Risk factors for hand-wrist disorders in repetitive work.

OBJECTIVES: To identify the risk of hand-wrist disorders related to repetitive movements, use of hand force and wrist position in repetitive monotonous work. METHODS: Using questionnaires and physical examinations, the prevalence and incidence of hand-wrist pain and possible extensor tendonitis (wrist pain and palpation tenderness) were determined in 3123 employees in 19 industrial settings. With the use of questionnaires and video recordings of homogenous work tasks number of wrist movements, hand force requirements and wrist position were analysed as risk factors for hand-wrist disorders, controlling for potential personal and psychosocial confounders. All participants were re-examined three times during a follow-up period of three years. RESULTS: Force but not repetition and position was related to hand-wrist pain and possible tendonitis in the baseline analyses showing an exposure-response pattern. Odds ratios for the risk of hand pain was 1.7 (95% CI 1.3 to 2.2) and for possible tendonitis 1.9 (95% CI 1.1 to 3.3). There was no significant interaction between the ergonomic factors. In the follow-up analyses force remained a risk factor for hand pain (OR 1.4, 95% CI 1.1 to 1.8) and for possible tendonitis (OR 2.9, 95% CI 1.3 to 6.8). Repetition was also a risk factor for the onset of hand-wrist pain (OR 1.6, 95% CI 1.2 to 2.3). CONCLUSIONS: Increasing levels of force were associated with prevalent and incident hand-wrist pain and possible extensor tendonitis. The results for repetition were less consistent. Working with the hand in a non-neutral position could not be identified as a risk factor.

Understanding work related musculoskeletal pain: does repetitive work cause stress symptoms?

BACKGROUND: Pain in the neck and upper extremity is reported with high frequency in repetitive work. Mechanical overload of soft tissues seems a plausible mechanism, but psychological factors have received considerable attention during the past decade. If psychological factors are important for development of regional pain in repetitive work, stress symptoms would likely be on the causal path. AIMS: To examine whether objective measures of repetitive monotonous work are related to occurrence and development of stress symptoms. METHODS: In 1994-95, 2033 unskilled workers with continuous repetitive work and 813 workers with varied work were enrolled. Measures of repetitiveness and force requirements were quantified using video observations to obtain individual exposure estimates. Stress symptoms were recorded at baseline and after approximately one, two, and three years by the Setterlind Stress Profile Inventory. RESULTS: Repetitive work, task cycle time, and quantified measures of repetitive upper extremity movements including force requirements were not related to occurrence of stress symptoms at baseline or development of stress symptoms during three years of follow up. CONCLUSIONS: The findings do not indicate that repetitive work is associated with stress symptoms, but small effects cannot be ruled out. Thus the results question the importance of mental stress mechanisms in the causation of regional pain related to repetitive work. However, the findings should be interpreted with caution because the stress inventory has not been validated against a gold standard.

Adaptation to sudden unexpected loading of the low back--the effects of repeated trials.

The purpose of this study was to investigate short-term changes in reactions to sudden unexpected loading of the low back. The study utilized a set-up where a horizontal force of 58 N pointing forward suddenly was applied to the upper part of the subject's trunk. EMG activity from the erector spinae muscles and trunk movement data were recorded during 10 trials for 19 subjects. The analysis included EMG reaction time, mean rectified EMG amplitude during the period 50-250 ms after the sudden loading, and time elapsed until stopping of the forward movement of the trunk (stopping time). Reaction time means ranged from 66 to 97 ms (79+/-9 ms), and no difference was found between the trials. Conversely, the mean stopping time for the first trial (468 ms) was significantly higher than for trials 3-10 (359- 371 ms), and the average EMG amplitude during the period 50-250 ms after the sudden loading was lower for the first trial. This study showed that some subjects adapted to sudden unexpected loadings of the low back through a reduction in stopping time and a progression in EMG response during the first few trials. This possible adaptation to repeated trials have been overlooked in previous studies.

Physical exposure assessment in monotonous repetitive work--the PRIM study.

