Park Jaebum, Xu Dayuan
Department of Physical Education, Seoul National UniversitySeoul, South Korea.
Institute of Sport Science, Seoul National UniversitySeoul, South Korea.
Front Hum Neurosci. 2017 Jun 19;11:318. doi: 10.3389/fnhum.2017.00318. eCollection 2017.
The aim of this study was to discover finger interaction indices during single-finger ramp tasks and multi-finger coordination during a steady state force production in two directions, flexion, and extension. Furthermore, the indices of anticipatory adjustment of elemental variables (i.e., finger forces) prior to a quick pulse force production were quantified. It is currently unknown whether the organization and anticipatory modulation of stability properties are affected by force directions and strengths of in multi-finger actions. We expected to observe a smaller finger independency and larger indices of multi-finger coordination during extension than during flexion due to both neural and peripheral differences between the finger flexion and extension actions. We also examined the indices of the anticipatory adjustment between different force direction conditions. The anticipatory adjustment could be a neural process, which may be affected by the properties of the muscles and by the direction of the motions. The maximal voluntary contraction (MVC) force was larger for flexion than for extension, which confirmed the fact that the strength of finger flexor muscles (e.g., flexor digitorum profundus) was larger than that of finger extensor (e.g., extensor digitorum). The analysis within the uncontrolled manifold (UCM) hypothesis was used to quantify the motor synergy of elemental variables by decomposing two sources of variances across repetitive trials, which identifies the variances in the uncontrolled manifold () and that are orthogonal to the UCM (V). The presence of motor synergy and its strength were quantified by the relative amount of and V. The strength of motor synergies at the steady state was larger in the extension condition, which suggests that the stability property (i.e., multi-finger synergies) may be a direction specific quantity. However, the results for the existence of anticipatory adjustment; however, no difference between the directional conditions suggests that feed-forward synergy adjustment (changes in the stability property) may be at least independent of the magnitude of the task-specific apparent performance variables and its direction (e.g., flexion and extension forces).
本研究的目的是发现单指斜坡任务中的手指交互指标以及在两个方向（屈曲和伸展）的稳态力产生过程中的多手指协调情况。此外，还对快速脉冲力产生之前基本变量（即手指力）的预期调整指标进行了量化。目前尚不清楚在多手指动作中，稳定性属性的组织和预期调制是否受力的方向和强度影响。由于手指屈曲和伸展动作在神经和外周方面存在差异，我们预期观察到与屈曲相比，伸展过程中手指独立性更小，多手指协调指标更大。我们还研究了不同力方向条件下预期调整的指标。预期调整可能是一个神经过程，可能受肌肉属性和运动方向影响。屈曲时的最大自主收缩（MVC）力大于伸展时，这证实了手指屈肌（如指深屈肌）的力量大于手指伸肌（如指伸肌）这一事实。在非控制流形（UCM）假设内进行分析，通过分解重复试验中的两个方差源来量化基本变量的运动协同，这两个方差源分别识别非控制流形（）中的方差以及与UCM正交的方差（V）。运动协同的存在及其强度通过和V的相对量来量化。伸展条件下稳态时运动协同的强度更大，这表明稳定性属性（即多手指协同）可能是一个方向特异性量。然而，关于预期调整存在情况的结果；然而，方向条件之间没有差异表明前馈协同调整（稳定性属性的变化）可能至少独立于任务特定表观性能变量的大小及其方向（如屈曲和伸展力）。
