James A. Foulke

Investigation of cumulative trauma disorders in a poultry processing plant

Cumulative trauma disorders such as carpal tunnel syndrome and tenosynovitis can be caused, precipitated, or aggravated by repeated exertions with the hand. This paper describes a study in a poultry processing factory that proceeds from an analysis of health records to an analysis of work methods, postures and forces. Alternative work procedures and knife designs are recommended to reduce stressful work postures and forces.

Development and Evaluation of an Observational Method for Assessing Repetition in Hand Tasks

Several physical stressors, including repetitive, sustained, and forceful exertions, awkward postures, localized mechanical stress, highly dynamic movements, exposures to low temperatures, and vibration have been linked to increased risk of work-related musculoskeletal disorders. Repetitive exertions have been among the most widely studied of these stressors, but there is no single metric for assessing exposure to repetitive work. A new methodology enables repetitive hand activity to be rated based on observable characteristics of manual work. This method uses a series of 10-cm visual-analog scales with verbal anchors and benchmark examples. Ratings for repetition reflect both the dynamic aspect of hand movements and the amount of recovery or idle hand time. Trained job analysis experts rate the jobs individually and then agree on ratings. For a group of 33 jobs, repetition ratings using this system were compared to measurements of recovery time within the cycle, exertion counts, and cycle time. Amount of recovery time within the job cycle was found to be significantly correlated with the analysis ratings (r2 = 0.58), as were the number of exertions per second (r2 = 0.53). Cycle time was not related to the analyst ratings. Repeated analyses using the new method were performed 1 1/2 to 2 years apart on the same jobs with the same group of raters. Ratings for repetition differed less than 1 point (on the 10-cm scale), on average, among the different sessions. These results indicate that the method is sensitive to exertion level and recovery time, and that the decision criteria and benchmark examples allow for a consistent application of these methods over a period of time. This method of rating repetition can be combined with similar scales for other physical stressors.

Keyboard reaction force and finger flexor electromyograms during computer keyboard work

This study examines the relationship between forearm EMGs and keyboard reaction forces in 10 people during keyboard tasks performed at a comfortable speed. A linear fit of EMG force data for each person and finger was calculated during static fingertip loading. An average r2 of .71 was observed for forces below 50% of the maximal voluntary contraction (MVC). These regressions were used to characterize EMG data in force units during the typing task. Averaged peak reaction forces measured during typing ranged from 3.33 N (thumb) to 1.84 N (little finger), with an overall average of 2.54 N, which represents about 10% MVC and 5.4 times the key switch make force (0.47 N). Individual peak or mean finger forces obtained from EMG were greater (1.2 to 3.2 times) than force measurements; hence the range of r2 for EMG force was .10 to .46. A closer correspondence between EMG and peak force was obtained using EMG averaged across all fingers. For 5 of the participants the force computed from EMG was within ±20% of the reaction force. For the other 5 participants forces were overestimated. For 9 participants the difference between EMG estimated force and the reaction force was less than 13% MVC. It is suggested that the difference between EMG and finger force partly results from the amount of muscle load not captured by the measured applied force.

A methodology for documenting hand positions and forces during manual work

In the course of a study to determine work methods associated with occupational wrist injuries, a low cost method was developed for estimating the frequencies that various hand positions and the corresponding hand forces were used for certain manual jobs. Hand positions were documented by filming the hands of a worker with a super 8 mm motion picture camera at four frames per sec. (gee Fig. 1). The film was then reviewed frame by frame through several work cyclest. The positions from each frame were noted, plotted and summarized as is shown in Fig. 2. The hand forces were estimated from the integrated Fig. 1. Cinematography and ekctromyography were used to

Muscle responses to simulated torque reactions of hand-held power tools

The aim of this work was to investigate physiological responses to torque reaction forces produced by hand-held power tools used to tighten threaded fasteners. Such tools are used repetitively by workers in many industries and are often associated with upper limb musculoskeletal complaints. The tools considered for stimulation in this study had straight handles and required from 100 to 400 ms to tighten fasteners to a peak torque of 1.0 to 2.5 Nm and from 50 to 150 ms for the torque to decay to zero. A tool stimulator was constructed to apply a programmed torque profile to a handle similar to that of a straight in-line power screwdriver. Wrist flexor and extensor surface EMGs and handle position were recorded as subjects held handles subjected to controlled torque loads that tended to flex the wrist. It was found that: (1) very high EMG values occurred even though torques were of short duration (50 to 600 ms) and the peak torques were low (7-28% of maximum strength); (2) high EMGs in anticipation of torque are directly related to torque build-up rate and peak torque; (3) high peak flexor and extensor EMGs during and following torque onset are related to torque build-up rate and peak torque; (4) minimum time of peak EMGs of 72-87 ms following the onset of torques with 50 ms build-up suggests the contribution of an extensor muscle stretch reflex component; delayed peak for longer build-ups suggests a central control of muscle force in response to torque; (5) angular excursions of handles increase with decreasing torque build-up time and increasing torque magnitude causes increasing eccentric work; (6) the results show that the slow torque build-up times (450 ms) correspond to minimum peak EMGs; and (7) accumulated EMGs increase with increasing torque and torque build-up times. Further studies are needed to evaluate fatigue and musculoskeletal injuries associated with prolonged periods of tool use.

