. This case report describes an investigation conducted to identify and evaluate possible causes of back and lower extremity pain among 22 workers at a Montessori day care facility. Investigators met with and distributed a questionnaire to school employees, and made measurements of workstation and furniture dimensions. Investigators also recorded the normal work activities of school employees on videotape, and performed a work sampling study to estimate the percentage of time employees spend performing various tasks and in certain postures. Questionnaire results from 18 employees indicated that back pain/discomfort was a common musculoskeletal complaint, reported by 61% of respondents. Neck/shoulder pain, lower extremity pain and hand/wrist pain were reported by 33, 33 and 11% of respondents, respectively. Observation and analysis of work activities indicated that employees spend significant periods of time kneeling, sitting on the floor, squatting, or bending at the waist. Furthermore, staff members who work with smaller children (i.e. six weeks to 18 months of age) performed more lifts and assumed more awkward lower extremity postures than employees who work with older children (3-4 years of age). Analysis of two lifting tasks using the revised NIOSH lifting equation indicated that employees who handle small children may be at increased risk of lifting-related low back pain. Investigators concluded that day care employees at this facility are at increased risk of low back pain and lower extremity (i.e. knee) injury due to work activities that require awkward or heavy lifts, and static working postures. Recommendations for reducing or eliminating these risks by modifying the workplace and changing the organization and methods of work are presented.

An analysis of scanning postures among grocery cashiers and its relationship to checkstand design.

Mounting evidence suggests that musculoskeletal disorders are prevalent among US retail food workers. Cashiers who use electronic scanners appear to be at especially high risk for upper extremity musculoskeletal disorders. Checkstand design has been implicated as a contributor to musculoskeletal injury among cashiers because workstation design can significantly impact working posture. The present study examines working posture among two groups of cashiers to determine if checkstand design is associated with substantial differences in posture and movement during scanning. The work activities of twenty grocery cashiers using one of two checkstand designs (front-facing and right-hand takeaway) were examined. Videotapes of cashiers performing scanning tasks were observed and associated postures and movements were visually coded. The right-hand takeaway design was associated with a significantly higher percentage of non-neutral trunk postures than the front-facing design. However, there were no significant differences in shoulder posture, grasp, or scanning motion associated with checkstand/scanner design. Factors that appeared to affect cashier work posture during scanning included stature, order size, and product type. Although improving the checkstand design may reduce the occurrence of certain awkward postures and static muscle loading conditions among cashiers, the success of these interventions is likely to be limited unless follow-up programmes are instituted to ensure that cashiers are able to use these designs effectively. Furthermore, fundamental changes in cashier work may be required to fully eliminate hazards for musculoskeletal disorders from this job.

An ergonomics evaluation of cashier work activities at checker-unload workstations.

The ergonomic suitability of the 'over-the-counter' (OTC) or 'checker unload' workstation for grocery-scanning operations has been questioned by a number of ergonomists, safety and health professionals, and retail food industry executives in the USA. There is concern that requiring cashiers to remove grocery items directly from the customer's cart for scanning exacerbates the risk of musculoskeletal disorders associated with this job. For this reason, a study was conducted to determine whether supermarket cashiers are exposed to increased biomechanical stress due to the use of checker-unload workstations for standing work. The work activities of 12 grocery cashiers from three supermarkets were recorded on videotape. Postures and movements associated with the scanning task were visually evaluated and compared with those of 10 grocery cashiers using a front-facing, customer-unload workstation examined in a previous study. The results indicate that use of the checker-unload workstation places additional stresses on the cashier beyond those imposed by customer-unload checkstands. Specifically, the task of removing groceries directly from the cart for scanning increases the frequency of long reaches, awkward shoulder postures, and lifts. These stresses can be mitigated by eliminating checker-unload operations and providing checkstands with conveyor belts for delivering groceries to the cashier. Implementing additional workstation modifications and encouraging cashiers to adopt alternative work practices also may reduce the frequencies of awkward postures and stressful motions associated with this checkstand design.

Evaluation of occupational knee-joint stress using liquid crystal thermography: a case study.

This paper describes a method to detect knee stress using liquid crystal thermography and presents the results of a case study in which the system was applied to two carpet installers. The method involves placing heat-sensitive sheets of film on the knees of workers at various intervals during the work day. The thermographic sheets react to variations in heat by changing colour. The measurements are taken with the worker's knee positioned in an illuminated, enclosed box. Once the patch stabilizes, the exhibited colours are recorded with an 8 mm video camera. The colour pattern, ranging from brown to blue, provides a thermal record of what is believed to be knee stress resulting from installing carpet. The thermographic records are stored in computer memory for subsequent analysis using an AT&T TARGA 16 video board. Custom software allows computation of the area of each distinct colour pattern as a percentage of total patch size. These records provide a characterization of knee response (inflammation) resulting from the biomechanical load sustained by the knee during the carpet installation task.

Carpal tunnel area as a risk factor for carpal tunnel syndrome.

Carpal tunnel area was investigated as a risk factor for carpal tunnel syndrome (CTS). It was hypothesized that if canal area is a risk factor for the syndrome, individuals who develop the syndrome should have smaller carpal canal areas than those who remain free of the syndrome. Sixty-one subjects, approximately equally divided by sex, age group, and diagnosis, were examined. A measurement of cross-sectional areas of the carpal canal by computerized axial tomography indicated that individuals diagnosed as carpal tunnel patients had significantly larger carpal canal areas than controls. The results indicate that a small carpal canal area does not appear to be a risk factor for carpal tunnel syndrome.

Use of EMG in a kinesiological study in industry.

The study was conducted in an automobile upholstery plant which manufactures interior trim panels and seat covers. The job was one which required workers to lean repetitively across a 965 mm (38 in) high flat table-like die while securing sheets of material to the die. Two employees in the embossing department volunteered to participate in a comparative evaluation of the accumulation of low back fatigue from working for a full day using a die with a 914 mm (35 in) maximum reach requirement versus that of a die with a 813 mm (32 in) maximum reach requirement. Electromyography (EMG) of the low back muscles was the measure used for the evaluation. EMG recordings from static muscular contractions were made at selected intervals for an 8 h work day while maintaining normal production. Integrated EMG amplitude and power frequency shifts formed the bases for comparison. The integrated EMG amplitude increase over the course of the day was 47% and 100%, respectively, for the two subjects while working with the 813 mm (32 in) die; the respective EMG amplitude increases for the day while working with the 914 mm (36 in) die were 83% and 263%. None of the power frequency shifts exceeded a predetermined minimum level considered necessary to indicate fatigue. As a result of this study, the plant reduced as much as possible the maximum reach required on every die in the embossing department in order to reduce worker fatigue.