Occupational Ergonomics - Volume 5, issue 3

Authors: Garg, Arun | Hegmann, Kurt T. | Kapellusch, Jay

Article Type: Research Article

Abstract: A laboratory study was conducted to determine the maximum voluntary strength (MVC) and maximum voluntary torque for one-handed lift and hold and hold only tasks as a function of shoulder posture. Twelve female volunteers of 21–33 years of age, claimed to be in good physical health and stated they had never had any musculoskeletal or cardiovascular problems participated in the study. One-handed maximum voluntary strength was defined as the maximum weight that a subject could lift and hold for 4 seconds (lift and hold) or hold the weight for 4 seconds without lifting from table height (hold only). MVC was …measured in six different postures most commonly used in automobile assembly: 0/90 (shoulder flexion angle=0° and included elbow angle=90°), 30/90, 60/90, 90/120, 120/150, and 150/180. An analysis of variance showed that hold only MVCs were significantly higher than lift and hold MVCs by an average of 26%. Shoulder posture had significant effect on both types of MVCs. The strongest posture was 0/90 and the weakest posture was 90/120. There was large variability between subjects and some subjects had maximum shoulder strength as low as 4.3 kg. The findings of this study indicate that female have very low shoulder strength especially for jobs requiring overhead work. Show more

Keywords: Shoulder posture, overhead work, maximum voluntary strength, maximum voluntary torque

DOI: 10.3233/OER-2005-5301

Citation: Occupational Ergonomics, vol. 5, no. 3, pp. 131-140, 2005

Authors: Iridiastadi, Hardianto | Aghazadeh, Fereydoun

Article Type: Research Article

Abstract: The present study is aimed at determining Physiological Fatigue Limit (PFL) values for Combined Manual Materials Handling (CMMH) tasks while handling Maximum Acceptable Weight of Lift (MAWL), and to compare the PFL of handling MAWL and PFL values expressed as percentages of treadmill aerobic capacity and values expressed as percentages of CMMH aerobic capacity. Results of the study show that PFL values of CMMH tasks, on the average, are approximately 25% of treadmill aerobic capacity and 35% of CMMH aerobic capacity. This difference is statistically significant. It is suggested that the PFL figures used for designing manual materials handling jobs …should be based on physiological data collected using real or simulated manual materials handling tasks rather than standard tasks of treadmill, etc. Show more

Keywords: Fatigue, manual materials handling tasks, psychophysics, aerobic capacity

DOI: 10.3233/OER-2005-5302

Citation: Occupational Ergonomics, vol. 5, no. 3, pp. 141-148, 2005

Authors: Dunk, Nadine M. | Keown, Kiera J. | Andrews, David M. | Callaghan, Jack P.

Article Type: Research Article

Abstract: The aim of this research was to examine the repeatability of task cycle loading to assess the feasibility of data extrapolation approaches for calculating a shift cumulative exposure. The number of trials of a lifting task that would be necessary to provide a stable estimate of the cumulative low back loads sustained during manual material handling tasks throughout a normal working day was examined. Both a lab-based experiment (n=10 males) with a highly constrained task, and an externally paced industrial sample performing their regular workday task (n=8 males), were studied. Both study groups were videotaped while performing lifting trials and …10 consecutive trials were chosen for biomechanical analysis. Cumulative loading variables were determined for each lift and accumulating means were calculated for comparison with the gold standard, or criterion measure, which was the average of all 10 trials. It was found that a minimum of 4 trials was required to provide a stable estimate of cumulative loading in the lab-based task. The lab data were tightly clustered with an overall average coefficient of variation of 5.7%. Data obtained in the industrial setting were more variable with an average coefficient of variation of 24.8%. When individual lifting cycles were extrapolated to an 8 hour shift exposure, cumulative compression for the industrial task varied by 6.3 MN·s (range=15.2 to 21.5 MN·s) for one subject and for the constrained laboratory task it varied by 5.0 MN·s (range=32.0 to 37.0 MN·s). These results highlight the importance of using multiple cycle samples to establish a stable estimate of cumulative loading prior to extrapolating for a shift exposure. Show more

Keywords: Cumulative loading, lifting, spinal load, repeatability, biomechanical spine model, compression, shear, industrial tasks

DOI: 10.3233/OER-2005-5303

Citation: Occupational Ergonomics, vol. 5, no. 3, pp. 149-159, 2005

Authors: MacKinnon, Scott N. | Vaughan, Christopher L.

Article Type: Research Article

Abstract: This study examined the effects of reach distance on the lumbar spine kinematics and electromyographical activities (EMG) of eight selected muscles of the trunk and shoulder during submaximal horizontal pulling exertions (12% of lean body mass) all located at elbow height. Eleven healthy male volunteer subjects were asked to pull on a load located at varying distances (10, 15, 20, 25, 30, 35 and 40% of subject stature) from the frontal plane containing the load handle. Trunk kinematics in the sagittal plane, as monitored by a Lumbar Motion Monitor, increased significantly as reach distance increased. EMG data revealed increasing erector …spinae activity as reach distance increased and this muscle group was found to be co-active with external oblique muscles during the exertion. Shoulder complex muscles were found to be highly active in all conditions, but only the trapezius and deltoid demonstrated significantly decreasing activity as pull reach increased. These data provide some direction in positioning the operator within a workstation demanding pull force exertions. Show more

Keywords: Single-handed pull exertions, lumbar motion, electromyography

DOI: 10.3233/OER-2005-5304

Citation: Occupational Ergonomics, vol. 5, no. 3, pp. 161-172, 2005

Authors: Calvino, Francesco | La Gennusa, Maria | Nucara, Antonino | Rizzo, Gianfranco | Scaccianoce, Gianluca

Article Type: Research Article

Abstract: The evaluation of comfort conditions of people in confined environments requires a knowledge of the human body's radiation data. This is essentially represented by the projected area of the body in a given direction. From this factor, other important parameters can be computed, such as projected area factors and angle factors. Presently, these parameters are evaluated using graphs deriving from a pioneering field study carried out by P.O. Fanger for which a piece of apparatus using mirrors and weight operations on film negatives is used. Obviously, these graphs, apart from referring to a limited number of subjects, also involve some …reading errors. With the aim of enlarging the number of experimental cases and in order to provide a simplified method of making measurements, this work proposes a new experimental procedure based on digital images of the human body which are processed using a computer-based system. The first part of the paper is dedicated to the description of this procedure and to some early comparison with data found in the literature on the subject. The second part concerns the introduction of a new method for computing the effective area of people, starting from the projected areas taken by means of the present apparatus. Show more

Keywords: Projected area, thermal comfort, predicted mean vote, ergonomics, working places, image treatment

DOI: 10.3233/OER-2005-5305

Citation: Occupational Ergonomics, vol. 5, no. 3, pp. 173-185, 2005