Background

Generating a force at the hand requires moments about multiple joints by a theoretically infinite number of arm and shoulder muscle force combinations. This allows for learning and adaptation and can possibly be captured using the complexity (entropy) of an isometrically generated force curve. Patients with Subacromial Pain Syndrome have difficulty to explore alternative, pain-avoiding, motor strategies and we questioned whether loss of motor complexity may contribute to this. We assessed whether patients with Subacromial Pain Syndrome have reduced entropy of an isometrically generated abduction and adduction force curve.

Methods

Forty patients and thirty controls generated submaximal isometric ab- and adduction force at the wrist. The force curve was characterized by the magnitude of force variability [standard deviation and coefficient of variation], and the entropy (complexity) of force variability [approximate entropy].

Findings

Patients showed reduced entropy both during the abduction (−0.16, confidence interval: [−0.33; −0.00], p: 0.048) and adduction task (−0.20, confidence interval: [−0.37; −0.03], p: 0.024) and reduced force variability during abduction (standard deviation: −0.006, confidence interval: [−0.011; −0.001], p: 0.013 and coefficient of variation: −0.51, confidence interval: [−0.93; −0. 10], p: 0.016).

Interpretations

Isometric force curves of patients with Subacromial Pain Syndrome show reduced complexity compared to asymptomatic controls, which may indicate more narrow and stereotype use of motor options. In future studies, it should be investigated whether the finding of reduced force (motor) entropy indicates functional decline, contributing to decreased ability to acquire and optimize motor strategies in Subacromial Pain Syndrome.

Level of evidence

Level II prognostic study.

中文翻译：

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肩峰下疼痛综合征的力熵降低：横断面分析。

背景

在手部产生力需要理论上无限数量的手臂和肩膀肌肉力量组合在多个关节处产生力矩。这允许学习和适应，并且可以使用等距生成的力曲线的复杂性（熵）来捕获。肩峰以下疼痛综合征患者难以探索替代的，避免疼痛的运动策略，我们质疑运动复杂性的丧失是否可能对此有所贡献。我们评估了患有肩峰以下疼痛综合征的患者是否减少了等轴测外展和内收力曲线的熵。

方法

四十名患者和三十​​名对照者在手腕处产生了最大的等轴吸收和内收力。力曲线的特征在于力变化的大小[标准偏差和变异系数]，以及力变化的熵（复杂度）[近似熵]。

发现

患者在绑架（-0.16，置信区间：[-0.33; -0.00]，p：0.048）和内收任务（-0.20，置信区间：[-0.37; -0.03]，p：0.024）期间均显示熵降低绑架时力变化性降低（标准偏差：-0.006，置信区间：[-0.011； -0.001]，p：0.013，变异系数：-0.51，置信区间：[- 0.93； -0.10 ]，p：0.016 ）。

释义

与无症状对照组相比，肩峰下疼痛综合征患者的等轴测力曲线显示降低了复杂性，这可能表明更狭窄和定型的运动选择使用。在未来的研究中，应该调查发现力（运动）熵降低是否表明功能下降，从而导致肩峰以下疼痛综合征的获得和优化运动策略的能力下降。

证据水平

II级预后研究。