Although plantar flexion force steadiness (FS) is reduced in persons with Parkinson’s disease (PD), the underlying causes are unknown. The aim of this exploratory design study was to ascertain the influence of maximal voluntary contraction (MVC) force and gastrocnemius-Achilles muscle-tendon unit behaviour on FS in persons with PD. Nine persons with PD and nine age- and sex-matched non-PD controls (~70 years, 6 females per group) performed plantar flexion MVCs and sub-maximal tracking tasks at 5, 10, 25, 50 and 75% MVC. Achilles tendon elongation and medial gastrocnemius fascicle lengths were recorded via ultrasound during contraction. FS was quantified using the coefficient of variation (CV) of force. Contributions of MVC and tendon mechanics to FS were determined using multiple regression analyses. Persons with PD were 35% weaker during MVC (p = 0.04) and had 97% greater CV (p = 0.01) with 47% less fascicle shortening (p = 0.004) and 38% less tendon elongation (p = 0.002) than controls. Reduced strength was a direct contributor to lower FS in PD (ß = 0.631), and an indirect factor through limiting optimal muscle-tendon unit interaction. Interestingly, our findings indicate an uncoupling between fascicle shortening and tendon elongation in persons with PD. To better understand limitations in FS and muscle-tendon unit behavior, it is imperative to identify the origins of MVC decrements in persons with PD.

中文翻译：

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最大强度和肌腱力学对改善帕金森氏病患者力量稳定性的重要性。

尽管帕金森氏病（PD）患者的足底屈曲力稳定度（FS）降低，但其根本原因尚不清楚。这项探索性设计研究的目的是确定最大的自愿收缩（MVC）力和腓肠肌-跟腱肌腱单位行为对PD患者FS的影响。九名PD患者和九名年龄和性别匹配的非PD对照者（约70岁，每组6名女性）以5、10、25、50和75％MVC进行足底屈曲MVC和次最大的跟踪任务。收缩期间通过超声记录跟腱伸长和腓肠肌内侧束长度。使用力的变异系数（CV）对FS进行量化。MVC和肌腱力学对FS的贡献使用多元回归分析确定。在MVC期间，PD患者的虚弱程度降低了35％（p = 0.04），CV比对照组高97％（p = 0.01），而短束缩短（p = 0.004）少47％，腱伸长（p = 0.002）少38％。力量下降是PD FS降低的直接原因（ß= 0.631），并且是通过限制最佳肌腱单元相互作用的间接因素。有趣的是，我们的发现表明PD患者的束缩短和肌腱伸长之间不存在耦合。为了更好地了解FS和肌腱单位行为的局限性，必须确定PD患者MVC减量的起源。