Ultrasound-Based Sensing and Control of Functional Electrical Stimulation for Ankle Joint Dorsiflexion: Preliminary Study

Toward a wearable monitor of local muscle fatigue during electrical muscle stimulation using tissue Doppler imaging

“…The potential for TDI to monitor muscle fatigue during EMS brings about unique opportunities in biomechanics, rehabilitation, and sports performance. EMS parameters such as timing, duration, and intensity are commonly controlled without any feedback from the targeted muscle (Shields et al, 2006 ; Freeman et al, 2016 ; Hallock et al, 2018 ; Phongamwong et al, 2019 ), though finding real time feedback to close the loop for human–robot interaction is an active area of research (Zhou et al, 2018 ; Zhang et al, 2022b ). By integrating muscle fatigue as feedback, EMS protocols can be better refined to optimize the desired stimulation outcomes.…”

“…We envision future wearable feedback devices can use ultrasound to monitor EMS-induced muscle fatigue in real time. Wearable ultrasound is still an emerging technology (Sikdar et al, 2014 ; AlMohimeed and Ono, 2020 ), and we are optimistic that other ultrasound approaches besides TDI may have utility to quantify muscle fatigue (Zhang et al, 2022b ). Although TDI provides robust and detailed velocity information, current implementations of TDI typically have high power requirements, impractically large physical forms, extensive computational and memory demands, and are thus generally unsuited for wearable applications.…”

“…Various noninvasive techniques have attempted to quantify localized muscle fatigue using methods that are not as susceptible to electrical interference (Al-Mulla et al, 2011 ), such as mechanomyography (Uwamahoro et al, 2021 ), near-infrared spectroscopy (Yoshitake et al, 2001 ), and sonomyography (Zhang et al, 2022b ). Mechanomyography can be considered the mechanical equivalent of sEMG by recording low-frequency (i.e., 2–200 Hz) surface vibrations produced by muscle fibers during contraction (Islam et al, 2013 ), but it has limited utility due to its sensitivity to acoustic/vibrational interference during movement (Woodward et al, 2019 ).…”