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Biomedical subjects

R H Westgaard

Publications and source records attributed to R H Westgaard.

At least 55 records · Page 3Linked to original sources
PubMed1993

Electromyographic evaluation of muscular work pattern as a predictor of trapezius myalgia.

Electromyographic (EMG) measurements and interviews concerning muscular pain and disability were performed prospectively every 10th week on 30 healthy new female employees of a chocolate manufacturing plant. The static muscle activity and rate of short unconscious interruptions in EMG activity (EMG gaps) of the trapezius muscle during repetitive work tasks were evaluated as possible risk factors for patient status with trapezius myalgia. At the start of employment, the static and median contraction levels were significantly higher in future patients than in the rest of the subjects (nonpatients). In subsequent recordings these values were reduced to the level of the nonpatients. Throughout the study, the future patients had a lower frequency of EMG gaps than the nonpatients. A regression analysis showed a significant value for a low rate of EMG gaps to predict future patient status.

Adult↗
PubMed1993

Development of trapezius myalgia among female workers performing light manual work.

The aim of this prospective study was to detect a possible development of trapezius myalgia likely to be work-related in initially healthy female packers. Symptoms were recorded on a five-step intensity scale in a daily diary and in an interview at ten-week intervals. All of the subjects were interviewed concerning assumed risk factors during work and leisure time, and a clinical examination was performed. Within their first year of employment, 17 of 30 subjects developed work-related trapezius myalgia of sufficient intensity to be classified as patients. The median time before a clinically confirmed patient status was 23 (range 6-51) weeks. The symptoms showed a fluctuating pattern, decreasing on the weekends and during some holidays. In conclusion, likely work-related trapezius myalgia of a nonchronic character showed a high one-year cumulative incidence at a plant with repetitive light work.

Adult↗
PubMed1992

Individual and work related factors associated with symptoms of musculoskeletal complaints. I. A quantitative registration system.

A registration system for symptoms of occupational musculoskeletal injuries has been developed and evaluated. The system is based on the recording of two aspects of the pain sensation: the intensity (five point scale) and the frequency (three point scale) of pain. The two primary indicators are summed to give a combined symptom score. The scoring system was evaluated in terms of its ability to predict the probability of a medical consultation due to a musculoskeletal pain problem. The intensity and frequency parameters were shown to contribute significantly and to carry equal weight when optimising the symptom score by a logistic regression analysis. In the scoring of pain symptoms a distinction was made between pain experienced during and outside working hours and only the first category was included. The separation eliminated some symptoms that the workers did not consider work related (mostly due to migraine, arthritis). Repeated interviews of 14 subjects showed, however, that this procedure could cause classification problems.

Absenteeism↗
PubMed1992

Individual and work related factors associated with symptoms of musculoskeletal complaints. II. Different risk factors among sewing machine operators.

Individual and work related risk factors in the development of occupational musculoskeletal complaints were studied in a group of 210 female production workers, mainly sewing machine operators. Another group of 35 female employees performing secretarial or laboratory duties were also included. The production workers had significantly higher symptom scores with respect to self reported musculoskeletal complaints than the group with more varied work tasks for the head, neck, shoulders, and arms, but not for the low back, hips, and the lower extremities. No significant differences were found in symptom level between geographically separate groups of production workers with similar work tasks. The main individual risk factor identified in this study was the experience of previous, similar symptoms in the same body region, but this factor only accounted for 2-3% of total variance in symptom score for the neck and shoulders. Other individual factors of importance for symptoms in the neck and shoulders were "signs of psychological problems" and "tendency of muscle tension," but these only account for about 1% of total variance in symptom score. Symptoms in the head and low back showed complex relations with individual parameters.

Absenteeism↗
PubMed1991

Shoulder muscle tension induced by two VDU-based tasks of different complexity.

