Current views on the diagnosis and treatment of upper limb overuse syndromes.
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Cumulative Trauma Disorders↗
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Accuracy and validity of observational estimates of wrist and forearm posture.
Numerous observational methods for analysis of working posture of the wrist/forearm have been reported in the literature yet few of these methods have been validated for the accuracy of their posture classification. The present study evaluated the accuracy of estimates of working posture made by 28 experienced ergonomists using methods of scaling upper limb posture typical of those reported in the literature. Observational estimates of wrist/forearm posture of four jobs presented on video-recording were compared with posture levels measured directly with an electrogoniometer system. Ergonomists using a visual analogue scale tended to underestimate peak and average wrist extension with mean errors of -29.4% and -10.5% of the joint ROM, respectively (p<0.05). While estimates of wrist flexion, pronation and supination resulted in less bias, variability in observer error was large for all wrist postures. The probability of an analyst misclassifying the most frequently occurring posture using a three- and a six-category scale was 54 and 70%, respectively. The probability of misclassifying peak posture was 22 and 61% using a three- and a six-category scale respectively. This suggests a trade-off between the degree of precision afforded by the categorical scale and the likelihood of posture misclassification. Estimates of the temporal distribution of posture among the categories appeared to be biased towards more neutral postures than were measured for the jobs. This indicated the possibility of a trend towards underestimation of posture duration severity by the ergonomists.
Bias↗
Determination of worker physiological cost in workspace reach envelopes.
Oxygen uptake (VO2), heart rate (HR) and myoelectric activity (EMG) were measured while performing a repetitive task in the normal, maximum and extreme workspace reach envelopes. The VO2 and HR increased significantly from the normal to the maximum to the extreme workspace reach envelope. The average increases in VO2 when compared to the normal workspace were 19 and 52%, respectively. The corresponding average increases in HR were 6 and 14%, respectively. The increase in EMG for anterior deltoid, upper trapezious and erector spinae showed a significant increase from normal to maximum and from maximum to extreme workspaces. The average increases in EMG for anterior deltoid, upper trapezious and erector spinae, compared to the normal workspace were 96, 37 and 48% respectively for the maximum workspace and 193, 95 and 106% for the extreme workspace, respectively. The research indicated for the first time that during task performance, worker physiological cost would increase significantly with the increase in workspace reach levels.
Back↗
Wrist discomfort levels for combined movements at constant force and repetition rate.
Sixteen male subjects each performed a repetitive, downwards, non-prehensile wrist exertion task with the arm pronated, at a rate of 15 times per minute and with a force of 10N +/- 1N in 49 combinations of flexion/extension and radial/ulnar deviation to 0%, 18%, 38% and 55% of the Range of Motion (ROM) for 5 min each. The dependent measure was discomfort measured on a 100 mm visual analogue scale and for most of the analyses these were standardized by using the min-max procedure of . These Standardised Discomfort Levels (SDLs) were fitted to mathematical equations from which iso-discomfort contours were derived relative to the percentages of flexion/extension and radial/ulnar-deviation ROM used. The lowest standardized discomfort was found for the neutral wrist posture, followed by 18% extension with neutral radial/ulmar deviation. The results reveal interesting features of the processes involved and provide useful avenues for further research.
Adult↗
The effects of warnings and an educational brochure on computer working posture: a test of the C-HIP model in the context of RSI-relevant behaviour.
This study tested whether warnings can result in a better working posture with respect to RSI prevention compared with an educational brochure. By using a warning, the information provision on how to prevent RSI can be shorter and only interrupts with the task at hand for a short time. Five conditions were created to compare the effects on position adjustments of a warning displayed on the computer screen, a warning hanging on the wall, an educational brochure, a neutral interruption on the computer screen, and no intervention. Systematic observations of respondents' working postures showed that the computer warning led to significantly more correct position adjustments than the educational brochure and the two control situations, whereas the wall warning condition did not differ significantly from all other conditions. Questionnaires were used to study whether the number of position adjustments in the conditions could be explained by Wogalter's communication-human information processing (C-HIP) model. The questionnaire data suggest that the effect of the computer warning is caused by heightened attention for this type of intervention. The other stages of the C-HIP model--knowledge, attitude change, and motivation--might not be necessary in this situation in the explanation of behavioural changes. The conclusion is that warnings may be able to successfully replace educational brochures to produce behavioural changes.