OBJECTIVES: A program called the Project on Research and Intervention in Monotonous Work (PRIM) was initiated in 1994 as a prospective cohort study of work-related musculoskeletal disorders. The group-based exposure assessment strategy, focusing on task-related exposure and used to obtain baseline measures of physical exposures, is reported in this paper. METHODS: Monotonous, repetitive worktasks were evaluated at 19 factories. Tasks with an estimated similarity in physical exposure were aggregated before 103 exposure groups were formed. Subjects from the exposure groups were randomly sampled for measurements, and task-related exposure levels were quantified by 43 single exposure items using a real-time video-based observation method that allowed computerized estimates of repetitiveness, body postures, force, and velocity. In combination with questionnaire-based data on task distribution, the duration of exposure was calculated at the individual level. RESULTS: The video-based observational method and the large number of exposure variables enabled the establishment of detailed quantitative exposure profiles in 103 task-based exposure groups. However, methodological problems associated with the use of grouped exposure assessment were revealed. Despite efforts to optimize group homogeneity, the within-group variance was larger than the between-group variance for several shoulder postural variables. CONCLUSIONS: A task-based exposure-assessment strategy can be successful in solving some of the main problems associated with the assessment of physical workplace exposures. The large within-group variance in exposure to nonneutral shoulder postures may eventually require individual assessment or the inclusion of groups with maximal contrast in exposure or both.

Assessment of work postures and movements using a video-based observation method and direct technical measurements.

The aim was to study postures and movements during repetitive work using video-based observations and direct technical measurements (inclinometers and goniometers). A total of 21 healthy women from a poultry processing plant volunteered. Neck flexion > 20 degrees was registered during 92% of the recorded time with the observation method, while the corresponding value measured with the inclinometer was 65%. Different reference positions and different measured variables apparently contributed to the differences between the methods. Mean wrist position was measured to be 0 degrees in flexion-extension and 19 degrees in ulnar deviation. Differences between the methods in the registered hand positions were small. The number of repetitive movements/minute and mean power frequency (MPF) of the electrogoniometer data was significantly related, showing both variables to be relevant measures of repetitiveness. In conclusion, the observation method and the technical measurements supplemented each other well. A reduction in class categories was suggested for future observation methods.

Exposure assessment of upper limb repetitive movements: a consensus document developed by the Technical Committee on Musculoskeletal Disorders of International Ergonomics Association (IEA) endorsed by International Commission on Occupational Health (ICOH).

This consensus document intends to supply a set of definitions, criteria and procedures useful to describe and, wherever possible, to assess the work conditions that can represent a physical overload for the upper limbs. The document is aimed at all the operators, i.e. occupational doctors but mainly technicians, who are, involved in risk exposure assessment and management. The document intends to provide methods and procedures easily applicable in the field, possibly not requiring sophisticated instrumentation and when possible based on observation procedures. The proposed methods shall be based as far as possible on knowledge and data from scientific literature: should they be contradictory or deficient, reference will be made to standards or pre-standards issued by national and international agencies and bodies, with the experience of researchers involved and common sense. In this regard, it is to be emphasized that the potential users increasingly demand an easily applicable method for description and assessment of work with repetitive movements. The group intends to give a response even if there are still uncertainties from a strictly scientific standpoint: however the group commits itself to perform subsequent validations especially of as yet unconsolidated issues. This document focuses specifically on identification of risk factors and describes some of the methods that have been developed for evaluating them. There is a rapidly developing body of literature on job analysis and not yet agreement on a single best way to analyze jobs. Professional judgement is required to select the appropriate methods. Analysis and design of jobs should to be integrated into an ongoing ergonomics program that includes management commitment, training, health surveillance, and medical case management. In summing up this report, space must be given to the check lists that are so often seen in the medical press, although this is not the occasion to propose a detailed analytical review.

Low back injury risk during repositioning of patients in bed: the influence of handling technique, patient weight and disability.

The objective of the study was to investigate the low back load during repositioning of patients in bed and to assess the influence of patient's weight and disability. Nine female health care workers (HCWs) carried out six patient-handling tasks with different patient weight (59 +/- 1, 83 +/- 2 and 110 +/- 4 kg) and handicap (hemiplegia, paraplegia and near-paralysis). The tasks were performed with optional use of simple, low-tech assistant devices (draw and sliding sheets). Peak low back compression exceeded the National Institute for Occupational Safety and Health action level of 3400 N in 25% of all trials (418). The influence of the HCW, i.e. the technique and assistive devices used, was higher than the effect of weight and disability in all tasks studied. ANOVA showed that on average for the six tasks 37%, 10% and 6% of the variance in low back loading was caused by variation in the factors HCW, patient's weight and disability, respectively. The result of this study is relevant for HCWs. It is shown that the repositioning technique and use of friction-reducing devices have higher influence on the low back load of the HCW than the patient's weight and disability.

The effect of delayed-onset muscle soreness on stretch reflexes in human low back muscles.

