| 1. |
- Gerdle, Björn, et al.
(författare)
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Altered neuromuscular control mechanisms of the trapezius muscle in fibromyalgia
- 2010
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Ingår i: BMC Musculoskeletal Disorders. - : Springer Science and Business Media LLC. - 1471-2474. ; 11:42
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Tidskriftsartikel (refereegranskat)abstract
- Background: fibromyalgia is a relatively common condition with widespread pain and pressure allodynia, but unknown aetiology. For decades, the association between motor control strategies and chronic pain has been a topic for debate. One long held functional neuromuscular control mechanism is differential activation between regions within a single muscle. The aim of this study was to investigate differences in neuromuscular control, i.e. differential activation, between myalgic trapezius in fibromyalgia patients and healthy controls. Methods: 27 fibromyalgia patients and 30 healthy controls performed 3 minutes bilateral shoulder elevations with different loads (0-4 Kg) with a high-density surface electromyographical (EMG) grid placed above the upper trapezius. Differential activation was quantified by the power spectral median frequency of the difference in EMG amplitude between the cranial and caudal parts of the upper trapezius. The average duration of the differential activation was described by the inverse of the median frequency of the differential activations. Results: the median frequency of the differential activations was significantly lower, and the average duration of the differential activations significantly longer in fibromyalgia compared with controls at the two lowest load levels (0-1 Kg) (p andlt; 0.04), but not at the two highest load levels (2 and 4 Kg). Conclusion: these findings illustrate a different neuromuscular control between fibromyalgia patients and healthy controls during a low load functional task, either sustaining or resulting from the chronic painful condition. The findings may have clinical relevance for rehabilitation strategies for fibromyalgia.
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| 2. |
- Gerdle, Björn, 1953-, et al.
(författare)
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Firing rate and conduction velocity of single motor units in the trapezius muscle in fibromyalgia patients and healthy controls
- 2008
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Ingår i: Journal of Electromyography & Kinesiology. - : Elsevier. - 1050-6411 .- 1873-5711. ; 18:5, s. 707-716
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Tidskriftsartikel (refereegranskat)abstract
- Fibromyalgia is a common chronic pain condition in the population (2-4%), which often is associated with prominent negative consequences with respect to participation in daily activities. There are several reports in the literature concerning the effects of acute experimental pain on motor control. However, a more heterogeneous picture exists in the literature with respect to whether chronic pain conditions affect motor control. This study compares firing rate and conduction velocity (CV) of single motor units (MUs) in the trapezius muscle of fibromyalgia patients (FM) and healthy controls (CON). Multi-channel surface electromyography was used to estimate both MU firing rate and CV because this technique allows simultaneous estimation of both these variables and the measurements are easy and non-invasive. In this study, 29 FM and 30 CON subjects participated and performed isometric shoulder elevations using weights up to 4 kg. No significant differences in the firing rate of MUs in the trapezius muscle were found between the FM and CON groups (95% confidence interval was -1.9 and 1.3 pulses per second). There were no significant differences in CV between the groups at 1 and 2 kg load. However, the FM group had significantly higher CV in contractions without external load (p=0.004). We were unable to confirm the pain-adaptation model since no differences in firing rate between the two groups were found. CV was significantly higher in FM than in healthy controls; this might be due to alterations in histopathology and microcirculation.
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| 3. |
- Grönlund, Christer, et al.
(författare)
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Motor unit synchronization during fatigue : a novel quantification method.
- 2009
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Ingår i: Journal of Electromyography & Kinesiology. - : Elsevier BV. - 1050-6411 .- 1873-5711. ; 19:2, s. 242-251
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Tidskriftsartikel (refereegranskat)abstract
- Motor unit (MU) synchronization is the result of commonality in the pre-synaptic input to MUs. Previously proposed techniques to estimate MU synchronization based on invasive and surface electromyography (sEMG) recordings have been, respectively, limited by the analyzed MU population size and influence of changes in muscle fibre conduction velocities (MFCVs). The aim of this paper was to evaluate a novel descriptor of MU synchronization on a large MU population, and to minimize its dependency on MFCV. The method is based on the asymmetry of MU action potentials, causing synchronized MU action potentials to skew the monopolar sEMG signal distribution. The descriptor was the skewness statistic used on sub-band filtered monopolar sEMG signals (sub-band skewness). The method was evaluated using simulated signals and its performance was evaluated in terms of bias and sensitivity of the sub-band skewness quantifying the MU synchronization level. The best sensitivity was obtained using sub-band filtering at scale 5 (Mexican hat wavelet). The sensitivity was in general about 0.1units per 5% MU synchronization level. Changes in MFCV had a minimal influence, and caused at most a 5% deviant MU synchronization quantification level. A halved recruitment level had higher bias and a 20% lower sensitivity. Increased firing rate (14-34Hz) reduced the sensitivity about 50%. The sensitivity of the descriptor was robust to noise, and different volume conduction properties. It should be noted that the sub-band skewness comprises a subject-dependent component implying that only changes in MU synchronization level can be quantified.
