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PubMed2006

Sensory-motor control of ligaments and associated neuromuscular disorders.

The ligaments were considered, over several centuries, as the major restraints of the joints, keeping the associated bones in position and preventing instability, e.g. their separation from each other and/or mal-alignment. This project, conducted over 25 years, presents the following hypothesis: 1. Ligaments are also major sensory organs, capable of monitoring relevant kinesthetic and proprioceptive data. 2. Excitatory and inhibitory reflex arcs from sensory organs within the ligaments recruit/de-recruit the musculature to participate in maintaining joint stability as needed by the movement type performed. 3. The synergy of the ligament and associated musculature allocates prominent role for muscles in maintaining joint stability. 4. The viscoelastic properties of ligaments and their classical responses to static and cyclic loads or movements such as creep, tension-relaxation, hysteresis and strain rate dependence decreases their effectiveness as joint restraint and stabilizers and as sensory organs and exposes the joint to injury. 5. Long-term exposure of ligaments to static or cyclic loads/movements in a certain dose-duration paradigms consisting of high loads, long loading duration, high number of load repetitions, high frequency or rate of loading and short rest periods develops acute inflammatory responses which require long rest periods to resolve. These inflammatory responses are associated with a temporary (acute) neuromuscular disorder and during such period high exposure to injury is present. 6. Continued exposure of an inflamed ligament to static or cyclic load may result in a chronic inflammation and the associated chronic neuromuscular disorder known as cumulative trauma disorder (CTD). 7. The knowledge gained from basic and applied research on the sensory - motor function of ligaments can be used as infrastructure for translational research; mostly for the development of "smart orthotic" systems for ligament deficient patients. Three such "smart orthosis", for the knee and lumbar spine are described. 8. The knowledge gained from the basic and applied research manifests in new physiotherapy modalities for ligament deficient patients. Ligaments, therefore, are important structures with significant impact on motor control and a strong influence on the quality of movement, safety/stability of the joint and potential disorders that impact the safety and health of workers and athletes.

Clinical Trials as Topic↗
PubMed2001

Computer terminal work and the benefit of microbreaks.

Microbreaks are scheduled rest breaks taken to prevent the onset or progression of cumulative trauma disorders in the computerized workstation environment. The authors examined the benefit of microbreaks by investigating myoelectric signal (MES) behavior, perceived discomfort, and worker productivity while individuals performed their usual keying work. Participants were randomly assigned to one of three experimental groups. Each participant provided data from working sessions where they took no breaks, and from working sessions where they took breaks according to their group assignment: microbreaks at their own discretion (control), microbreaks at 20 min intervals, and microbreaks at 40 min intervals. Four main muscle areas were studied: the cervical extensors, the lumbar erector spinae, the upper trapezius/supraspinatus, and the wrist and finger extensors. The authors have previously shown that when computer workers remained seated at their workstation, the muscles performing sustained postural contractions displayed a cyclic trend in the mean frequency (MNF) of the MES (McLean et al., J. Electrophysiol. Kinesiol. 10 (1) (2000) 33). The data provided evidence (p < 0.05) that all microbreak protocols were associated with a higher frequency of MNF cycling at the wrist extensors, at the neck when microbreaks were taken by the control and 40 min protocol groups, and at the back when breaks were taken by the 20 and 40 min protocol groups. No significant change in the frequency of MNF cycling was noted at the shoulder. It was determined (p < 0.05) that microbreaks had a positive effect on reducing discomfort in all areas studied during computer terminal work, particularly when breaks were taken at 20 min intervals. Finally, microbreaks showed no evidence of a detrimental effect on worker productivity. The underlying cause of MNF cycling, and its relationship to the development of discomfort or cumulative trauma disorders remains to be determined.

Adult↗
PubMed2003

Neuromuscular dysfunction elicited by cyclic lumbar flexion.

