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ABSTRACT: In the literature enlarged/increased cross-sectional area (CSA) of type I muscle fibres has been reported as a morphological mark of work-related localised myalgia in the descending part of the trapezius muscle of women. These studies did not use enough subjects or lacked an adequate control group. The recording of surface electromyograms (EMG) is central to the research field of work-related myalgia. However, the influence of intrinsic muscle properties such as the effect of muscle fibre distribution upon surface EMG has to be better understood in order properly to evaluate this method as a possible diagnostic and preventive tool. This study had two aims. Firstly, it investigated the muscle fibre distribution and CSA in work-related myalgia in trapezius muscles. Secondly, the multivariate relationships among muscle morphology and histochemistry [ragged-red (RR) fibres, and cytochrome-c-oxidase-negative-fibre changes] EMG, perceived fatigue, and biomechanical output of shoulder flexions were analysed. The raw data have been presented in an earlier study. The participants in this study were 25 female cleaners with work-related myalgia of the trapezius muscle and 25 female cleaners not experiencing work-related myalgia of this muscle. The control group comprised 21 healthy female teachers who had not been exposed to highly repetitive work or static muscle work. Smaller CSA of type II fibres were found in cleaners compared to teachers. In this study the CSA of type I fibres of the trapezius muscles associated with myalgia were no greater than in muscles without myalgia. The prevalence of RR fibres together with age, fibre type proportions, CSA and working as a cleaner correlated with the ability to relax as recorded electromyographically. The relative mean frequency of the EMG of the trapezius muscle correlated with the prevalence of RR fibres, but it did not correlate with the proportions and CSA of different fibre types. Low biomechanical outputs and low signal amplitude increases of the EMG during the test were associated with high proportions of type -IIB fibres. The smaller CSA of type II fibres in cleaners might have reflected a different muscle activation pattern due to different occupational demands in cleaners than in teachers. Morphological or histopathological variables can influence the three EMG variables investigated.
Arbeitsphysiologie 07/2001; 84(6):492-502. · 2.15 Impact Factor
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ABSTRACT: To investigate if muscle tension according to the surface electromyogram (EMG) of the shoulder flexors is increased in consecutive patients with fibromyalgia (FM) or chronic whiplash associated disorders (WAD).
A total of 59 consecutive patients with FM (n = 36) or chronic WAD (n = 23) performed 100 maximal isokinetic contractions combined with surface electromyography of the trapezius and infraspinatus. A randomized group of pain-free female (n = 27) subjects served as control group. Peak torque initially (Pti) and absolute and relative peak torque at endurance level (PTe, PTer) were registered as output variables, together with the EMG level of unnecessary muscle tension, i.e., the signal amplitude ratio (SAR).
The patient groups had a higher level of unnecessary tension initially and at the endurance level. The patients had lower absolute output (PTi and PTe), but the relative levels (PTer) did not differ comparing all 3 groups. Subjects with FM had significantly higher body mass index (BMI) than the other groups. BMI did not influence the SAR but correlated positively with PTi.
The results confirmed earlier findings that groups of patients with chronic pain have increased muscle tension and decreased output during dynamic activity compared to pain-free controls. However, the results indicated there is heterogeneity within groups of patients with the same chronic pain disorder and that not all patients with chronic pain have increased muscle tension.
The Journal of Rheumatology 07/2001; 28(6):1361-8. · 3.69 Impact Factor
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ABSTRACT: This cross-sectional study aimed at investigating the influence of occupational exposure to static and highly repetitive work involving the neck and shoulder muscles, myalgia of and tender point in the trapezius muscle on biomechanical output, and electromyogram (EMG) variables (mean frequency MNF, signal amplitude and ability to relax) during maximal forward flexions of the shoulder muscles. Groups of 25 cleaners suffering from chronic myalgia of the trapezius muscle, 25 cleaners free from myalgia of the trapezius muscle and 21 teachers performed 150 forward flexions using an isokinetic dynamometer. Perception of fatigue was reported and surface EMG was recorded from four muscles during the endurance test. The cleaners were stronger than the teachers. Myalgia was associated with lower levels of endurance and a high degree of perceived fatigue. The ability to relax the trapezius muscle decreased with age and was even lower in cleaners with and without myalgia. Higher MNF of the deltoid muscle but not of the trapezius muscle was found in the group suffering from myalgia compared to the groups free from myalgia. This cross-sectional study indicated that myalgia of the trapezius muscle did not influence the strength but did influence the endurance of the forward flexor muscles of cleaners. The observed decrease in the ability to relax the trapezius muscle in cleaners compared to healthy teachers might be indicative of a future insufficiency in the muscle. Prospective studies are needed to define the significance of the results presented here.
