Park Jaebum, Pažin Nemanja, Friedman Jason, Zatsiorsky Vladimir M, Latash Mark L
Pennsylvania State University, University Park, PA, USA; Montana State University, Bozeman, MT, USA.
University of Belgrade, Belgrade, Serbia.
Clin Biomech (Bristol). 2014 Feb;29(2):129-37. doi: 10.1016/j.clinbiomech.2013.11.022. Epub 2013 Dec 4.
Mechanical properties of human digits may have significant implications for the hand function. We quantified several mechanical characteristics of individual digits in young and older adults.
Digit tip friction was measured at several normal force values using a method of induced relative motion between the digit tip and the object surface. A modified quick-release paradigm was used to estimate digit apparent stiffness, damping, and inertial parameters. The subjects grasped a vertical handle instrumented with force/moment sensors using a prismatic grasp with four digits; the handle was fixed to the table. Unexpectedly, one of the sensors yielded leading to a quick displacement of the corresponding digit. A second-order, linear model was used to fit the force/displacement data.
Friction of the digit pads was significantly lower in older adults. The apparent stiffness coefficient values were higher while the damping coefficients were lower in older adults leading to lower damping ratio. The damping ratio was above unity for most data in young adults and below unity for older adults. Quick release of a digit led to force changes in other digits of the hand, likely due to inertial hand properties. These phenomena of "mechanical enslaving" were smaller in older adults although no significant difference was found in the inertial parameter in the two groups.
The decreased friction and damping ratio present challenges for the control of everyday prehensile tasks. They may lead to excessive digit forces and low stability of the grasped object.
人类手指的力学特性可能对手部功能有重大影响。我们对年轻人和老年人单个手指的几种力学特性进行了量化。
采用手指尖与物体表面之间诱导相对运动的方法，在几个法向力值下测量指尖摩擦力。使用一种改进的快速释放范式来估计手指的表观刚度、阻尼和惯性参数。受试者用四个手指采用棱柱形抓握方式握住一个装有力/力矩传感器的垂直手柄；手柄固定在桌子上。意外的是，其中一个传感器出现故障，导致相应手指快速位移。使用二阶线性模型拟合力/位移数据。
老年人手指垫的摩擦力显著较低。老年人的表观刚度系数值较高，而阻尼系数较低，导致阻尼比更低。年轻人的大多数数据的阻尼比高于1，而老年人的阻尼比低于1。手指的快速释放会导致手部其他手指的力发生变化，这可能是由于手部的惯性特性。尽管两组的惯性参数没有显著差异，但老年人中这些“机械奴役”现象较小。
摩擦力和阻尼比的降低给日常抓握任务的控制带来了挑战。它们可能导致手指用力过大以及所抓物体的稳定性降低。
