The importance of work organization on workload and musculoskeletal health - Grocery store work as a model.

We have evaluated the consequences of work organization on musculoskeletal health. Using a postal questionnaire, answered by 1600 female grocery store workers, their main work tasks were identified and four work groups were defined (cashier, picking, and delicatessen work, and a mixed group, who performed a mix of these tasks). The crude odds ratios (ORs) for neck/shoulder complaints were 1.5 (95% CI 1.0-2.2), 1.1 (0.7-1.5) and 1.6 (1.1-2.3), respectively, compared to mixed work. Adjusting for individual and psychosocial factors had no effect on these ORs. For elbows/hands, no significant differences were found. Technical measurements of the workload showed large differences between the work groups. Picking work was the most strenuous, while cashier work showed low loads. Quantitative measures of variation revealed for mixed work high between minutes variation and the highest between/within minutes variation. Combining work tasks with different physical exposure levels increases the variation and may reduce the risk of musculoskeletal complaints

Goniometer Crosstalk Compensation for Knee Joint Applications

Electrogoniometers are prone to crosstalk errors related to endblocks rotation (general crosstalk) and to the characteristics of each sensor (individual crosstalk). The aim of this study was to assess the crosstalk errors due to endblock misalignments and to propose a procedure to compensate for these errors in knee applications. A precision jig was used to simulate pure ±100° flexion/extension movements. A goniometer was mounted with various degrees of valgus/varus (±20°) and rotation (±30°) misalignments. For valgus/varus misalignments, although offset compensation eliminated the error in the valgus/varus recordings for 0° of flexion/extension and reduced it to a few degrees for small (±30°) flexion/extension angles (root mean square error = 1.1°), the individual crosstalk caused pronounced errors for large (±100°) angles (18.8°). Subsequent compensation for this crosstalk reduced these errors to 0.8° and 4.5°, respectively. For rotational misalignment, compensation for the general crosstalk by means of coordinate system rotation, in combination with compensation for the individual crosstalk, reduced the errors for small (±30°) and large (±100°) flexion/extension angles from 3.6° to 0.5° and from 15.5° to 2.4°, respectively. Crosstalk errors were efficiently compensated by the procedures applied, which might be useful in preprocessing of knee functional data, thereby substantially improving goniometer accuracy

Methods for measuring physical workload with relevance for musculoskeletal disorders of neck and upper limb

Work-related musculoskeletal disorders of the neck and upper limb are a major problem. Women in repetitive manual work is one large affected group. Preventive actions are hampered by the lack of knowledge regarding quantitative exposure-response relations for physical workload. The present work shows, that available electrogoniometers are, with a sampling frequency of 20 Hz, feasible for measuring wrist positions and calculation of movements. The main error, caused by crosstalk, does not invalidate the results. Mean power frequency is a suitable generalized measure of repetitiveness. Inclinometers, based on 3 one-axial accelerometers, were developed. These provide, in combination with comprehensive data processing, measures of the forces that act on the body. During ordinary occupational work, data can be interpreted as inclination, e.g., of the head, upper back and arms. A questionnaire, regarding physical workload, was validated. It had a low agreement with direct measurements and showed differential misclassification due to musculoskeletal complaints and gender. Hence, direct measurements are preferable in epidemiological studies. We found a quantitative exposure-response relation between repetitive wrist movements and wrist/hand disorders among women in repetitive manual work. No relation between muscular load, using task-related electromyography (EMG) measures of "static" load, and neck/shoulder disorders were observed. To characterize low muscular load in the trapezius muscle, muscular rest in EMG is suitable for describing work tasks, while gap frequency rather reflects individual properties. Normalization to a submaximal reference contraction, rather than a maximal one, is preferable for characterization of muscular load in different work tasks. The developed methods can, combined with high-capacity data loggers, give whole-day ambulatory recordings of physical workload, and have a potential in evidence-based risk assessment and prevention

The effect on workload by using a support arm in parlour milking

Swedish agriculture is currently undergoing radical changes with respect to the working environment. New production milking systems may alter the physical workload and thus have an effect on the development of musculoskeletal disorders. Earlier studies have shown that there is a manifest risk of suffering injury to the forearm, wrist and hand during machine milking especially during the attaching task (when holding the milking cluster in one hand while attaching the four teat-cups to the udder). High degrees of dorsiflexion and deviation of the wrist in combination with peak values of muscle activity in the forearm during milking might contribute injuries to the wrist and hand. Large-scale milk production increases the time spent performing the tasks involved. As a consequence, the cumulative engagement in extreme positions and rapid movements, and high level of muscular load on the upper extremities will also increase. The aim of this study was to investigate the impact of the workload on the milker's forearm, wrist and hands resulting from using the prototype of a device designed to facilitate the attaching task. The device is constructed as a support arm where the milking cluster is suspended in order to reduce the workload. The study was carried out in a loose-housing system where the cows come to be milked in a parlour. Eleven milkers participated in the study. The muscle activity in the biceps and the forearm flexors, as well as positions and movements of the wrists were measured by electromyography and electrogoniometry. The attaching task was measured both with and without the device. When the prototype was used only a minor decrease in the muscular load on the holding side was recorded. Surprisingly, the effect on the wrist positions and movements was small. This marginal effect could be due to the fact that all the milkers were used to milking without the support arm and despite the training period, they were unable to make full use of the device