Adult↗
Decrease of force capabilities as an index of upper limb fatigue.
The aim of the study was to assess upper limb fatigue on the basis of the force change index (FCI), which expresses changes in developed force, and to demonstrate that this index differentiates muscle fatigue of the upper limb depending on external load. The study was performed on ten young men in 12 conditions of external load. Ten conditions characterized repetitive work in a two-period cycle, in which both or one of the periods were loaded, and two conditions characterized continuous work with constant load. The participants tried to maintain hand-grip force at an imposed level during a determined time in the standard upper limb posture. Changes in values of recorded force exerted during successive cycles were approximated by a regression function. In most cases there was a strong correlation between the measurement data and the logarithmic regression curve. However, several cases of lower external load showed absence of such correlation. In 75% of the cases, there were statistically significant differences between the values of FCI calculated for individual conditions of external load. That means that FCI not only expresses muscle fatigue quantitatively but also points to the differences in upper limb fatigue resulting from differences in the external load. The study results have shown that the developed index (FCI) can be applied for fatigue assessment and discrimination with a more sophisticated model of a repetitive task than just a simple two-period work and rest model.
Adult↗
Hand and arm problems in flautists and a design for prevention.
Hand and arm problems are frequent in flautists. Severity is greatest in professional players, which can result in being unable to work. Based on a biomechanical analysis a support for the right hand was designed, which can be easily clipped on to the flute. Tests by professional flautists demonstrated that the right hand thumb support prevented rotation of the flute about its longitudinal axis. The latter reduces tension in forearm, wrist and fingers. This is the most important result of the study, which led to the introduction of the right hand thumb rest on the market.
Biomechanical Phenomena↗
Effect of cycle time and duty cycle on psychophysically determined acceptable levels in a highly repetitive task.
Psychophysical methodology has been used to develop guidelines for lifting and more recently similar methods have been applied to repetitive upper limb movements. While a range of cycle times are usually used, there is often no control for duty cycle. The purpose of this paper is to present psychophysically determined acceptable torques for a common upper limb task, with both cycle time and duty cycle conditions set by the researcher. Eight female participants, sitting at adjustable workstations, performed a simulated in-line screw running task. A computer-controlled torque motor applied a torque every 3, 6, 12 or 20 s with a duty cycle of 25, 50 or 83%. The participants worked with one set of conditions each day and self-selected the highest torque that they felt was acceptable without developing undue pain and discomfort. Duty cycle was found to significantly affect the amount of torque selected. With duty cycle controlled, cycle time was no longer found to have any significant effect on selected torque. Acceptable torques for 25, 50 and 83% duty cycles were 1.09, 0.9 and 0.73 Nm. Discomfort and stiffness were concentrated on the back of the hand and on the thumb web. These findings suggest that increased perception of discomfort with increased frequency (decreased cycle time) may be related to decreased rest/recovery time for muscles.
Adult↗
Back to basics with ProFlex.
Despite advances in tool and machine design and a growing emphasis on safety, the potential for certain painful and expensive occupational injuries continues in the workplace. Wrist and low-back injuries are a case in point. Low-back pain is clearly the most costly occupational health problem. About half of all back injuries result from poor lifting and handling techniques. In order to augment the effect of training and educating workers in lifting techniques, safety consultants have been suggesting that certain at-risk groups be provided with flexible, externally worn lower-back support. Susceptibility to repetitive strain injuries to the wrist, such as carpal tunnel syndrome, is not limited to users of heavy industrial machinery. Actions that cause the wrist to deviate from the neutral position, as well as repeated gripping and squeezing, can lead to median nerve compression. A useful supplement to the standard preventive approach is the use of palm pads.
Back Pain↗
Evaluation of impact loading in overhead work using a bolt pistol support.
