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Karlsson, Stefan
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Publications (10 of 35) Show all publications
Gerdle, B., Grönlund, C., Karlsson, S. J., Holtermann, A. & Roeleveld, K. (2010). Altered neuromuscular control mechanisms of the trapezius muscle in fibromyalgia.. BMC Musculoskeletal Disorders, 11, 42
Open this publication in new window or tab >>Altered neuromuscular control mechanisms of the trapezius muscle in fibromyalgia.
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2010 (English)In: BMC Musculoskeletal Disorders, ISSN 1471-2474, E-ISSN 1471-2474, Vol. 11, p. 42-Article in journal (Refereed) Published
Abstract [en]

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 < 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.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:umu:diva-33174 (URN)10.1186/1471-2474-11-42 (DOI)000275666200001 ()20205731 (PubMedID)
Available from: 2010-04-14 Created: 2010-04-14 Last updated: 2018-06-08Bibliographically approved
Holtermann, A., Grönlund, C., Ingebrigtsen, J., Karlsson, J. S. & Roeleveld, K. (2010). Duration of differential activations is functionally related to fatigue prevention during low-level contractions.. Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, 20(2), 241-245
Open this publication in new window or tab >>Duration of differential activations is functionally related to fatigue prevention during low-level contractions.
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2010 (English)In: Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, ISSN 1873-5711, Vol. 20, no 2, p. 241-245Article in journal (Refereed) Published
Abstract [en]

The aim of this study was to investigate the importance of duration of differential activations between the heads of the biceps brachii on local fatigue during prolonged low-level contractions. Fifteen subjects carried out isometric elbow flexion at 5% of maximal voluntary contraction (MVC) for 30 min. MVCs were performed before and at the end of the prolonged contraction. Surface electromyographic (EMG) signals were recorded from both heads of the biceps brachii. Differential activation was analysed based on the difference in EMG amplitude (activation) between electrodes situated at the two heads. Differential activations were quantified by the power spectral median frequency of the difference in activation between the heads throughout the contraction. The inverse of the median frequency was used to describe the average duration of the differential activations. The relation between average duration of the differential activations and the fatigue-induced reduction in maximal force was explored by linear regression analysis. The main finding was that the average duration of differential activation was positively associated to relative maximal force at the end of the 30 min contraction (R(2)=0.5, P<0.01). The findings of this study highlight the importance of duration of differential activations for local fatigue, and support the hypothesis that long term differential activations prevent fatigue during prolonged low-level contractions.

Keywords
Differential activation, fatigue, biceps brachii, low force, high-density surface EMG
National Category
Medical Biotechnology
Identifiers
urn:nbn:se:umu:diva-31270 (URN)10.1016/j.jelekin.2009.04.011 (DOI)000274980100008 ()19481957 (PubMedID)
Available from: 2010-02-04 Created: 2010-02-04 Last updated: 2018-06-08Bibliographically approved
Åström, C., Lindkvist, M., Burström, L., Sundelin, G. & Karlsson, J. S. (2009). Changes in EMG activity in the upper trapezius muscle due to local vibration exposure.. Journal of Electromyography & Kinesiology, 19(3), 407-415
Open this publication in new window or tab >>Changes in EMG activity in the upper trapezius muscle due to local vibration exposure.
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2009 (English)In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 19, no 3, p. 407-415Article in journal (Refereed) Published
Abstract [en]

Exposure to vibration is suggested as a risk factor for developing neck and shoulder disorders in working life. Mechanical vibration applied to a muscle belly or a tendon can elicit a reflex muscle contraction, also called tonic vibration reflex, but the mechanisms behind how vibration could cause musculoskeletal disorders has not yet been described. One suggestion has been that the vibration causes muscular fatigue. This study investigates whether vibration exposure changes the development of muscular fatigue in the trapezius muscle. Thirty-seven volunteers (men and women) performed a sub-maximal isometric shoulder elevation for 3min. This was repeated four times, two times with induced vibration and two times without. Muscle activity was measured before and after each 3-min period to look at changes in the electromyography parameters. The result showed a significantly smaller mean frequency decrease when performing the shoulder elevation with vibration (-2.51Hz) compared to without vibration (-4.04Hz). There was also a slightly higher increase in the root mean square when exposed to vibration (5.7% of maximal voluntary contraction) compared to without (3.8% of maximal voluntary contraction); however, this was not statistically significant. The results of the present study indicate that short-time exposure to vibration has no negative acute effects on the fatiguing of upper trapezius muscle.

