Objective: An electrophysiological technique was established to determine Motor Unit Number Index (MUNIX), and to investigate the stability of MUNIX. Methods: Fifty healthy subjects (25 males and 25 females) from the Outpatient Service of Peking University Third Hospital between December 2017 and September 2018 were included and divided into 5 groups according to age. The relevant parameters were detected in bilateral deltoid muscle (axillary nerve), double little finger abductor muscle (ulnar nerve), double quadriceps muscle (femoral nerve), double tibialis anterior muscle (peroneal nerve). The same muscle and the same healthy subjects were tested again three months later. Three-step detection were conducted: first, the surface electrode was attached to the muscle belly of each muscle, and the reference electrode was placed 2-3 cm away from the muscle belly. At the same time, the maximum compound muscle action potential (CMAP) of corresponding nerve was obtained, and the negative peak amplitude was measured. The second step was to collect the interference phase of the surface electromyography (SIP). There were 10 levels in total. And the measurement was repeated for three times, and the whole interference phase range was measured in the end. In the third step, the negative peak amplitude and SIP value of CMAP were substituted into the Excel table, and the MUNIX and motor unit number size (MUSIX) values were automatically calculated by the instrument through mathematical functions. Results: The mean MUNIX values of deltoid, extensor little finger, quadriceps femoris and tibial anterior were 193.2, 189.0, 159.7, 147.2, MUSIX were 46.9, 54.3, 49.6, 48.1 μV, respectively. The detection rates of MUNIX and MUSIX in the four muscles were 100%, respectively. With the increase of age, it could be seen that MUNIX declined, with statistically significant difference (P<0.05), but there was no significant change in MUSIX. There was no statistically significant difference in MUNIX and MUSIX between different gender, lateral sides and baseline and 3-month's reexamination results (P>0.05). Conclusions: MUNIX technology can improve the motor unit count of proximal upper limb and lower limb muscles. Its parameters are monitored using a mathematical model based on the composite muscle action potential and the interference phase of surface electromyography. Result is stable and reliable.
目的： 通过建立运动单位数量指数（MUNIX）这一电生理技术，探讨其稳定性。 方法： 收集2017年12月至2018年9月北京大学第三医院门诊健康受试者50名（男25名、女25名），按年龄分为5组。均检测双三角肌（腋神经）、双小指展肌（尺神经）、双股四头肌（股神经）、双胫前肌（腓神经），相同肌肉相同健康受试者在3个月后再检测一次。分三步检测：首先表面电极贴于各肌肉肌腹，参考电极置于肌腹旁2~3 cm，同时给予超强刺激，获取相应神经最大复合肌肉动作电位（CMAP），测量负峰波幅；第二步，进行表面肌电图干扰相（SIP）采集，用力共10个水平，每一次用力尽量恒定，并重复3次，最后测量整个干扰相范围；第三步，把CMAP负峰波幅与SIP值代入Excel表中，仪器通过数学函数自动计算MUNIX及运动单位大小指数（MUSIX）值。 结果： 健康受试者三角肌、小指展肌、股四头肌、胫前肌的MUNIX均值分别为193.2、189.0、159.7、147.2，MUSIX均值分别为46.9、54.3、49.6、48.1 μV；其中四块肌肉MUNIX、MUSIX的检出率均为100%；随着年龄增长，可以看到MUNIX有所下降，差异有统计学意义（P<0.05），但MUSIX无明显变化；MUNIX及MUSIX在性别、侧别、3个月复检结果，差异均无统计学意义（均P>0.05）。 结论： MUNIX技术能够完善上肢近端及下肢肌肉的运动单位计数，它的参数使用数学模型，基于复合肌肉动作电位及表面肌电图干扰相进行监测，数据稳定可靠。.
Keywords: Compound muscle action potential; Motor unit number index; Motor unit size index; Musculoskeletal; Surface electromyographic interference pattern.