In repetitive upper limb activities, variability of muscle activity (a feature of motor variability) is linked to upper limb fatigability. Prior studies suggest that the variability response may change with age and could be related to the oxygen saturation of hemoglobin within the muscle. We determined, in female adults, how age affects adjustments in movement-to-movement variability of electromyograph (EMG) amplitude (RMS), oxygenation, and thickness with fatigue, and explored how these responses were related.

Fifteen young (23.3 ± 3.1 years) and ten older (62.8 ± 6.9 years) females completed repeated trials of low-load, isokinetic, concentric/eccentric elbow flexion until maximal torque ≤ 70% of baseline. Movement-to-movement variability of EMG RMS in concentric phases of movement was quantified by the coefficient of variation (EMG CV), and muscle oxygenation and thickness (MTH) were quantified using near-infrared spectroscopy, and B-mode ultrasonography. Age*Time and Spearman ρ analyses were conducted.

Age did not affect fatigability or Time-related changes in muscular measures (p > 0.05). Biceps brachii and brachialis EMG CV decreased, biceps brachii HbO₂ decreased and did not fully recover, and biceps brachii and brachialis MTH increased. Higher initial brachialis EMG CV was related to less blunted oxygenation in young females (p = 0.021). Oxygenation responses were related to altered anterior deltoid EMG CV in young females but altered biceps brachii and brachialis EMG CV in older females.

Age was not associated with changes in EMG CV, oxygenation, or thickness at similar performance fatigability in the concentric/eccentric elbow flexion task studied. Adjustments in biceps brachii oxygenation were linked to changes in EMG CV more local to the site of fatigue with older age.

在重复的上肢活动中，肌肉活动的可变性（运动可变性的一个特征）与上肢易疲劳有关。先前的研究表明，可变性反应可能会随着年龄的增长而变化，并且可能与肌肉内血红蛋白的氧饱和度有关。我们在成年女性中确定了年龄如何影响肌电图 (EMG) 振幅 (RMS)、氧合和疲劳厚度的运动间变异性的调整，并探讨了这些反应是如何相关的。

十五名年轻 (23.3 ± 3.1 岁) 和十名年长 (62.8 ± 6.9 岁) 女性完成了低负荷、等速、同心/偏心肘关节屈曲的重复试验，直到最大扭矩≤ 基线的 70%。EMG RMS 在运动的同心阶段的运动间变异性通过变异系数 (EMG CV) 进行量化，肌肉氧合和厚度 (MTH) 使用近红外光谱和 B 型超声进行量化。进行了年龄*时间和 Spearman ρ 分析。

年龄不影响肌肉测量的易疲劳性或与时间相关的变化（p > 0.05）。肱二头肌和肱肌 EMG CV 降低，肱二头肌 HbO ₂降低且未完全恢复，肱二头肌和肱肌 MTH 升高。较高的初始肱肌 EMG CV 与年轻女性中较少的钝性氧合有关（p = 0.021）。氧合反应与年轻女性三角肌前肌 EMG CV 的改变有关，但老年女性的肱二头肌和肱肌 EMG CV 改变。

在研究的同心/偏心肘关节屈曲任务中，年龄与 EMG CV、氧合或厚度的变化无关。随着年龄的增长，肱二头肌氧合的调整与更局部于疲劳部位的 EMG CV 变化有关。