This paper evaluates task complexity as a task-related factor causing the development of psychologically mediated ('psychogenic') shoulder muscle tension. Eighteen subjects performed an experimental work session, responding to simple and complex reaction time tasks which were presented on a VDU screen. Most subjects generated low-level static muscle tension during the tests. On a group level the two tasks did not have a differential effect on muscle tension. However, a subgroup of eight subjects which consistently generated higher muscle tension in the complex tests, was identified. It is argued that for these subjects the difference in muscle tension is due to an increased mental effort invested, because of the higher computational demands in the complex task.

Adult↗
PubMed1991

Working hours as a risk factor in the development of musculoskeletal complaints.

The length of daily working hours as a risk factor for the development of musculoskeletal complaints was studied by comparing the sick leave statistics of 408 sewing machine operators on full-time schedules (8 h working day) with 210 operators on part-time schedules (5 h working day). Working part-time was shown to postpone the occurrence of sick leave due to musculoskeletal disorders by approximately half a year. There was no lasting effect on the reduction in working hours on sick leave due to shoulder-neck complaints, but a reduction in low back complaints was indicated. It is suggested that any reorganization of work activities to counteract musculoskeletal injuries from repetitive work should aim to break up the muscular activity patterns over time periods considerably shorter than the 5 h working day of the part-time workers in the present study.

Absenteeism↗
PubMed1990

Pattern of muscle activity during stereotyped work and its relation to muscle pain.

Standardized and machine-paced work tasks at a packing machine were examined to evaluate interindividual variability of muscle activity patterns. Ten trained female workers, without musculo-skeletal complaints at the time of the recording, performed the work tasks while electromyographic (EMG) recordings were obtained from both upper trapezius muscles. Static muscle activity and periods of between 0.2 and 2 s duration with low muscle activity, EMG gaps, were analysed. Complaints of muscular fatigue, soreness or pain in the neck and shoulders during the last 12 months were recorded. The level of static muscle activity was 1.6 (range 0.4 to 2.5) per cent of maximal voluntary contraction and median number of EMG gaps was 4.8 (range 0.8 to 20) per minute. Workers with previous episodes of complaints (five subjects) had higher levels of static muscle activity and fewer EMG gaps than workers without such episodes (p less than 0.05, Wilcoxon 2-sample test, one-tailed). Considerable interindividual variability of muscle activity patterns was found in spite of stereotyped work. No causal relations may be inferred from the correlation between the level of trapezius activity and complaints, though it indicates that individual, inexpedient muscle activity patterns may constitute an important risk factor for development of musculo-skeletal complaints.

Adult↗
PubMed1988

Measurement and evaluation of postural load in occupational work situations.

This paper describes methodological considerations and problems experienced when quantifying muscle load in occupational work situations. A system for the quantification of the health effect of prolonged muscle load on the shoulder muscles is also described. Combined measurements of postural load and health effects can be used in a quantitative evaluation of postural load as a risk factor for the development of musculo-skeletal injury. Postural muscle load may be quantified by electromyography or by biomechanical methods. Problems associated with quantitative electromyography are described, including selective inhibition of functional compartments in a muscle. This phenomenon results in other compartments coming under proportionally higher strain, disturbing the force-EMG calibration curves. It is suggested that fatigue measurements, indicated by a shift in the centre frequency of the EMG frequency spectrum, are not easily used for evaluation of vocational EMG recordings if the purpose is to indicate the risk of occupational muscle injury. Load measurements using biomechanical methods may provide an acceptable alternative to electromyography, but more work is required before these methods can be used on a routine basis.

Back↗
PubMed1988

Respiratory interneurones in the thoracic spinal cord of the cat.

