Sharma K R, Miller R G
Department of Neurology, California Pacific Medical Center, University of California, San Francisco, USA.
Muscle Nerve. 1996 Nov;19(11):1391-400. doi: 10.1002/(SICI)1097-4598(199611)19:11<1391::AID-MUS3>3.0.CO;2-7.
To investigate the mechanical efficiency of surviving motor units of anterior tibial muscle in patients with amyotrophic lateral sclerosis (ALS), we studied motor unit action potentials, muscle force, and muscle fatigability in patients with ALS and controls using 25 min of low to moderate intensity voluntary isometric exercise. During exercise, tetanic force (TF) and maximum voluntary contraction declined more in patients than in controls. The mean motor unit action potential duration, amplitude, and polyphasia were increased in patients compared to controls but did not change during 9 months of disease progression. The enlarged motor units in patients were negatively correlated to the muscle force and positively correlated to muscle fatigability. Furthermore, after a mean follow-up period of 9 months, the decline in force-generating capacity of the anterior tibial muscle in patients (twitch tension by 37.5 +/- 11.2%, TF by 30.6 +/- 7.4%) was greater than the decline in the amplitude of the compound muscle action potential (21.1 +/- 8.8%, P < 0.05), suggesting a relative dissociation between electrical and mechanical properties. In conclusion, the enlarged motor units in patients with ALS are mechanically less efficient and fatigue relatively more than in healthy muscles, possibly due to an abnormality that is primarily distal to the muscle membrane.
为了研究肌萎缩侧索硬化症（ALS）患者胫前肌存活运动单位的机械效率，我们对ALS患者和对照组进行了25分钟的低至中等强度的自愿等长运动，研究了他们的运动单位动作电位、肌肉力量和肌肉疲劳性。运动期间，患者的强直力量（TF）和最大自主收缩下降幅度比对照组更大。与对照组相比，患者的运动单位动作电位平均持续时间、幅度和多相波增多，但在疾病进展的9个月期间没有变化。患者中增大的运动单位与肌肉力量呈负相关，与肌肉疲劳性呈正相关。此外，平均随访9个月后，患者胫前肌产生力量能力的下降（单收缩张力下降37.5±11.2%，TF下降30.6±7.4%）大于复合肌肉动作电位幅度的下降（21.1±8.8%，P<0.05），这表明电特性和机械特性之间存在相对分离。总之，ALS患者中增大的运动单位在机械方面效率较低，且比健康肌肉更容易疲劳，这可能是由于主要在肌膜远端的异常所致。
