Fereydoun Aghazadeh

The effect of work-rest schedules and type of task on the discomfort and performance of VDT users.

Consideration of the literature survey indicates that video display terminal (VDT) operators tend to have a high incidence of musculoskeletal problems, visual fatigue, and job stress. Although a number of ergonomic improvements in workstation design and work environment can help to reduce these problems, a proper work-rest schedule deserves consideration since it is easily applicable and inexpensive. The objective of this study was to compare the work-rest schedules for VDT operators considering data entry and mental arithmetic tasks. An experiment was conducted with 10 male college students as participants. The methodology included a discomfort questionnaire and performance measures. The independent variables were the work-rest schedule (60-minute work/10-minute rest, 30-minute work/5-minute rest, and 15-minute work/micro breaks) and the type of task (data entry and a mental arithmetic task). The results were analysed using multiple analysis of variance followed by separate analyses. The 15/micro schedule resulted in significantly lower discomfort in the neck, lower back, and chest than the other schedules for data entry task. The 30/5 schedule followed by 15/micro schedule resulted in the lowest eyestrain and blurred vision. Discomfort in the elbow and arm was the lowest with the 15/micro schedule for the mental arithmetic task. The 15/micro schedule resulted in the highest speed, accuracy, and performance for both of the tasks, compared with the 60/10 and 30/5 schedules. The data entry task resulted in significantly increased speed, accuracy, and performance, and lower shoulder and chest discomfort than the mental arithmetic task.

A comparison of dynamic- and static-strength models for prediction of lifting capacity

Abstract An experiment was designed and conducted for the development, testing and comparison of models for prediction of weight lifting capacity of individuals incorporating static and dynamic strengths. The dependent variable was the maximum acceptable amount of lift and the independent variables were static strengths, and dynamic strengths of the individual in a simulated lifting position and task variables—height and frequency of lift. Data from nine male subjects were used for analysis. It was concluded that both the dynamic and static models developed in this study can predict the maximum acceptable amount of lift with a reasonable degree of accuracy. However, a comparison of the models revealed that the use of the dynamic model with one operator variable resulted in less absolute error between the actual and predicted load than the static model. This study, which is based on data from a limited number of subjects, indicates that the dynamic approach may be superior to the static approach.

Biomechanics and electromyography of a common idiopathic low back disorder.

Study Design. In vivo feline preparation groups loaded into lumbar flexion at different magnitudes and an unloaded control group. Objective. To demonstrate that a static, constant load flexion of the lumbar spine results in a complex neuromuscular disorder. Summary of Background Data. Epidemiology suggests that static lumbar flexion is a cause of low back disorders. There is little direct experimental evidence describing the physiologic and biomechanical processes that elicit the disorder. Recent evidence shows that static flexion of the spine under constant displacement results in muscular spasms and a prolonged recovery period. The response of the spine to flexion under constant load of various magnitudes (as opposed to constant displacement) is not known. It was hypothesized that static lumbar flexion under constant load may elicit creep in spinal ligaments, discs, etc., causing microdamage and development of a neuromuscular disorder. Methods. The lumbar spine of the feline was subjected to 20 minutes of constant load static flexion at physiologic load intensities from light to heavy while creep of lumbar viscoelastic tissues and EMG from the multifidus muscles of L3–L4 to L5–L6 were recorded. Recordings were continued over a 7-hour rest period after the static flexion was terminated. Results. Spasms and decreasing reflexive EMG were evident during the loading period, and a transient surge of EMG activity occurred at the beginning of the rest period. A second surge of EMG activity was seen 3–4 hours later. The four components of the neuromuscular disorder were present regardless of the load magnitude. A model was developed to quantify the disorder. Conclusion. A four-component neuromuscular disorder was elicited by a 20-minute constant load static flexion even when very light loads were applied. The disorder was elicited by creep of the viscoelastic tissues, which resulted in spasms and muscular hyperexcitability lasting for >24 hours. Although the disorder was transient, the physiologic and biomechanical principles associated with its development could also explain cumulative trauma disorders.

Evaluating lifting tasks using subjective and biomechanical estimates of stress at the lower back

The objective of this study was to evaluate five different lifting tasks based on subjective and biomechanical estimates of stress at the lower back. Subjective estimates were obtained immediately after the subjects performed the lifting tasks. Rankings for different tasks were obtained according to the perceived level of stress at the lower back. A biomechanical model was used to predict the compressive force at the L5/S1 disc for the weight lifted considering link angles for the particular posture. The tasks were also ranked according to the compressive force loading at the L5/S1 disc. The weight lifted in these tasks for obtaining the subjective estimate of stress was the maximum acceptable weight of lift (MAWOL). This was determined separately for each subject using a psychophysical approach. Subjective estimates of stress were obtained for infrequent lifting, specifically for a single lift, as well as for lifting at a frequency of four lifts per min. The results showed that a lifting task acceptable from the biomechanical point of view may not be judged as a safe or acceptable task by the worker based on his subjective perception. This may result in a risk of the worker not performing the recommended task or not following the recommended method.

