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Criterion validation of surface EMG variables as fatigue indicators using peak torque: a study of repetitive maximum isokinetic knee extensions
Linköping University, Department of Neuroscience and Locomotion, Rehabilitation Medicine. Östergötlands Läns Landsting, Pain and Occupational Centre, Pain and Rehabilitation Centre. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Neuroscience and Locomotion, Rehabilitation Medicine. Linköping University, Faculty of Health Sciences.
Department of Biomedical Engineering and Informatics, University Hospital, Umeå, Sweden.
2000 (English)In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 10, no 4, 225-232 p.Article in journal (Refereed) Published
Abstract [en]

A number of studies have been published that have used variables of the electromyogram (EMG) power spectrum during dynamic exercise. Despite these studies there is a shortage of studies of the validity of surface EMG registrations during repetitive dynamic contractions with respect to fatigue. The aim of this study was to investigate if the surface EMG variables mean frequency (MNF [Hz]) and the signal amplitude (RMS [μV]) are valid indicators of muscular fatigue (defined as “any exercise-induced reduction in the capacity to generate force or power output”) during maximum repeated isokinetic knee extensions (i.e. criterion validity using peak torque).

Twenty-one healthy volunteers performed 100 isokinetic knee extensions at 90° s-1. EMG signals were recorded from the vastus lateralis, the rectus femoris and the vastus medialis of the right thigh by surface electrodes. MNF and RMS of the EMG together with peak torque (PT [Nm]) were determined for each contraction. MNF showed consequently higher correlation coefficients with PT than RMS did. Positive correlations generally existed between MNF and PT. The majority of the subjects had positive correlations between RMS and PT (i.e. decreases both in PT and in RMS).

In conclusion, at the individual level MNF generally — in contrast to RMS — showed good criterion validity with respect to biomechanical fatigue during dynamic maximum contractions.

Place, publisher, year, edition, pages
2000. Vol. 10, no 4, 225-232 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-27761DOI: 10.1016/S1050-6411(00)00011-0Local ID: 12506OAI: oai:DiVA.org:liu-27761DiVA: diva2:248313
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Evaluation of surface electromyography and aspects of muscle strength in persons without motor impairment and in children with hemiplegic cerebral palsy
Open this publication in new window or tab >>Evaluation of surface electromyography and aspects of muscle strength in persons without motor impairment and in children with hemiplegic cerebral palsy
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Impaired muscle function significantly affects persons with Cerebral Palsy (CP), affects that include muscle strength, fatigue and endurance. This thesis evaluates a test method, an endurance test, and estimates aspects of muscle fatigue and muscle endurance in persons without impaired muscle function and in children with CP. The test is preformed during dynamic movements and uses an isokinetic dynamometer and surface electromyography (SEMG). In persons without muscle impairment, muscle strength variables with simultaneous SEMG recordings during fatigue knee extensions test are evaluated with respect to reliability and validity. The endurance test consisted of 100 concentric maximum muscle contractions. SEMG were investigated in the agonist and the antagonist muscle. The SEMG variables mean frequency (MNF) and root mean square (RMS) were calculated. The relationship between maximal muscle strength variables, SEMG, and muscle morphology were investigated in healthy participants during plantar flexions. Muscle strength, muscle fatigue, and muscle endurance in children with CP, and in a control group, were examined together with SEMG recordings during knee extensions. Activity level in the children with CP was estimated using Gross Motor Function Measure (GMFM) and Gross Motor Function Classification System (GMFCS).

In healthy young and middle-aged subjects, it is highly reliable to test concentric muscle strength and endurance with isokinetic dynamo meters at moderate movement velocity. The reliability was high for the SEMG variables MNF and RMS of the agonist but low for the antagonist muscle. MNF is the SEMG variable describing fatigue with respect to the decrease in peak torque during repeated maximum concentric dynamic contractions. MNF correlated with the fibre area and the proportion of Type I muscle fibres during the endurance test of plantar flexors. Area of Type II muscle fibres and sex were the most important factors contributing to muscle strength during plantar flexion. The Proportion of Type I muscle fibres and area of Type I were the most important factors for high muscle endurance level.

Generally, the affected leg in children with hemiplegic CP was significantly weaker than the less-affected leg, and RMS values were higher for the agonists of the less-affected leg than for the affected leg. The children were divided in two groups, a younger and an older group. At the endurance level, the younger children with hemiplegic CP were as strong as the young children in the control group and there were no difference between the affected and the less affected leg. The older children with CP had impaired maximum muscle strength and endurance strength compared to the control group. The children with CP did not improve strength with increasing age; instead, high values of GMFM correlated with muscle strength.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2005. 58 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 882
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-29556 (URN)14928 (Local ID)91-7373-860-3 (ISBN)14928 (Archive number)14928 (OAI)
Public defence
2005-02-04, Berzeliussalen, Hälsouniversitetet, Linköping, 13:00 (Swedish)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-09-28Bibliographically approved

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Gerdle, BjörnLarsson, Barbro

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