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| 4. |
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| 5. |
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| 6. |
- Holtermann, A., et al.
(författare)
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Differential activation of regions within the biceps brachii muscle during fatigue
- 2008
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Ingår i: Acta Physiologica. - : Wiley-Blackwell. - 1748-1708 .- 1748-1716. ; 192:4, s. 559-567
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Tidskriftsartikel (refereegranskat)abstract
- Aim: To examine the occurrence of repeated differential activation between the heads of the biceps brachii muscle and its relation to fatigue prevention during a submaximal contraction.Methods: Thirty‐nine subjects carried out an isometric contraction of elbow flexion at 25% of maximal voluntary contraction (MVC) until exhaustion. A grid of 13 by 10 electrodes was used to record surface electromyographic signals from both heads of the biceps brachii. The root‐mean‐square of signals recorded from electrodes located medially and laterally was used to analyse activation differences. Differential activation was defined as periods of 33% different activation level between the two heads of the biceps brachii muscle.Results: Differential muscle activation was demonstrated in 30 of 33 subjects with appropriate data quality. The frequency of differential activation increased from 4.9 to 6.6 min−1 at the end of the contractions with no change in duration of the differential activations (about 1.4 s). Moreover, the frequency of differential activation was, in general, negatively correlated with time to exhaustion.Conclusion: The observed differential activation between the heads of the biceps brachii can be explained by an uneven distribution of synaptic input to the motor neurone pool. The findings of this study indicate that differential activation of regions within a muscle does not prevent fatigue at a contraction level of 25% of MVC.
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| 7. |
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| 8. |
- Holtermann, Andreas, et al.
(författare)
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Motor unit synchronization during fatigue : described with a novel sEMG method based on large motor unit samples.
- 2009
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Ingår i: Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology. - : Elsevier BV. - 1873-5711. ; 19:2, s. 232-241
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Tidskriftsartikel (refereegranskat)abstract
- The amount of documented increase in motor unit (MU) synchronization with fatigue and its possible relation with force tremor varies largely, possibly due to inhomogeneous muscle activation and methodological discrepancies and limitations. The aim of this study was to apply a novel surface electromyographical (EMG) descriptor for MU synchronization based on large MU populations to examine changes in MU synchronization with fatigue at different sites of a muscle and its relation to tremor. Twenty-four subjects performed an isometric elbow flexion at 25% of maximal voluntary contraction until exhaustion. Monopolar EMG signals were recorded using a grid of 130 electrodes above the biceps brachii. Changes in MU synchronization were estimated based on the sub-band skewness of EMG signals and tremor by the coefficient of variation in force. The synchronization descriptor was dependent on recording site and increased with fatigue together with tremor. There was a general association between these two parameters, but not between their fluctuations. These results are in agreement with other surface EMG studies and indicate that the novel descriptor can be used to attain information of synchronization between large MU populations during fatigue that cannot be retrieved with intra-muscular EMG.
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| 9. |
- Holtermann, Andreas, et al.
(författare)
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Selective activation of neuromuscular compartments within the human trapezius muscle.
- 2009
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Ingår i: Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology. - : Elsevier BV. - 1873-5711. ; 19:5, s. 896-902
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Tidskriftsartikel (refereegranskat)abstract
- Task-dependent differences in relative activity between "functional" subdivisions within human muscles are well documented. Contrary, independent voluntary control of anatomical subdivisions, termed neuromuscular compartments is not observed in human muscles. Therefore, the main aim of this study was to investigate whether subdivisions within the human trapezius can be independently activated by voluntary command using biofeedback guidance. Bipolar electromyographical electrodes were situated on four subdivisions of the trapezius muscle. The threshold for "active" and "rest" for each subdivision was set to >12% and <1.5% of the maximal electromyographical amplitude recorded during a maximal voluntary contraction. After 1h with biofeedback from each of the four trapezius subdivisions, 11 of 15 subjects learned selective activation of at least one of the four anatomical subdivisions of the trapezius muscle. All subjects managed to voluntarily activate the lower subdivisions independently from the upper subdivisions. Half of the subjects succeeded to voluntarily activate both upper subdivisions independently from the two lower subdivisions. These findings show that anatomical subdivisions of the human trapezius muscle can be independently activated by voluntary command, indicating neuromuscular compartmentalization of the trapezius muscle. The independent activation of the upper and lower subdivisions of the trapezius is in accordance with the selective innervation by the fine cranial and main branch of the accessory nerve to the upper and lower subdivisions. These findings provide new insight into motor control characteristics, learning possibilities, and function of the clinically relevant human trapezius muscle.
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| 10. |
- Holtermann, Andreas, et al.
