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Article

Ultrasound Echogenicity as an Indicator of Muscle Fatigue during Functional Electrical Stimulation

by 1,2, 1,2, 1,2, 3,4,5,6 and 1,2,*
1
UNC/NCSU Joint Department of Biomedical Engineering, North Carolina State University, Raleigh, NC 27695, USA
2
UNC/NCSU Joint Department of Biomedical Engineering, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27514, USA
3
The Department of Bioengineering, School of Engineering, University of Pittsburgh, Pittsburgh, PA 15260, USA
4
The Center for Ultrasound Molecular Imaging and Therapeutics, Department of Medicine and Heart and Vascular Institute, University of Pittsburgh School of Medicine, University of Pittsburgh Medical Center, Pittsburgh, PA 15213, USA
5
The Department of Mechanical Engineering and Materials Science, School of Engineering, University of Pittsburgh, Pittsburgh, PA 15260, USA
6
The McGowan Institute for Regenerative Medicine, University of Pittsburgh Medical Center, University of Pittsburgh, Pittsburgh, PA 15219, USA
*
Author to whom correspondence should be addressed.
Academic Editors: Kei Masani and Maysam Abbod
Sensors 2022, 22(1), 335; https://doi.org/10.3390/s22010335
Received: 8 November 2021 / Revised: 10 December 2021 / Accepted: 31 December 2021 / Published: 3 January 2022
Functional electrical stimulation (FES) is a potential neurorehabilitative intervention to enable functional movements in persons with neurological conditions that cause mobility impairments. However, the quick onset of muscle fatigue during FES is a significant challenge for sustaining the desired functional movements for more extended periods. Therefore, a considerable interest still exists in the development of sensing techniques that reliably measure FES-induced muscle fatigue. This study proposes to use ultrasound (US) imaging-derived echogenicity signal as an indicator of FES-induced muscle fatigue. We hypothesized that the US-derived echogenicity signal is sensitive to FES-induced muscle fatigue under isometric and dynamic muscle contraction conditions. Eight non-disabled participants participated in the experiments, where FES electrodes were applied on their tibialis anterior (TA) muscles. During a fatigue protocol under either isometric and dynamic ankle dorsiflexion conditions, we synchronously collected the isometric dorsiflexion torque or dynamic dorsiflexion angle on the ankle joint, US echogenicity signals from TA muscle, and the applied stimulation intensity. The experimental results showed an exponential reduction in the US echogenicity relative change (ERC) as the fatigue progressed under the isometric (R2=0.891±0.081) and dynamic (R2=0.858±0.065) conditions. The experimental results also implied a strong linear relationship between US ERC and TA muscle fatigue benchmark (dorsiflexion torque or angle amplitude), with R2 values of 0.840±0.054 and 0.794±0.065 under isometric and dynamic conditions, respectively. The findings in this study indicate that the US echogenicity signal is a computationally efficient signal that strongly represents FES-induced muscle fatigue. Its potential real-time implementation to detect fatigue can facilitate an FES closed-loop controller design that considers the FES-induced muscle fatigue. View Full-Text
Keywords: muscle fatigue; electrical stimulation; ankle joint; biomechanical phenomena; ultrasonography; linear models; nonlinear dynamics muscle fatigue; electrical stimulation; ankle joint; biomechanical phenomena; ultrasonography; linear models; nonlinear dynamics
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Figure 1

  • Externally hosted supplementary file 1
    Doi: 10.5281/zenodo.5637439
    Link: https://zenodo.org/record/5637439
    Description: This supplementary material contains four videos of the tibialis anterior muscle's ultrasound imaging during the functional electrical stimulation (FES)-induce muscle fatigue progressions. Both isometric and dynamic conditions are included for two participants, Sub03 and Sub05. Under the isometric condition, there are 15 FES-induced muscle contraction cycles during the 120-second fatigue progression. Under the dynamic condition, there are 30 FES-induced muscle contraction cycles during the 240-second fatigue progression. In each video, the left y-axis represents the depth (unit: mm) from the skin to the deep muscle layer and the x-axis represents the width (unit: mm) of the ultrasound transducer with the middle point as 0 mm. The right gray-scaled bar represents the normalized ultrasound intensity value for each pixel in the image.
MDPI and ACS Style

Zhang, Q.; Iyer, A.; Lambeth, K.; Kim, K.; Sharma, N. Ultrasound Echogenicity as an Indicator of Muscle Fatigue during Functional Electrical Stimulation. Sensors 2022, 22, 335. https://doi.org/10.3390/s22010335

AMA Style

Zhang Q, Iyer A, Lambeth K, Kim K, Sharma N. Ultrasound Echogenicity as an Indicator of Muscle Fatigue during Functional Electrical Stimulation. Sensors. 2022; 22(1):335. https://doi.org/10.3390/s22010335

Chicago/Turabian Style

Zhang, Qiang, Ashwin Iyer, Krysten Lambeth, Kang Kim, and Nitin Sharma. 2022. "Ultrasound Echogenicity as an Indicator of Muscle Fatigue during Functional Electrical Stimulation" Sensors 22, no. 1: 335. https://doi.org/10.3390/s22010335

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