Effects of exercise breaks on performance, muscular load, and perceived discomfort in data entry and cognitive tasks

An effective work-rest schedule is an economical way to potentially reduce physical and psychological problems associated with computer usage. In this study, three different work-rest schedules were investigated: 60-min work/10-min rest, 30-min work/5-min rest, and for the third schedule (15/micro), the participants received four breaks from each hour in addition to a 14-min break after 2 h (three of these breaks were 30 s in length and the fourth break was 3 min in length). The study also considered the effect of the type of task. Participants were asked to enter alphanumeric data as a data entry task and to solve addition/subtraction problems as a cognitive task.The results indicated that the effect of work-rest schedule was significant on various perceived discomfort categories and the performance of the subjects. Similarly, the type of task had significant effects on discomfort, performance, and muscular load levels. The 15/micro schedule was superior to the other schedules in terms of discomfort levels of the neck, back, and elbow/arm, eyestrain, speed, accuracy, and performance for both tasks. The lowest levels of trapezius muscle tension for data entry and flexor carpi radialis (FCR) for cognitive tasks obtained with the 15/micro schedule. The cognitive task resulted in a higher psychological discomfort (nervousness, tiredness, dizziness, and headache), but lower physical discomfort and performance than the data entry task. The results of the study suggest that the 15/micro schedule is preferable to the longer and infrequent rest break schedules considering upper extremity discomfort, eyestrain, speed, accuracy, and performance of participants.

Modification of CAPP systems for CAPP/scheduling integration

Abstract This paper presents a new approac—through the modification of an existing CAPP system, i.e. CMPP—for achieving CAPP/scheduling integration. An operation-machine index is developed as a relative measure for selecting the best machine from all the alternatives in the processs planning stage to satisfy two scheduling criteria: mean flow time and number of jobs tardy. The software program for implementing the integrated system has been written in C. A sample part is used to illustrate that both the mean flow time and the number of jobs tardy can be reduced with the use of the integrated system.

Relative importance of isometric and isokinetic lifting strengths in estimating maximum lifting capabilities

This paper compares the suitability of isokinetic lifting strengths with the suitability of isometric lifting strengths for estimating the maximum lifting capabilities of individuals for either frequent or infrequent tasks. The results of two independent studies indicate that isokinetic lifting strengths are better suited for estimating maximum lifting capabilities. The two devices for measuring isokinetic strengths, CYBEX and Mini-Gym, are also compared.

Psychophysical determination and modeling of load carrying capacity

Abstract This paper presents a study that was conducted to review the research on the determination of maximum acceptable carrying capacity using the psychophysical method. The characteristics of load carrying activity are first discussed. The psychophysics and its validity when applied to load carrying activity are then examined. The dependent, independent, and fixed variables in past psychophysical studies of load carrying activities are summarized, and the experiment design and procedure are reviewed. Both the factors affecting maximum carrying capacity studied by past research and the main results are also summarized. Finally, modeling efforts in determining maximum carrying capacity are reviewed. The results indicate many areas needing further study. The factors that may affect the maximum carrying capacity and that are unique to carrying activity should be emphasized. These factors include carrying mode, walking speed, carrying distance, time, and terrain/grade. Research is also needed to integrate the psychophysical method with other objective research approaches such as the physiological method and biomechanical method.

Comparison of Current U.S. and Canadian Cigarette Pack Warnings

Cigarette smoking is the single most preventable cause of death in the United States. From 1985 to date, one of four mandatory cigarette warnings proposed by the Comprehensive Smoking Education Act of 1984 has been displayed on cigarette packages. In addition to cigarette warnings, states like California, Massachusetts, Arizona, Oregon and Maine have implemented “Tobacco Control Programs” (TCP) to reduce the overall number of smokers. However, the decline in the rate of smoking is not occurring fast enough to meet the national health objective by 2010. The present U.S. cigarette warnings are verbal in form and provide information, which is inadequate but appropriate to make it legally adequate. On the other hand, warnings in other countries such as Canada and Brazil are more descriptive and specific and are accompanied by vivid and sometimes gruesome pictures. In the present study, six pictorial Canadian labels and four U.S. verbal labels were analyzed for potential effectiveness among eighty subjects using a survey questionnaire. The survey findings are compared with recent Canadian smoking data. It is concluded that placing pictorial labels on cigarette packages in the U.S. will allow the product to carry warnings that potentially provide better results than current verbal messages and less TCP funds will need to be used.

Effect of driving experience on visual behavior and driving performance under different driving conditions

Drivers’ ability to perform the primary task of driving a vehicle and be able to handle the interference caused by the secondary tasks such as the use of cell phone is greatly influenced by their driving experience. In this study, thirty-eight drivers with different levels of driving experience were studied to evaluate their driving performance during simple versus complex driving tasks performed with and without cell phone. The driving performance was evaluated by studying the visual behavior of the drivers using eye-tracking systems, driving error, and subjective workload assessment tool. Results demonstrate that the novice drivers fixated more on the dashboard area (36.33%) than on the front and center view (14.33%). On the other hand, the experienced drivers fixated more on the front and center (39.5%) as compared to the dashboard area (12%). Same trend was observed for complex driving but with lower percentage of total fixations than the simple driving conditions. The visual distraction caused by secondary task of cell phone use contributes to the decline in driving performance. Although all drivers reported higher workloads during driving while using cell phones and committed more driving errors, the errors were comparatively lower for experienced drivers than the inexperienced drivers.