Rearick Matthew P, Santello Marco
Department of Exercise Science, Arizona State University, Tempe, AZ 85287, USA.
Exp Brain Res. 2002 May;144(1):38-49. doi: 10.1007/s00221-002-1024-x. Epub 2002 Mar 2.
To grasp with five digits of the hand requires an efficient parceling of contact forces in order to maintain static equilibrium as an object is lifted and held. In a previous study, subjects were asked to reach, grasp and lift a five-digit grip apparatus whose center of mass (CM) location was changed for each block of trials. Despite a modulation of force sharing patterns among the digits as a function of center of mass location, consistent in-phase and out-of-phase relationships between normal forces were found in the frequency domain. In the present study, we have used the same task to assess the effect of (a) predictability of an object's CM location (random vs blocked presentation) and (b) handedness (dominant vs non-dominant hand). Contrary to our original expectations, we found a similar modulation of normal forces to CM location during the hold phase across all conditions. Specifically, the force sharing pattern, i.e., the rank order of force contributed by each digit, emerged very early in the grasp sequence, remaining relatively stable throughout the duration of the lift and hold. Nevertheless, the extent to which force sharing patterns could be discriminated as a function of CM location was lower in the random than in the blocked conditions. Lastly, normal forces exerted by pairs of digits tended to be synchronized, both in-phase (thumb and fingers) and out-of-phase (pairs of digits) across a large proportion of the functional frequency range (up to 10 Hz) in all conditions. The composite of these findings suggests that the central nervous system uses stereotyped control strategies for coordinating multiple grip forces during grasping. Specific aspects of these schemes appear to be affected by predictability of object CM location, but not by hand dominance.
用手的五根手指抓握物体时，需要有效地分配接触力，以便在提起并握住物体时保持静态平衡。在之前的一项研究中，受试者被要求伸手、抓握并提起一个五指抓握装置，该装置的质心（CM）位置在每个试验组中都会改变。尽管随着质心位置的变化，各手指间的力分配模式有所调整，但在频域中发现法向力之间存在一致的同相和异相关系。在本研究中，我们采用相同的任务来评估（a）物体质心位置的可预测性（随机呈现与分组呈现）和（b）利手性（优势手与非优势手）的影响。与我们最初的预期相反，我们发现在所有条件下的握持阶段，法向力对质心位置的调制方式相似。具体而言，力分配模式，即每个手指所贡献力的排序，在抓握序列的早期就出现了，并且在提起和握持的整个过程中保持相对稳定。然而，在随机条件下，根据质心位置区分力分配模式的程度低于分组条件。最后，在所有条件下，大部分功能频率范围（高达10Hz）内，成对手指施加的法向力倾向于同步，包括同相（拇指和手指）和异相（成对手指）。这些研究结果综合表明，中枢神经系统在抓握过程中使用定型的控制策略来协调多个抓握力。这些策略的具体方面似乎受物体质心位置可预测性的影响，但不受手的优势性影响。