The aim of the study was to investigate the effect of moderate delayed-onset muscle soreness (DOMS) on the short latency stretch reflex (SLR) and long latency stretch reflex (LLR) response i.e. electromyographic (EMG) onset latencies and EMG amplitudes in erector spinae (ES). Nine males with muscle soreness (DOMS group) were tested 24, 48 h, and 7 days post-exercise. Eight males (control group) were tested likewise. EMG was measured from ES bilaterally at the level of L3/L4. The SLR was elicited by mechanically tapping the ES at L3/L4, and the LLR was elicited by sudden loadings of the spine. Significant reductions in force during maximal voluntary contractions and range of motion, and a significant increase in muscle soreness (measured by pressure algometry) and subjective experience of soreness in the low back indicated DOMS 24, and 48 h post-exercise in the DOMS group. No changes were observed in the control group. The SLR and LLR response were unaffected by DOMS, i.e. no changes in EMG latencies and amplitudes were observed. In conclusion, despite changes in DOMS indicators, the reflex system protecting the stability of the lumbar spine is apparently capable of maintaining an appropriate triggering of SLR and LLR.

Blood pressure response to low level static contractions.

The present study re-examines the 15% MVC concept, i.e. the existence of a circulatory steady-state in low intensity static contractions below 15% of maximal voluntary contraction (MVC). Mean arterial blood pressure was studied during static endurance contractions of the elbow flexor and extensor muscles at forces corresponding to 10% and 40% MVC. Mean value for endurance time at 10% MVC was significantly longer for flexion [111.3 (SD 56.1) min] than for extension [18.1 (SD 7.5) min; n = 7]. At 40% MVC the difference in mean endurance time disappeared [2.3 (SD 0.7) min for elbow flexion and 2.3 (SD 0.7) min for elbow extension]. Mean arterial blood pressure exhibited a continuous and progressive increase during the 10% MVC contractions indicating that the 15% MVC concept would not appear to be valid. The terminal blood pressure value recorded at the point of exhaustion in the 10% MVC elbow extension experiment was identical to the peak pressure attained in the 40% MVC contraction. For the elbow flexors the terminal pressor response was slightly but significantly lower at 10% MVC [122.3 (SD 10.1) mmHg, 16.3 (SD 1.4) kPa] in comparison with 40% MVC [130.4 (SD 7.4) mmHg, 17.4 (SD 1.0) kPa]. When the circulation to the muscles was arrested just prior to the cessation of the contraction, blood pressure only partly recovered and remained elevated for as long as the occlusion persisted, indicating the level of pressure-raising muscle chemoreflexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Work load during floor cleaning. The effect of cleaning methods and work technique.

Cardiovascular and muscle load levels were evaluated during floor cleaning. A group of 12 experienced female cleaners participated in the study. Of the subjects 6 used a mopping method and 6 a traditional scrub and cloth method. Heart rate, oxygen consumption, rating of perceived exertion, electromyography from the trapezius muscle and video recordings were obtained during floor cleaning. With respect to relative heart rate and oxygen consumption the two groups did not differ. The results revealed a high cardiovascular load corresponding on average to 53 percent of the individual maximal oxygen uptake. In addition 65 percent of the observed period was spent with the back in a position forward flexed more than 20 degrees C. The time spent in extreme forward back flexion was shorter for the mopping group. Both groups exhibited high static, median and peak shoulder muscle load levels of 10 percent, 25 percent and 54 percent maximal voluntary contraction, respectively. At the same time, however, the mopping group tended to have a higher shoulder load than the group using the scrub and cloth method. Furthermore, electromyographic signs of fatigue in the trapezius muscle indicated a more stereotype activation of the shoulder muscles during mopping than during scrubbing. Based on these results, it was concluded that mopping cannot be recommended as less strenuous than scrubbing.

Blood pressure, heart rate and EMG in low level static contractions.

