Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill and North Carolina State University, Chapel Hill, North Carolina.
J Appl Physiol (1985). 2021 Oct 1;131(4):1348-1360. doi: 10.1152/japplphysiol.00262.2021. Epub 2021 Sep 2.
Activation of the plantar flexors is critical in governing ankle push-off power during walking, which decreases due to age. However, electromyographic (EMG) signal amplitude alone is unable to fully characterize motor unit recruitment during functional activity. Although not yet studied in walking, EMG frequency content may also vary due to age-related differences in muscle morphology and neural signaling. Our purpose was to quantify plantar flexor activation differences in the time-frequency domain between young and older adults during walking across a range of speeds and with and without horizontal aiding and impeding forces. Ten healthy young (24.0 ± 3.4 yr) and older adults (73.7 ± 3.9 yr) walked at three speeds and walked with horizontal aiding and impeding force while muscle activations of soleus (SOL) and gastrocnemius (GAS) were recorded. The EMG signals were decomposed in the time-frequency domain with wavelet transformation. Principal component analyses extracted principal components (PCs) and PC scores. Compared with young adults, we observed that GAS activation in older adults: ) was lower across all frequency ranges during midstance and in slow to middle frequency ranges during push-off, independent of walking speed and ) shifted to slower frequencies with earlier timing as walking speed increased. Our results implicate GAS time-frequency content, and its morphological and neural origins, as a potential determinant of hallmark ankle push-off deficits due to aging, particularly at faster walking speeds. Rehabilitation specialists may attempt to restore GAS intensity across all frequency ranges during mid-to-late stance while avoiding disproportionate increases in slower frequencies during early stance. We use time-frequency analyses of calf muscle activation to quantify age-related differences in motor recruitment in walking. Gastrocnemius activation in older versus young adults was lower across all frequencies during midstance and in slow-to-middle frequencies during push-off, independent of speed, and shifted to slower frequencies with earlier timing as speed increased. Our results implicate gastrocnemius time-frequency content as a potential determinant of hallmark ankle push-off deficits due to aging, particularly at faster speeds.
在行走过程中，跖屈肌的激活对于控制踝关节蹬离力量至关重要，而随着年龄的增长，这种力量会下降。然而，肌电图（EMG）信号幅度本身并不能完全描述功能活动期间运动单位的募集情况。虽然在行走中尚未进行研究，但由于肌肉形态和神经信号传递的年龄相关差异，EMG 频率内容也可能发生变化。我们的目的是在时域和频域内量化行走过程中年轻和老年个体之间的跖屈肌激活差异，包括不同速度、有无水平助力和阻碍力等情况下。10 名健康的年轻（24.0±3.4 岁）和老年（73.7±3.9 岁）个体以三种速度行走，行走过程中施加水平助力和阻碍力，同时记录比目鱼肌（SOL）和腓肠肌（GAS）的肌电活动。使用小波变换对 EMG 信号进行时频分解。主成分分析提取主成分（PC）和 PC 得分。与年轻个体相比，我们观察到老年个体的 GAS 激活：1）在整个中足期和慢至中频范围的蹬离期，在所有频率范围内均低于年轻个体，与行走速度无关；2）随着行走速度的增加，GAS 激活向较慢的频率转移，且启动时间更早。我们的结果表明，GAS 的时频内容及其形态和神经起源可能是衰老导致踝关节蹬离力量下降的标志性缺陷的潜在决定因素，尤其是在较快的行走速度下。康复专家可能会尝试在从中足后期到后期维持 GAS 强度，同时避免在早期阶段过快增加较慢频率。我们使用小腿肌肉激活的时频分析来量化行走过程中与年龄相关的运动募集差异。在整个中足期和慢至中频范围的蹬离期，老年个体的 GAS 激活在所有频率下均低于年轻个体，与速度无关，并且随着速度的增加，GAS 激活向较慢的频率转移，且启动时间更早。我们的结果表明，GAS 的时频内容可能是衰老导致踝关节蹬离力量下降的标志性缺陷的潜在决定因素，尤其是在较快的速度下。