(författare)
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Spatial distribution of active muscle fibre characteristics in the upper trapezius muscle and its dependency on contraction level and duration
- 2008
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Ingår i: Journal of Electromyography & Kinesiology. - : Elsevier. - 1050-6411 .- 1873-5711. ; 18:3, s. 372-381
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to provide direct in vivo information of the physiological and structural characteristics of active muscle fibres from a large part of the upper trapezius muscle. Two-dimensional (2-D) multi-channel surface electromyography recordings were used, with 13 × 10 electrodes covering 6 × 4.5 cm of the skin’s surface. A previously developed method was applied to detect individual propagating motor unit action potentials and to estimate their corresponding muscle fibre conduction velocity (MFCV) and muscle fibre orientation (MFO). Using these estimates, spatial distributions of MFCV and MFO were examined for five male subjects performing isometric shoulder elevation at different force levels. The main results were: (1) the general relationship between MFCV and force generation was non-systematic, with a positive relationship at the inferior part of the muscle, (2) the spatial distribution of MFCV at different force levels and fatigue was inhomogeneous and (3) the MFO was slightly different (6°) of the muscle fibres with origin superior compared to inferior to the C7 vertebra. These findings provide new information of the MFO of contracting muscle fibres and knowledge of the physiological characteristics of a large part of the upper trapezius muscle that previously was based on observations from human cadavers only.
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| 11. |
- Holtermann, Andreas, et al.
(författare)
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The relation between neuromuscular control and pain intensity in fibromyalgia
- 2011
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Ingår i: JOURNAL OF ELECTROMYOGRAPHY AND KINESIOLOGY. - : Elsevier Science B.V., Amsterdam.. - 1050-6411 .- 1873-5711. ; 21:3, s. 519-524
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Tidskriftsartikel (refereegranskat)abstract
- Fibromyalgia patients are shown to have a different neuromuscular control (differential activation) than healthy persons. Before clinical trials can be initiated, the relation between differential activations and pain intensity among fibromyalgia patients needs to be investigated. Twenty-seven fibromyalgia patients performed 3 min bilateral shoulder elevations with different loads (0-4 kg) with a high-density surface electromyographical (EMG) grid placed on the upper trapezius. Differential activation was quantified by the power spectral median frequency of the difference in EMG amplitude between the cranial and caudal parts of the upper trapezius. The average duration of the differential activation was described by the inverse of the median frequency of the differential activations. The relation between frequency and duration of differential activations as an average of the 4 loads and pain intensity the same day prior to the experiment was explored by Pearsons correlation coefficients. A strong negative relation between frequency of differential activations and pain intensity (R = -0.67, p andlt; 0.001) and a strong positive association between duration of differential activations and pain intensity (R = 0.66, p andlt; 0.001) were found. The significant association between frequency and duration of differential activations and pain intensity among the fibromyalgia patients indicates a relation between this neuromuscular control pattern and pain intensity. This finding support initiation of clinical trials for investigating effects on pain intensity of modifying differential activations among fibromyalgia patients.
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| 12. |
- Karlsson, J Stefan, et al.
(författare)
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Signal processing of the surface electromyogram to gain insight into neuromuscular physiology.
- 2009
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Ingår i: Philosophical Transactions. Series A. - : The Royal Society. - 1364-503X .- 1471-2962. ; 367:1887, s. 337-356
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Tidskriftsartikel (refereegranskat)abstract
- A surface electromyogram (sEMG) contains information about physiological and morphological characteristics of the active muscle and its neural strategies. Because the electrodes are situated on the skin above the muscle, the sEMG is an easily obtainable source of information. However, different combinations of physiological and morphological characteristics can lead to similar sEMG signals and sEMG recordings contain noise and other artefacts. Therefore, many sEMG signal processing methods have been developed and applied to allow insight into neuromuscular physiology. This paper gives an overview of important advances in the development and applications of sEMG signal processing methods, including spectral estimation, higher order statistics and spatio-temporal processing. These methods provide information about muscle activation dynamics and muscle fatigue, as well as characteristics and control of single motor units (conduction velocity, firing rate, amplitude distribution and synchronization).
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| 13. |
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| 14. |
- Östlund, Nils, 1977-, et al.
(författare)
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Adaptive spatial filtering of multichannel surface electromyogram signals
- 2004
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Ingår i: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 42:6, s. 825-831
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Tidskriftsartikel (refereegranskat)abstract
- Spatial filtering of surface electromyography (EMG) signals can be used to enhance single motor unit action potentials (MUAPs). Traditional spatial filters for surface EMG do not take into consideration that some electrodes could have poor skin contact. In contrast to the traditional a priori defined filters, this study introduces an adaptive spatial filtering method that adapts to the signal characteristics. The adaptive filter, the maximum kurtosis filter (MKF), was obtained by using the linear combination of surrounding channels that maximises kurtosis. The MKF and conventional filters were applied to simulated EMG signals and to real EMG signals recorded with an electrode grid to evaluate their performance in detecting single motor units. The MKF was compared with conventional spatial filtering methods. Simulated signals, with different levels of spatially correlated noise, were used for comparison. The influence of one electrode with poor skin contact was also investigated. The MKF was found to be considerably better at enhancing a single MUAP than conventional methods for all levels of spatial correlation of the noise. For a spatial correlation of 0.97 of the noise, the improvement in the signal-to-noise ratio, where a MUAP could be detected, was at least 6dB. With a simulated poor skin contact for one electrode, the improvement over the other methods was at least 19 dB.
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