Individuals with Parkinson's disease (PD) demonstrate deficits in muscle activation such as decreased amplitude and inappropriate bursting. There is evidence that some of these disturbances are more pronounced in extensor vs. flexor muscles. Surface EMG has been used widely to quantify muscle activation deficits in PD, but analysis of discharge of the underlying motor units may provide greater insight and be more sensitive to changes early in the disease. Of the few studies that have examined motor unit discharge in PD, the majority were conducted in the first dorsal interosseous, and no studies have measured motor units from extensor and flexor muscles within the same cohort. The objective of this study was to characterize the firing behavior of single motor units in the elbow flexor and extensor muscles during isometric contractions in people with mild-to-moderate PD. Ten individuals with PD (off-medication) and nine healthy controls were tested. Motor unit spike times were recorded via intramuscular EMG from the biceps and triceps brachii muscles during 30-s isometric contractions at 10% maximum voluntary elbow flexion and elbow extension torque, respectively. We selected variables of mean motor unit discharge rate, discharge variability, and torque variability to evaluate motor abnormalities in the PD group. The effects of group, muscle, and group-by-muscle on each variable were determined using separate linear mixed models. Discharge rate and torque variability were not different between groups, but discharge variability was significantly higher in the PD group for both muscles combined (p < 0.0001). We also evaluated the asymmetry in these motor variables between the triceps and biceps for each individual participant with PD to evaluate whether there was an association with disease severity. The difference in torque variability between elbow flexion and extension was significantly correlated with both the Hoehn and Yahr scale (rho = 0.71) and UPDRS (rho = 0.62). Our findings demonstrate that variability in motor output, rather than decreased discharge rates, may contribute to motor dysfunction in people with mild-to-moderate PD. Our findings provide insight into altered neural control of movement in PD and demonstrate the importance of measuring from multiple muscles within the same cohort.

中文翻译：

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轻度至中度帕金森氏病患者的运动单位放电变异性增加。

帕金森氏病（PD）的患者表现出肌肉激活不足，例如振幅降低和不适当的爆发。有证据表明，其中某些干扰在伸肌与屈肌中更为明显。表面肌电图已被广泛用于量化PD中的肌肉激活缺陷，但是对潜在运动单元放电的分析可能会提供更多见识，并且对疾病早期的变化更敏感。在检查PD的运动单位放电的少数研究中，大多数是在第一背骨间进行的，没有研究测量同一队列中伸肌和屈肌的运动单位。这项研究的目的是表征轻度至中度PD患者等距收缩期间肘部屈肌和伸肌的单个运动单位的放电行为。测试了十名患有PD（非药物治疗）的个体和九名健康对照。在30-s等距收缩期间，分别以10％最大自动肘屈和肘伸扭矩通过肌内肌电图记录肱二头肌和肱三头肌的运动单位高峰时间。我们选择了平均电动机单位放电率，放电可变性和转矩可变性的变量，以评估PD组中的电​​动机异常。使用单独的线性混合模型确定组，肌肉和逐组肌肉对每个变量的影响。两组之间的放电率和扭矩变化无差异，但是PD组的两种肌肉的放电变异性明显更高（p <0.0001）。我们还评估了PD个体参与者在三头肌和二头肌之间的这些运动变量的不对称性，以评估是否与疾病严重程度相关。肘部弯曲和伸展之间的扭矩可变性差异与Hoehn和Yahr标度（rho = 0.71）和UPDRS（rho = 0.62）均显着相关。我们的发现表明，轻度至中度PD患者的运动输出而不是放电速率降低可能会导致运动功能障碍。我们的发现提供了对PD运动神经控制改变的见解，并证明了从同一队列中的多个肌肉进行测量的重要性。