Andrew and Marjorie McCain Human Performance Laboratory, Faculty of Kinesiology, University of New Brunswick, Fredericton, NB, E3B 5A3, Canada.
Tecnologico de Monterrey, Monterrey, Mexico.
J Physiol Anthropol. 2020 Apr 15;39(1):11. doi: 10.1186/s40101-020-00219-9.
Multichannel surface electromyography (EMG) is a method to examine properties of motor unit (MU) activity using multiple electrodes arranged on a two-dimensional grid. This technique can be used to examine alterations in EMG activity distribution due to contraction intensity as well as due to physiological differences such as age or sex. Therefore, the purpose of this study was to compare strength and high-density surface EMG (HDsEMG) features during isometric and isokinetic knee extensions between older and younger men and women.
Twenty younger (ages 19-25 years) and twenty older (ages 64-78) men and women performed submaximal and maximal isometric (at a joint angle of 90°) and isokinetic knee extensions, while HDsEMG was recorded from the vastus lateralis. Spatial distribution was estimated using the root mean square (RMS), and 2-dimensional (2D) maps were developed to examine spatial features. Coefficient of variation (CV) and modified entropy were used to examine alterations in muscle heterogeneity and pattern. Peak torque and HDsEMG parameters were compared across age and gender.
Younger males and females produced significantly higher mean torque than the older group (p < 0.001) for all contractions. Both age- and sex-related significant differences (p < 0.05) were found for EMG spatial features suggesting neuromuscular differences. Modified entropy was significantly higher and CV was lower for young females compared to young males (p < 0.05) across both isometric and isokinetic contractions.
We found that isometric and isokinetic knee extension strength, spatial distribution, and intensity differ as a function of age and sex during knee extensions. While there were no differences detected in entropy between age groups, there were sex-related differences in the younger age category. The lack of age-related differences in entropy was surprising given the known effects of aging on muscle fiber composition. However, it is often reported that muscle coactivation increases with age and this work was limited to the study of one muscle of the knee extensors (vastus lateralis) which should be addressed in future work. The findings suggest while both age and sex affect muscle activation, sex had a greater effect on heterogeneity. The results obtained will help to develop improved rehabilitation programs for aging men and women.
多通道表面肌电图（EMG）是一种使用二维网格上排列的多个电极来检查运动单位（MU）活动特性的方法。该技术可用于检查由于收缩强度以及由于生理差异（如年龄或性别）引起的 EMG 活动分布的变化。因此，本研究的目的是比较年轻和年老男性和女性在等长和等速膝关节伸展过程中的强度和高密度表面肌电图（HDsEMG）特征。
20 名年轻（年龄 19-25 岁）和 20 名年老（年龄 64-78 岁）男性和女性进行了亚最大和最大等长（关节角度为 90°）和等速膝关节伸展，同时从股外侧肌记录 HDsEMG。使用均方根（RMS）估计空间分布，并开发 2 维（2D）图以检查空间特征。变异系数（CV）和修正熵用于检查肌肉异质性和模式的变化。比较了不同年龄和性别的峰值扭矩和 HDsEMG 参数。
在所有收缩中，年轻男性和女性产生的平均扭矩明显高于年长组（p < 0.001）。在 EMG 空间特征方面，发现了与年龄和性别相关的显著差异（p < 0.05），表明存在神经肌肉差异。与年轻男性相比，年轻女性在等长和等速收缩时的修正熵明显较高，CV 较低（p < 0.05）。
我们发现，在膝关节伸展过程中，等长和等速膝关节伸展强度、空间分布和强度会随着年龄和性别而变化。虽然在熵方面没有检测到年龄组之间的差异，但在年轻年龄组中存在性别差异。令人惊讶的是，由于衰老对肌肉纤维组成的影响，在熵方面没有发现年龄相关的差异。然而，人们经常报告说，随着年龄的增长，肌肉协同激活增加，而这项工作仅限于对膝关节伸肌（股外侧肌）的一块肌肉进行研究，这在未来的工作中应予以解决。研究结果表明，年龄和性别都会影响肌肉激活，但性别对异质性的影响更大。获得的结果将有助于为衰老的男性和女性制定更好的康复计划。