An attempt was made to develop an in vivo model that could explain the neurophysiological and biomechanical processes active in the development of the idiopathic low back disorder common in workers who perform repetitive lifting tasks in industry. Passive cyclic flexion of the feline lumbar spine at 0.1 HZ for 20 min resulted in creep of the supraspinous ligament and other lumbar viscoelastic tissues as well as spasms superimposed on a decreasing electromyogram (EMG) elicited reflexly from the multifidus muscles. Rest for 7 h did not allow full recovery of the viscoelastic creep; the multifidus EMG gradually increased with initial and delayed hyperexcitability. Increasing the peak load of the cyclic flexion resulted in larger creep in the passive tissues and required a longer time for recovery of reflex EMG activity and longer delayed hyperexcitability, but development of spasms and hyperexcitability was unaffected. It is conceivable that damage to the viscoelastic tissues elicits an inflammatory process that in turn triggers a transient neuromuscular disorder. The present findings provide a biomechanical and neurophysiological explanation for a common idiopathic low back disorder as well as for the development of a cumulative trauma disorder often seen in workers engaged in repetitive lumbar flexion.

Animals↗
PubMedDate not supplied

Determining the cause of upper extremity complaints in the workplace.

Occupational musculoskeletal disorders of the upper extremity have been termed cumulative trauma disorders (CTDs) and are considered to result from repetitive job function. Determination of work-relatedness of CTDs has far-reaching consequences. The physician equipped with objective, scientific knowledge is less likely to encourage disability or stress the workers' compensation system.

Arm Injuries↗
PubMed1993

Occupational risk factors associated with soft tissue disorders of the shoulder: a review of recent investigations in the literature.

Cumulative trauma illness currently accounts for over half of all occupational illness in the United States. From 1987 to 1989 there was a 100% increase in the reported number of cases of cumulative trauma illness (Bureau of Labor Statistics 1990). Shoulder region pain ranks second only to low back and neck pain in clinical frequency, and the occurrence of occupational shoulder illness is on the rise. This paper summarizes findings of a subset of recent epidemiologic, laboratory, and field studies conducted in order to identify occupational risk factors for cumulative trauma disorders (CTDs) of the shoulder region. These studies have identified the following risk factors as being associated with particular shoulder pain syndromes: awkward or static postures, heavy work, direct load bearing, repetitive arm movements, working with hands above shoulder height, and lack of rest. The paper begins with a discussion of several shoulder disorders, includes problems in studying cumulative trauma, presents results of recent studies, and concludes with suggested ergonomic controls that could help to reduce the incidence of shoulder disorders, by eliminating or reducing exposure to the associated risk factors.

Bursitis↗
PubMed1995

Psychophysical frequency and sustained exertion at varying wrist postures for a drilling task.

Two laboratory experiments were conducted; first, to utilize the psychophysical approach (method of adjustment) to establish maximum acceptable frequency (MAF) for a sheet metal drilling task and, second, to examine the effect of sustained, static exertion upon objective and subjective measures under similar task conditions. In both experiments, the wrist posture (flexation, ulnar deviation) required by the task was varied. Twelve healthy females served as subjects. Results show that the psychophysically adjusted task frequency was significantly lower when wrist deviation was required, particularly flexion. MAF for one-third (25 degrees) and two-thirds (50 degrees) flexion were 88% and 73%, respectively, of those selected in the neutral posture. Furthermore, these results were supported by trends in grip strength, heart rate, blood pressure, EMG and perceived exertion. Results from the sustained exertion trials revealed that significant increases in physiological parameters occurred during 3-minute sessions and that this trend was exasperated with deviated wrist posture, particularly flexion. Considering results of both experiments, it was concluded that while the neutral wrist posture may be preferred for a drilling operation, task frequency should be reduced for deviated postures when redesign is not feasible and it is further recommended that deviation be limited to one-third maximum flexion (25 degrees) and two-thirds maximum ulnar deviation (30 degrees). It is also suggested that the psychophysical approach may be utilized to establish 'acceptable' parameters for other industrial tasks involving upper extremity stress, particularly in the current absence of more objective biomechanical and/or physiological criteria for reducing the risk of exposure to cumulative trauma disorders.

Adult↗
PubMed1990

"Negative symptoms": a cumulative trauma stress disorder?