Effects of Key Stiffness on Force and the Development of Fatigue While Typing

An experiment was conducted to investigate the effect of key stiffness on the development of fatigue, keyboard reaction forces, and muscle electromyography (EMG) responses. Six subjects typed continuously for 2 hours on each of two keyboards (0.28 N or 0.83 N resistance keys, presented in random order). Keyboard reaction force and root mean square finger flexor and extensor EMG were recorded for 2 minutes at 250 Hz for every 10 minutes subjects typed. After typing for 2 hours subjects were given a 2-hour rest break and then typed on the remaining keyboard for an additional 2 hours Fifty-four percent more peak force, 34% more peak finger flexor EMG, and 2% more peak finger extensor EMG were exerted while using the 0.83 N keyboard. Peak and 90th percentile values showed similar trends and were well correlated for force and finger flexor and extensor EMG. Subjects typed much harder than necessary (4.1 to 7.0 times harder on the 0.28 N keyboard and 2.2 to 3.5 times harder on the 0.83 N keyboard) to activate the keys. Fatigue was observed on the 0.83 N keyboard during 2 hours of continuous typing, but the trends were mild. It appears that the ratio of typing force to flexor EMG may not be a sensitive enough indicator of fatigue for low-force high repetition work.

Motion times, hand forces, and trunk kinematics when using material handling manipulators in short-distance transfers of moderate mass objects.

The risk of musculoskeletal injury associated with manual materials handling tasks has led in part to the use of material handling manipulators, yet there is limited empirical data to facilitate selection, design, and evaluation of these devices. A laboratory study of two types of mechanical manipulators (articulated arm and overhead hoist) was conducted of short-distance transfers of moderate loads, and the influence of various task parameters and transfer method on motion times, peak hand forces, and torso kinematics was obtained. Use of manipulators increased elemental motion times for symmetric sagittal plane transfers by 36-63%, and asymmetric transfers (in the frontal plane) by 62-115%, compared to similar transfers performed manually. Peak hand forces were significantly lower with both manipulators (40-50%), and approximately 10% higher for asymmetric versus symmetric transfers. Overall torso kinematics were grossly similar with and without a manipulator. These results suggest that for self-paced job tasks, moderate mass objects will be transferred slower over short distances and with lower levels of external (hand) forces when using mechanical aids. These simple effects, however, were influenced by object mass and transfer height.

Investigation of flexible hose insertion forces and selected factors.

Flexible hoses are widely used in automobiles. Understanding the force required to insert a hose, independent of worker variation, is important for engineers, designers and health professionals. Various parameters affect the insertion forces including the interference between the hose and flange. Also, it has been observed that workers often add motions during the insertion process, including rotation and oscillation. This paper describes the effects of these parameters on axial insertion forces. A programmable mill was used to isolate the effects of four variables on hose insertion force: fit, insertion speed, rotational velocity and oscillation magnitude. The results show that the magnitude of the interference of the 19 mm inside diameters (ID) heater hose and the flange, and the insertion technique affect the insertion forces; resulting in a range of insertion forces from 11.1+/-0.2 to 128.4+/-11.3N.

Exposure to forceful exertions and vibration in a foundry

The purpose of this research is to describe the results of a study that investigated the exposure of workers in a foundry to ergonomic risk factors. This presentation describes the characteristics of the tools investigated during this research with respect to physical work factors such as muscle activity, upper extremity posture, hand repetition, and exposure to hand/arm vibration. The analysis is based on the use of instrumentation as well as the use of observational methods to quantify these physical work elements.

An EMG preamplifier system for biomechanical studies

A method for documenting hand and wrist positions using cinematography and electromyography was described by Armstrong, Chaffin and Foulke (1979). The purpose of this paper is to provide information for the construction of an inexpensive system for amplifying and rectifying surface EMG signals. Simple modification of the Heath Schlumberger AC Voltmeter (Model SM-5238, Heath Schlumberger) adapts it for use as an electromyographic amplifier. The jack input was replaced with a five pin DIN connector providing input and power leads for an external preamplifier, as shown in Fig. 1. A preamplifier for interfacing the electrode signal into the Heath Schlumberger AC Voltmeter was built using a low cost monolithic integrated circuit instrumentation amplifier (AD5213 Analog Devices, Box 280, Norwood, MA 02062, U.S.A.) as shown in Fig. 1. The instrumentation amplifier is a high input impedance precision differential voltage gain device to maximize noise isolation. The differentially balanced inputs and a high common mode rejection ratio (up to 120 dB) make it possible to measure low level EMG signals (typically 3pV to 1 mV r.m.s.) despite large common mode noise voltages at the electrode sites. Cables may also introduce extraneous noise inputs (i.e. cable capacitance noise) and a.c. coupling input networks affect both impedance and input balance conditions, particularly for higher frequency noise. To com-