UNC/NCSU Joint Department of Biomedical Engineering, North Carolina State University, Raleigh, NC 27695, USA.
UNC/NCSU Joint Department of Biomedical Engineering, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27514, USA.
Sensors (Basel). 2022 Jan 3;22(1):335. doi: 10.3390/s22010335.
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.
功能性电刺激（FES）是一种有潜力的神经康复干预措施，可以使患有导致运动障碍的神经疾病的人实现功能性运动。然而，在 FES 过程中肌肉疲劳的快速出现是维持更长时间所需的功能性运动的一个重大挑战。因此，人们仍然非常关注开发可靠地测量 FES 诱导的肌肉疲劳的传感技术。本研究提出使用超声（US）成像衍生的回声信号作为 FES 诱导的肌肉疲劳的指标。我们假设，在等长和动态肌肉收缩条件下，US 衍生的回声信号对 FES 诱导的肌肉疲劳敏感。八名非残疾参与者参与了实验，在他们的胫骨前肌（TA）上施加 FES 电极。在等长和动态踝关节背屈条件下的疲劳协议期间，我们同步收集踝关节的等长背屈扭矩或动态背屈角度、TA 肌肉的 US 回声信号和施加的刺激强度。实验结果表明，在等长（R2=0.891±0.081）和动态（R2=0.858±0.065）条件下，随着疲劳的进展，US 回声相对变化（ERC）呈指数下降。实验结果还暗示 US ERC 与 TA 肌肉疲劳基准（背屈扭矩或角度幅度）之间存在很强的线性关系，等长和动态条件下的 R2 值分别为 0.840±0.054 和 0.794±0.065。本研究的结果表明，US 回声信号是一种计算效率高的信号，能够强烈表示 FES 诱导的肌肉疲劳。它在检测疲劳方面的潜在实时实现可以促进考虑 FES 诱导的肌肉疲劳的 FES 闭环控制器设计。
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