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Evaluation of surface electromyography and aspects of muscle strength in persons without motor impairment and in children with hemiplegic cerebral palsy
Linköping University, Department of Neuroscience and Locomotion, Rehabilitation Medicine. Linköping University, Faculty of Health Sciences.
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: urn:nbn:se:liu:diva-29556Local ID: 14928ISBN: 91-7373-860-3 (print)OAI: oai:DiVA.org:liu-29556DiVA: diva2:250372
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
List of papers
1. Reproducibility of surface EMG variables and peak torque during three sets of ten dynamic contractions
Open this publication in new window or tab >>Reproducibility of surface EMG variables and peak torque during three sets of ten dynamic contractions
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1999 (English)In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 9, no 5, 351-357 p.Article in journal (Refereed) Published
Abstract [en]

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 [μV]), 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.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-27732 (URN)10.1016/S1050-6411(99)00006-1 (DOI)12473 (Local ID)12473 (Archive number)12473 (OAI)
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2012-09-28Bibliographically approved
2. Test–retest reliability of EMG and peak torque during repetitive maximum concentric knee extensions
Open this publication in new window or tab >>Test–retest reliability of EMG and peak torque during repetitive maximum concentric knee extensions
2003 (English)In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 13, no 3, 281-287 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this study was to investigate the reliability of peak torque and surface electromyography (EMG) variable’s root mean square (RMS) and mean frequency (MNF) during an endurance test consisting of repetitive maximum concentric knee extensions. Muscle fatigue has been quantified in several ways, and in isokinetic testing it is based on a set of repetitive contractions. To assess test–retest reliability, two sets of 100 dynamic maximum concentric knee extensions were performed using an isokinetic dynamometer. The two series were separated by 7–8 days. The subjects relaxed during the passive flexion phase. Twenty (10 men and 10 women) clinically healthy subjects volunteered.

Peak torque and EMG from rectus femoris, vastus medialis, vastus lateralis and biceps femoris were recorded. RMS and MNF were calculated from the EMG signal. The reliability was calculated with intraclass correlation coefficient ICC (1.1) and standard error of measurements (SEM). The reliability of peak torque was good (ICC=0.93) and SEM showed low values. ICC was good for absolute RMS of rectus femoris (ICC≥0.80), vastus medialis (ICC≥0.88) and vastus lateralis (ICC≥0.82) and MNF of rectus femoris (ICC≥0.82) and vastus medialis (ICC≥0.83). Peak torque, and MNF and RMS of rectus femoris and vastus medialis are reliable variables obtained from an isokinetic endurance test of the knee extensors.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-27737 (URN)10.1016/S1050-6411(03)00022-1 (DOI)12478 (Local ID)12478 (Archive number)12478 (OAI)
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2012-09-28Bibliographically approved
3. Criterion validation of surface EMG variables as fatigue indicators using peak torque: a study of repetitive maximum isokinetic knee extensions
Open this publication in new window or tab >>Criterion validation of surface EMG variables as fatigue indicators using peak torque: a study of repetitive maximum isokinetic knee extensions
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.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-27761 (URN)10.1016/S1050-6411(00)00011-0 (DOI)12506 (Local ID)12506 (Archive number)12506 (OAI)
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2012-09-28Bibliographically approved
4. Surface electromyography and peak torque of repetitive maximum isokinetic plantar flexions in relation to aspects of muscle morphology
Open this publication in new window or tab >>Surface electromyography and peak torque of repetitive maximum isokinetic plantar flexions in relation to aspects of muscle morphology
2006 (English)In: Journal of Electromyography & Kinesiology, ISSN 1050-6411, E-ISSN 1873-5711, Vol. 16, no 3, 281-290 p.Article in journal (Refereed) Published
Abstract [en]

This study investigates the relationships between surface electromyography (EMG [Mean frequency of the power spectrum (MNF)]) and peak torque variables obtained during 100 maximum concentric plantar flexions with the right limb at 60° s−1 and different muscle morphological variables. Surface EMG was recorded from the right gastrocnemius lateralis and muscle biopsies were taken from the same site as the EMG electrodes were positioned. Muscle fibre area and fibre type composition were determined on serial muscle cross sections using both histochemistry (myofibrillar adenosine triphosphatase) and immunohistochemistry (monoclonal antibodies against specific myosin heavy chain isoforms). Forty-three female and nine male students participated in the study. Gastrocnemius lateralis contained predominantly type I fibres (50%) and type IIA fibres (40%) in both sexes and large individual differences were found. Principal component analysis (PCA) was used for the intercorrelation analyses, and projection to latent structures (PLS) was used for the multivariate regression analysis. MNF correlated positively with different fibre areas and with the proportion of type I fibres. Fibre areas and sex were the most important factors in the regression of maximum peak torque. High proportion of type I fibres and sex were the most important regressors of peak torque endurance normalised for lean body mass.

More studies are needed to understand the complex interrelationships between intrinsic muscle properties and the frequency content of the surface EMG before theoretical models can be formulated that incorporate both fibre areas and fibre type proportions.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-35931 (URN)10.1016/j.jelekin.2005.07.009 (DOI)29091 (Local ID)29091 (Archive number)29091 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2012-09-28Bibliographically approved
5. Muscle performance during maximum repeated knee extensions in children with hemiplegic cerebral palsy
Open this publication in new window or tab >>Muscle performance during maximum repeated knee extensions in children with hemiplegic cerebral palsy
2008 (English)In: Isokinetics and exercise science, ISSN 0959-3020, Vol. 16, no 4, 221-230 p.Article in journal (Refereed) Published
Abstract [en]

The aim of the present study was to compare isokinetic muscle performance of the knee extensors including surface EMG during repetitive maximum contractions between children with hemiplegic CP and healthy controls. A group of children with hemiplegic cerebral palsy (CP) (16 boys and eight girls; mean age 11 years with SD 2; range 7 to 15 years) and a control group (14 boys and eight girls; mean age 10 years with SD 2; range 7 to 15 years) participated. The relationships between maximum peak torque and the surface electromyography (EMG) variable root mean square (RMS) were obtained during 100 concentric knee extensions at 90°/s. Surface EMG was recorded from rectus femoris, vastus lateralis, and biceps femoris. The children with CP were also tested using Gross Motor Function Measure (GMFM). There were no differences between the groups in muscle endurance for the younger children. The results indicated that the children with CP had less strength enhancement in the hemiplegic leg during puberty. Peak torque correlated with GMFM and with RMS in rectus femoris and vastus lateralis. Co-activation was found in biceps femoris, but it did not affect muscle strength.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-16531 (URN)
Available from: 2009-01-30 Created: 2009-01-30 Last updated: 2012-09-28

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