Lin F M, Sabbahi M
School of Physical Therapy, Texas Woman's University, Houston, USA.
Electromyogr Clin Neurophysiol. 1998 Sep;38(6):323-31.
The purpose of this study is to investigate the effects of aging on the human stretch reflexes. The EMG and torque responses of the stretch reflex of the wrist flexors were evoked by ramp-and-hold mechanical perturbations. The stretch reflexes were recorded at seven test conditions with different stretch velocity and muscle preload. The test results from young and older healthy adult subjects were compared. In average, the absolute amplitude of the short-latency (20-40 ms) EMG (recorded from flexor carpi radialis) reflex response was significantly lower in the older group. If the data were normalized and expressed in percentage of the maximal voluntary EMG activity, however, this group difference was not significant. There was no change in the reflex gain of the short-latency reflex with aging. For the long-latency (50-90 ms) EMG reflex response, both the normalized amplitude and the reflex gain were significantly enhanced with aging, probably through supraspinal mechanisms. There was no significant difference in the threshold velocity for the evoked EMG reflexive activities between age groups. There were also no changes in the reflexive wrist flexion torque with aging. These results suggested that the number of motor units recruited during the stretch reflex activity declined with aging although the percentage of motor units recruited was not affected by aging. It is concluded that the central regulating mechanisms of the spinal motoneuron excitability are not compromised by aging. The automatic gain compensation phenomenon is also preserved with aging.
本研究的目的是调查衰老对人体牵张反射的影响。通过斜坡-保持机械扰动诱发腕屈肌牵张反射的肌电图（EMG）和扭矩反应。在七种不同牵张速度和肌肉预负荷的测试条件下记录牵张反射。比较了年轻和老年健康成人受试者的测试结果。平均而言，老年组中短潜伏期（20 - 40毫秒）EMG（从桡侧腕屈肌记录）反射反应的绝对幅度显著较低。然而，如果将数据标准化并以最大自主EMG活动的百分比表示，该组间差异并不显著。短潜伏期反射的反射增益不会随衰老而改变。对于长潜伏期（50 - 90毫秒）EMG反射反应，标准化幅度和反射增益均随衰老显著增强，可能是通过脊髓上机制。不同年龄组之间诱发EMG反射活动的阈值速度没有显著差异。随着衰老，反射性腕部屈曲扭矩也没有变化。这些结果表明，虽然所募集运动单位的百分比不受衰老影响，但在牵张反射活动期间募集的运动单位数量随衰老而减少。结论是脊髓运动神经元兴奋性的中枢调节机制不会因衰老而受损。自动增益补偿现象在衰老过程中也得以保留。
