Lee Gyusung, Fradet Laetitia, Ketcham Caroline J, Dounskaia Natalia
Department of Kinesiology, Movement Control and Biomechanics Lab, Arizona State University, Tempe, AZ 85287-0404, USA.
Exp Brain Res. 2007 Feb;177(1):78-94. doi: 10.1007/s00221-006-0648-7. Epub 2006 Aug 30.
The present study addresses the influence of aging on the ability to regulate mechanical effects arising during arm movements due to the multi-joint structure of the arm. Two mechanical factors were considered, interaction torque (IT) and inertial resistance (IR). Regulation of these two factors can be demanding in terms of the timing and magnitude of the required muscle torque (MT), specifically during fast movements. We hypothesized that aging exacerbates the challenge regarding the regulation of these effects with muscular control due to declines in the motor system. This hypothesis was tested by comparing performance of a cyclic line-drawing task in two age groups, young and older adults. Only two joints, the shoulder and elbow, participated in motion. Four orientations of the lines were used to provide variations in the requirements for regulation of IT and IR. Cyclic frequency was manipulated to emphasize the dependence of the mechanical factors on movement speed. Various characteristics of fingertip motion showed that there were no age-related deteriorations in accuracy of line drawing. However, older adults were systematically slower, particularly in the directions of high IR. A detailed analysis of the magnitude of MT and the contribution of this torque to production of net torque at each joint demonstrated that older adults modified joint control and decreased the demands for MT by skillful exploitation of IT in a way specific for each particular line orientation. The results point to a tendency in older adults to decrease the production of muscle force. Nevertheless, older adults also demonstrated an ability to partially compensate for declines in the force production by developing sophisticated strategies of joint control that exploit the multi-joint mechanical structure of the arm. This ability suggests that the internal representation of inter-segmental dynamics and the capability to use it for movement control does not decay with age. The study emphasizes the importance of analysis of joint motion and control characteristics for the investigation of arm movements and for comparison of these movements between different subject populations.
本研究探讨衰老对因手臂多关节结构而在手臂运动过程中调节机械效应能力的影响。考虑了两个机械因素，即相互作用扭矩（IT）和惯性阻力（IR）。就所需肌肉扭矩（MT）的时间和大小而言，尤其是在快速运动期间，对这两个因素的调节可能具有挑战性。我们假设，由于运动系统功能下降，衰老会加剧肌肉控制对这些效应调节的挑战。通过比较两个年龄组（年轻人和老年人）在循环线绘制任务中的表现来检验这一假设。只有肩部和肘部两个关节参与运动。使用线条的四种方向来提供对IT和IR调节要求的变化。操纵循环频率以强调机械因素对运动速度的依赖性。指尖运动的各种特征表明，线绘制的准确性没有与年龄相关的下降。然而，老年人系统地更慢，特别是在高IR方向上。对MT大小以及该扭矩对每个关节净扭矩产生的贡献的详细分析表明，老年人通过以特定于每个特定线条方向的方式巧妙地利用IT来修改关节控制并降低对MT的需求。结果表明老年人有减少肌肉力量产生的趋势。尽管如此，老年人也表现出通过开发利用手臂多关节机械结构的复杂关节控制策略来部分补偿力量产生下降的能力。这种能力表明，节段间动力学的内部表征以及将其用于运动控制的能力不会随着年龄增长而衰退。该研究强调了分析关节运动和控制特征对于研究手臂运动以及比较不同受试者群体之间这些运动的重要性。