The purposes of the present investigation were: to evaluate a possible use of changes in the mean spectral frequency (MSF) of the EMG power spectra as a measure of reflex cardiovascular responses originating from the muscles during static exercise; and to study the relation between muscle fibre composition, EMG, and the cardiovascular response. Heart rate (HR), arterial blood pressure (BP), myoelectric signal (EMG), and intramuscular temperature (Tm) were measured during prolonged static contractions in five healthy male subjects (25-44 yrs). Two studies were performed. In study I constant EMG contraction muscle force in the first 5 s of the knee-extensor contraction was set to 20% MVC, (maximal voluntary contraction), and in the rest of the 5 min contraction the myoelectric signal was kept constant by visual feedback from an oscilloscope. In study II, (constant force contraction) two 1 h 7% MVC isometric contractions of the elbow-flexors and extensors were performed on two separate days. During the 5 min constant EMG contraction, the force fell from 20 to 11% MVC, mean BP (MAP) increased from 97 +/- 5 to 120 +/- 4 mmHg (P less than 0.01), and the EMG MSF decreased from 87 +/- 16 to 66 +/- 9 Hz (P less than 0.01). The decrease in MSF was strongly correlated to the increase in MAP (r = 0.96, P less than 0.01). The intramuscular temperature showed a small increase from 34.3 degrees C to 35.3 degrees C (P less than 0.01). During the 1 h constant force contraction involving m. triceps, MAP increased from 104 +/- 10 to 120 +/- 12 mmHg, with a simultaneous decrease in the EMG MSF from 96 +/- 11 to 70 +/- 19 Hz and an increase in the EMG amplitude (247% of the initial value). In the contractions involving m. biceps, however, both MAP and EMG MSF remained almost unchanged, but EMG amplitude increased (197% of the initial value). Very modest changes in HR were observed: 63 +/- 6 to 66 +/- 6 beats min-1 and 61 +/- 5 to 59 +/- 7 beats min-1 in the contractions involving m. triceps and m. biceps, respectively. The intramuscular temperature increased simultaneously, 1.3 degrees C and 0.7 degrees C in m. triceps and m. biceps, respectively. The results from the constant EMG contractions indicate the existence of a common 'trigger' for both the increase in BP and the decrease in EMG MSF; and the extracellular [K] is put forward as a candidate.(ABSTRACT TRUNCATED AT 400 WORDS)

Motor unit recruitment during prolonged isometric contractions.

Motor unit recruitment patterns were studied during prolonged isometric contraction using fine wire electrodes. Single motor unit potentials were recorded from the brachial biceps muscle of eight male subjects, during isometric endurance experiments conducted at relative workloads corresponding to 10% and 40% of maximal voluntary contraction (MVC), respectively. The recordings from the 10% MVC experiment demonstrated a characteristic time-dependent recruitment. As the contraction progressed both the mean number of motor unit spikes counted and the mean amplitude of the spikes increased significantly (P < 0.01). This progressive increase in spike activity was the result of a discontinuous process with periods of increasing and decreasing activity. The phenomenon in which newly recruited motor units replace previously active units is termed "motor unit rotation" and appeared to be an important characteristic of motor control during a prolonged low level contraction. In contrast to the 10% MVC experiment, there was no indication of de novo recruitment in the 40% MVC experiment. Near the point of exhaustion a marked change in action potential shape and duration dominated the recordings. These findings demonstrate a conspicuous difference in the patterns of motor unit recruitment during a 10% and a 40% MVC sustained contraction. It is suggested that there is a close relationship between intrinsic muscle properties and central nervous system recruitment strategies which is entirely different in fatiguing high and low level isometric contractions.

Plasma potassium concentration and doppler blood flow during and following submaximal handgrip contractions.

The aim of the present study was to investigate the time-course of blood velocity in the forearm during and following isometric handgrip contractions and to reveal a possible temporal relationship between the circulatory response and venous effluent potassium concentration ([K]) not only during contractions but also during the post-exercise recovery period. Contractions of 15% maximal voluntary contraction (MVC) and 30% MVC with and without 3 min of arterial occlusion following the contractions were studied. All contractions induced a significant increase in venous plasma [K] from an average resting level of 4.0 to 5.0 mM during 15% MVC and 5.8 mM during 30% MVC. Blood velocity increased from a resting level of 0.07 to 0.22 m s-1 and 0.36 m s-1 during 15% and 30% MVC, respectively. MVC of 30% always elicited a larger blood velocity and [K] response than 15% MVC. Following the contractions hyperaemia was elicited. Recovery of the local blood velocity was markedly slower than the K recovery, since [K] remained significantly above resting level for only 25 s following 15% MVC and 45 s following 30% MVC, while blood velocity remained elevated for 2 min and more than 7 min following 15 and 30% MVC, respectively. Further, a larger hyperaemia following the occlusion was elicited as compared to the contraction without occlusion, in spite of [K] being lower immediately after the occlusion period than immediately after the contraction. Finally, [K] decreased below resting level in the recovery period while the blood velocity remained elevated. Therefore, the present study showed that the venous plasma [K] is not causally related to the prolonged post-exercise hyperaemia. The skin temperature remained unchanged during the contractions, while during the recovery period the skin temperature increased for several minutes. The major part of the temperature increase was likely to be due to conductance of heart from muscles to skin surface as a consequence of muscle hyperaemia.

