Maximal voluntary fingertip force production is not limited by movement speed in combined motion and force tasks.
Maximal voluntary fingertip force production is not limited by movement speed in combined motion and force tasks.
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DOI：
10.1523/jneurosci.0853-09.2009
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发表时间：
2009-07-08
期刊：
影响因子：
--
通讯作者：
Valero-Cuevas FJ
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文献类型：
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作者：
Keenan KG;Santos VJ;Venkadesan M;Valero-Cuevas FJ
对四肢和手指的大量研究表明，肌肉的力-速度特性限制了在非等速任务中（即肌肉缩短或延长时）产生的最大自主力。虽然这个命题看起来合乎逻辑，但我们对同时产生指尖运动和力的研究不同意这个普遍持有的观点。我们要求8名成年人在特定的姿势（静态试验）中，使用他们的主要食指最大限度地向水平表面施加自主向下的力，同时在一个不对称的“抓”任务中，沿着5.8±0.5厘米的目标线有节奏地移动指尖。节拍器计时的屈伸运动速度从“慢”（1.0±0.5 cm/s）到“快”（35.9±7.8 cm/s）变化了36倍。正如预期的那样，当任何运动（慢或快）添加到任务中时，最大向下自主力减少（44.8±15.6%;p=0.001）。然而，令人惊讶的是，速度增加36倍并没有影响力大小的减少。对于如此普通的任务，这些显著的结果挑战了通常归因于肌肉力-速度特性的主导作用，并提供了神经力学相互作用的见解。我们提出了一种解释，即运动和力的机械约束的同时实施减少了可行的电机命令集，从而使力-速度特性不再是力限制因素。虽然需要更多的工作来揭示控制机制，但同时实施运动和力约束对力输出的巨大影响开始解释灵巧功能对发育，衰老甚至轻度神经肌肉病理的脆弱性。
Numerous studies of limbs and fingers propose that force-velocity properties of muscle limit maximal voluntary force production during anisometric tasks, i.e. when muscles are shortening or lengthening. Although this proposition appears logical, our study on the simultaneous production of fingertip motion and force disagrees with this commonly held notion. We asked eight consenting adults to use their dominant index fingertip to maximize voluntary downward force against a horizontal surface at specific postures (static trials), and also during an anisometric “scratching” task of rhythmically moving the fingertip along a 5.8±0.5 cm target line. The metronome-timed flexion-extension movement speed varied 36-fold from “slow” (1.0±0.5 cm/s) to “fast” (35.9±7.8 cm/s). As expected, maximal downward voluntary force diminished (44.8±15.6%; p=0.001) when any motion (slow or fast) was added to the task. Surprisingly, however, a 36-fold increase in speed did not affect this reduction in force magnitude. These remarkable results for such an ordinary task challenge the dominant role often attributed to force-velocity properties of muscle and provide insight into neuromechanical interactions. We propose an explanation that the simultaneous enforcement of mechanical constraints for motion and force reduces the set of feasible motor commands sufficiently so that force-velocity properties cease to be the force-limiting factor. While additional work is necessary to reveal the governing mechanisms, the dramatic influence that the simultaneous enforcement of motion and force constraints has on force output begins to explain the vulnerability of dexterous function to development, aging and even mild neuromuscular pathology.