Institute for Aging Research, Hebrew SeniorLife, Boston, MA 02131, USA.
J Biomech. 2009 Oct 16;42(14):2231-7. doi: 10.1016/j.jbiomech.2009.06.038. Epub 2009 Aug 6.
To facilitate stable walking, humans must generate appropriate motor patterns and effective corrective responses to perturbations. Yet most EMG analyses do not address the continuous nature of muscle activation dynamics over multiple strides. We compared muscle activation dynamics in young and older adults by defining a multivariate state space for muscle activity. Eighteen healthy older and 17 younger adults walked on a treadmill for 2 trials of 5 min each at each of 5 controlled speeds (80-120% of preferred). EMG linear envelopes of v. lateralis, b. femoris, gastrocnemius, and t. anterior of the left leg were obtained. Interstride variability, local dynamic stability (divergence exponents), and orbital stability (maximum Floquet multipliers; FM) were calculated. Both age groups exhibited similar preferred walking speeds (p=0.86). Amplitudes and variability of individual EMG linear envelopes increased with speed (p<0.01) in all muscles but gastrocnemius. Older adults also exhibited greater variability in b. femoris and t. anterior (p<0.004). When comparing continuous multivariate EMG dynamics, older adults demonstrated greater local and orbital instability of their EMG patterns (p<0.01). We also compared how muscle activation dynamics were manifested in kinematics. Local divergence exponents were strongly correlated between kinematics and EMG, independent of age and walking speed, while variability and max FM were not. These changes in EMG dynamics may be related to increased neuromotor noise associated with aging and may indicate subtle deterioration of gait function that could lead to future functional declines.
为了实现稳定行走，人类必须生成适当的运动模式，并对干扰做出有效的纠正反应。然而，大多数肌电图分析并没有解决肌肉激活动力学在多个步态中的连续性问题。我们通过定义肌肉活动的多维状态空间来比较年轻和老年成年人的肌肉激活动力学。18 名健康的老年和 17 名年轻成年人在跑步机上以 5 种控制速度（80-120%的首选速度）各行走 2 次，每次 5 分钟。获得左腿外侧 v.、股二头肌 b.、腓肠肌 gastrocnemius 和 t.前肌的肌电图线性包络。计算了步态间变异性、局部动态稳定性（发散指数）和轨道稳定性（最大 Floquet 乘数；FM）。两个年龄组的首选行走速度相似（p=0.86）。所有肌肉的 EMG 线性包络的幅度和变异性均随速度增加（p<0.01），但腓肠肌除外。老年组的股二头肌和 t.前肌的变异性也更大（p<0.004）。在比较连续的多变量肌电图动力学时，老年组的肌电图模式表现出更大的局部和轨道不稳定性（p<0.01）。我们还比较了肌肉激活动力学在运动学中的表现方式。局部发散指数在运动学和肌电图之间具有很强的相关性，与年龄和行走速度无关，而变异性和最大 FM 则没有。这些肌电图动力学的变化可能与与衰老相关的神经运动噪声增加有关，并且可能表明步态功能的微妙恶化，这可能导致未来的功能下降。
