Motor Unit Synchronization as a Measure of Localized Muscle Fatigue

Motor Unit Synchronization as a Measure of Localized Muscle Fatigue

Sridhar P. Arjunan (School of Electrical and Computer Engineering, RMIT University, Melbourne, VIC, Australia) and Dinesh K. Kumar (School of Electrical and Computer Engineering, RMIT University, Melbourne, VIC, Australia)
Copyright: © 2013 |Pages: 11
DOI: 10.4018/ijbce.2013010104
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Abstract

There is spectral compression of the surface Electromyogram (sEMG) towards lower frequencies and corresponding increase in amplitude of sEMG associated with muscle fatigue. While it is possible to use these features to compare pre and post onset of muscle fatigue, it is not possible to use these features alone to identify fatigued muscles due to the large inter-subject and inter-experimental variations. This is further compounded when the contraction is not isometric but cyclic because there is large variation of sEMG within each cycle. This research has developed and demonstrated a technique that measures motor unit synchronization within a muscle which can be used to determine if the associated muscle is fatigued or non-fatigued. This technique measures the level of independence between two channel sEMG recorded from the muscles measured by determinant of the Global matrix generated by performing independent component analysis. When the muscle is non-fatigued, the two channels have a high degree of independence with a high value of the determinant (0.35 to 0.98), while the channels become dependent when the muscles get fatigued and the determinant is close to zero (0.0007 to 0.0018). This is irrespective of the contraction being isometric or cyclic, and is valid for all subjects.
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Materials And Methods

Motor unit activation pattern is referred to as motor recruitment and is known to be temporally varying and pseudo random (Kukulka & Clamann, 1981). This results in smooth muscle contraction and prevents muscle fibres from getting fatigued (Farina et al., 2002). Changes to motor unit recruitment patterns (Kleine at al., 2001; Stegeman & Linssen, 1992) are associated with muscle fatigue, with increased synchronization associated with the onset of localized muscle fatigue and may occur due to increased central drive leading to synaptic input that is common to more than one neuron, or reduction in conduction velocity.

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