Arbeitsphysiologie 12/2000; 83(4 -5):257-67. · 2.15 Impact Factor
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ABSTRACT: The aim of the present study was to analyse the effects of gender and age in a population-based sample of clinically healthy subjects on: (1) strength, endurance and perception of fatigue, (2) mean frequency (MNF) of the electromyogram (EMG), and (3) the ability to relax between active contractions (signal amplitude ratio; SAR) of the surface EMG of an isokinetic shoulder forward flexion test. With this aim we have analysed aspects of the validity of MNF as an indicator of fatigue, using peak torque as a criterion variable. The subjects were 27 men and 28 women (age range: 20-60 years), who were obtained by random sample from the official census lists (participation rate: 66%). The peak torque and surface EMG of two portions of the trapezius, deltoid and infraspinatus muscles were recorded throughout 100 repetitive maximal isokinetic shoulder forward flexions. No significant differences in the perception of fatigue and relative endurance levels of peak torque and work were found between males and females. Males were significantly stronger than females and, on average, females produced approximately 60% of the output of the males; 76% after normalisation for body mass. The men had significantly lower MNF endurance levels for three of the investigated muscles. When controlled for age and body mass, the men had a significantly higher MNF of the deltoid muscle than did the females. These differences were only found for the deltoid muscle. Significant correlations existed between the MNF of the four muscles and biomechanical output, indicating criterion validity for the MNF variable with respect to fatigue. There were no significant effects of gender or age on the ability to relax between repetitive contractions (SAR). The higher prevalence of musculoskeletal complaints of the neck-shoulder region in females cannot be explained by a higher intrinsic muscle tension. Age, gender, body mass index and biomechanical output can have significant effects upon MNF. These effects are important considerations in the interpretation of MNF, for instance in ergonomic situations.
Arbeitsphysiologie 12/2000; 83(4 -5):246-56. · 2.15 Impact Factor
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ABSTRACT: This study is an investigation of the relationship between muscle morphology and surface electromyographic (EMG) parameters [mean frequency of the power spectrum (MNF), signal amplitude (root mean square, RMS) and the signal amplitude ratio (SAR; i.e. the ratio between the RMS level during the passive part of the contraction cycle and the RMS level during the active part of the contraction cycle)] during 100 maximal dynamic knee extensions at 90 degrees. s(-1). Each contraction cycle comprised of 1 s of active knee extension and 1 s of passive knee flexion. The surface EMG was recorded from the vastus lateralis muscle. Twenty clinically healthy subjects participated in the study, and muscle biopsy samples of the vastus lateralis were obtained from 19 of those subjects. The relationships between muscle morphology and EMG were investigated at three stages of the test: initially, during the fatigue phase (initial 40 contractions), and at the endurance level (the final 50 contractions). Major findings on correlations are that SAR and MNF tended to correlate positively with the proportion of type 1 fibres, and RMS correlated positively with the proportion of type 2 muscle fibres. The muscle fibre areas showed little correlation with the EMG variables under investigation. The results of the present study showed that the three EMG variables of a dynamic endurance test that were investigated (RMS, MNF and SAR) were clearly correlated with the proportions of the different fibre types, but only to a small extent with fibre areas. These findings contradict some of the theoretical models of the EMG, especially for parameters in the frequency domain.
