Department of Medicine, University of Udine, Udine, Italy.
School of Sport Sciences, University of Udine, Udine, Italy.
Eur J Appl Physiol. 2021 Jun;121(6):1653-1664. doi: 10.1007/s00421-021-04647-y. Epub 2021 Mar 3.
Neuromuscular Electrical Stimulation (NMES) is commonly used in neuromuscular rehabilitation protocols, and its parameters selection substantially affects the characteristics of muscle activation. Here, we investigated the effects of short pulse width (200 µs) and higher intensity (short-high) NMES or long pulse width (1000 µs) and lower intensity (long-low) NMES on muscle mechanical output and fractional oxygen extraction. Muscle contractions were elicited with 100 Hz stimulation frequency, and the initial torque output was matched by adjusting stimulation intensity.
Fourteen able-bodied and six spinal cord-injured (SCI) individuals participated in the study. The NMES protocol (75 isometric contractions, 1-s on-3-s off) targeting the knee extensors was performed with long-low or short-high NMES applied over the midline between anterior superior iliac spine and patella protrusion in two different days. Muscle work was estimated by torque-time integral, contractile properties by rate of torque development and half-relaxation time, and vastus lateralis fractional oxygen extraction was assessed by Near-Infrared Spectroscopy (NIRS).
Torque-time integral elicited by the two NMES paradigms was similar throughout the stimulation protocol, with differences ranging between 1.4% (p = 0.877; able-bodied, mid-part of the protocol) and 9.9% (p = 0.147; SCI, mid-part of the protocol). Contractile properties were also comparable in the two NMES paradigms. However, long-low NMES resulted in higher fractional oxygen extraction in able-bodied (+ 36%; p = 0.006).
Long-low and short-high NMES recruited quadriceps femoris motor units that demonstrated similar contractile and fatigability properties. However, long-low NMES conceivably resulted in the preferential recruitment of vastus lateralis muscle fibers as detected by NIRS.
神经肌肉电刺激（NMES）常用于神经肌肉康复方案中，其参数选择对肌肉激活特性有重要影响。本研究旨在探讨短脉冲宽度（200µs）和高刺激强度（短高）NMES 或长脉冲宽度（1000µs）和低刺激强度（长平）NMES 对肌肉力学输出和氧分数提取的影响。肌肉收缩采用 100Hz 刺激频率，通过调整刺激强度来匹配初始扭矩输出。
14 名健康人和 6 名脊髓损伤（SCI）患者参与了本研究。采用 NMES 方案（100 个等长收缩，1s 开-3s 关）刺激股四头肌，在前后上髂嵴和髌骨突出之间的中线部位分别施加长平或短高 NMES，在两天内进行。通过扭矩-时间积分评估肌肉做功，通过扭矩发展速率和半松弛时间评估收缩特性，通过近红外光谱（NIRS）评估股外侧肌氧分数提取。
两种 NMES 方案在整个刺激过程中引起的扭矩-时间积分相似，差异范围在 1.4%（p=0.877；健康人，协议中间部分）和 9.9%（p=0.147；SCI，协议中间部分）之间。两种 NMES 方案的收缩特性也相似。然而，长平 NMES 导致健康人股外侧肌氧分数提取增加（+36%；p=0.006）。
长平 NMES 和短高 NMES 募集股四头肌运动单位，其收缩特性和疲劳特性相似。然而，NIRS 检测到，长平 NMES 可能导致股外侧肌纤维的优先募集。
