Abe Masaki O, Yamada Norimasa
Department of Rehabilitation for Movement Functions, Research Institute, National Rehabilitation Center for Persons with Disabilities, 4-1 Namiki, 359-8555 Tokorozawa, Japan.
Exp Brain Res. 2003 Dec;153(3):394-9. doi: 10.1007/s00221-003-1583-5. Epub 2003 Sep 25.
The purpose of the present study was to determine how joint stiffness during cyclic movement in a vertical plane is modulated at lower or higher frequencies than the natural frequency of the system. Five male subjects were instructed to swing their forearms rhythmically in a vertical plane under various frequency conditions (0.7-2.25 Hz). To estimate the mechanical properties of the elbow joint, external perturbations were applied by an electromagnetic torque motor system to the forearm of each subject during the movement. Joint stiffness showed a significant quadratic trend with a minimum close to the natural frequency of the apparatus-forearm system (1.09+/-0.08 Hz). The resonant frequency showed the similar tendencies to joint stiffness and was significantly different from movement frequency in the lower frequency range (0.7-0.9 Hz). In addition, the ratio of joint stiffness to the background torque (ST(ratio)) was greater in the frequency conditions below the natural frequency than in the frequency conditions above the natural frequency and was relatively constant in the latter. These results suggested that: (1) the modulation of joint stiffness for movement in a vertical plane, by which the resonant frequency of the system is kept close to the movement frequency, may be limited to the movement frequency range above the natural frequency; and (2), in the case of movement in a vertical plane, the mechanism by which joint stiffness is modulated may change according to the relation between natural frequency and movement frequency.
本研究的目的是确定在垂直平面内进行周期性运动时，关节刚度在低于或高于系统固有频率的频率下是如何调节的。五名男性受试者被要求在各种频率条件下（0.7 - 2.25赫兹）在垂直平面内有节奏地摆动他们的前臂。为了估计肘关节的力学特性，在运动过程中通过电磁转矩电机系统对每个受试者的前臂施加外部扰动。关节刚度呈现出显著的二次趋势，最小值接近器械 - 前臂系统的固有频率（1.09±0.08赫兹）。共振频率与关节刚度呈现出相似的趋势，并且在较低频率范围（0.7 - 0.9赫兹）内与运动频率有显著差异。此外，在低于固有频率的频率条件下，关节刚度与背景转矩的比值（ST(ratio)）大于高于固有频率的频率条件下的比值，并且在后者中相对恒定。这些结果表明：（1）对于在垂直平面内的运动，关节刚度的调节，即系统的共振频率保持接近运动频率，可能仅限于高于固有频率的运动频率范围；（2）在垂直平面内运动的情况下，关节刚度调节的机制可能会根据固有频率和运动频率之间的关系而改变。