Role of potassium in the reflex regulation of blood pressure during static exercise in man.

1. The relationship between [K+] in venous effluent blood and alterations in mean arterial blood pressure was studied during static handgrip contractions at 15 and 30% of maximal voluntary contraction (MVC). 2. To further elucidate the importance of K+ in the reflex regulation of blood pressure a situation with normal recovery was compared with a situation in which 3 min of post-exercise occlusion was applied by arresting the circulation to the forearm just prior to the cessation of the contraction. 3. There was a temporal as well as quantitative correlation between venous [K+] and the blood pressure response during and after static exercise. During 30% MVC mean arterial blood pressure (MAP) attained 161.7 mmHg and venous [K+] 5.8 mM, while the corresponding values during 15% MVC were 121.5 mmHg and 5.0 mM. 4. In the occlusion period mean arterial blood pressure remained elevated above resting level and provided a measure of the magnitude of muscle chemoreflexes. In the same period venous [K+] was maintained at 5.3 mM and 4.6 mM following 30% MVC and 15% MVC respectively. This is indicative of interstitial concentrations of above 8-10 mM. This level is sufficiently high to stimulate type III and IV muscle afferents involved in the reflex regulation of blood pressure, and strengthens the notion that K+ may play an important role in eliciting the pressor reflex. 5. In contrast to [K+] the time course of venous blood concentrations of lactate and ammonia (NH3) exhibited a clear dissociation from the blood pressure recordings.

Electromyography and fatigue during prolonged, low-level static contractions.

Findings from five separate studies of EMG changes and muscle fatigue during prolonged low-level static contractions are summarized, and the possible mechanisms behind the changes are briefly discussed. Sustained static contractions (10%, 7% and 5% MVC) of up to 1 h duration were performed by finger flexors, elbow flexors and extensors, and knee extensors. In one experiment, intermittent static arm pulling (triceps) (10 s contraction and 5 s rest, average work load 14% and 10% MVC) was performed for 7 h. The endurance time for the sustained contractions was around one hour for 10% MVC, and it was shown--all in all--that the concept of "indefinite" endurance times at contractions below 15-20% MVC cannot be maintained. After 5% MVC sustained contractions for one hour a 12% reduction in MVC was seen, and significant increases in EMG amplitude and decreases in the mean spectral frequency of the EMG-power spectrum were found. Marked differences were also seen in the EMG changes in the elbow flexors and extensors, and transcutaneous electrical stimulation of the knee extensors showed that low frequency fatigue was present after the contraction. With intermittent contractions similar changes in the EMG parameters were seen after 2-3 h of contractions at 14% MVC. On average, during contractions of 10% MVC no EMG changes were detected. Increased extracellular potassium concentration in the contracting muscles is suggested as a possible explanation of these findings.

Motor unit activation patterns during concentric wrist flexion in humans with different muscle fibre composition.

Muscle activity was recorded from the flexor carpi radialis muscle during static and dynamic-concentric wrist flexion in six subjects, who had exhibited large differences in histochemically identified muscle fibre composition. Motor unit recruitment patterns were identified by sampling 310 motor units and counting firing rates in pulses per second (pps). During concentric wrist flexion at 30% of maximal exercise intensity the mean firing rate was 27 (SD 13) pps. This was around twice the value of 12 (SD 5) pps recorded during sustained static contraction at 30% of maximal voluntary contraction, despite a larger absolute force level during the static contraction. A similar pattern of higher firing rates during dynamic exercise was seen when concentric wrist flexion at 60% of maximal exercise intensity [30 (SD 14) pps] was compared with sustained static contraction at 60% of maximal voluntary contraction [19 (SD 8) pps]. The increase in dynamic exercise intensity was accomplished by recruitment of additional motor units rather than by increasing the firing rate as during static contractions. No difference in mean firing rates was found among subjects with different muscle fibre composition, who had previously exhibited marked differences in metabolic response during corresponding dynamic contractions. It was concluded that during submaximal dynamic contractions motor unit firing rate cannot be deduced from observations during static contractions and that muscle fibre composition may play a minor role.

Mechanisms contributing to different joint moments observed during human walking.

