Browsing by Author "Dr. Gary Mirka, Committee Chair"

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    Effect of personality type on performance of an overhead task
    (2003-05-21) Sudhakaran, Sunil; Dr. Gary Mirka, Committee Chair; Dr. Nelson Couch, Committee Member; Dr. Hester Lipscomb, Committee Member
    Individual factors are becoming increasingly more prevalent in studies that explore occupational musculoskeletal injury/illness. Empirical and theoretical evidence supports further research into the role of individual differences in psychosocial attributes in the occupational exposure, especially the injury outcome process and potential mechanisms that may be at work. The goal of the current work was to understand whether certain individuals may place themselves at risk by taking infrequent breaks (i.e. working through pain or fatigue) if they are given the freedom to decide the work pace and work-rest schedule. The hypothesis is that individuals with certain personality characteristics like type A maybe at higher risk due to their choice of less frequent breaks and a fast paced approach to work just to get the job done as compared to type B personality. This hypothesis is based on the inherent time-urgency characteristic of type A individuals. Sixteen subjects (8 of each personality type) were asked to perform a 40 cycle overhead assembly work involving running nuts onto bolts located on an overhead board. The whole 40 cycle session was self paced and subjects had the freedom to take as many breaks as they wanted and these breaks could be as long as they wanted. The results showed that there was no significant effect of personality type on the task performance variables- total cycle time, total break time, average break time, average cycle time, # of breaks, average pain scale and average pain scale at breaks. These results were not consistent with the theory which supported the fast working of type As based on their time-urgency characteristic. Although no previous studies have looked at an overhead assembly task, the results of this study were consistent with other recent studies in our laboratory showing no performance effects of personality type on simple, unchallenging tasks.
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    Effects of Time of Day and Warm-Up on Lifting Kinematics
    (2007-06-13) McClure, Leigh R; Dr. Gary Mirka, Committee Chair; Dr. Sharon Joines, Committee Member; Dr. Nelson Couch, Committee Member
    There is a real need to be able to understand the etiology of back injury. One area that has had only limited research is that of time of day effects. Previous studies have measured both the static (Adams et al., 1987) and dynamic (Fathallah et al., 1995) effects time of day has on the low back. These studies, however, measured maximum capabilities and did not relate their results to real world applications. The objective of the current study is to explore the effects that time of day and warm-up have on trunk kinematics during an industry inspired lifting task. Nine male and three female subjects participated in the study. A series of four separate experimental sessions, two AM sessions held one hour after rising and two PM sessions held nine hours after rising, were performed. During one AM and one PM session the subject was led through a series of physical warm-up exercises prior to performing the lifting exertions. Upon conclusion of the warm-up, subjects completed a lifting task with two separate weight conditions, 3.6 kg and 10.9 kg. The lifting task consisted of lifting a box from the floor, rotating approximately 130°, and placing the load on an adjacent conveyer. Twenty consecutive lifts were completed for each load condition. The independent variables were SESSION (AM and PM), WARM-UP, and LOAD (low-3.6 kg and high-10.9 kg). The dependent variables considered in this study were peak trunk range of motion and peak trunk velocity in the sagittal and rotational planes, and the (x,y) coordinate positions of each knee in the anterior/posterior and lateral directions at the peak trunk position. The experiment was of a split plot design and used MANOVA and subsequent univariate ANOVA to test for statistical significance. LOAD was the only independent variable that proved statistically significant, and was significant for trunk sagittal position, trunk sagittal velocity, and lateral knee position. Trunk sagittal position increased from 75 (±0.48)° to 78 (±0.50)° for the low and high conditions, respectively. Trunk sagittal velocity on the other hand decreased from the low (140 (±0.87)°/s) to the high (130 (±0.92)°/s) condition. Neither SESSION nor WARM-UP were found to affect these kinematics variables. The lack of statistical significance could have occurred for several reasons. The current study chose to measure range of motion (ROM) while doing an industry inspired lifting task. In order to complete the task subjects were not necessarily required to use a full range of motion. Instead, they used only the range of motion needed to accomplish the task. Results showed that SESSION had little effect on this ROM. Subjects were also allowed to complete the lifting task in any way they chose, which introduced inter-subject variability to the experiment because no two subjects used the same lifting technique. Overall intra-subject lifting strategies did not change with regard to SESSION or level of muscle WARM-UP.
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    Redesign and Evaluation of the Grocery Store Self-Checkout Systems from Universal Design Perspectives.
    (2003-09-19) Bajaj, Komal; Dr. Carolyn M Sommerich, Committee Member; Prof. Haig Khachatoorian, Committee Member; Dr. Gary Mirka, Committee Chair
    Each one of us is physically challenged at some point in life. Old age, extreme statures (short or long, thin or fat), or some accident might produce conditions wherein we are unable to continue our work like we normally do. So it is in the best interests of everyone to design a product that accommodates the needs of all of its users. Being ergonomists, our task is to assess the existing products and services, showing where and how they fail to 'fit' the user (in every sense of the word) and suggest ways to improve the fit in order to make the products and services safer, more comfortable and more productive for the whole range of people who use them — including children, the elderly and the disabled. — Universal design is the design of products and environments to be usable by all people, to the greatest extent possible, without the need for adaptation or specialized design?- Ron Mace (1994). In this sense, the two fields — Ergonomics and Design — merge. In the summer of 2002, while interning with the Center for Universal Design, Raleigh, NC, I had the opportunity to get involved in a focus group study of the recently emerged grocery store Self-Checkout Systems (SCO's). People with various kinds of disabilities — mobility, hearing, vision, perceptual and cognitive disabilities — were asked to perform the process of Self-Checkout (SCO) in actual grocery stores. Although no quantitative variables were analyzed in that study, it was observed that the SCO's were far from being usable by the disabled population. Thus, emerged the idea of applying my knowledge of ergonomics to the redesign of one of the most prevalent models of the SCO (the U-Scan Express) so that the redesigned system is more 'universally' acceptable than the existing system. Because of time and resource constraints, the redesign focused on the accessibility for wheelchair users and non-wheelchair users from the physical perspective considering ergonomic factors such as fit, reach, posture etc. Two prototypes — one of the conventional SCO and another of a redesigned version — were built in the Ergonomics Laboratory at North Carolina State University. Fifteen subjects— five wheelchair users and ten non-wheelchair users — were asked to simulate the process of self-checkout on the two different workstations. The workstations were evaluated on the basis of productivity, posture and users' subjective feedback. Results indicate that productivity was not significantly affected across workstations, for either of the two user groups. Posture was significantly improved across workstations for both the groups. Shoulder posture was significant ly improved for both the groups — a maximum shoulder angle reduction of 64% for wheelchair users and 69% for non-wheelchair users was recorded. Trunk posture was significantly improved for wheelchair users with a maximum trunk angle reduction of 66.5% while for the non-wheelchair users, the trunk flexion angle did not significantly increase. Subjective feedback from both the groups showed a preference for the new design in terms of ease, accuracy, quickness and overall preference although, the preference was higher for the wheelchair group than the nonwheelchair group. The average scores of both the user groups on 'willingness' in using the redesigned system in preference to the existing system were also above neutral ? all five of the wheelchair users and 8 out of 10 of the non-wheelchair users responded with a score above neutral for willingness. Thus, it was concluded that the redesigned SCO would be more 'universally' acceptable than the conventional/existing SCO.