A. Waikar

An Electromyographic Investigation of Neck Angles for Microscopists

This study investigated the musculoskeletal stress experienced by microscopists for different neck angles. Electromyography was employed for objective evaluation of the musculoskeletal stress which was compared with the subjective assessmnent obtained through questionnaire. Subjects viewed through the microscopes for two hours at a time in a constrained posture with neck angles of 25, 45 and 65 degrees. Electromyograms (EMG) were recorded for the cervical, trapezius, lattisimus dorsi and erector spinae regions. Subjects also reported the perceived level of stress every fifteen minutes. Both objective and subjective criteria revealed significant increases in the levels of musculoskeletal stress over time of the experiment for all levels of neck angles, in most muscles tested. Higher levels of stress were observed for erector spinae and cervical regions for 65 and 45 degree neck angles. It was concluded that the stress may be reduced by utilizing optimal neck angle in designing the microscope workplace layout.

Utilization of Direct Estimation Method to Determine the Effects of Task Variables on the Capacity to Lift Loads

This paper presents results of a pilot study in which the “direct estimation” method was used to determine the lifting capacity of individuals. Using the capacity of subjects to lift a load from floor to overreach height at frequency of 4 lifts per minute as a base, their capacity to lift under condition of varying task variables was determined. In this study 9 lifting heights, 5 frequencies, and 3 box sizes were used. The amount of load which the subjects were willing to lift was determined by the standard psychophysical methodology. Then the subjects lifted the same loads to various heights at different frequencies using different size boxes. A relationship was established between load lifted to the various lifting heights and the perceived difficulty of the lifting task. A similar relationship was determined for various frequencies and box sizes. An analysis of the results of this methodology reveals that the use of “direct estimation method” provides the effects of task variables on the amount of the lifted load accurately in a short period of time.

Determination of the Optimal Location of Ripcord Handles in Parachutes

The purpose of this research was to determine a location for the ripcord handle in parachutes, most compatible with human capabilities. Seven different locations were tested for the ripcord handle. Maximum voluntary forces were measured with the subjects pulling the ripcord handle using their right, left, and both hands at all seven locations. A comparison of single-handed versus both-handed pulls was made. Results indicated that with the handle located at the left or right thigh the subjects were able to exert more force than any other locations. Also the use of two hands yielded the largest force.

Determination of optimal location for parachute ripcord handle in a suspended position

A number of parachuting fatalities are attributed every year to the inability of the parachutist to pull the ripcord. The purpose of this study was to determine a location for the ripcord handle in parachutes, which would be most compatible with human capabilities. Eight different ripcord handle locations were selected for this investigation. Eighteen male and 18 female subjects participated in the study. The subjects were tested while being suspended 5 cm above floor level wearing a parachute harness. Maximum voluntary force exertions were measured with the subjects pulling the ripcord handle using their left, right and both hands at all locations. The results indicate that the thigh locations are superior in regard to pull forces for all hand applications (left, right, and both). Also, two-handed pulls yield the largest forces at all locations.

Endurance in Restricted Postures

This paper presents results of a study to find a relationship between the strength required to perform a task and the endurance time in restricted postures. A laboratory experiment was conducted to find the endurance for workers exerting selected percentage of their maximum strength in certain restricted postures. Endurance times of 15 college students were measured at various predetermined strength in postures such as standing, sitting, and lying on the stomach with and without elbow support. It was found that the endurance time was significantly reduced in the restricted postures. Experimental analysis clearly reveals that the average endurance time in the sitting position was only 5.15 minutes when 23 pounds of strength exertion was required; while the endurance time in standing position was more than 90 minutes. The reduction was more significant in the case of postures involving lying on stomach. Subjects could not endure any weight heavier than 10 pounds for longer than 5 minutes. The endurance time was also significantly reduced when the required force level was more than 25% of the maximum strength. A regression model which estimates maximum strength that can be sustained for a given endurance time has been developed and presented.

A protocol for distributed simulation on a microcomputer network

Abstract The computer industry has evolved very rapidly from single-user computers to computer networks where users are able to share both local and remote files. Networks of microcomputers facilitate the integration of all information processing for distributed applications such as database processing and electronic mail. One management application of promising potential for computer networks is distributed simulation. Simulation analysis can be useful to essentially all problem-solving and decision-making on the job. To implement a particular distributed application, computer communication between processors must be considered. Unlike expensive multiprocessor computers, networks of less-expensive microcomputers do not have pre-established communication paths between processors. This paper addresses how this obstacle may be overcome by using communication protocols based on the Open Systems Interconnection (OSI) reference model. Protocol services needed to support a distributed simulation environment will be identified, and their implementation through a prototype will then be investigated and evaluated.

Subjective and Biomechanical Evaluation of Lifting Tasks

Careful selection and training of workers, and good job design have not substantially reduced the incidence of low back injuries. Therefore, reduction in number and severity of such injuries has become a priority concern of many researchers. The specific question addressed by this research was “Are there any discrepancies between the rankings for the lifting tasks based on the subjective estimates of stress at the lower back and the rankings based on compressive force at L5/S1 predicted by the biomechanical model?” The results showed that some of the tasks evaluated to be less severe biomechanically were evaluated to be severe based on the subjective estimation of stress at the lower back.

Evaluation of Trailer Hitches Using Ergonomic Principles

This paper presents a field experiment designed to test and evaluate two functionally different trailer hitches, conventional and newly designed, for driving effectiveness and safety. The evaluation was performed using three different approaches. The first used subjective evaluation obtained through subject questionnaire. The second involved estimating the strength required for the control of steering wheel using electromyogram (EMG). The third involved monitoring the extent of the oscillations of the steering system of the experimental car. The independent variables were the type of hitch, driving pattern and the trailer load. Each of the six subjects participated in 24 driving runs in the experiment. The results showed that the new trailer hitch provides greater driving effectiveness and safety than the conventional trailer hitch.