The quick onset of muscle fatigue is a critical issue when applying neuromuscular electrical stimulation (NMES) to generate muscle contractions for functional limb movements, which were lost/impaired due to a neurological disorder or an injury. For in situ assessment of the effect of NMES-induced muscle fatigue, a novel noninvasive sensor modality that can quantify the degraded contractility of a targeted muscle is required. In this study, instantaneous strain maps of a contracting muscle were derived from ultra-high-frame-rate (2 kHz) ultrasound images to quantify the contractility. A correlation between strain maps and isometric contraction force values was investigated. When the muscle reached its maximum contraction, the maximum and the mean values of the strain map were correlated with the force values and were further used to stage the contractility change. During the muscle activation period, a novel methodology based on the principal component regression (PCR) was proposed to explore the strain–force correlation. The quadriceps muscle of 3 able-bodied human participants was investigated during NMES-elicited isometric knee extension experiments. Strong to very strong correlation results were obtained and indicate that the proposed measurements from ultrasound images are promising to quantify the muscle contractility changes during NMES.

当应用神经肌肉电刺激 (NMES) 来产生功能性肢体运动的肌肉收缩时，肌肉疲劳的快速发作是一个关键问题，由于神经系统疾病或受伤而失去/受损。对于原位为了评估 NMES 引起的肌肉疲劳的影响，需要一种新型的无创传感器模式，可以量化目标肌肉的收缩性下降。在这项研究中，收缩肌肉的瞬时应变图来自超高帧率 (2 kHz) 超声图像，以量化收缩性。研究了应变图和等长收缩力值之间的相关性。当肌肉达到最大收缩时，应变图的最大值和平均值与力值相关，并进一步用于分阶段收缩性变化。在肌肉激活期间，提出了一种基于主成分回归 (PCR) 的新方法来探索应变-力的相关性。在 NMES 引发的等长膝关节伸展实验中，研究了 3 名身体健全的人类参与者的股四头肌。获得了强到非常强的相关结果，并表明从超声图像中提出的测量值有望量化 NMES 期间的肌肉收缩力变化。