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Biomedical subjects

G M Hägg

Publications and source records attributed to G M Hägg.

18 recordsLinked to original sources
PubMed2000

Human muscle fibre abnormalities related to occupational load.

Ten biopsy studies addressing structural and histochemical muscle fibre abnormalities related to occupational work and myalgia have been reviewed. Eight of these were focused on the upper trapezius muscle while the two others were made on the first dorsal interosseous muscle and the extensor carpi radialis brevis muscle. Standard histological methods have mainly been used with some variations. All except two studies were on women. To achieve desirable contrasts in effect, subject groups usually were individuals with myalgia exposed to static and/or highly repetitive work and healthy non-exposed subjects. In three studies work-exposed subjects without myalgia were included, in two others two groups with myalgia were formed based on the degree of disorder. Major findings in the subjects with myalgia or exposed to work load were increased fibre cross-sectional areas, various indications of mitochondrial disturbances in type I fibres and reduced capillarisation per normal fibre cross-sectional area, the last only in women. The relationship between these findings and pain perception are unclear and frequently similar findings are made also in work-exposed pain-free subjects. Some signs of mitochondrial disturbances in the trapezius muscle were also found in reference groups. However, there are some indications of a relationship between degree of abnormality and degree of pain. There are also indications of differences between the type of finding in the trapezius muscle and in the hand/forearm muscles.

Adenosine Triphosphate↗
PubMed2000

Methodologies for evaluating electromyographic field data in ergonomics.

Surface electromyography (SEMG) is an important tool for work load assessment in ergonomics. Several different approaches using amplitude as well as frequency parameters give fruitful information depending on question at issue in the laboratory as well as in field studies. One basic factor determining the choice of analysis method is whether the SEMG is interpreted as an indicator of forces/torques or pure muscular activation. Two methods for occupational SEMG data reduction representing two different approaches to SEMG applications in ergonomics, Exposure Variation Analysis (EVA), and Joint Analysis of EMG Spectrum and Amplitude (JASA), applied on the same SEMG recording from three muscles during urology surgeon work, have been compared. The EVA method categorised the three muscle recordings as too static with no EMG gaps while the JASA method identifies fatigue in two of the three recordings. The practical relevance of these findings is discussed.

Electromyography↗
PubMed1999

Perception of surface pressure applied to the hand.

The study aimed to determine the relationship between the physical magnitude and the subjective perception of applied pressure, and to determine discomfort and pain thresholds. Free modulus magnitude estimation of the subjective pressure level was made on three points: on the finger, the palm and the thenar area. The pressure was judged to be higher at the thenar point than at the finger and palm points. The slopes of the linear functions (log magnitude estimates as a function of log pressure) were 0.66, 0.78 and 0.76 for the finger, palm and thenar points respectively. The discomfort threshold was 38% of the pain pressure threshold at the finger point, 40% at the palm and 22% at the thenar point. The results are probably of importance in the performance of hand-intensive work, in particular in the design of hand tools.

Adolescent↗
PubMed1997

Load pattern and pressure pain threshold in the upper trapezius muscle and psychosocial factors in medical secretaries with and without shoulder/neck disorders.

OBJECT: A current hypothesis for the genesis of muscular complaints in the shoulder/neck region postulates that short periods with a completely relaxed muscle are essential to avoid complaints. Another hypothesis is that these disorders are related to psychosocial conditions at work. In order to test these hypotheses, 23 medical secretaries were investigated. METHODS: The load pattern during work in the upper trapezius muscle bilaterally was assessed with electromyographic (EMG) technique and exposure variation analysis (EVA). In addition, pressure pain threshold (PPT) was measured on the trapezius muscle bilaterally and on the sternum. Psychosocial conditions at work were assessed with a questionnaire. RESULTS: The medical secretaries with complaints had significantly fewer episodes with totally or close to totally relaxed muscle compared with the healthy group. The group with complaints tended to have a more monotonous load pattern at low levels (approx. 1%-5% maximum voluntary contraction) while the healthy group had more frequent pauses but also somewhat more frequent short load peaks. The group with complaints showed lower PPT readings compared with the healthy group. However, the whole group had considerably lower PPTs than is usually reported in the literature. Of the 12 questions in the psychosocial questionnaire only one regarding work task satisfaction showed a significant difference between the two groups. CONCLUSION: Support is found for hypothesis that secretaries without complaints have more frequent episodes with totally relaxed muscle. A significant difference is found regarding work task satisfaction.

Adult↗
PubMed1997

Isotonic and isoelectric endurance tests for the upper trapezius muscle.