National Category
Neurosciences Physiology
Research subject
Physiotherapy
Identifiers
urn:nbn:se:umu:diva-20909 (URN)10.1016/j.jelekin.2007.11.003 (DOI)18096405 (PubMedID)
Available from: 2009-03-27 Created: 2009-03-27 Last updated: 2018-06-09
Grönlund, C., Holtermann, A., Roeleveld, K. & Karlsson, J. S. (2009). Motor unit synchronization during fatigue: a novel quantification method.. Journal of Electromyography & Kinesiology, 19(2), 242-251
Open this publication in new window or tab >>Motor unit synchronization during fatigue: a novel quantification method.
2009 (English)In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 19, no 2, p. 242-251Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
synchronization, motor unit, electromyography, surface EMG, fatigue, conduction velocity
Identifiers
urn:nbn:se:umu:diva-24073 (URN)10.1016/j.jelekin.2007.07.012 (DOI)18036832 (PubMedID)
Available from: 2009-06-30 Created: 2009-06-30 Last updated: 2018-06-08
Holtermann, A., Grönlund, C., Karlsson, J. S. & Roeleveld, K. (2009). Motor unit synchronization during fatigue: described with a novel sEMG method based on large motor unit samples.. Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, 19(2), 232-241
Open this publication in new window or tab >>Motor unit synchronization during fatigue: described with a novel sEMG method based on large motor unit samples.
2009 (English)In: Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, ISSN 1873-5711, Vol. 19, no 2, p. 232-241Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
Force tremor, electrode location, multi-channel surface EMG, motor unit synchronization, fatigue
Identifiers
urn:nbn:se:umu:diva-25809 (URN)10.1016/j.jelekin.2007.08.008 (DOI)18207421 (PubMedID)
Available from: 2009-09-03 Created: 2009-09-03 Last updated: 2018-06-08
Holtermann, A., Roeleveld, K., Mork, P. J., Grönlund, C., Karlsson, J. S., Andersen, L. L., . . . Søgaard, K. (2009). Selective activation of neuromuscular compartments within the human trapezius muscle.. Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, 19(5), 896-902
Open this publication in new window or tab >>Selective activation of neuromuscular compartments within the human trapezius muscle.
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2009 (English)In: Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, ISSN 1873-5711, Vol. 19, no 5, p. 896-902Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
EMG biofeedback, trapezius, compartments, motor control
Identifiers
urn:nbn:se:umu:diva-25804 (URN)10.1016/j.jelekin.2008.04.016 (DOI)18585928 (PubMedID)
Available from: 2009-09-03 Created: 2009-09-03 Last updated: 2018-06-08
Karlsson, J. S., Roeleveld, K., Grönlund, C., Holtermann, A. & Östlund, N. (2009). Signal processing of the surface electromyogram to gain insight into neuromuscular physiology.. Philosophical Transactions. Series A: Mathematical, physical, and engineering science, 367(1887), 337-356
Open this publication in new window or tab >>Signal processing of the surface electromyogram to gain insight into neuromuscular physiology.
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2009 (English)In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 367, no 1887, p. 337-356Article in journal (Refereed) Published
Abstract [en]

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).

Keywords
electromyography, multi-channel, spatio-temporal processing, neuromuscular physiology, muscle function, muscle control
Identifiers
urn:nbn:se:umu:diva-24027 (URN)10.1098/rsta.2008.0214 (DOI)18974034 (PubMedID)
Available from: 2009-06-30 Created: 2009-06-30 Last updated: 2018-06-08
Skönevik, J., Karlsson, S., Hallberg, P., Nyström, L. & Olsén, L. (2008). A technical platform for remote monitoring of biosignals in real time. In: A technical platform for remote monitoring of biosignals in real time: . Paper presented at Phealth 2008.
Open this publication in new window or tab >>A technical platform for remote monitoring of biosignals in real time
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2008 (English)In: A technical platform for remote monitoring of biosignals in real time, 2008Conference paper, Oral presentation only (Other academic)
National Category
Medical Engineering
Identifiers
urn:nbn:se:umu:diva-160197 (URN)
Conference
Phealth 2008
Available from: 2019-06-14 Created: 2019-06-14 Last updated: 2019-06-19Bibliographically approved
Grip, H., Sundelin, G., Gerdle, B. & Karlsson, S. J. (2008). Cervical helical axis characteristics and its center of rotation during active head and upper arm movements-comparisons of whiplash-associated disorders, non-specific neck pain and asymptomatic individuals.. Journal of Biomechanics, 41(13), 2799-2805
Open this publication in new window or tab >>Cervical helical axis characteristics and its center of rotation during active head and upper arm movements-comparisons of whiplash-associated disorders, non-specific neck pain and asymptomatic individuals.
2008 (English)In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 41, no 13, p. 2799-2805Article in journal (Refereed) Published
Abstract [en]

