Interindividual variation of physical load in a work task.
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OBJECTIVES: This study analyzed the variation in physical work load among subjects performing an identical work task. METHODS: Electromyographs from the trapezius and infraspinatus muscles and wrist movements were recorded bilaterally from 49 women during a highly repetitive industrial work task. An interview and a physical examination were used to define 12 potential explanatory factors, namely, age, anthropometric measures, muscle strength, work stress, and musculoskeletal disorders. RESULTS: For the electromyographs, the means of the 10th percentiles were 2.2% and 2.8% of the maximal voluntary electrical activity (%MVE) for the trapezius and infraspinatus muscles, respectively. However, the interindividual variations were very large [coefficients of variation (CV) 0.75 and 0.62, respectively]. Most of the variance could not be explained; only height, strength, and coactivation of the 2 muscles contributed significantly (R2(adj)0.20-0.52). The variation was still large, though smaller (CV < or =0.63), for values normalized to relative voluntary electrical activity (RVE). For the wrist movements, the median velocity was 29 degrees per second, and the interindividual variations were small (CV < or =0.24). Six factors contributed to the explained variance (R2(adj)0.12-0.55). CONCLUSIONS: The interindividual variation is small for wrist movements when the same work tasks are performed. In contrast, the electromyographic variation is large, even though less after RVE normalization, which reduces the influence of strength, than when MVE is used. Because of these variations, several electromyographs are needed to characterize the exposure of a specific work task in terms of muscular load, and individual electromyographs are preferable when the worker' s risk of myalgia is being studied. (+info)
In vivo finger flexor tendon force while tapping on a keyswitch.
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Force may be a risk factor for musculoskeletal disorders of the upper extremity associated with typing and keying. However, the internal finger flexor tendon forces and their relationship to fingertip forces during rapid tapping on a keyswitch have not yet been measured in vivo. During the open carpal tunnel release surgery of five human subjects, a tendon-force transducer was inserted on the flexor digitorum superficialis of the long finger. During surgery, subjects tapped with the long finger on a computer keyswitch, instrumented with a keycap load cell. The average tendon maximum forces during a keystroke ranged from 8.3 to 16.6 N (mean = 12.9 N, SD = 3.3 N) for the subjects, four to seven times larger than the maximum forces observed at the fingertip. Tendon forces estimated from an isometric tendon-force model were only one to two times larger than tip force, significantly less than the observed tendon forces (p = 0.001). The force histories of the tendon during a keystroke were not proportional to fingertip force. First, the tendon-force histories did not contain the high-frequency fingertip force components observed as the tip impacts with the end of key travel. Instead, tendon tension during a keystroke continued to increase throughout the impact. Second, following the maximum keycap force, tendon tension during a keystroke decreased more slowly than fingertip force, remaining elevated approximately twice as long as the fingertip force. The prolonged elevation of tendon forces may be the result of residual eccentric muscle contraction or passive muscle forces, or both, which are additive to increasing extensor activity during the release phase of the keystroke. (+info)
The wrist of the formula 1 driver.
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OBJECTIVES: During formula 1 driving, repetitive cumulative trauma may provoke nerve disorders such as nerve compression syndrome as well as osteoligament injuries. A study based on interrogatory and clinical examination of 22 drivers was carried out during the 1998 formula 1 World Championship in order to better define the type and frequency of these lesions. METHODS: The questions investigated nervous symptoms, such as paraesthesia and diminishment of sensitivity, and osteoligamentous symptoms, such as pain, specifying the localisation (ulnar side, dorsal aspect of the wrist, snuff box) and the effect of the wrist position on the intensity of the pain. Clinical examination was carried out bilaterally and symmetrically. RESULTS: Fourteen of the 22 drivers reported symptoms. One suffered cramp in his hands at the end of each race and one described a typical forearm effort compartment syndrome. Six drivers had effort "osteoligamentous" symptoms: three scapholunate pain; one medial hypercompression of the wrist; two sequellae of a distal radius fracture. Seven reported nerve disorders: two effort carpal tunnel syndromes; one typical carpal tunnel syndrome; one effort cubital tunnel syndrome; three paraesthesia in all fingers at the end of a race, without any objective signs. CONCLUSIONS: This appears to be the first report of upper extremity disorders in competition drivers. The use of a wrist pad to reduce the effects of vibration may help to prevent trauma to the wrist in formula 1 drivers. (+info)
A vascular basis for repetitive strain injury.
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OBJECTIVE: The blanket term 'repetitive strain injury' (RSI) covers a wide variety of work-related clinical syndromes, most of which are localized lesions. However, some patients complain of diffuse forearm pain, a clinically distinct form of RSI, the aetiology of which is unknown. METHODS: Using Doppler ultrasound, we measured the vascular responses to muscular work in the radial artery in 13 patients with bilateral diffuse forearm pain, seven with unilateral diffuse pain and 19 controls with localized arm pain. RESULTS: We found that in diffuse forearm pain the radial artery is relatively constricted compared to the controls and fails to vasodilate with exercise, which suggests that diffuse forearm pain may be due to physiological claudication of the working forearm muscle. CONCLUSION: A possible explanation is inhibition of local endothelial nitric oxide function, and this may be an unusual secondary, but self-perpetuating, pain condition which can follow other more specific, but chronic, arm pain syndromes in susceptible individuals. (+info)
Work related risk factors for musculoskeletal complaints in the spinning industry in Lithuania.