1. The discharges of spontaneously firing neurones, whose activity was modulated in phase with the central respiratory cycle, were recorded in the thoracic ventral horn (T3-T9) of anaesthetized, paralysed cats. 2. Out of 310 neurones, forty-six were positively identified as motoneurones by antidromic activation or spike-triggered averaging, fifty-four were positively identified as interneurones by antidromic activation from other spinal cord segments and ninety were indirectly identified as interneurones by virtue of their positions or firing rates as compared to the motoneurones. 3. Units were classified as inspiratory (64%), expiratory (25%) or post-inspiratory (7%) according to the times of their maximum firing rates. The remaining 4% consisted of units whose discharges were either strongly locked to the respiratory pump cycle or did not fit into the other categories. All but one of the motoneurones were classified as inspiratory or expiratory. 4. Inspiratory and expiratory units were further classified as early, late or tonic according to the starting times of their discharges in the respiratory cycle. The interneurones (both positively and indirectly identified) included more of the early and tonic categories and more fast-firing units than did the motoneurones in both the inspiratory and expiratory groups. 5. The locations of the motoneurones corresponded to the known positions of the intercostal and interchondral motor nuclei, including clear segregation of inspiratory and expiratory populations. The locations of neither the interneurones nor the unidentified units were segregated according to their firing patterns. These neurones were concentrated in the medial half of the ventral horn and were found generally more dorsally than the positions of the motoneurones, though their positions overlapped considerably with this group. 6. The axons of the positively identified interneurones were identified from one to five segments caudally and mostly contralaterally, but were not traced to their terminations. Some axons were located by microstimulation and found to run in the ventral or ventromedial white matter. Conduction velocities covered a wide range, 8 to around 100 m/s, mean 53 m/s. 7. Preliminary calculations indicate that there may be almost 10 times more respiratory thoracic interneurones as respiratory bulbospinal neurones.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1988

Slow-to-fast transformation of denervated soleus muscles by chronic high-frequency stimulation in the rat.

1. Adult soleus muscles were denervated and stimulated directly for 2-130 days with 'fast' (short pulse trains at 100 Hz) or 'slow' (continuously at 10 Hz, or long pulse trains at 15 Hz) stimulus patterns. 2. At the end of the period of stimulation isometric twitches and tetani and isotonic shortening velocities were measured. Frozen cross-sections were later examined with antibodies against myosin heavy chains specific for adult fast, adult slow and fetal myosin. 3. Isometric twitch duration (twitch time-to-peak and half-relaxation time) decreased during intermittent 100 Hz stimulation to values that were almost as fast as in the normal extensor digitorum longus (EDL) (95 and 94% transformation). The major part of the decrease occurred between 2 and 21 days after the onset of stimulation, and was accompanied by post-tetanic potentiation of the twitch, 'sag' in tension during an unfused tetanus, lower twitch/tetanus ratio and marked shifts to the right (higher frequencies) of the tension-frequency curve of the muscle. In contrast, during 10 or 15 Hz stimulation the isometric twitch duration remained slow, the twitch continued to show post-tetanic depression and absence of 'sag', while the twitch/tetanus ratio increased. 4. Denervation per se led to a slight increase and, then, after about a month, to a moderate and gradual decrease in twitch duration. The twitch/tetanus ratio increased markedly and post-tetanic depression became less pronounced or disappeared. Muscle weight and particularly tetanic tension were markedly reduced and these reductions were to a large extent counteracted by electrical stimulation. 5. Implantation of sham electrodes had no effect on twitch duration of denervated or innervated control muscles, but reduced tetanic tension in the innervated control muscles. 6. Maximum isotonic shortening velocity of the whole muscle (mm/s) increased during intermittent 100 Hz stimulation to a value as fast as in the normal EDL (110% transformation). Since the muscle fibres also increased in length (35%) maximum intrinsic shortening velocity (fibre lengths/s) was only incompletely transformed (55%). The increase in Vmax occurred between 7 and 14 days after the onset of stimulation. 7. All the fibres stimulated intermittently at 100 Hz were strongly labelled with anti-fast myosin and more than 90% were in addition weakly labelled by anti-slow myosin. Weak and variable labelling with anti-fast myosin was first detected 7 days after the onset of stimulation. In contrast, essentially all the fibres stimulated at 10 or 15 Hz showed no binding of anti-fast but strong binding of anti-slow myosin.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1988

Control of contractile properties within adaptive ranges by patterns of impulse activity in the rat.

