Farinelli Veronica, Bolzoni Francesco, Marchese Silvia Maria, Esposti Roberto, Cavallari Paolo
Human Physiology Section of the Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Milan, Italy.
Department of Biomedical Sciences, Humanitas University, Pieve Emanuele, Italy.
Front Hum Neurosci. 2021 Oct 11;15:709780. doi: 10.3389/fnhum.2021.709780. eCollection 2021.
Anticipatory postural adjustments (APAs) are the coordinated muscular activities that precede the voluntary movements to counteract the associated postural perturbations. Many studies about gait initiation call APAs those activities that precede the heel-off of the leading foot, thus taking heel-off as the onset of voluntary movement. In particular, leg muscles drive the center of pressure (CoP) both laterally, to shift the body weight over the trailing foot and backward, to create a disequilibrium torque pushing forward the center of mass (CoM). However, since subjects want to propel their body rather than lift their foot, the onset of gait should be the CoM displacement, which starts with the backward CoP shift. If so, the leg muscles driving such a shift are the prime movers. Moreover, since the disequilibrium torque is mechanically equivalent to a forward force acting at the pelvis level, APAs should be required to link the body segments to the pelvis: distributing such concentrated force throughout the body would make all segments move homogeneously. In the aim of testing this hypothesis, we analyzed gait initiation in 15 right-footed healthy subjects, searching for activities in trunk muscles that precede the onset of the backward CoP shift. Subjects stood on a force plate for about 10 s and then started walking at their natural speed. A minimum of 10 trials were collected. A force plate measured the CoP position while wireless probes recorded the electromyographic activities. Recordings ascertained that at gait onset APAs develop in trunk muscles. On the right side, Rectus Abdominis and Obliquus Abdominis were activated in 11 and 13 subjects, respectively, starting on average 33 and 54 ms before the CoP shift; Erector Spinae (ES) at L2 and T3 levels was instead inhibited (9 and 7 subjects, 104 and 120 ms). On the contralateral side, the same muscles showed excitatory APAs (abdominals in 11 and 12 subjects, 27 and 82 ms; ES in 10 and 7 subjects, 75 and 32 ms). The results of this study provide a novel framework for distinguishing postural from voluntary actions, which may be relevant for the diagnosis and rehabilitation of gait disorders.
预期姿势调整（APAs）是在自主运动之前进行的协调性肌肉活动，以抵消相关的姿势扰动。许多关于步态起始的研究将领先脚足跟离地之前的那些活动称为APAs，因此将足跟离地视为自主运动的开始。特别是，腿部肌肉驱动压力中心（CoP）横向移动，将体重转移到后脚，并向后移动，以产生一个向前推动质心（CoM）的不平衡扭矩。然而，由于受试者想要推动身体而不是抬起脚，步态的起始应该是CoM的位移，它始于CoP向后移动。如果是这样，驱动这种移动的腿部肌肉就是主要推动者。此外，由于不平衡扭矩在机械上等同于作用在骨盆水平的向前力，因此需要APAs将身体各部分与骨盆连接起来：将这种集中力分布到全身会使所有部分均匀移动。为了验证这一假设，我们分析了15名右利足健康受试者的步态起始，寻找在CoP向后移动开始之前躯干肌肉中的活动。受试者站在测力板上约10秒，然后以自然速度开始行走。至少收集了10次试验。测力板测量CoP位置，而无线探头记录肌电图活动。记录确定在步态起始时APAs在躯干肌肉中发展。在右侧，腹直肌和腹外斜肌分别在11名和13名受试者中被激活，平均在CoP移动前33毫秒和54毫秒开始；而L2和T3水平的竖脊肌（ES）被抑制（9名和7名受试者，分别在104毫秒和120毫秒）。在对侧，相同的肌肉表现出兴奋性APAs（腹直肌在11名和12名受试者中，分别在27毫秒和82毫秒；ES在10名和7名受试者中，分别在75毫秒和32毫秒）。这项研究的结果为区分姿势动作和自主动作提供了一个新的框架，这可能与步态障碍的诊断和康复有关。