Arbeitsphysiologie 02/2000; 81(1-2):2-10. · 2.15 Impact Factor
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ABSTRACT: The interpretation of the electromyogram (EMG) of dynamic contractions might be difficult because the movement per se introduces additional factors that could affect its characteristics. There is a lack of studies concerning the reproducibility of surface EMG registrations during dynamic contractions. The aim was to investigate the during-the-day reproducibility (using intra-class correlation; ICC) of the peak torque (PT) and the EMG variables (without removing the electrodes) of dynamic contractions. Ten healthy subjects performed three sets of 10 dynamic maximum right-knee extensions with a one-hour interval in between, using an isokinetic dynamometer and the PT was determined. EMG signals were recorded from the right vastus lateralis, rectus femoris and vastus medialis muscles using surface electrodes and the mean frequency of the power spectrum (MNF [Hz]) and the signal amplitude (RMS [microV]), were computed. The ability to relax in-between the maximum extensions was calculated as a ratio of the RMS during the passive flexion phase and the RMS during the active extension phase of each contraction cycle: the signal amplitude ratio (SAR). Both PT (ICC = 0.99) and RMS (ICC = 0.83-0.98) had good reproducibility. The reproducibility of MNF was good for all muscles when the mean of contraction nos.: 1-10 was used. Vastus lateralis had the highest ICC among the three muscles. The reproducibility of SAR was generally poor (ICC < 0.60). The present study showed good reproducibility for common EMG variables (MNF and RMS) obtained during maximum isokinetic contractions.
Journal of Electromyography and Kinesiology 11/1999; 9(5):351-7. · 1.97 Impact Factor
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ABSTRACT: There is a shortage of studies concerning the reproducibility of surface electromyography (EMG) during dynamic contractions. The movement per se introduces factors that could have the potential to affect the characteristics of the electromyogram. The aim of this study was to investigate the during-the-day reproducibility (using intra-class coefficient, ICC) of the peak torque (PT) and the EMG variables (without removing electrodes) of dynamic shoulder forward flexions. Eleven healthy women performed three sets of 10 dynamic maximum right-shoulder flexions at 1 h intervals using an isokinetic dynamometer. The PT of each flexion was determined. EMG signals were recorded from four muscles (trapezius, deltoid, infraspinatus and biceps brachii) using surface electrodes, and the mean frequency of the power spectrum (MNF [Hz]) and the signal amplitude (RMS [microV]), were computed. The ability to relax between maximum flexions was calculated as a ratio between the RMS during the passive extension phase and the RMS during the active flexion phase of each contraction cycle. This ratio is the signal amplitude ratio (SAR). The present study showed good reproducibility for PT, MNF and RMS, while the reproducibility of SAR was generally acceptable (fair) according to the criteria used.
Clinical Physiology 10/1999; 19(5):433-9.
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ABSTRACT: The aim was to investigate whether output and electromyogram (EMG) variables obtained from an isokinetic endurance test of the shoulder flexor muscles of 23 women with neck and shoulder problems in a car and truck industry correlated with improvement or worsening of complaints 1 year later. Each subject performed 100 maximal isokinetic shoulder forward flexions at 60 degrees x s(-1). Surface EMG of the trapezius, deltoid, biceps brachii and infraspinatus muscles and mechanical output (peak torque) were determined for each contraction. The EMG was used to determine mean frequency fmean and the ratio between the signal amplitudes of the EMG of the passive relaxation and active flexion parts of each contraction cycle (SAR). The subjects also rated the degree of fatigue they experienced throughout the test. The magnitude of the shift in fmean was correlated with whether improvement or worsening occurred for complaints in the neck and or shoulders; a significant relationship (r2 = 0.44; P = 0.001) existed between the total frequency shift of the four muscles and the variables measuring improvement in complaints. In the multivariate predictions other fmean variables and perception of fatigue were also of significance. The present study would indicate that a high degree of fmean shift correlates with improvement in neck and shoulder complaints 1 year later. One possible reason could be that fmean reflects the muscle morphology and/or a pathological situation for the type-1 muscle fibres.
European Journal of Applied Physiology and Occupational Physiology 01/1999; 79(1):7-16.