This paper evaluates the effects of a bolt gun support stand on impact loading of the hand-arm system while firing spiked bolts into a steel beam. Ten healthy male subjects fired two bolts into the centre of the beam, one with and one without the aid of the support stand. During firing of a bolt gun, the shock sequences were recorded by two accelerometers. The analysis showed that peak values of acceleration decreased more than eightfold during firing with the bolt pistol support. The shock damping effect due to the bolt support was noted at the thumb (metacarpal level) and elbow bones.
Accidents, Occupational↗
An analytical method for characterizing repetitive motion and postural stress using spectral analysis.
The availability of small, inexpensive electrogoniometers has made wrist posture measurement during repetitive manual work practical. Efficient analytical methods, however, are not currently available for quantifying the degree of repetitiveness and the interaction with postural stress. Spectral analysis was investigated as a method for characterizing repetitive wrist motion and postural stress using a simple peg transfer task. Wrist posture was controlled by adjusting the pegboard location and by having subjects reach over an obstruction. Work pace was externally controlled using an auditory signal. Angular wrist flexion/extension and ulnar/radial deviation was recorded using a 60 Hz sample rate. Power spectra were computed by stratifying data segments into individual work elements, divided by break points associated with the task. Peak spectral magnitudes and frequency components corresponded closely with joint displacement amplitudes and repetition rates. Spectrum DC component magnitudes were directly related to sustained wrist postures.
Cumulative Trauma Disorders↗
Carpal tunnel syndrome: a products liability prospective.
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Carpal Tunnel Syndrome↗
A system for a strain-oriented analysis of the layout of assembly workplaces.
A measuring system for the more thorough analysis of muscular strain at assembly workplaces was developed. These workplaces were often based on the application of systems of predetermined motion time. The new measuring system makes use of the well-established method of electromyography, and synchronous recording of the hand-arm-shoulder motions by means of ultrasonic signals. Furthermore, a new calibration apparatus was installed, and used for the recording of maximum forces of several hand-arm-shoulder muscles during dynamic arm movements. The experimental arrangement aimed to support the design of a workplace layout, which could be used to indicate low strain motions and low strain work areas for the reach of the upper extremities. The results, yielded by the application of the measuring and evaluation system, can be the basis for a system of predetermined strain. Monitoring five muscles as an example, the application of the system for the analysis of different work rates and a worker-friendly assembly area is illustrated.
Arm↗
Psychophysical studies of repetitive wrist flexion and extension.
The purpose of this experiment was to investigate the feasibility of using psychophysical methods to determine maximum acceptable forces for various types and frequencies of repetitive wrist motion. Four adjustable work stations were built to simulate repetitive wrist flexion with a power grip, wrist flexion with a pinch grip, and wrist extension with a power grip. The study consisted of two separate experiments. Subjects worked for two days per week during the first experiment, and five days per week during the second experiment. Fifteen women completed the first experiment, working seven hours each day, two days per week, for 20 days. Repetition rates of 2, 5, 10, 15 and 20 motions per minute were used with each flexion and extension task. Maximum acceptable torques were determined for the various motions, grips, and repetition rates without dramatic changes in wrist strength, tactile sensitivity, or number of symptoms. Fourteen different women completed the second experiment, performing a wrist flexion motion (power grip) fifteen times per minute, seven hours per day, five days per week, for 23 days. There were no significant differences in maximum acceptable torque from day to day. However, the average maximum acceptable torque for a five days per week exposure was 36.3% lower than for the same task performed two days per week. Assuming that maximum acceptable torques decrease 36.3% for other repetition rates and motions, tables of maximum acceptable force were developed for female wrist flexion (power grip), female wrist flexion (pinch grip), and female wrist extension (power grip).
Adult↗
A single metric for quantifying biomechanical stress in repetitive motions and exertions.