As an alternative to a conventional endurance electromyogram (EMG) test for assessment of muscle capacity in the upper trapezius muscle (isotonic test, IT), an isoelectric test (IE) has been investigated. Nine subjects performed the two endurance tests. The tests were performed with a straight horizontal arm in the plane of the scapula. In IE, EMG amplitude was fed back to the subject and the subject was instructed to maintain a constant EMG activity equal to the level with the arm unsupported. Subjective ratings of local fatigue were obtained during the experiments. The EMG recordings from both tests were analysed for the root mean square value as well as according to the mean power frequency (MPF) technique. All the subjects endured maximal 15 min IE while in IT the median endurance was 11.9 min. Average subjective ratings of perceived fatigue increased more in IT compared to IE. The average normalised MPF curve from IT increased while that from IE was unaffected. There was a significant difference between the MPF results at 6 and 8 min. It is noteworthy that the MPF was higher in IT in spite of a higher accumulated biomechanical load. It was concluded from these studies that the interpretation of decreased MPF as an indicator of increased local muscle fatigue is doubtful at low contraction levels. It is suggested that an IE is a more appropriate method for the functional evaluation of low threshold motor units of the upper trapezius muscle in research into occupational disorders.

Adult↗
PubMed1997

Forearm muscular load and wrist angle among automobile assembly line workers in relation to symptoms.

Electromyographic activity (EMG) from m. flexor carpi radialis (FCR) and m. extensor carpi radialis longus (ECRL) of the right forearm was recorded together with wrist angles in the flexion/extension and radial/ulnar plane in 20 healthy automobile assembly line workers during work. Eleven of these were randomly recruited from assembly stations with a low prevalence of subjective wrist/forearm symptoms (LPS), while the rest came from stations with a high prevalence of symptoms (HPS). The main EMG finding was a clear difference in activation pattern between flexors and extensors. ECRL was activated more statically, while FCR had a more dynamic pattern with more pauses but also higher peak loads. The main wrist angle finding was a difference in angle distribution as well as absolute angular velocity in the radial/ulnar plane between LPS and HPS work stations. Workers in HPS stations worked longer times in a more ulnar deviated hand position and had higher absolute deviation angular velocity compared to LPS workers, indicating ulnar deviation as a risk factor. Generally, ulnar deviation from a neutral position was more frequent than angular displacement in the flexion/extension plane.

Adult↗
PubMed1997

Forearm extensor and flexor muscle exertion during simulated gripping work -- an electromyographic study.

OBJECTIVE: To study forearm muscular exertion during intermittent gripping work at three different regimes resembling vocational work. DESIGN: An electromyographic laboratory study of forearm fatigue during intermittent gripping work at 25% MVC with 10/10, 20/10 and 30/10 s of work/rest was performed. BACKGROUND: Data from the literature indicate that forearm flexors as well as extensors are activated during gripping. However, no systematic quantitative assessment of the muscular exertion has been made hitherto. METHODS: Nine female subjects participated. EMG was detected from five forearm muscles, three extensors and two flexors. Zero crossing rate alterations were used as an index of fatigue. RESULTS: The results show significant (P < 0.05) fatigue signs in at least two of the extensor muscles at all regimes while significant signs of fatigue was seen only at the 30/10 regime for the flexor muscles. CONCLUSIONS: Fatigue effects are generally larger on the extensor side. None of the studied regimes is acceptable from EMG fatigue point of view. RELEVANCE: The muscular fatigue of the forearm extensors in relation to the flexors during gripping work has not been systematically assessed before. Forearm fatigue distribution is probably of great importance for the understanding of forearm disorders related to muscular exertion.

Journal Article↗
PubMed1995

Recent developments in the field of physical load measurements.

As a consequence of the large changes of industry work during the last decades, the measurement techniques used for load assessment have undergone a corresponding development to, if possible, reveal hazardous load situations associated with modern production technology. This development has implied methods focusing localized loads on muscles, tendons and joints. Posture is one externally observable load factor of great importance. Load distribution within the body can be assessed by computerized biomechanical models. Another important approach is the registration of the electromyographic (EMG) activity. The latter technique provides information on time patterns of loads which lately have gained increasing attention.

Biomechanical Phenomena↗
PubMed1992

One-handed load carrying--cardiovascular, muscular and subjective indices of endurance and fatigue.

A group of 5 women and 11 men walked on a treadmill, each carrying a weight in the right hand. In separate experiments, the mass was varied to give total exhaustion within 3 min, 5 min, 9 min, and 13 min. In additional experiments 50% and 25% of the masses leading to exhaustion after 5 min were used, and these were stopped after 16 min. Heart rate (fc) and systolic blood pressure (BPs) were measured noninvasively. There was a consistent increase in fc x BPs during the experiments leading to exhaustion, while steady-states were obtained in the nonexhausting trials. An electromyogram (EMG) was recorded with cutaneous electrodes over the flexor carpi ulnaris and flexor digitorum superficialis muscles and the number of zero crossings (ZC) of the EMG signal per time unit were analysed. As the subjects approached exhaustion, the number of ZC declined exponentially, reaching approximately 50% of their initial values. In the nonexhausting experiments, however, the decline was slower and less marked, and during the second half of the experiment the number of ZC increased again. Subjectively, endurance was underestimated by all the subjects. It was concluded that cardiovascular and muscle criteria of fatigue in carrying coincided. Prolonged carrying in one hand of more than 6 kg or 10 kg for young healthy women and men respectively should not be recommended, since it could lead to cardiovascular non steady-states and EMG signs of fatigue.