Physical workload in neck, shoulders and wrists/hands in dental hygienists during a work-day.

Physical workload was recorded by electromyography, inclinometry and goniometry for twelve female dental hygienists during authentic work. Their work was, in relation to other types of work, characterised by pronounced head flexion (90th percentile 46°), high loads on the forearm extensor muscles (90th percentile 23% and 18% of maximal EMG (MVE), for the right and left sides, respectively), average loads on trapezius muscles (90th percentile 15% and 14% MVE), average arm elevation (99th percentile 83° and 72°) and average wrist flexion and velocities (50th percentiles 17° of extension and 7.3°/s, for the right side). Manual scaling and machinery (use of ultrasonic scaling and hand-pieces) showed higher loads on the trapezius muscles, regarding muscular rest, as well as the 10th and 50th percentiles, than the other tasks, and for the forearm extensor muscles, an almost complete lack of muscular rest (0.1% time), and much higher loads regarding the 10th and 50th percentiles. Further, more pronounced head flexion and lower head and upper arm velocities were found, indicating more constrained postures for the neck and shoulders for the manual scaling and machinery. Use of ultrasonic scaler reduced the 50th percentile loads on the right forearm extensor muscles, but had no effect on the fraction of muscular rest and on the 10th percentile load. These findings are consistent with the high prevalences of musculoskeletal disorders among dental hygienists

Effects of prismatic glasses including optometric correction on head and neck kinematics, perceived exertion and comfort during dental work in the oral cavity - A randomised controlled intervention

Aim: To quantify the effects of using prismatic glasses including optometric correction, on head and neck kinematics, perceived exertion and comfort, during work in the oral cavity. Methods: The study population consisted of forty-five participants. After a basic ergonomic education, baseline measurements of head and neck kinematics were made using inclinometers. Perceived exertion and comfort were rated by the participants. An intervention group (n = 25), selected at random from the participants, received prismatic glasses and optometric correction when needed and were compared with a control group (n = 20). Follow up assessments were made after the intervention. Results: At follow up there was a reduction in both the intervention group (8.7 degrees) and in the control group (3.6 degrees) regarding head flexion. Neck flexion was reduced by 8.2 degrees in the intervention group and 3.3 degrees in the control group. The difference between the intervention and the control groups, i.e. the effect of the intervention, was statistically significant for both head (5.1 degrees; p = 0.009) and neck (4.9 degrees; p = 0.045) flexion. No effect of the intervention was seen regarding perceived exertion and comfort. Conclusion: The reduction in head and neck flexion achieved by the prismatic glasses is likely to reduce the risk of neck pain during dental work. The effect of the prismatic lenses could not be separated from the effect of the optometric correction. The possible effect of the ergonomic education was not evaluated. (C) 2011 Elsevier Ltd and The Ergonomics Society. All rights reserved

Physical workload on upper extremities in various operations during machine milking

The aim of the study was to quantify the workload on the upper extremity for fundamental work tasks during machine milking. Eleven milkers working in a loose-housing system with a milking parlour participated in the study. Muscle activity for the biceps and the forearm flexors, as well as positions and movements of the wrists were simultaneously measured by electromyography and electrogoniometry while videorecording the work. The milking work was broken up in three main tasks "Drying (the cow's udder)", "Pre-milking (the First milk)" and "Attaching (thr: milking unit to the udder)" and three supplementary tasks. All three main tasks show high muscle load values and almost no time for rest. The highest load values for the biceps and flexor muscles were found during the tasks "Attaching, holding the milking unit" and "Drying", respectively. For 10% of the recording time, the milkers held active hands in 42 degrees dorsal flexion during the milking tasks "Pre-milking" and "Attaching" and in deviated positions exceeding 50% of their maximum values during "Attaching" and "Drying". The high muscle loads in combination with extreme positions and movements of the hand and forearm might contribute to the development of injuries among milkers. The result from the study aims to form a basis for technical improvements of the milking equipment to decrease the risk for arm wrist and hand disorders