Björn Gerdle

Muscle performance, electromyography and fibre type composition in fibromyalgia and work-related Myalgia

Muscle performance and fibre type composition were investigated in women with fibromyalgia, work-related trapezius myalgia and healthy volunteers. Each subject performed 100 repetitive shoulder flexions using an isokinetic dynamometer during simultaneous registration of surface electromyography. A biopsy from the trapezius muscle was obtained. The groups differed neither in mechanical performance nor in fibre type proportions. An inability to relax between contractions was found in all registered muscles in patients with fibromyalgia. The patients with work-related myalgia displayed an inability to relax only in the myalgic trapezius muscle. An inability to relax during repetitive movements might play an important role both in initiating and upholding muscle pain.

The relationship between contraction and relaxation during fatiguing isokinetic shoulder flexions. An electromyographic study

SummaryKnowledge 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 decreased 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.

Inter-relationship between muscle morphology, mechanical output and electromyographic activity during fatiguing dynamic knee-extensions in untrained females

Abstract Changes in mechanical performance and electromyographic activity during fatiguing dynamic knee-extensions were evaluated with respect to muscle fibre type composition of the vastus lateralis muscle in nine sedentary female [23 (3) years] volunteers. The subjects performed 150 repetitive maximum knee-extensions using a Cybex dynamometer at 1.57u2009radu2009·u2009s−1. EMG activity was recorded from the vastus lateralis, the vastus medialis and the rectus femoris muscles. For each contraction, mean power frequency (MPF) and the root mean square (RMS) of the EMG were calculated, simultaneously with the peak torque (PT), contractional work (CW) and the mean power (MP). The MPF showed an initial decrease followed by a stable phase. The RMS increased during the initial seven contractions, after which a period of variability was displayed until about the 60th contraction. At the plateau level (last 50 contractions) the relative RMS values were not significantly different from the initial values. The PT, CW and MP increased during the initial five to ten contractions, after which a two-phase pattern was displayed, with a gradual decline followed by a stable phase. The absolute plateau level of MPF for the vastus lateralis muscle showed a significant negative correlation with the area percentage of type-1 fibres (ru2009=u2009−0.71). Significant correlations were also demonstrated to occur between the absolute plateau levels of PT, CW and MP and the relative proportion of type-1 fibres (ru2009=u20090.80, ru2009=u20090.82 and ru2009=u20090.82 respectively). Thus, in female subjects the mechanical performance and the MPF during fatigue are at least partly determined by muscle morphology.

Prediction of peak torque and contraction work at different isokinetic angular velocities of plantarflexion

SummaryContraction work (CW) and peak torque (PT) of maximum isokinetic plantar flexions were measured in clinically healthy subjects randomly chosen from the official census list of Umeå, Sweden, in three groups: 40–44, 50–54 and 60–64 years of age, with similar proportions of men and women. Maximum isokinetic plantarflexions were performed at angular velocities of 30, 60, 120 and 180‡ · s−1. Body-weight, height and crural circumference were measured. Subjects rated their levels of leisure and occupational activities.To establish formulae to predict CW and PT, stepwise regression procedures were applied. The predictive powers (r2) of the formulae which incorporated age, sex and crural circumference, were higher for PT (30‡ · s−1: 0.82, 60‡ · s−1: 0.79, 120‡ · s−1: 0.75, 180‡ · s−1: 0.56) than for CW (30‡ s−1: 0.63, 60‡ s−1: 0.63, 120‡ s−1: 0.60, 180‡ s−1: 0.52). Thus the part of the variance explained decreased with increasing angular velocity, but more than 50% was still explained at 180‡ s−1.The results indicate that the mechanical output of the plantar flexors is predictable.

The interrelationships between EMG, peak torque and perceived fatigue during repeated maximum isokinetic knee flexion with and without active knee extension

This study of the knee flexors and extensors investigated the interrelationships between peak torque, mean power frequency (MPF) and the signal amplitude (RMS: root mean square) of the EMG and perception of fatigue throughout repeated dynamic contractions when the contraction cycle included maximum performance of both the agonists and the antagonists. Ten females performed two tests, which consisted of 100 repeated maximum knee flexions with passive or active knee extensions using an isokinetic dynamometer with simultaneous surface EMG. Peak torque and MPF displayed a pattern with two phases throughout both tests-a steep decrease during the initial 40 contractions followed by a period of stabilisation (the endurance level). In agreement with earlier studies, peak torque and MPF were stable, while the perception of fatigue increased at the endurance level. These results question whether MPF shifts can be used to detect risk situations, with respect for example to work-related myalgia, for endurance-profile...

Alcohol Consumption and Complaints from the Musculoskeletal System among Engine Drivers—an Epidemiological Study

The purpose of this study was to test the hypothesis that a positive correlation exist between level of alcohol consumption and complaints from the musculoskeletal system. 150 randomly selected engine drivers from Sweden were interviewed about complaints from the musculoskeletal system during the last 12 months. In this study the complaints from the neck, shoulders and lower back were investigated. An index counting number of regions with complaints was computed. The subjects were asked to report their level of alcohol consumption during the last month (beer, wine and spirits). The total alcohol cornsumption was calculated expressed in terms of 40% pure alcohol. The median consumption was 39.5 cl/month. The engine drivers reporting complaints from the neck had a significantly higher consumption of alcohol than those without such complaints. A positive significant correlation existed between the number of complaints (index) and alcohol consumption.