The present study investigated factors that contribute to the formation of a previously reported knee joint flexor moment during the stance phase of walking. Contradictory results have been reported on this flexor moment, which some but not all individuals exhibit. Seven healthy male subjects were high speed filmed while walking across a force platform, and EMG recordings were obtained from five leg muscles. To investigate segment interactions, net joint moments about the ankle, knee and hip joint were calculated by inverse dynamics and each term in the equation used for the moment calculation was evaluated during the time-course of the step cycle. To test the hypothesis that net joint moments are balanced by an external moment formed by the resulting ground reaction vector multiplied by the perpendicular distance to the actual joint, external moment arms were calculated by the floor reaction force vector approach (FRFV). Contrasting two subjects with different net joint moments about the knee and ankle joint revealed that the knee joint flexor moment could not be explained by an opposite external moment. The external moments were calculated by a simplified method (FRFV) in which the point of force application is incorrect for joints above the ankle joint. However, at the ankle joint the net joint moment was always opposed by an external moment of opposite polarity. A detailed examination of the equation used for the net joint moment calculation showed that a knee joint flexor moment can be caused directly by a large plantar flexor moment about the ankle joint. For example. the soleus muscle can pull the tibia and generate an extensor moment about the knee joint, which in turn has to be opposed by a knee flexor moment from the hamstring muscles. Otherwise the desired joint angles cannot be obtained during human walking. It is therefore suggested that the kinematics regarding how the foot is placed on the ground may influence the net ankle joint moment, while the moment patterns about the knee and hip joint are determined by segment interaction and the requirements for controlling the direction of the resulting ground reaction vector. In vertical jumping it is advantageous to generate extensor moments about the knee and hip joint simultaneously, while in horizontal locomotion this would result in inefficient vertical movements.

Risk factors in the onset of neck/shoulder pain in a prospective study of workers in industrial and service companies.

AIMS: To quantify the relative contribution of work related physical factors, psychosocial workplace factors, and individual factors and aspects of somatisation to the onset of neck/shoulder pain. METHODS: Four year prospective cohort study of workers from industrial and service companies in Denmark. Participants were 3123 workers, previously enrolled in a cross sectional study, where objective measurement of physical workplace factors was used. Eligible participants were followed on three subsequent occasions with approximately one year intervals. Outcomes of interest were: new onset of neck/shoulder pain (symptom cases); and neck/shoulder pain with pressure tenderness in the muscles of the neck/shoulder region (clinical cases). RESULTS: During follow up, 636 (14.1%) participants reported neck/shoulder pain of new onset; among these, 82 (1.7%) also had clinical signs of substantial muscle tenderness. High shoulder repetition was related to being a future symptom case, and a future clinical case. Repetition was strongly intercorrelated with other physical measures. High job demands were associated with future status as a symptom case, and as a clinical case. A high level of distress predicted subsequent neck/shoulder pain, and neck/shoulder pain with pressure tenderness. CONCLUSIONS: High levels of distress, and physical and psychosocial workplace factors are predictors of onset of pain in the neck and/or shoulders, particularly pain with pressure tenderness in the muscles.

Prognosis of shoulder tendonitis in repetitive work: a follow up study in a cohort of Danish industrial and service workers.

BACKGROUND: The physical and psychosocial work environment is expected to modify recovery from shoulder disorders, but knowledge is limited. METHODS: In a follow up study of musculoskeletal disorders in industrial and service workers, 113 employees were identified with a history of shoulder pain combined with clinical signs of shoulder tendonitis. The workers had yearly re-examinations up to three times. Quantitative estimates of duration, repetitiveness, and forcefulness of current tasks were obtained from video recordings. Perception of job demands, decision latitude, and social support was recorded by a job content questionnaire. Recovery of shoulder tendonitis was analysed by Kaplan-Meier survival technique and by logistic regression on exposure variables and individual characteristics in models, allowing for time varying exposures. RESULTS: Some 50% of workers recovered within 10 months (95% CI 6 to 14 months). Higher age was strongly related to slow recovery, while physical job exposures were not. Perception of demands, control, and social support at the time when the shoulder disorder was diagnosed, were associated with delayed recovery, but these psychosocial factors did not predict slow recovery in incident cases identified during follow up. CONCLUSION: The median duration of shoulder tendonitis in a cross sectional sample of industrial and service workers was in the order of 10 months. This estimate is most likely biased towards too high a value. Recovery was strongly reduced in higher age. Physical workplace exposures and perceived psychosocial job characteristics during the period preceding diagnosis seem not to be important prognostic factors.