PURPOSE Motivated by the goal of developing new methods to detect early signs of sarcopenia, we investigated if surface electromyographic (SEMG) data recorded during the performance of cyclic, submaximal back extensions are marked by age-specific differences in their time and frequency characteristics. Furthermore, day-to-day retest reliability of the EMG measures was examined. METHODS A total of 86 healthy volunteers used a back dynamometer to perform a series of three maximal voluntary contractions (MVC) consisting of isometric back extensions, followed by an isometric back extension at 80% MVC, and finally 25 slow cyclic back extensions at 50% MVC. SEMG data was recorded bilaterally at L1, L2, and L5 from the iliocostalis lumborum, longissimus, and multifidus muscles, respectively. Tests were repeated two days and six weeks later. A linear mixed-effects model with fixed effects "age, sex, test number" and the random effect "person" was performed to investigate age-specific differences in both the initial value and the time-course (as defined by the slope of the regression line) of the root mean square (RMS-SEMG) values and instantaneous median frequency (IMDF-SEMG) values calculated separately for the shortening and lengthening phases of the exercise cycles. Generalizability Theory was used to examine reliability of the EMG measures. RESULTS Back extensor strength was comparable in younger and older adults. The initial value of RMS-SEMG and IMDF-SEMG as well as the RMS-SEMG time-course did not significantly differ between the two age groups. Conversely, the IMDF-SEMG time-course showed more rapid changes in younger than in older individuals. Absolute and relative reliability of the SEMG time-frequency representations were comparable in older and younger individuals with good to excellent relative reliability but variable absolute reliability levels. CONCLUSIONS The IMDF-SEMG time-course derived from submaximal, cyclic back extension exercises performed at moderate effort showed significant differences in younger vs. older adults even though back extension strength was found to be comparable in the two age groups. We conclude that the SEMG method proposed in this study has great potential to be used as a biomarker to detect early signs of sarcopenic back muscle function.

中文翻译：

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在次最大循环向后伸展运动期间记录的表面肌电图数据的时频表示的年龄特异性差异：一种有前途的检测肌肉减少症早期迹象的生物标志物。


目的出于开发新方法来检测肌肉减少症早期症状的目标，我们研究了在循环、次最大向后伸展过程中记录的表面肌电图 (SEMG) 数据是否具有时间和频率特征的年龄特异性差异。此外，还检查了肌电图测量的日常重新测试可靠性。方法 共有 86 名健康志愿者使用背部测力计进行一系列 3 次最大自主收缩 (MVC)，其中包括等长背部伸展，然后是 80% MVC 等长背部伸展，最后是 25 次 50% 缓慢循环背部伸展MVC。 SEMG 数据分别从腰髂肋肌、最长肌和多裂肌的 L1、L2 和 L5 处记录。两天和六周后重复了测试。采用具有固定效应“年龄、性别、测试数量”和随机效应“人”的线性混合效应模型来研究初始值和时间过程（由斜率定义）的年龄特异性差异。分别为运动周期的缩短和延长阶段计算的均方根 (RMS-SEMG) 值和瞬时中频 (IMDF-SEMG) 值的回归线）。普遍性理论用于检查肌电图测量的可靠性。结果年轻人和老年人的背部伸肌力量相当。 RMS-SEMG 和 IMDF-SEMG 的初始值以及 RMS-SEMG 时间进程在两个年龄组之间没有显着差异。相反，IMDF-SEMG 时间进程显示年轻人比老年人的变化更快。 SEMG 时频表示的绝对和相对可靠性在老年人和年轻人中具有相当的相对可靠性，但绝对可靠性水平可变。结论 中等强度的次最大循环背部伸展运动得出的 IMDF-SEMG 时间进程显示，年轻人与老年人之间存在显着差异，尽管发现两个年龄组的背部伸展强度相当。我们得出的结论是，本研究中提出的 SEMG 方法具有很大的潜力，可以用作检测肌肉减少性背部肌肉功能早期迹象的生物标志物。