Biomedical subjects

T J Armstrong

Publications and source records attributed to T J Armstrong.

At least 37 records · Page 2Linked to original sources

PubMed1997

Test-retest reliability of an upper-extremity discomfort questionnaire in an industrial population.

OBJECTIVES: Efforts to understand or to monitor upper-extremity musculoskeletal disorders among workers have usually involved the use of questionnaires. The goal of this study was to assess the test-retest reliability of an upper-extremity discomfort questionnaire among industrial workers. METHODS: Test-retest agreement among 148 workers was analyzed using the kappa coefficient for categorical outcomes. Values of kappa greater than 0.75 are considered excellent, values between 0.40 and 0.75 are fair to good, and values of less than 0.40 represent poor agreement beyond chance alone. Test-retest results of continuous measures (eg, visual analogue scale responses) were compared with paired t-tests. RESULTS: The test-retest reliability of the questionnaire used to elicit demographic information, medical history, exercise participation, and information on musculoskeletal symptoms among industrial workers appears to be good to excellent in most instances. CONCLUSIONS: These results suggest that most results of this discomfort questionnaire are reliable and suitable for use in epidemiologic studies. For reassurance of the robustness of these findings, similar studies should be carried out in other worker populations with this, and other, questionnaire instruments.

Adult↗

PubMed1996

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.

Adult↗

PubMed1996

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.

Adult↗

PubMed1995

Effect of friction and load on pinch force in a hand transfer task.

The effect of friction and load on pinch force was studied in a simple hand transfer task using a repeated measures design and ten men. Subjects moved a container between two targets, 450 mm apart, at a slow, self-paced speed. The levels of mass in the container were set at 0.8, 2.5 and 4.2 kg (7.5, 24.5 and 41.5 N respectively). The handle materials were sandpaper and smooth aluminum. Applied pinch force was measured via a strain gauge mounted in a specially-designed handle attached to the container. Dependent variables were peak and 'steady-state' pinch force. The main and interaction effects of load and friction were significant. The friction effect was significant only for the highest load which, on average, elicited peak pinch forces of 16-70% of maximum voluntary force. This suggests that these men were not sensitive to friction effects at the lower loads. Results suggest that the use of tool handle friction enhancements may reduce required pinch forces for objects requiring upwards of 50% or more of maximum pinch strength.

Adolescent↗

PubMed1994

The relationship between body mass index and the diagnosis of carpal tunnel syndrome.

Increased weight and, more recently, body mass index (BMI), have been suggested as risk factors for carpal tunnel syndrome (CTS). In an effort to determine the relative risk (RR) of obesity in the development of CTS, 949 patients who had an evaluation of the right upper extremity that included motor and sensory conduction studies of the median and ulnar nerves were reviewed. Of these patients, 261 were diagnosed with a median mononeuropathy at the wrist. Those individuals who were classified as obese (BMI > 29) were 2.5 times more likely than slender individuals (BMI < 20) to be diagnosed with CTS. Forty-three percent of obese women and 32% of obese men had the diagnosis of CTS compared to 21% of slender women and 0% of slender men.

Adult↗

PubMed1994

A computerized method for assessment of musculoskeletal discomfort in the workforce: a tool for surveillance.

A musculoskeletal discomfort survey was conducted to assess musculoskeletal discomforts among rural mail carriers in two post offices. Perceived musculoskeletal discomfort was collected directly from the workforce by means of a computerized discomfort assessment system (DAS). This investigation aimed at: (1) assessing the rural mail carrier's perception of DAS; and (2) assessing the rural mail carrier's musculoskeletal discomforts resulting from work. Most participants in the study found the computer tool easy to learn and easy to use. The information collected by DAS was used: (1) to determine the number of participating employees who were experiencing some kind of musculoskeletal problem; (2) to determine subtasks associated with discomfort; (3) to determine the body areas most affected by different subtasks; and (4) to investigate the patterns of discomfort that occurred with time.

Adult↗

PubMed1994

Investigation of applied forces in alphanumeric keyboard work.

This paper considers one way that occupational health professionals can assess the force exerted by keyboard users and the possible relationship between that force and the key force-displacement relationship. First, three personal-computer keyboards with the standard QWERTY layouts were tested as described by the American National Standard for Human Factors Engineering of Visual Display workstations (ANSI/HFS 100-1988) to determine the peak forces, 0.47-0.89N; displacements prior to the "breakaway" force that acknowledges key registration, 2.0-2.5 mm; and total key travel, 3.3-4.3 mm. Second, keyboard reaction forces were recorded while 10 subjects typed 4 alphanumeric sentences on the keyboards. It was found that the peak forces corresponding to each keystroke were 2.5 to 3.9 times the required activation forces, indicating that the subjects consistently displaced the keys to their limits. The average of the peak forces for all keystrokes was lowest for the keyboard with the lowest required activation force. It was concluded that keyboard reaction forces can be used as an index of finger forces for keying tasks. Further studies are necessary to evaluate the relationship between keyboard reaction forces, fatigue, and chronic muscle, tendon, and nerve disorders.