These experiments explore the relationship between patterned impulse activity and contractile properties of skeletal muscles. Soleus (SOL) and extensor digitorum longus (EDL) muscles of adult rats were denervated and stimulated directly from 4 to 15 weeks with the same number of pulse trains at different intratrain pulse frequencies (1-500 Hz), with different numbers of pulse trains (864-4,320,000 pulses/d) at the same intratrain pulse frequencies, or with different combinations of pulse trains at 10 and 100 Hz. Chronic stimulation of the denervated SOL resulted in twitch times-to-peak and half-relaxation times that varied in a graded manner between values longer than those in the normal SOL to values as fast as those in the normal EDL, depending upon the pattern used. Increasing pulse frequencies (constant number) resulted in faster twitches, lower twitch/tetanus ratios, increasing post-tetanic potentiations, and larger tetanic tensions. Increasing pulse numbers (constant frequencies) resulted in slower twitches, lower twitch/tetanus ratios, post-tetanic depressions, and higher fatigue indices. The effect of varying the pulse number on twitch parameters was greater at low frequencies (10-20 Hz) than at high frequencies (100 Hz). SOL muscles receiving pulse trains at both 10 and 100 Hz became much faster than muscles receiving pulse trains at 10 Hz only, even in the experiments where the stimulation pattern contained 9 times as many pulses at 10 as at 100 Hz. Chronic stimulation of both the denervated and the innervated EDL with large numbers of pulses at 10 or 15 Hz resulted in twitches that were only half as slow as those induced in the SOL by the same "slow" patterns. In addition, these patterns led to a marked decrease in maximum tetanic tension and a marked increase in twitch/tetanus ratio. During stimulation with a small number of pulses at 150 Hz, on the other hand, twitch speed, twitch/tetanus ratio, and maximum tetanic tension remained normal or almost normal. We conclude that the isometric twitch and related properties of the rat SOL muscle can be graded within wide "adaptive ranges" by varying either the number or the frequency of pulses. In the EDL, the corresponding adaptive ranges appear much narrower, suggesting that the EDL and the SOL contain intrinsically different muscle fibers.

Adaptation, Physiological↗
PubMed1987

Intercostal muscles and purring in the cat: the influence of afferent inputs.

Feline purring has previously been reported as originating in a central oscillator, independent of afferent inputs, and also as not involving expiratory muscles. Here we show, via electromyographic recordings from intercostal muscles, quantified by cross-correlation, that expiratory muscles can be involved and that even if the oscillator is central, reflex components nevertheless play a considerable part in the production of the periodic pattern of muscle activation seen during purring.

Animals↗
PubMed1987

Further studies of postural load and musculo-skeletal injuries of workers at an electro-mechanical assembly plant.

Following two previous papers, a further analysis of epidemiological and physiological data collected at a small electro-mechanical assembly plant in Norway is presented. Data on trapezius load might allow argument of a causal relationship between the level of postural load and the risk of developing musculo-skeletal injury. The second part of the paper provides an epidemiological analysis of sick-leave statistics of workers at old and more recent work systems.

Journal Article↗
PubMed1985

The effect of improved workplace design on the development of work-related musculo-skeletal illnesses.

An earlier paper (Westgaard and Aaras, 1984) described the work environment and the health situation of production workers at a small Norwegian factory, prior to an extensive ergonomics effort which primarily aimed to reduce static muscle strain by constructing new workplaces. It was concluded that the old work situation significantly contributed to a high level it musculo-skeletal disorders, most likely because the old work situation made it necessary to work with high level of muscle load for long periods of the working day. This second paper concerns the other important query which initiated Have the extensive ergonomics and environmental efforts at this factory had any effect in terms of improved health of the workers? The factory, the old workplaces and the ergonomics adaptations were described in the preceding paper, and are therefore not included here.

Journal Article↗
PubMed1984

Postural muscle strain as a causal factor in the development of musculo-skeletal illnesses.

Musculo-skeletal complaints account for 30% of time loss through sick leave. A study was made at a small manufacturing plant in Norway among workers subjected to static muscle load, with particular reference to the relationship between such illness and muscle strain due to working conditions. The paper covers old working standards and ergonomic improvements made in 1975. The results show an increase in musculo-skeletal illness with increased length of employment and increased age.

Journal Article↗