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OBJECTIVES: To describe the prevalence of self reported musculoskeletal complaints in the back, arms or neck, and legs among workers in the spinning industry, and to investigate the relations between these complaints and work related variables. METHODS: An interview based questionnaire survey was carried out in two spinning industry factories in Lithuania. RESULTS: The study group consisted of all workers in production (n = 363). Symptoms of the legs were the musculoskeletal symptom reported most often (61%). Many subjects had arms or neck (55%) or back problems (28%). 20% had experienced pain from all three sites. Almost 25% had had musculoskeletal pain every day and 16% had experienced constant pain during previous year. Packers had the highest risk of arms or neck problems whereas spinners had the highest risk of back or leg problems. Working in a strained posture (bending, work with arms raised up above shoulder level, and repetitive movements of the fingers) was associated with all three complaints. Only arms or neck complaints were associated with age. CONCLUSIONS: Musculoskeletal disorders are a common problem among workers producing gobelin or synthetic thread in Lithuania and working in a strained posture is a risk factor for developing musculoskeletal disorders in three body sites: legs, arms or neck, and back. To better understand the different aspects of physical load as risk factors, a more detailed study of the frequency of postural changes as well as an observation of individually adopted postures would be necessary. This applies to intervention studies in factories of the spinning industry to prevent complaints of the legs and shoulders. (+info)
Do repetitive tasks give rise to musculoskeletal disorders?
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Repetitive tasks can undoubtedly cause discomfort and pain, but whether they cause or worsen the pathology causing the pain is most uncertain. Research in this area is difficult as the 'work-related upper limb disorders' do not occur exclusively in workers and because there is no simple, reliable and reproducible test for most 'work-related upper limb disorders'. Furthermore many studies are difficult to interpret as they detect disease by the presence of symptoms: one would expect manual workers to complain of more symptoms than sedentary workers and symptom aggravation does not tell one anything about the causation of the underlying pathology. (+info)
PURPOSE: Finger ischemia caused by embolic occlusion of digital arteries originating from the palmar ulnar artery in a person repetitively striking objects with the heel of the hand has been termed hypothenar hammer syndrome (HHS). Previous reports have attributed the arterial pathology to traumatic injury to normal vessels. A large experience leads us to hypothesize that HHS results from trauma to intrinsically abnormal arteries. METHODS: We reviewed the arteriography, histology, and clinical outcome of all patients treated for HHS in a university clinical research center study of hand ischemia, which prospectively enrolled more than 1300 subjects from 1971 to 1998. RESULTS: Twenty-one men had HHS. All had occupational (mechanic, carpenter, etc) or avocational (woodworker) exposure to repetitive palmar trauma. All patients underwent upper-extremity and hand arteriography, unilateral in eight patients (38%) and bilateral in 13 patients (62%). By means of arteriogram, multiple digital artery occlusions were shown in the symptomatic hand, with either segmental ulnar artery occlusion in the palm or characteristic "corkscrew" elongation, with alternating stenoses and ectasia. Similar changes in the contralateral asymptomatic (and less traumatized) hand were shown by means of 12 of 13 bilateral arteriograms (92%). Twenty-one operations, consisting of segmental ulnar artery excision in the palm and vein grafting, were performed on 19 patients. Histology was compatible with fibromuscular dysplasia with superimposed trauma. Patency of arterial repairs at 2 years was 84%. One patient (5%) required amputative debridement of necrotic finger tips. No other tissue loss occurred. There have been no recurrences of ischemia in patients with patent bypass grafts. CONCLUSION: To our knowledge, this is the largest reported group of HHS patients. The characteristic angiographic appearance, histologic findings, and striking incidence of bilateral abnormalities in patients with unilateral symptoms lead us to conclude that HHS occurs when persons with preexisting palmar ulnar artery fibrodysplasia experience repetitive palmar trauma. This revised theory for the etiology of HHS explains why HHS does not develop in most patients with repetitive palmar trauma. (+info)
Evaluation of overuse elbow injuries.
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The evaluation of elbow pain can be challenging because of the complexity of the joint and its central location in the upper extremity. Diagnosing the injury correctly requires an understanding of the anatomy of the elbow, which includes three articulations, two ligament complexes, four muscle groups and three major nerves. The history should be directed at pinpointing the location of symptoms and the activities that cause the patient's pain. It is important to identify the specific musculotendinous structures that are at risk for overuse or have been injured through overuse. Mechanical symptoms are indicative of intra-articular pathology, whereas neurologic symptoms are characteristic of nerve entrapment syndromes. Physical examination of the elbow and related structures should confirm the diagnosis. Only a minority of patients require diagnostic studies. Basic treatment principles are described by the acronym PRICEMM: protection, rest, ice, compression, elevation, medication and modalities (physical therapy). Surgical consultation is warranted in selected patients. (+info)