The helical axis model can be used to describe translation and rotation of spine segments. The aim of this study was to investigate the cervical helical axis and its center of rotation during fast head movements (side rotation and flexion/extension) and ball catching in patients with non-specific neck pain or pain due to whiplash injury as compared with matched controls. The aim was also to investigate correlations with neck pain intensity. A finite helical axis model with a time-varying window was used. The intersection point of the axis during different movement conditions was calculated. A repeated-measures ANOVA model was used to investigate the cervical helical axis and its rotation center for consecutive levels of 15 degrees during head movement. Irregularities in axis movement were derived using a zero-crossing approach. In addition, head, arm and upper body range of motion and velocity were observed. A general increase of axis irregularity that correlated to pain intensity was observed in the whiplash group. The rotation center was superiorly displaced in the non-specific neck pain group during side rotation, with the same tendency for the whiplash group. During ball catching, an anterior displacement (and a tendency to an inferior displacement) of the center of rotation and slower and more restricted upper body movements implied a changed movement strategy in neck pain patients, possibly as an attempt to stabilize the cervical spine during head movement.

Place, publisher, year, edition, pages
Springer, 2008
Keywords
Prostate cancer, Carcinogenesis, Radiation treatment, DVH, Fractionation
Identifiers
urn:nbn:se:umu:diva-46147 (URN)10.1016/j.jbiomech.2008.07.005 (DOI)18707689 (PubMedID)
Available from: 2011-08-26 Created: 2011-08-26 Last updated: 2018-06-08Bibliographically approved
Grip, H., Sundelin, G., Gerdle, B. & Karlsson, J. S. (2008). Cervical helical axis characteristics and its centre of rotation during active head movements: comparisons of whiplash-associated disorders, non-specific neck pain and asymptomatic individuals. Journal of Biomechanics, 41(13), 2799-2805
Open this publication in new window or tab >>Cervical helical axis characteristics and its centre of rotation during active head movements: comparisons of whiplash-associated disorders, non-specific neck pain and asymptomatic individuals
2008 (English)In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 41, no 13, p. 2799-2805Article in journal (Refereed) Published
Abstract [en]

The helical axis model can be used to describe translation and rotation of spine segments. The aim of this study was to investigate the cervical helical axis and its center of rotation during fast head movements (side rotation and flexion/extension) and ball catching in patients with non-specific neck pain or pain due to whiplash injury as compared with matched controls. The aim was also to investigate correlations with neck pain intensity. A finite helical axis model with a time-varying window was used. The intersection point of the axis during different movement conditions was calculated. A repeated-measures ANOVA model was used to investigate the cervical helical axis and its rotation center for consecutive levels of 15° during head movement. Irregularities in axis movement were derived using a zero-crossing approach. In addition, head, arm and upper body range of motion and velocity were observed. A general increase of axis irregularity that correlated to pain intensity was observed in the whiplash group. The rotation center was superiorly displaced in the non-specific neck pain group during side rotation, with the same tendency for the whiplash group. During ball catching, an anterior displacement (and a tendency to an inferior displacement) of the center of rotation and slower and more restricted upper body movements implied a changed movement strategy in neck pain patients, possibly as an attempt to stabilize the cervical spine during head movement.

Place, publisher, year, edition, pages
Elsevier, 2008
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:umu:diva-3068 (URN)10.1016/j.jbiomech.2008.07.005 (DOI)
Available from: 2008-03-31 Created: 2008-03-31 Last updated: 2018-06-09Bibliographically approved
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