The relative effects of repetition, force and posture were studied in order to investigate how continuous biomechanical measurements can be combined into a single metric corresponding to subjective discomfort. A full factorial experiment was conducted involving repetitive wrist flexion from a neutral posture to a given angle against a controlled force. Seven subjects performed the task using two paces (20 and 4 motions/min), two force levels (15 and 45 N) and two angles (15 and 45 degrees) for 1 h each. Discomfort was reported on a 10 cm visual analogue scale anchored between 'no discomfort' and 'very high discomfort'. Repeated measures analysis of variance showed that all main effects were statistically significant (p < 0.05) and no significant interactions were observed. A linear regression model was fitted to the data and used for generating frequency weighted digital filters that shape continuous recordings of repetitive motions and exertions into an output proportional to relative discomfort. The resulting high-pass digital filter had a 22 dB/decade attenuation slope. A simulated industrial task used for validating the model involved repetitively transferring pegs across a horizontal bar and inserting them into holes against a controlled resistance. Angular wrist data were recorded using an electrogoniometer and filtered. Six subjects performed the task of the three conditions consisting of (1) 15 wrist flexion, 15 N resistance and 6 motions min, (2) 15 wrist flexion. 45 N resistance and 12 motions/min, and (3) 45 degrees wrist flexion, 45 N resistance and 15 motions/min. Subjective discomfort was reported after performing the task for 1 h. Pearson correlations between subjective discomfort ratings and the integrated filtered biomechanical data for individual subjects ranged from 0.90 to 1.00. The pooled correlation across subjects was 0.67. This approach may be useful for physical stress exposure assessment and for design of tasks involving repetitive motions and exertions.
Adult↗
Agreement between a frequency-weighted filter for continuous biomechanical measurements of repetitive wrist flexion against a load and published psychophysical data.
A previous pilot study demonstrated that a force and frequency-weighted filter network could be developed for processing continuous biomechanical measures of repetitive wrist motions and exertions. The current study achieves the objective by modelling subjective discomfort for repetitive wrist flexion using controlled posture, pace and force. A three-level fractional factorial experiment was conducted involving repetitive wrist flexion (2 s/motion, 6 s/motion, 10 s/motion) from a neutral posture to a given angle (10 degrees, 28 degrees, 45 degrees) against a controlled resistance (5 N, 25 N, 50 N) using a Box Behnken design. Ten subjects participated. Discomfort was reported on a 10 cm visual analogue scale. Results of response surface regression analysis revealed that main effects of force, wrist flexion angle, and repetition were all significant (p < 0.05) and that no second-order effects were observed. Linear regression analysis on these factors established a discomfort model on which the filter characteristics were based. The pure error test model revealed no significant lack of fit (p > 0.05). The continuous model was compared and agreed with discrete psychophysical data from other published studies. The model was used for generating parameters for a force and frequency-weighted digital filter that weighs continuous wrist postural signals with corresponding force in proportion to the equal discomfort function as a function of frequency of repetition. These filters will enable integration of large quantities of biomechanical data in field studies.
Adult↗
Validation of a frequency-weighted filter for continuous biomechanical stress in repetitive wrist flexion tasks against a load.
This experiment validates a frequency-weighted filter for continuous measurements of force, posture and repetition using a stimulated industrial task. A peg transfer task was used requiring subjects to repetitively insert pegs into holes with controlled resistance. Ten subjects performed the task for six conditions. All wrist flexion angular data were recorded continually using an electrogoniometer and processed through the filter. Subjective discomfort was reported after performing the task for 1 h using a 10 cm visual analogue scale. Results from linear regression analysis showed that the instrument reliably estimated subjective discomfort (r2 = 0.873). Applications and limitations of this instrument are explored.
Adult↗
Analysis of multiple activity manual materials handling tasks using A Guide to Manual Materials Handling.
Manual handling of materials continues to be a hazardous activity, leading to a very significant number of severe overexertion injuries. Designing jobs that are within the physical capabilities of workers is one approach ergonomists have adopted to redress this problem. As a result, several job design procedures have been developed over the years. However, these procedures are limited to designing or evaluating only pure lifting jobs or only the lifting aspect of a materials handling job. This paper describes a general procedure that may be used to design or analyse materials handling jobs that involve several different kinds of activities (e.g. lifting, lowering, carrying, pushing, etc). The job design/analysis procedure utilizes an elemental approach (breaking the job into elements) and relies on databases provided in A Guide to Manual Materials Handling to compute associated risk factors. The use of the procedure is demonstrated with the help of two case studies.
Accidents, Occupational↗