Documents motion study 19 results

"Research on the hazards of manual materials handling in industry is summarized and recommendations to reduce the human and economic burden imposed by improper materials handling are provided. Epidemiological, biomechanical, physiological, and psychophysical criteria are discussed for establishing work practice guidelines. Recommendations regarding the safe load weight, size, location and frequency of handling are presented along with mitigating factors such as worker training and physical fitness. Worker training and selection criteria are listed, and engineering guidelines are provided for the design of workplaces where manual materials handling is performed."

This study represents a continuation of a series of psychophysical studies on repetitive motions of the wrist and hand conducted at the Liberty Mutual Research Center for Safety and Health. The purpose of this study was to compare maximum acceptable torques of ulnar deviation determined after a replicated training protocol from an earlier single-movement study of ulnar deviation with maximum acceptable torques of ulnar deviation from both the previous single-movement study and two multi-movement studies. A psychophysical methodology was used in which the subject adjusted the resistance on the handle, and the experimenter manipulated or controlled all other variables. After the 1-week training protocol, 14 subjects performed a ulnar deviation task for six 7-hour work days, 2 days at each repetition rate of 15, 20 and 25 motions per minute. The subjects were instructed to work as if they were on an incentive basis, getting paid for the amount of work they performed. The subjects recorded symptoms during the last 5 minutes of each hour. By replicating the training protocol of a previous single-movement study, the results of this experiment revealed that maximum acceptable torque of ulnar deviation in this study (1.65Nm or 22% of maximum isometric torque) approached a similar level of torque to that reported in the previous single-movement study for a frequency of 15 per minute. However, when further accommodation was shortened in the 20 and 25 per minute conditions, the acceptable torque levels departed from the previous single-movement study and approached lower levels achieved in the multiple-movement studies which had shorter accommodation times for each movement. These results suggests that the maximum acceptable torque determined through psychophysical methods is dependent upon accommodation time in the protocol and that effect of experimental design (single- vs multi-movement) needs to be further explored.

This study represents a continuation of a series of psychophysical studies on repetitive motions of the wrist and hand conducted at the Liberty Mutual Research Center for Safety and Health. The purpose of the study was to quantify maximum acceptable forces of six motions performed on separate days but within the context of the same experiment. The six motions were wrist flexion with a power grip, wrist extension with a power grip, wrist flexion with a pinch grip, wrist extension with a pinch grip, ulnar deviation with a power grip, and a handgrip task (with a power grip). A psychophysical methodology was used in which the subject adjusted the resistance on the handle and the experimenter manipulated or controlled all other variables. Thirty-one subjects performed the six tasks at repetition rates of 15, 20 and 25 motions/min. Subjects performed the tasks for 7 h per day, 5 days per week, for 4 weeks. The subjects were instructed to work as if they were on an incentive basis, getting paid for the amount of work performed. Symptoms were recorded by the subjects during the last 5 min of each hour. The results revealed that maximum acceptable torques ranged from 11 to 19% of maximum isometric torque depending on frequency and motion. Maximum acceptable torques for the tasks that could be compared with previous studies showed the same patterns of response. However, the selected forces were substantially lower using the mixed protocol. A table of maximum acceptable torques and forces is presented for application in the field.

"The focus of this study was to assess the amount of error present in several approaches that have been commonly used to estimate the cumulative spinal loading during manual materials handling tasks. Three male subjects performed three sagittal plane lifting tasks of varying loads and postural requirements. Video recordings of the tasks were digitized and a biomechanical model was used to calculate the spinal loading (compression, joint shear, reaction shear, and flexion/extension moment) at L4/L5 for each frame of data. The 'gold standard' for cumulative loading experienced by the subjects was obtained by integrating the resultant biomechanical model outputs for the entire lifting cycle. Five approaches that quantify cumulative spinal loading, four that use discrete measures and one that reduces the number of frames used (5 Hz), were used and compared with the gold standard. The four methods using discrete measures to quantify the cumulative demands of a task resulted in substantial errors (average error across task and subjects was 27-69%). Reducing the number of frames of data processed to 5 frames/s preserved the time varying information and was the only approach examined that did not induce significant error into the cumulative loading estimates. This study indicates that errors in cumulative spinal loading estimates can be large depending upon the approach used, which will hinder any progress in developing a dose-response link between cumulative exposure and an increased risk of low-back pain or injury."

Cette étude s'inscrit dans une démarche épidémiologique de quantification des troubles musculodquelettiques (TMS). Dans un objectif de prévention, son but était de rechercher une relation entre les variations inter et intra-individuelles dans l'exécution de tâches manuelles répétitives et le risque de plaintes musculodquelettiques,Sa réalisation a nécessité la mise au point d'une méthode originale d'évaluation des stratégies gestuelles des opérateurs qui est une inovation intéressante.

The prevention of work-related musculoskeletal disorders has become a national priority in many countries. Increasingly, attempts are made to quantify those exposures that increase risk in order to set exposure limit values. This study used commonly employed field measurement methods and tools in order to perform an inter-method comparison between three primary methods of risk factor exposure assessment: self-report questionnaires, observational video analysis and direct measurement. Extreme posture duration, repetition, hand force (estimated from electromyography) and movement velocity were assessed for 18 subjects while performing each of three jobs processing tree seedlings. Results indicated that self-reports were the least precise assessment method, which consistently overestimated exposures for each of the measured risk factors. However, adjustment of the reports as psychophysical scales may increase agreement on a group level. Wrist flexion/extension duration and repetition were best measured by electrogoniometer. Electrogoniometric measures of wrist deviation duration and frequency were less precise than video analysis. Forearm rotation duration and repetition, grip force and velocity appeared to be best quantified by direct measurement as measured by electrogoniometer and electromyography (EMG) (as root-mean-square amplitude). The results highlight the fact that it is as important to consider and report estimated measurement error in order to reduce potential exposure misclassification in epidemiologic studies.

The importance of different motion patterns in the assessment of work technique is rarely addressed in the literature and even less information can be found regarding gender differences. In this study the possible gender differences in lifting technique from lifting experiments on 12 female and 10 male participants were examined. The participants performed squat and stoop lifts of a box. Movements were measured by means of opto-electronic measurement systems. Kinematic data derived from the measurements revealed some differences between the men and the women, e.g. in trunk motion and knee angle ranges. The hip-knee interjoint coordination was more synchronized for women than for men in terms of the relative phase angle. It is concluded that so far gender differences in motion patterns have not been sufficiently explored and that men and women need to be considered separately in the evaluation of work technique in manual handling tasks. Advantages and disadvantages of different coordination patterns need to be further investigated.

Physical exposure to risks for potential work-related musculoskeletal injuries has been assessed using a variety of methods, including pen and paper based observation methods, videotaping and computer-aided analysis, direct or instrumental techniques, and various approaches to self-report assessment. These methods are critically reviewed in this paper. The applications of these techniques in ergonomic and epidemiologic studies are considered, and their advantages and shortcomings are highlighted. Finally, a strategy that considers both the ergonomics experts' view and the practitioners' needs for developing a practical exposure assessment tool is then discussed.

"In the manufacturing industry highly repetitive movement patterns in the work situation are common. This work situation is often the cause of pain in the neck-arm region. To measure these movement patterns a new method has been developed by registering acceleration during ordinary industrial work. Three small accelerometers were fastened horizontally, tranversely and vertically in a small box at the wrist. The data were fed into a computer memory at the work site and analysed later. The method can be used during ordinary work in a factory causing no interference to the work."