Daniel J. Habes

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 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 arms 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.

An electromyographic study of maximum torques and upper extremity muscle activity in simulated screwdriving tasks

The effects of workstation and tool handle design on strength and upper extremity muscle activity during a simulated manual screwdriving task were examined. Fifteen male participants performed maximal (100%) and submaximal (75% and 50%) exertions with a screwdriver using postures frequently observed in industry. Investigators varied handle height, reach distance, handle diameter, and handle orientation during the experiment. The activity of the anterior deltoid, triceps brachii, biceps, extensor digitorum, flexor digitorum superficialis and flexor pollicis longus was monitored using surface electromyography (EMG). The ratio of normalized EMG activity to torque produced during the exertion was computed for each muscle under each condition. The results indicated that increased torque capability was associated with the use of a larger (3.7 cm), vertically oriented handle. EMG/torque ratio generally increased as handle height was increased, reach distance and handle diameter were reduced, and the handle orientation was changed from vertical to horizontal. This study supports the premise that workstations and tools can be configured to maximize worker capabilities while minimizing the potential for muscle strain and fatigue. These data may be useful to job analysts for assessing the relative demands of construction and assembly work. Relevance to industry These data can be used by job analysts to grade the level of muscle activity required by screwdriving tasks (relative to similar exertions in different postures), and to justify workstation changes to reduce muscular stress on the upper extremities.

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.

Ergonomic Evaluation of Checkstand Designs in the Retail Food Industry: A Report Based on Expert Assessment

Abstract Increasing evidence suggests that musculoskeletal disorders are common in the U.S. retail food industry. Cashiers who use electronic scanners appear to be at especially high risk for upper extremity cumulative trauma disorders (CTDs). One potential source of biomechanical stress is the checkstand design. Checkstand design can greatly influence the cashiers posture and movement patterns during grocery checking tasks. It is hypothesized that designs which expose cashiers to stressful postures and unnatural movements may be associated with increased musculoskeletal complaints. The National Institute for Occupational Safety and Health (NIOSH) is conducting an industrywide study to evaluate the prevalence and possible causes of musculoskeletal disorders among retail food workers. An objective of this research is to evaluate the relationship between CTDs and different checkstand designs. This article describes initial activities to identify ergonomic stressors associated with five common checkstand ty...

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.

Ergonomics: Lifting Hazards at a Cabinet Manufacturing Company: Evaluation and Recommended Controls

Abstract Abstract: Hazardous conditions due to manual material handling activities at loading docks have long been observed. An attempt to evaluate the magnitude of lifting hazards in the shipping department of a wooden cabinet manufacturing company is described. Occupational Safety and Health Administration (OSHA) 200 logs were reviewed, employees were interviewed, and a symptoms survey was administered to all shipping department employees to assess the magnitude of the musculoskeletal problems. Material handling activities in the loading dock and staging areas were observed and videotaped, and measurements of box sizes, lifting heights, and cabinet weights were obtained. Representative lifts were analyzed using the Revised National Institute for Occupational Safety and Health (NIOSH) Lifting Equation. The records review and symptom survey revealed that 26 percent of the shipping department employees experienced an OSHA-recordable musculoskeletal disorder in the first eight months of 1995 and 79 percent ...

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 workers 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.

Electromyographic patterns associated with a carpet installation task

Abstract Previous studies have indicated that the knee joint is subject to impact forces greater than 3000 newtons when workers use a knee-kicker to install carpet. Such forces may be modified, however, by the action of large muscle groups in the legs and upper body. To evaluate the role of these key muscle groups, electromyographic (EMG) data were collected from the rectus femoris, long head of the biceps femoris, anterior deltoid, and extensor carpi radialis muscles of eight male subjects. Each subject simulated the four static body postures most commonly used during carpet installation. These were (a) on hands and knees, (b) beginning kick cycle, (c) mid-kick cycle and (d) impact kick cycle. To assess the dynamic component of the task, each subject performed the act of carpet stretching using a knee-kicker. For both static and dynamic activities, the anterior deltoid showed the highest normalized EMG values. It was also found that immediately before the impact phase the knee flexor muscles contracted, ...