| 1. |
- Gerdle, Björn, 1953-, et al.
(författare)
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Criterion validation of surface EMG variables as fatigue indicators using peak torque : a study of repetitive maximum isokinetic knee extensions
- 2000
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Ingår i: Journal of Electromyography & Kinesiology. - 1050-6411 .- 1873-5711. ; 10:4, s. 225-232
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Karlsson, J.S, et al.
(författare)
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An estimation of the influence of force decrease on the mean power spectral frequency shift of the EMG during repetitive maximum dynamic knee extensions
- 2003
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Ingår i: Journal of Electromyography & Kinesiology. - 1050-6411 .- 1873-5711. ; 13:5, s. 461-468
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Tidskriftsartikel (refereegranskat)abstract
- Frequency analysis of myoelectric (ME) signals, using the mean power spectral frequency (MNF), has been widely used to characterize peripheral muscle fatigue during isometric contractions assuming constant force. However, during repetitive isokinetic contractions performed with maximum effort, output (force or torque) will decrease markedly during the initial 40-60 contractions, followed by a phase with little or no change. MNF shows a similar pattern. In situations where there exist a significant relationship between MNF and output, part of the decrease in MNF may per se be related to the decrease in force during dynamic contractions. This study estimated force effects on the MNF shifts during repetitive dynamic knee extensions. Twenty healthy volunteers participated in the study and both surface ME signals (from the right vastus lateralis, vastus medialis, and rectus femoris muscles) and the biomechanical signals (force, position, and velocity) of an isokinetic dynamometer were measured. Two tests were performed: (i) 100 repetitive maximum isokinetic contractions of the right knee extensors, and (ii) five gradually increasing static knee extensions before and after (i). The corresponding ME signal time-frequency representations were calculated using the continuous wavelet transform. Compensation of the MNF variables of the repetitive contractions was performed with respect to the individual MNF-force relation based on an average of five gradually increasing contractions. Whether or not compensation was necessary was based on the shape of the MNF-force relationship. A significant compensation of the MNF was found for the repetitive isokinetic contractions. In conclusion, when investigating maximum dynamic contractions, decreases in MNF can be due to mechanisms similar to those found during sustained static contractions (force-independent component of fatigue) and in some subjects due to a direct effect of the change in force (force-dependent component of fatigue). In order to compare MNF shifts during sustained static and repetitive dynamic contractions it is necessary to estimate the force-dependent component of fatigue of dynamic contractions. Our results are preliminary and have to be confirmed in larger experiments using single dynamic contractions when determining the MNF-force relationship of the unfatigued situation.
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| 3. |
- Karlsson, Stefan, et al.
(författare)
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Mean frequency and signal amplitude of the surface EMG of the quadriceps muscles increase with increasing torque - A study using the continuous wavelet transform
- 2001
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Ingår i: Journal of Electromyography & Kinesiology. - 1050-6411 .- 1873-5711. ; 11:2, s. 131-140
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Tidskriftsartikel (refereegranskat)abstract
- The continuous wavelet transform (CWT), a time-frequency method, was used when calculating mean frequency of the power spectrum (MNF) and signal amplitude (RMS) of the surface EMG to investigate their relationships to force during a gradually increasing knee extension (ramp). Based upon the CWT, MNF was redefined to include time dependence on the EMG signal frequency contents, the short-time MNF (STMNF). Surface EMG was recorded from vastus lateralis, rectus femoris and vastus medialis in 21 clinically healthy subjects during a brief, gradually increasing contraction up to 100% of a maximum voluntary contraction (MVC), with a duration of approximately 10 s. The relationships between the EMG variables and force using linear regression were determined for each subject. For vastus lateralis, we also investigated if certain aspects of the muscle morphology (i.e., proportions and areas of different fibre types) influenced the EMG-force relationship.For the majority of subjects (17-18 out of 21 subjects) there were significant positive correlations between STMNF and force in the three muscles. No sex differences were found in intercepts or regression coefficients of STMNF. The muscle morphology had a significant influence on the STMNF-force intercept and the regression coefficient. Positive and highly significant linear correlations between RMS and force were found for all subjects and all three muscles.In conclusion, time frequency methods can be applied when investigating EMG during brief contractions associated with non-stationarity. In a great majority of the subjects, and in the three muscles, significant linear force dependencies were found for STMNF. Thus, when evaluating muscle fatigue, e.g., in ergonomic situations, it is important to consider the force level as one factor that can influence the results. Morphological variables (fibre proportions and fibre areas) influenced the STMNF-force relationship in vastus lateralis. Copyright
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| 4. |
- Larsson, Barbro, 1952-, et al.
(författare)
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Test–retest reliability of EMG and peak torque during repetitive maximum concentric knee extensions
- 2003
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Ingår i: Journal of Electromyography & Kinesiology. - 1050-6411 .- 1873-5711. ; 13:3, s. 281-287
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Forsman, Mikael, 1963, et al.
(författare)
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Motor unit recruitment in the trapezius muscle with special reference to coarse arm movements.
- 2001
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Ingår i: Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology. - 1050-6411 .- 1873-5711. ; 11:3, s. 207-16
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Tidskriftsartikel (refereegranskat)abstract
- Chronic shoulder pain is common in a variety of occupations. The "Cinderella hypothesis" suggests that the pain originates from damaged type I muscle fibres driven into degenerative processes as a result of too long activation and too short recovery time. The main purpose of this study was to investigate if the same motor units are active during all phases of coarse arm movements. Eight healthy volunteers participated in the study. Intramuscular electromyographic signals were picked up with a four-lead fine wire electrode, during a unilateral straight arm movement. The movement started with either (part 1) an abduction or a flexion, then (2) a movement in the horizontal plane from the sagittal to the frontal plane or vice versa, and finally (3) an adduction or an extension to the start position. The movement cycle was performed in three different speeds, slow, medium, and high, with one, two or five cycles per 20 s, respectively. On an average, the motor unit action potentials (MUAPs) of 6 motor units (range, 1-15) were identified per trail. In total 94% of the MUAP trains that were identified showed firings in all 3 parts of the movements. The findings support the Cinderella hypothesis, although there is a need to further investigate the temporal pattern of long-term motor unit activity.
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| 10. |
- Ageberg, Eva
(författare)
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Consequences of a ligament injury on neuromuscular function and relevance to rehabilitation - using the anterior cruciate ligament-injured knee as model.
- 2002
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Ingår i: Journal of Electromyography & Kinesiology. - 1873-5711. ; 12:3, s. 12-205
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this article is to survey current knowledge concerning the consequences of a ligament injury on neuromuscular function and its relevance to rehabilitation, in relation to clinical practice. Although it deals with the ACL-injured knee, these views may also apply to other joints. The effects of a ligament injury on neuromuscular function are first considered - i.e., proprioception, postural control, muscle strength, functional performance, movement and activation pattern, central mechanisms, motor control and learning. The treatment and effects of rehabilitation on neuromuscular function are then discussed. The survey is concluded by discussing the clinical significance.
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