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ABSTRACT: We have studied 23 women with neck and shoulder problems in a car factory with a 1-year interval. Our main aim was to investigate the reproducibility and stability of the tension pattern. In addition, the mean frequency (MNF) of the power spectrum and the signal amplitude (RMS) of the surface electromyograph (EMG) of the trapezius, deltoid and infraspinatus muscles and mechanical output were determined throughout 100 maximal isokinetic shoulder forward flexions. The signal amplitude ratio (SAR) was calculated as the ratio between the signal amplitude of the EMG of the passive relaxation and the active flexion part of each contraction cycle. The SAR variable can be reproduced (r = 0.47-0.76) with a 1-year interval. There was a significantly lower SAR of the trapezius at the second test, which might have been due to lower work pace at the factory. The longitudinal patterns of SAR throughout the two tests were similar at both tests. There were significant correlations between tests for 18 out of 22 EMG variables, even though the correlations were generally lower than for SAR (initial MNF: r = 0.39-0.48; MNF endurance level: r = 0.55-0.83; RMS (%): r = 0.08-0.46). Peak torque had better reproducibility than work. In conclusion, SAR has a long-term reproducibility equal to or better than other EMG and biomechanical variables. The present results indicate that SAR has potential to measure unnecessary muscle tension in intervention studies and to identify individual movement patterns.
Clinical Physiology 12/1998; 18(6):529-38.
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ABSTRACT: The purpose of this report is to describe how patients with multiple sclerosis increased the isokinetic peak torque of their knee flexors and perceived well-being after an endurance training program.
Five patients trained for 4 to 6 weeks using an endurance program for the lower extremities. Before and after training, the subjects performed 50 repeated maximum knee flexions, with simultaneous recording of surface electromyographic activity of two knee flexors, on 3 separate days using an isokinetic dynamometer. Throughout the tests, the subjects rated their perception of peripheral muscle fatigue. Visual analog scales (VAS) were used to rate different aspects of well-being.
Both the perception of peripheral fatigue and the different VAS ratings had changed positively after training. Three patients achieved higher peak torque levels throughout the posttraining endurance test.
Based on these positive results, the authors conclude that more comprehensive studies of exercise prescription in patients with multiple sclerosis are desirable.
Physical Therapy 12/1994; 74(11):1017-26. · 3.11 Impact Factor
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ABSTRACT: The interrelationships between reported complaints, certain sociodemographic data and ergonomic, physical and psychosocial aspects of the work-environment were investigated in a cross-sectional study of home care service personnel using a questionnaire. Ninety-seven out of 160 randomly selected women took part in pre-tests (presented here), post-tests and one year exercise program. Significant correlations existed between musculoskeletal complaints, other (somatic and psychosomatic) symptoms and anxiety/threat for differently, mainly work-related negative changes. The group of subjects could be divided into three subgroups. A "complaint group" was identified with a high prevalence of musculoskeletal and other somatic/psychosomatic symptoms. This group had the most negative ratings on the ergonomic and physical work-environment indices. A "young group" had the most negative perception of the psychosocial work-environment. The "healthy group" generally perceived the situation best. The present preliminary study could indicate that work-related interventions/rehabilitation programmes undertaken for the complaint group must be designed in another way and with other goals than those directed towards the other two identified groups.
Scandinavian Journal of Rehabilitation Medicine 07/1994; 26(2):51-8.
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ABSTRACT: The study investigated the temporal occurrence of the mean power frequency shift (MPF) of the EMG during prolonged (dynamic and static) working cycles. Ten healthy subjects took part in the experiment. The experimental protocol required each subject to first complete 70 maximum isokinetic knee extensions at 90 degrees s-1). Without any rest, the subject then performed a maximum static knee extension with the dynamometer positioned at 45 degrees of flexion until subjective exhaustion. This sequence of dynamic and static exercise was repeated two more times with a 5-min rest interval preceding each sequence. The EMG signal of the rectus femoris was obtained simultaneously with the torque signal (PT) from the dynamometer. Dynamic contractions PT and MPF decreased throughout the three dynamic periods. Patterns composed of two phases were found; first an initial steep decrease during the first 40 contractions followed by a less steep decrease. Static contractions PT decreased significantly during the three static contractions. Significant (small) decreases in MPF occurred only during the second and third static contractions. Since the major part of the MPF shift occurred early in the exhaustive performance, it is questioned whether the MPF shift detects peripheral fatigue of the type 1 fibers.
International Journal of Sports Medicine 02/1994; 15 Suppl 1:S32-7. · 2.43 Impact Factor
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ABSTRACT: To investigate the relationships between personality traits, depressive symptomatology and continuous muscle tension.
These were investigated by means of a visual analog scale and the presence of continuous muscle tension during repeated isokinetic shoulder flexions in patients with muscle or joint pain and controls.