Biomechanical Phenomena↗

PubMed1994

Reverse Phalen's maneuver as an aid in diagnosing carpal tunnel syndrome.

A reverse Phalen's maneuver involves wrist and finger extension held for 1 minute. We showed that this maneuver results in a significantly higher intracarpal canal hydrostatic pressure as compared to a traditional Phalen's or a modified Phalen's maneuver. Additionally, 31 individuals with complaints of carpal tunnel syndrome symptoms and 20 normal controls were evaluated to see what effect the reverse Phalen's maneuver would have on median sensory latency and amplitude. Both groups demonstrated a prolongation of the median sensory revoked response after 1 minute of this maneuver. The control group had a prolongation of 0.05 ms compared to 0.13 ms in the carpal tunnel syndrome group. The difference between the two groups was significant at a p = 0.05 level. This may add to the sensitivity of conventional screening methods.

Adult↗

PubMed1993

Perceived exertion and discomfort associated with driving screws at various work locations and at different work frequencies.

Eighteen subjects drove screws with air-powered tools into perforated sheet metal at three vertical and two horizontal work locations using three different work paces (8, 10, and 12 screws/min). Subjects drove screws with a pistol-shaped tool on the vertical orientation at knee, elbow, and shoulder height. They used an in-line tool to drive screws on the horizontal surface. A horizontal beam was placed just below each subject's elbow height and they drove screws into it with the lower arm perpendicular to the torso and with the arms fully extended. Subjects drove screws for 10 min at each work location and frequency combination before they assessed the condition using the Borg ten-point ratio rating scale. Subjects also ranked seven body areas according to discomfort for each work location. A two-factor ANOVA (and comparable non-parametric statistics) showed that both work location and frequency were significant factors in determining the Borg ratings. As work pace increased, so did the Borg ratings of perceived exertion for each work location. For each incremental increase in work pace, the Borg ratings of perceived exertion increased 12% to 25%, depending on the work location. Driving screws at elbow height on the vertical surface and with the lower arm close to the body on the horizontal surface were the work locations with the smallest ratings of perceived exertion. The ratings of perceived exertion for driving screws at elbow height on the vertical surface were 18% to 50% lower than the ratings for driving screws at knee or shoulder height and the ratings of perceived exertion for driving screws with the lower arm close to the body on the horizontal surface were 21% to 24% lower than driving screws with the arms fully extended. No significant difference was found among the discomfort ranks given to the various body parts for the two horizontal work locations. Differences were found among the body part discomfort rankings for the vertical work locations. While driving screws at knee height, the torso was most stressed; the wrist and hand were most stressed while driving screws at elbow height, and the shoulder and upper arm were the body parts that were stressed the most while driving screws at shoulder height.

Adult↗

PubMed1993

Effect of tool shape and work location on perceived exertion for work on horizontal surfaces.

Thirty subjects drove screws into perforated sheet metal mounted on a horizontal surface using three air-powered tools that varied in shape (right-angle, in-line, and pistol-shaped). The four horizontal work locations ranged from 13-88 cm in front of the body and were placed at 25 cm intervals. The vertical placement of the horizontal beam was at midthigh, elbow, and midchest height. Subjects drove 25 screws at each tool/work location combination before rating that condition using the Borg 10-point ratio rating scale. The ratings of perceived exertion increased with increasing horizontal distance from the body. When tool shape was not considered, the perceived exertion was virtually equal for driving screws at midthigh or elbow height. The ratings at midchest height were significantly higher than elbow and midthigh height. When tool shape was taken into account, subjects perceived less exertion driving screws with the pistol-shaped tool at midthigh height. The in-line and right-angle tools had the lowest ratings of perceived exertion for driving screws at elbow and midchest height.

Adolescent↗

PubMed1993

A conceptual model for work-related neck and upper-limb musculoskeletal disorders.