A theory is proposed that "negative symptoms", which are usually associated with schizophrenia, are manifestations of a traumatic stress disorder that is fundamentally similar in terms of the clinical phenomena and pathophysiological disturbance to chronic post-traumatic stress disorder (PTSD) as defined in DSM-III-R. Wider theoretical implications are explored briefly.

Arousal↗
PubMed1998

Australian repetition strain injury phenomenon.

The industrial upper limb pain epidemic colloquially known as repetition strain injury rapidly increased in the early 1980s to peak in 1985. Its less precipitous decline coincided with an awareness that repetition strain injury was a nonphysical sociopolitical phenomenon and a corresponding loss of the pecuniary benefits enjoyed by the powerful vested interest groups. Although its protagonists incorrectly claimed that this was a new disease, the rise and fall of repetition strain injury followed its historical predecessors including telegraphists' wrist and writer's cramp. Those affected by this phenomenon, a clearly defined cohort, were all employees who were highly suggestible and engaged in menial repetitious tasks with little job satisfaction. These patients were differentiated from those with genuine work related injuries whose symptoms are reproducible, with physical signs easily defined, disease identifiable, and response to physical treatment predictable. Most patients with repetition strain injury genuinely suffered the symptoms of which they complained and made little secondary gain relative to the protagonists of repetition strain injury who had a vested interest. The similarities between Australian repetition strain injury in the 1980s and American cumulative trauma disorder in the 1990s is compelling.

Arm Injuries↗
PubMed2004

Upper extremity work-related musculoskeletal disorders: a treatment perspective.

Numerous terms, including repetitive-stress injuries and cumulative-trauma disorders, have been used to describe what is now commonly termed work-related musculoskeletal disorders. The etiology of work-related musculoskeletal disorders is multifactorial and includes physical, individual, and psychosocial factors that contribute to the presenting symptoms. Prolonged positioning away from the ideal posture will affect neural and other soft tissues in the upper extremity. Abnormal postures and positions may result in chronic nerve compression or may shorten muscles and, if the muscle crosses over a nerve, compression may occur. These postures may also contribute to muscle imbalance. A thorough clinical evaluation is necessary to identify all sites of nerve compression, muscle imbalance, and factors affecting patient symptoms so that appropriate intervention can be instituted. Management must include patient education, postural correction, and a specific physical therapy program to address the multiple levels of nerve compression and cervicoscapular muscle imbalance. In addition to physical therapy intervention, behavioral modification at home and at work may be necessary for successful management.

Cumulative Trauma Disorders↗
PubMedDate not supplied

Applying ergonomics to nurse computer workstations: review and recommendations.

Nursing is associated with high rates of musculoskeletal disorders from patient handling, and nurses are at high risk for developing cumulative trauma disorders, which can result from computer usage. Although there are many benefits to using computers in the workplace, nurses need to incorporate ergonomic factors into work settings to promote safe workplace environments. This article reviews recent literature about computer workstation ergonomics, discusses related policies, and makes recommendations about computer workstation design and related research in nursing workplace settings.

Computer Terminals↗
PubMed1997

Minimizing fatigue during repetitive jobs: optimal work-rest schedules.

Twenty women were asked to generate forces using a dynamometer that were consistent with one of three different work-rest schedules (a low-, medium-, and high-force schedule). Each work-rest schedule consisted of 6 identical blocks of 10 work-rest cycles. Each of the 10 work-rest cycles lasted 1 min. The first work-rest cycle in each block consisted of a 6-s maximal voluntary contraction and a 54-s rest. The remaining 9 work-rest cycles in each block consisted of a submaximal contraction and a rest period. The desired force of the submaximal contraction, the length of this contraction, and the duration of the rest period remained constant within schedules but varied across schedules. The amount of physiological work was kept constant among schedules. The fatigue that developed in the medium-force schedule was significantly lower than that developed in either the low- or high-force schedule. A model was developed that predicted the amount of fatiguable strength at the beginning and end of each contraction of a work-rest cycle. When fit to the results from the experiment, the model explained 94% of the variance. The model can be used to predict the work-rest schedule that minimizes fatigue in a given repetitive job, thereby potentially increasing productivity and reducing the incidence of cumulative trauma disorders.