A significantly higher level of muscle tension between contractions was found in the patient groups in painful muscles. The patients with primary fibromyalgia and trapezius myalgia differed in degree of depressive symptomatology compared to controls.
Inhibition of aggression correlated significantly with the tension level between contractions during the isokinetic test indicating interaction between psychological and somatic factors.
The Journal of Rheumatology 10/1993; 20(9):1550-6. · 3.69 Impact Factor
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The Journal of Rheumatology 01/1993; · 3.69 Impact Factor
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ABSTRACT: The interrelationships between reported complaints, clinical status, mechanical performance and EMG pattern of the shoulder flexors and the knee extensors, respectively, during maximum dynamic contractions were investigated. A group of 97 randomly selected women employed in the home care service participated. Those who reported complaints had more clinical findings, such as reduced mobility, tender points and muscle tightness, than non-complainers. The level of muscle activity during the passive part of the contraction cycle was significantly higher in the shoulder flexors than in the knee extensors. Subjects without reported complaints who had been employed for more than ten years had a significantly lower activity level in the shoulder muscles than subjects without complaints who had been employed for a shorter time. We suggest that a high muscle tension level between contractions might precede muscle pain. A cluster analysis including sociodemographic, clinical and physiological variables revealed different subgroups, which points to the need to investigate the work situation in a multivariate way.
Scandinavian Journal of Rehabilitation Medicine 10/1992; 24(3):141-50.
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ABSTRACT: Peak torque, work, mean power and electromyographic (EMG) activity were recorded for each of 150 repeated isokinetic maximal shoulder flexions (45 degrees-90 degrees) in 23 healthy females. From the EMG signals of trapezius, deltoid, infraspinatus and biceps brachii the mean power frequency and the signal amplitude were determined in real time. The mechanical output showed a steep decrease during the first 40 contractions, followed by a plateau maintained until the end. In all muscles, except the biceps brachii, significant decreases in mean power frequency occurred during the first 40 contractions, showing a tendency to stabilize around the same absolute frequency value. Signal amplitude increased in the trapezius, the deltoid and the infraspinatus, but was constant in the biceps brachii. For some individuals rather high EMG activity was recorded in the muscles during the time the arm was supposed to be passively extended to the starting position, and this was found to be associated with lower strength and endurance levels. Longitudinal analyses showed that the mean power frequencies correlated better than the signal amplitudes with the three mechanical variables. The results suggest that the initial steep decrease in mechanical performance and mean power frequency is caused by fatiguing of type 2 motor units.
European Journal of Applied Physiology and Occupational Physiology 02/1989; 58(6):666-73.
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ABSTRACT: Knowledge of the strength, endurance and coordination of the shoulder muscles during dynamic contractions in healthy women would contribute to the understanding of symptoms in that part of the body in patients with myalgia. Twenty clinically healthy women performed single maximal forward shoulder flexions at four different angular velocities (0.57-3.14 rad.s-1). The same subjects also took part in two endurance tests (at angular velocities of 0.57 and 2.09 rad.s-1, respectively) consisting of 150 repeated maximal shoulder flexions. Electromyographic activity (EMG) was registered from four shoulder flexors using surface electrodes. Work was used as the mechanical variable. During the endurance tests subjects rated their perception of fatigue in the shoulder muscles. Work and the amplitude of the EMG signals decreaesd with angular velocity. The mean power frequency of the EMG was constant in the span of angular velocities investigated. During the endurance tests, work and the mean power frequency decreased during the initial 40-60 contractions followed by stable levels. The relative work level was higher at 2.09 than at 0.57 rad.s-1. Greater relative increases of the signal amplitudes of EMG occurred at 2.09 than at 0.57 rad.s-1. The EMG activity between the flexions (during the supposed passive extension) was higher at 2.09 than at 0.57 rad.s-1. Such a high activity was associated with a low mechanical performance at 2.09 rad.s-1. It is suggested that the initial sharp decreases in work and in mean power frequency reflect the fatiguing of the fast twitch motor units. Dynamic work consisting of continuous activity could predispose to muscle complaints.
European Journal of Applied Physiology and Occupational Physiology 02/1989; 59(4):303-9.