This paper presents a conceptual model for the pathogenesis of work-related musculoskeletal disorders. The model contains sets of cascading exposure, dose, capacity, and response variables, such that response at one level can act as dose at the next. Response to one or more doses can diminish or increase the capacity for responding to successive doses. The model is used as a framework for discussing the development of work-related muscle, tendon, and nerve disorders. It is intended as a beginning, to be modified to explain new findings as they become available. In research, it can help to identify areas needing additional data for the development and expression of work-related musculoskeletal disorders. Researchers can use it to design laboratory and field studies. In practice, it demonstrates the relationship between common exposure factors and different responses. This information can be used to evaluate and design jobs for the prevention of work-related musculoskeletal disorders.

Arm Injuries↗

PubMed1992

A kinematic model of the human hand to evaluate its prehensile capabilities.

A kinematic model has been developed for simulation and prediction of the prehensile capabilities of the human hand. The kinematic skeleton of the hand is characterized by ideal joints and simple segments. Finger-joint angulation is characterized by yaw (abduction-adduction), pitch (flexion-extension) and roll (axial rotation) angles. The model is based on an algorithm that determines contact between two ellipsoids, which are used to approximate the geometry of the cutaneous surface of the hand segments. The model predicts the hand posture (joint angles) for power grasp of ellipsoidal objects by 'wrapping' the fingers around the object. Algorithms for two grip types are included: (1) a transverse volar grasp, which has the thumb abducted for added power; and (2) a diagonal volar grasp, which has the thumb adducted for an element of precision. Coefficients for estimating anthropometric parameters from hand length and breadth are incorporated in the model. Graphics procedures are included for visual display of the model. In an effort to validate the predictive capabilities of the model, joint angles were measured on six subjects grasping circular cylinders of various diameters and these measured joint angles were compared with angles predicted by the model. Sensitivity of the model to the various input parameters was also determined. On an average, the model predicted joint flexion angles that were 5.3% or 2.8 degrees +/- 12.2 degrees larger than the measured angles. Good agreement was found for the MCP and PIP joints, but results for DIP were more variable because of its dependence on the predictions for the proximal joints.

Algorithms↗

PubMed1992

Anthropometric data for describing the kinematics of the human hand.

The major goal of this investigation was to collect statistically-based anthropometry describing the kinematics of the human hand and to model this anthropometry as a function of external hand measurements, so that it may be predicted noninvasively. Joint centres were anatomically estimated as the centre of curvature of the head of the bone proximal to the given joint. Joint centres determined using Reuleaux's method for PIP and DIP were within 1.4 mm of this anatomical estimate. Models using bone length as the independent variable explain more than 97% of the variability in the anatomically estimated joint centre position along the mid-line of the bone. Models for estimating the lengths of the kinematic segments using external hand length as the independent variable account for between 49 and 99% of the variability in segment length. Models for estimating the axial location of the finger MCP and thumb CMC joints with respect to the distal wrist crease using external hand length as the independent variable account for between 82 and 96% of the variability in these locations. Models for estimating the radio-ulnar location of the finger MCP and thumb CMC joints with respect to the long axis of the third metacarpal using external hand breadth as the independent variable account for between 30 and 74% of the variability in these locations.

Anthropometry↗

PubMed1991

An ellipsoidal representation of human hand anthropometry.

The goal of this study was to collect anthropometric data that describe the geometry of the surface of the hand and to model this anthropometry as a function of gross external hand measurements. The depth and breadth of each segment of the hand were measured at points that were spaced at approximately equal distances between the joints of the hand. Linear models using hand breadth as the independent variable explained from 12% to 47% of the variation in segment breadths and from 6% to 74% in segment depths. Ellipsoids are used in biomechanical models as an efficient mathematical description of the shape of kinematic segments for use in the determination of contact with other objects. Therefore the primary objectives of this study were to approximate the semiaxis dimensions for these hand segment contact bodies using a linear model of the gross anthropometry and to evaluate the accuracy with which ellipsoids describe the geometry of the hand segments. Graphical comparisons showed that differences between the ellipsoidal approximations and the breadth and depth measurements were largest near the joints. Data collected in this study could be used to create a set of overlapping ellipsoids that would provide a more accurate representation of hand geometry, and this representation could be adapted to biomechanical models that use ellipsoids to define segment geometry.

Adult↗

PubMed1990

Use of computer aided drafting for analysis and control of posture in manual work.

