Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL 32611, USA.
Exp Brain Res. 2011 Sep;213(4):351-61. doi: 10.1007/s00221-011-2777-x. Epub 2011 Jul 29.
The purpose of this study was to compare control of force and modulation of agonist muscle activity of young and older adults when the amount of visual feedback was varied at two different force levels. Ten young adults (25 years ± 4 years, 5 men and 5 women) and ten older adults (71 years ± 5 years, 4 men and 6 women) were instructed to accurately match a constant target force at 2 and 30% of their maximal isometric force with abduction of the index finger. Each trial lasted 35 s, and the amount of visual feedback was varied by changing the visual angle at 0.05, 0.5, and 1.5°. Each subject performed three trials for each visual angle condition. Force variability was quantified as the standard deviation and coefficient of variation (CV) of force. Modulation of the agonist muscle activity was quantified as the normalized power spectrum density of the EMG signal recorded from two pairs of bipolar electrodes placed on the first dorsal interosseus muscle. The frequency bands of interest were between 5 and 100 Hz. There were significant age-associated differences in force control with changes in the amount of visual feedback. The CV of force did not change with visual angle for young adults, whereas it increased for older adults. Although older adults exhibited similar CV of force to young adults at 0.05° (5.95 ± 0.67 vs. 5.47 ± 0.5), older adults exhibited greater CV of force than young adults at 0.5° (8.49 ± 1.34 vs. 5.05 ± 0.5) and 1.5° (8.23 ± 1.12 vs. 5.49 ± 0.6). In addition, there were age-associated differences in the modulation of the agonist muscle activity. Young adults increased normalized power in the EMG signal from 13 to 60 Hz with an increase in visual angle, whereas older adults did not. These findings suggest that greater amount of visual information may be detrimental to the control of a constant isometric contraction in older adults, and this impairment may be due to their inability to effectively modulate the motor neuron pool of the agonist muscle.
本研究旨在比较年轻人和老年人在两种不同力水平下，当视觉反馈量发生变化时，对力的控制和对主动肌活动的调节。10 名年轻人（25 岁±4 岁，5 男 5 女）和 10 名老年人（71 岁±5 岁，4 男 6 女）被要求在食指外展时，以恒定的目标力准确匹配 2%和 30%的最大等长力。每次试验持续 35s，通过改变 0.05、0.5 和 1.5°的视场角来改变视觉反馈量。每位受试者对每个视场角条件进行三次试验。力变异性通过力的标准差和变异系数（CV）来量化。通过记录于第一背间骨间肌的两个双极电极上的 EMG 信号的归一化功率谱密度来量化主动肌活动的调节。感兴趣的频段在 5 到 100Hz 之间。随着视觉反馈量的变化，年轻人和老年人在力控制方面存在显著的年龄相关性差异。年轻人的力 CV 不随视场角而变化，而老年人的力 CV 随视场角而增加。尽管老年人在 0.05°（5.95±0.67 vs. 5.47±0.5）时与年轻人的力 CV 相似，但在 0.5°（8.49±1.34 vs. 5.05±0.5）和 1.5°（8.23±1.12 vs. 5.49±0.6）时，老年人的力 CV 大于年轻人。此外，主动肌活动的调节也存在年龄相关性差异。年轻人随着视场角的增加，EMG 信号的归一化功率从 13Hz 增加到 60Hz，而老年人则没有。这些发现表明，对于老年人来说，更大的视觉信息量可能会对等长收缩的控制产生不利影响，这种损伤可能是由于他们无法有效调节主动肌的运动神经元池。
