NONLINEAR VISCOSITY OF HUMAN WRIST
NONLINEAR VISCOSITY OF HUMAN WRIST
复制标题
DOI：
10.1152/jn.1984.52.3.553
复制
发表时间：
1984-01-01
影响因子：
2.5
通讯作者：
HOUK, JC
中科院分区：
文献类型：
--
作者：
GIELEN, CCAM;HOUK, JC
在5 - 500 mm/s的范围内，使用恒速斜坡拉伸和释放来检查人手腕的拉伸和卸载反射的非线性粘性特性。受试者被要求反对最初的屈肌预负荷，并被指示不要干预时，自愿改变位置。肌电图（EMG）活动和净力施加的手腕进行了测量。斜坡伸展进一步加载预载屈肌肌肉。EMG和力的响应最初急剧增加，但在apprx之后。1 cm位移时，这些响应的斜率降低至较低值，并在5 cm斜坡的剩余时间内保持不变。对于较高的拉伸速度，肌电和力的响应的幅度和斜率增加，但小于与斜坡速度成比例。除了最初的瞬态，在加载屈肌肌和力的反应的EMG可以描述的线性位置相关的长期和低分数功率的速度之间的乘积关系，在反射弧的延迟进行校正后。肌电和力的速度幂函数指数平均值分别为0.3和0.17。对于更高的预载荷，力的增量响应等速拉伸，绘制为手腕位置的函数，转移到更高的值和斜率的力与位置的增加变得有些陡峭。这种力迹线的上移反映了牵张反射表观阈值的变化。斜坡释放缩短和卸载预载屈肌肌肉和伸展最初不活跃的伸肌。屈肌肌电活动随着时间的推移逐渐下降，与速度无关。伸肌肌电反应依赖于前负荷。在高预载下，除了在最高速度下的一些爆裂外，没有活动。在低预负荷时，EMG活动最初不存在，但开始部分通过斜坡。对于更高的斜坡速度，活性的增加稍微更大。缩短斜坡的力响应取决于预载荷。在高预载荷下，力响应在所有低速度下叠加，但在较高速度下下降到略低的力。在低预载下，力迹线在低速时再次叠加，而在高速时仅在响应的初始部分叠加。肌电反应的速度敏感性可以反映肌梭反应的动力学特征。力的速度依赖性响应代表了非线性粘性，当涉及可变载荷时，该非线性粘性可以在阻尼肢体运动中执行重要功能。
Nonlinear viscous properties of stretch and unloading reflexes in the human wrist were examined using constant-velocity ramp stretches and releases in the range between 5-500 mm/s. Subjects were asked to oppose an initial flexor preload and were instructed not to intervene voluntarily when the changes in position were applied. Electromyographic (EMG) activity and net force exerted by the wrist were measured. Ramp stretches further loaded the preloaded flexor muscles. Responses of EMG and force increased steeply initially but after .apprx. 1-cm displacement, the slope of these responses decreased to a lower value and remained constant during the remainder of the 5-cm ramp. For higher stretch velocities, the magnitudes and slopes of the responses of EMG and force increased but less than proportionally with ramp velocity. Except for the initial transient, EMG in the loaded flexor muscles and force responses could be described by a product relationship between a linear position-related term and a low fractional power of velocity, after a correction was made for delays in the reflex arc. Mean value of the exponent in the power function of velocity was 0.3 for EMG and 0.17 for force. For higher preloads, incremental responses of force to constant-velocity stretches, plotted as a function of wrist position, shifted to higher values and the slope of increase of force with position became somewhat steeper. This upward shift of the force trace reflects a change of apparent threshold of the stretch reflex. Ramp releases shortened and unloaded the preloaded flexor muscles and stretched the initially inactive extensor muscles. Flexor EMG activity declined progressively with a time course that was independent of velocity. Extensor EMG response depended on preload. At high preloads, there was not activity except for some bursting at the highest velocities. At low preloads, EMG activity was initially absent but started part way through the ramp. The increase of activity was somewhat greater for higher ramp velocities. Force responses to shortening ramps depended on preload. At high preloads, force responses superimposed at all of the low velocities but fell to slightly lower forces at the higher velocities. At low preloads, force traces again superimposed for low velocities and at high velocities only during the initial part of the response. The velocity sensitivity of EMG responses may reflect the dynamic character of the responses of muscle spindles. The velocity-dependent responses of force represent a nonlinear viscosity that may perform an important function in damping limb movements when variable loads are involved.