Computer aided design (CAD) in conjunction with digitised anthropometric manikins can be used for analysis and control of stressful work postures, one of the most frequently cited occupational risk factors of upper extremity cumulative trauma disorders. This paper describes the use of macros for manipulating manikins and workstation components and for designing the workplace. AutoCAD, a popular computer aided design software package, was used to demonstrate the feasibility of these concepts. Specifically, macros are used for drawing work equipment using parametric designs, manipulating manikins and analysing jobs. In comparing the macros to the use of primitive CAD commands, the macros not only decrease the amount of time needed to create workstation components, but they also make the task easier for the user and decrease the risk of errors. Despite the limitation of anthropometric data and manikins, CAD is an effective method for identifying postural stresses and redesigning the workstation to control the identified stresses.

Journal Article↗

PubMed1990

Vibration exposure for selected power hand tools used in automobile assembly.

A practical method for assessing vibration exposure for workers operating vibrating hand tools on an automobile assembly line is presented. Vibration exposure is difficult to assess directly using many fast Fourier transform (FFT) spectral analyzers because of long task cycle times. Exposure time cannot be accurately estimated using time standards because of the high variability between operators and work methods. Furthermore, because workers frequently move about and get into inaccessible spaces, it is difficult to record vibration without interfering with the operation. A work sampling method was used for determining vibration exposure time by attaching accelerometers to the tools and suspending a battery-operated digital data logger from the air hose. Vibration acceleration and frequency spectra for each tool were obtained off-line replicating actual working conditions and analyzed together with exposure time data for determining individual worker vibration exposure. Eight pneumatic vibrating power hand tools, representing tools commonly used in an automobile assembly plant, were studied. Spectra for the rotary and reciprocating power tools and had large distinct dominant fundamental frequencies occurring in a narrow frequency range between 35 Hz and 150 Hz. These frequencies corresponded closely to tool free-running speeds, suggesting that major spectral component frequencies may be predicted on the basis of speed for some tools.

Automobiles↗

PubMed1990

Perceived exertion and discomfort versus work height with a pistol-shaped screwdriver.

Seven vertical locations were rated after 36 subjects drove 25 No. 6 sheet metal screws into 18-gauge perforated sheet metal (hole size of 0.28 cm) with an air-powered pistol-shaped screwdriver at each location. The seven vertical heights ranged from 38 to 191 cm. Subjects rated each level using three psychophysical scales and were asked to imagine that they were assembly line workers required to drive screws at that work location using that particular tool for 8 hr. The three scales were the Borg 10-point ratio rating scale and two visual analogue scales. All subjects, regardless of anthropometry (5th percentile females to 95th percentile males), preferred driving screws between 114 and 139 cm. At the highest level of 191 cm, the shortest subjects disliked the level twice as much as the taller subjects. The three psychophysical scales were found to be comparable in sensitivity and use, although most subjects preferred the Borg rating scale. Future research and limitations of the current study are discussed.

Adult↗

PubMed1989

Muscle response to pneumatic hand tool torque reaction forces.

Surface electromyography was used for studying the effects of torque reaction force acting against the hand, on forearm muscle activity and grip force for five subjects operating right angle, air shut-off nutrunners. Four tools having increasing spindle torque were operated using short and long torque reaction times. Nutrunner spindle torque ranged between 30 Nm and 100 Nm. Short torque reaction time was considered 0.5 s while long torque reaction time was 2 s. Peak horizontal force was the greatest component of the reaction force acting against the hand and accounted for more than 97% of the peak resultant hand force. Peak hand force increased from 89 N for the smallest tool to 202 N for the largest tool. Forearm muscle rms EMG, scaled for grip force, indicated average flexor activity during the Torque-reaction phase was more than four times greater than the Pre-start and Post Shut-off phases, and two times greater than the Run-down phase. Flexor EMG activity during the Torque-reaction phase increased for increasing tool peak spindle torque. Average flexor rms EMG activity, scaled for grip force, during the Torque-reaction phase increased from 372 N for the 30 Nm nutrunner to 449 N for the 100 Nm nutrunner. Flexor rms EMG activity averaged during the Torque-reaction phase and scaled for grip force was 390 N for long torque reaction times and increased to 440 N for short torque reaction times. Flexor rms EMG integrated over the torque reaction phase was 839 Ns for long torque reaction times and decreased to 312 Ns for short torque reaction times. The average latency between tool spindle torque onset and peak initial flexor rms EMG for long torque reaction times was 294 ms which decreased to 161 ms for short torque reaction times. The average latency between peak tool spindle torque, just prior to tool shut-off, and peak final rms EMG for long torque reaction times was 97 ms for flexors and 188 ms for extensors, which decreased for short torque reaction times to 47 ms for flexors and 116 ms for extensors. The results suggest that right angle nutrunner torque reaction forces can affect extrinsic hand muscles in the forearm, and hence grip exertions, by way of a reflex response.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