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Neuromuscular fatigue detection by mechanomyography in people with complete spinal cord injury



Functional electrical stimulation (FES) is a method of activating paralyzed muscles. During FES application, fast muscle fatigue can occur (the inability of stimulated muscles to generate force). Therefore, it is beneficial to estimate the muscle fatigue for FES closed-loop control for walking to prevent unexpected muscle collapse and adapt the FES strategy in real time. Mechanomyography (MMG) is a noninvasive technique for registering myofiber vibrations, representing an ideal candidate for the provision of feedback. The hypothesis was that MMG signals could effectively detect muscle fatigue and, thus, provide feedback.


We tested this hypothesis by analyzing the wavelet transform of signals from an MMG sensor positioned over the rectus femoris muscle during electrically evoked contractions in subjects with spinal cord injury (SCI). The signals were collected from a total of 24 lower limb muscles. We investigated both legs of 15 participants with spinal cord injury (male, YOA = 27.13 ± 5.05, M = 75.8 ± 10.35 kg, and H = 1.78 ± 0.07 m, American Spinal Injury Impairment Scale (AIS) A and B). All MMG signals were analyzed in 12 frequency bands from 5 to 53 Hz.


We found different trends in the magnitudes in different frequency bands. The magnitude decreased in 13, 16, 20, 25, and 35 Hz bands in correlation with fatigue. The greatest statistical difference was found at 20 Hz and 25 Hz.


This result suggests that processed MMG signals indicate muscle fatigue and can, thus, be used as the feedback in FES systems.

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Functional electrical stimulation


Spinal cord injury






Microelectromechanical systems


ASIA impairment scale


American Spinal Injury Association


Maximum electrically stimulated extension


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This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001. We would like to thank Ana Carolina Moura at the Xavier Rehabilitation Center for allowing and providing the clinical setting to conduct this research, and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for providing scholarships and financial resources (Process nos. 484325/2011-6, 309514/2014-2, and 151210/2018-7). The work on this project was partly supported by the grant III44008 from the Ministry of Education, Science and Technological Development of Serbia, Belgrade.

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Correspondence to Eddy Krueger.

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This research was approved by the Health Ethical Research Committee of the Parana State Institute, protocol number 189/2010, in conformity with the Helsinki Declaration of 1975, as revised in 1983. On behalf of all authors, the corresponding author states that there is no conflict of interest.

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The work was performed at the Ana Carolina Moura Xavier Rehabilitation Center, Curitiba, PR, Brazil

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Krueger, E., Popović-Maneski, L., Neto, G.N.N. et al. Neuromuscular fatigue detection by mechanomyography in people with complete spinal cord injury. Res. Biomed. Eng. 36, 203–212 (2020).

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  • Electrical stimulation
  • Evoked potentials
  • Lower limb
  • Muscle contraction
  • Vibration
  • Wavelet