Graduate School of Physical Education, National Institute of Fitness and Sports in Kanoya, 1 Shiromizu, Kanoya, Kagoshima, 8912393, Japan.
Department of Sports and Life Sciences, National Institute of Fitness and Sports in Kanoya, 1 Shiromizu, Kanoya, Kagoshima, 8912393, Japan.
Eur J Appl Physiol. 2017 Oct;117(10):2009-2019. doi: 10.1007/s00421-017-3689-7. Epub 2017 Aug 9.
The present study aimed to examine (1) the effect of task difficulty on unintended muscle activation (UIMA) levels in contralateral homologous muscle, (2) the difference between young and old adults in degree of UIMA with respect to task difficulty, and (3) temporal correlations between intended and contralateral unintended muscle activity at low frequency during unilateral intended force-matching tasks.
Twelve young (21.8 ± 2.4 years) and twelve old (69.9 ± 5.3 years) adult men performed steady isometric abductions with the left index finger at 20-80% of maximal voluntary contraction force. Two task difficulties were set by adjusting the spacing between two bars centered about the target force used for visual feedback on a monitor. The amplitude of surface electromyogram (aEMG) for both hands was calculated and normalized with respect to the maximal value. To determine if oscillations between intended and unintended muscle activities were correlated, cross-correlation function (CCF) of rectified EMG for both hands at low frequency was calculated for samples deemed adequate.
The unintended aEMG (right hand) had significant main effects in task difficulty, age, and target force (all P < 0.05) without any interactions. Distinct significant peaks in CCF (0.38 on average, P < 0.05) with small time lags were present between rectified EMGs of intended and unintended muscles in 14 of the 17 samples.
The current results indicate that UIMA increases with greater task difficulty regardless of age, and temporal correlations exist between intended and contralateral unintended muscle activities at low frequency.
本研究旨在检验：（1）任务难度对健侧同源肌肉的非预期肌肉激活（UIMA）水平的影响；（2）在任务难度方面，年轻和老年成年人之间 UIMA 程度的差异；（3）在单侧意图力匹配任务中低频时，意图和对侧非意图肌肉活动之间的时间相关性。
12 名年轻（21.8±2.4 岁）和 12 名老年（69.9±5.3 岁）成年男性以 20-80%最大自主收缩力的左食指进行稳定的外展。通过调整两个位于目标力中心的条形之间的间距来设置两个任务难度，目标力用于监视器上的视觉反馈。计算双手表面肌电图（aEMG）的幅度，并相对于最大值进行归一化。为了确定意图和非意图肌肉活动之间的振荡是否相关，计算了低频时双手经整流的 EMG 的互相关函数（CCF），对于被认为足够的样本进行了计算。
非预期的 aEMG（右手）在任务难度、年龄和目标力方面均有显著的主效应（均 P<0.05），没有任何交互作用。在 17 个样本中的 14 个样本中，经整流的意图和非意图肌肉之间的 CCF （平均 0.38，P<0.05）存在明显的显著峰值，时间滞后较小。
目前的结果表明，UIMA 随着任务难度的增加而增加，与年龄无关，并且在低频时意图和对侧非意图肌肉活动之间存在时间相关性。