Adult↗
PubMed2006

Upper extremity disorders in the workplace: costs and outcomes beyond the first return to work.

BACKGROUND: Cumulative trauma disorders of the upper extremities (CTD) have become increasingly important in workers' compensation caseloads over the last two decades. Relative to occupational back pain, CTD have been much less studied. METHODS: We analyzed post-injury employment patterns and return-to-work probabilities for a sample of Ontario workers with CTD, for up to five years after injury. Results for workers with CTD are compared to results for workers with back injuries or fractures. RESULTS: Most workers with CTD return to work at least once, but a first return does not necessarily mark the end of work disability. Among workers absent at least once, 26% with CTD report a second injury-related absence, compared to 18% with back pain and 12% with fractures. After five years, focusing on first returns underestimates work-loss days associated with CTD by 32%. CONCLUSIONS: A substantial proportion of workers with CTD or work-related back pain experience injury-related absences after their first return to work. Focusing on the first return to work is misleading for both injury groups, but even more so for CTD, as they appear to be even more susceptible to multiple spells of work absence.

Adult↗
PubMed1993

The purposes of occupational medical surveillance in US industry and related health findings.

The primary purpose for implementing medical surveillance is to protect the general health and fitness of all employees. The next most frequent purpose of medical surveillance programs is to determine whether employees have the physical capability to perform their jobs (ie, surveillance to establish "fitness for duty"). The most commonly reported uses of medical surveillance data for establishments across all industry divisions were to implement or change work practices, to implement or change administrative control programs, to modify training programs, and to change personal protective equipment. Eighteen percent of establishments in all size classes and industries that have medical surveillance programs have identified adverse health effects among employees. The health effects most commonly identified by the medical surveillance programs were repetitive trauma, hearing loss, and skin disorders. Programs designed to detect hearing loss and cumulative trauma disorders, are in fact, finding these adverse effects. Among employees actually receiving periodic medical surveillance tests (6 million), 5% were found to have an abnormal test result.

Humans↗
PubMed2003

Biomechanics and electromyography of a cumulative lumbar disorder: response to static flexion.

OBJECTIVE: To assess the mechanical and neurological processes active in the development of a cumulative trauma disorder (CTD) associated with repetitive exposure to periods of static lumbar flexion. METHODS: The spine of the feline model was subjected to a series of three 10 min sessions of static lumbar flexion with each session followed by a 10 min rest. A 7 h rest period was implemented after the series of three flexion-rest sessions while monitoring viscoelastic (disks, ligaments, etc.) creep and multifidus EMG. A model was fitted to the experimental data from the flexion-rest period and the 7 h recovery period. RESULTS: The creep developed in each 10 min static flexion period did not fully recovery during the following 10 min rest, resulting in a large cumulative creep at the end of the flexion-rest period. The cumulative creep did not fully recover over the following 7 h rest period. A neuromuscular disorder consisting of reduced muscular activity superimposed by spasms during static flexion periods and hyperexcitability during the 7 h recovery was evident. Comparison of the data to previous tests of continuous static flexion for 20 min reveal that the neuromuscular disorder elicited by the series of three 10 min flexion-rest was substantially attenuated when compared to a single 20 min static flexion although the overall work time was 50% larger. CONCLUSIONS: Frequent rest periods are highly beneficial in attenuating the development of a CTD, yet not able to prevent it, as viscoelastic tissues residual creep accumulates and its recovery is of extremely long duration. RELEVANCE: The data provides direct biomechanical and physiological evidence that explain the development of a CTD due to prolonged exposure to static lumbar flexion as well as confirms the epidemiological data correlating such work conditions with substantial increase in symptoms of low back disorders. The benefit of frequent rest periods in attenuating the risk of such a disorder is validated as an effective intervention.

Animals↗
PubMed1996

The effect of wrist and arm postures on peak pinch strength.