Adult↗
PubMed1992

Interpretation of EMG spectral alterations and alteration indexes at sustained contraction.

Alterations of the electromyographic power spectrum have been studied extensively to assess fatigue development in the neuromuscular system. Usually, a data reduction has been applied to create an index based on the mean power frequency or the median frequency. The physiological origin of the spectrum alterations has been (and to some extent still is) incompletely known. However, during the 1980s, substantial progress has been made in this field. The factors affecting the electromyographic power spectrum discussed in this review are action potential velocity decrease, firing statistics alterations, action potential modification, muscle temperature, additional recruitment at fatigue, and force level. Their impact on three commonly used fatigue indexes, mean power frequency, median frequency, and zero crossing rate, is also reviewed.

Animals↗
PubMed1991

Zero crossing rate of electromyograms during occupational work and endurance tests as predictors for work related myalgia in the shoulder/neck region.

The relationship between electromyographic signs of fatigue (ESF) during work and occupation-related myalgia in the shoulder/neck region was investigated in a longitudinal study. Forty-three healthy female assembly workers were studied over 2 years. Measurements were performed at the start of the study with follow-up measurements after 1 and 2 years. The ESF were estimated as the zero crossing rate of electromyograms (EMG) detected during short test contractions performed during short breaks in normal work. As a complement, an endurance test using EMG records was performed and analysed with the zero crossing technique. The occurrence of shoulder/neck disorders was assessed by a clinical investigation and a questionnaire. No significant relationship between ESF during work in year 0 and deterioration of the disorder was seen. On the other hand, the absolute zero crossing rate and the time constant of the zero crossing decline from the endurance test showed a significant relationship with deterioration of the disorder. The ESF during work year 2, showed a significant relationship with disorder year 2, while the endurance test parameters year 2 did not. It was concluded that ESF during work was not a predictor of muscle injury, whereas it could be useful as a diagnostic tool.

Adolescent↗
PubMed1991

Comparison of different estimators of electromyographic spectral shifts during work when applied on short test contractions.

EMG was recorded during short test contractions performed during occupational work. Mean power frequency (MPF) and median frequency (MF), calculated from EMG spectra, and zero crossing rate (ZC) of the EMG signal were compared as estimators of local muscular fatigue. The results show that there is a systematic difference between the three estimates. The difference can be explained by dividing the effect of muscle fatigue on EMG spectra into a motor unit action potential velocity effect and a firing statistics effect. Furthermore, it is shown that the phenomenon of increasing estimators of EMG spectrum shift is unlikely to be caused by motor unit action potential velocity increase. Successive recruitment of new motor units is suggested as a feasible explanation.

Electromyography↗
PubMed1989

Occupational lifting by nursing aides and warehouse workers.

Nursing aides (18 women and six men) at one traditional and one modern geriatric ward, and warehouse workers (16 men) at two different types of warehouse departments were studied during occupational work. The vertical load during manual handling was measured using strain gauges built into wooden shoes. The warehouse workers performed four times as many lifts as the nursing aides and transferred five times as great a mass per unit time. Less than 25% of the lifts were carried out with the load evenly distributed on both feet during both the upward lift and lowering. In the warehouses the lifts were short, while the nursing aides were exposed both to lifts of longer duration and to carrying, as well as a greater frequency of unexpected, sudden and high peak load. The heart rate and oxygen uptake values recorded were relatively low, and both groups utilized approximately 25% of their maximum aerobic power. According to official occupational injury statistics, both warehouse workers and nursing aides belong to risk groups with a high frequency of reported back injuries. However, more injuries are reported by nursing aides than by warehouse workers. Greater muscle strength in male workers may partly explain this difference. Qualitative differences in the design of the lifting work, with more lifts of long duration in awkward work postures, more carrying, more exertion of horizontal forces and a greater frequency of unexpected rapid lifts in the nursing aides may also contribute to the differences in risk of injury between these occupational groups. Considerable differences were found between the two hospital wards as regards lifting frequency, force, duration and the proportion of lifts with an even distribution of load on both feet during upward lift. The lifting work was approximately 50% less in the modern ward, which has easily maneuvered electric overhead hoists, spacious premises and better work organization than in the traditional ward, even though the patient handling needs were equivalent. In the warehouse department at which the wares were stored with easy access, the frequency of lifts with an even distribution of load on both feet was approximately 25%, compared to 7% in the other warehouse department. In conclusion, evaluations of occupational lifting work should include a quantitative assessment of the duration and load distribution of lifting, as well as of postures. Workstation design, technical aids and work organization have a profound effect on the lifting work load even in jobs with equal manual handling demands.

Accidents, Occupational↗