This paper examines the effect of various arm postures on peak pinch strength. Twenty (20) able-bodied, male subjects volunteered to participate in a set of two experiments. The first experiment examined the effect of shoulder and elbow posture on peak pinch strength. The second experiment examined the effect of forearm posture, wrist posture, and pinch type on peak pinch strength. Results from the first experiment indicated that elbow posture had a significant effect on pinch strength. It was documented that extreme elbow flexion decreased pinch strength by up to 9%. Results from the second experiment indicated that deviated wrist postures, forearm postures, and pinch type significantly decreased pinch strength as much as 33%. Ergonomic guidelines which utilize the above factors as significant modifiers of pinch strength capacity may assist ergonomists to reduce the risk of injury and development of cumulative trauma disorders in the workplace.

Adult↗
PubMed2006

High-repetition cyclic loading is a risk factor for a lumbar disorder.

Epidemiological data suggest that prolonged exposure to cyclic lumbar flexion elicits a chronic neuromuscular disorder and disability in workers. This study provides a physiological and biomechanical assessment of various repetitions of cyclic lumbar flexion sessions as a risk factor for development of an acute neuromuscular disorder. An in vivo feline model was subjected to 10 minutes of cyclic (0.25-HZ) loading, followed by a 10-minute rest period, repeated three times in one experimental group, six times in a second group, and nine times in the third group, followed by rest for 7 hours. Displacement of the lumbar viscoelastic tissue and reflex electromyographic (EMG) activity from the lumbar multifidus muscle were monitored. Creep developed and accumulated during each load/rest period and partially recovered during the subsequent rest. Loading periods were characterized by a decrease in reflex EMG activity with superimposed spasms. In the 7-hour recovery period, initial hyperexcitability was present in all groups, whereas only the six- and nine-repetition groups displayed significant delayed hyperexcitability, indicating the presence of acute inflammation. The mathematical model developed fit the data reasonably well, as the R2 values were generally near 0.90. It was concluded that the resulting delayed muscular hyperexcitability constitutes an acute neuromuscular disorder associated with exposure to many repetitions of cyclic lumbar flexion. The acute disorder can become chronic if not allowed sufficient rest to resolve itself. Workers engaged in cyclic lumbar flexion (e.g., loading/unloading, assembly workers) should avoid long-term exposure in order to prevent the development of a chronic neuromuscular condition known as cumulative trauma disorder.

Animals↗
PubMed1992

Ergonomic analysis to characterize task constraint and repetitiveness as risk factors for musculoskeletal disorders in telecommunication office work.

A modified activity analysis procedure was devised to quantify the presence of two task attributes identified in previous research as contributing to an increase in work demands and ergonomic hazards. The purpose of this study was to develop an exposure index based on the presence of two task attributes. The utility of this job activity analysis will, of course, be determined by the extent to which workers with varying degrees of muscular pain and discomfort correspond to the risk exposure group we have described. The results of both the medical and psychological assessments of the workers--contained in the final HETA report--will be used to assess the utility of our method and determine whether the task attributes of constraint and repetitiveness contribute to the onset of cumulative trauma disorders among clerical workers.

Cumulative Trauma Disorders↗
PubMed1998

Evaluation of supermarket bagging using a wrist motion monitor.

The supermarket industry has one of the highest numbers of repeated trauma illnesses. Checkout departments have a rate of musculoskeletal injuries 2 to 3 times higher than that of other supermarket departments. The primary objective of this study was to quantify the wrist motions required to bag groceries using a wrist motion monitor. The wrist motions included deviations, velocities, and accelerations for flexion-extension, radial-ulnar, and pronation-supination directions. The independent variables were handle type and object location. Objects with finger-thumb couplings required more extreme pronations, greater wrist velocities for pronation-supination deviations, and greater wrist accelerations for pronation-supination deviations than did other objects. Objects with 10-cm hand couplings required more extreme flexion, larger ranges of movement for radial-ulnar deviations and pronation-supination deviations, and greater wrist velocities in the radial-ulnar and pronation-supination directions than did 5-cm objects. The right and front locations required more extreme deviations than did the left and back locations. Because finger-thumb and 10-cm hand couplings require larger wrist deviations and greater velocities, these objects may pose a greater risk of developing cumulative trauma disorders to the bagger. Potential applications of this research include engineering design of grocery packaging and supermarket bagging workstations.

Adult↗