Sozzi Stefania, Ghai Shashank, Schieppati Marco
Independent Researcher, 27100 Pavia, Italy.
Department of Political, Historical, Religious and Cultural Studies, Karlstad University, 65188 Karlstad, Sweden.
Brain Sci. 2023 Jun 21;13(7):978. doi: 10.3390/brainsci13070978.
The ground reaction force (GRF) recorded by a platform when a person stands upright lies at the interface between the neural networks controlling stance and the body sway deduced from centre of pressure (CoP) displacement. It can be decomposed into vertical (VGRF) and horizontal (HGRF) vectors. Few studies have addressed the modulation of the GRFs by the sensory conditions and their relationship with body sway. We reconsidered the features of the GRFs oscillations in healthy young subjects (n = 24) standing for 90 s, with the aim of characterising the possible effects of vision, support surface and adaptation to repeated trials, and the correspondence between HGRF and CoP time-series. We compared the frequency spectra of these variables with eyes open or closed on solid support surface (EOS, ECS) and on foam (EOF, ECF). All stance trials were repeated in a sequence of eight. Conditions were randomised across different days. The oscillations of the VGRF, HGRF and CoP differed between each other, as per the dominant frequency of their spectra (around 4 Hz, 0.8 Hz and <0.4 Hz, respectively) featuring a low-pass filter effect from VGRF to HGRF to CoP. GRF frequencies hardly changed as a function of the experimental conditions, including adaptation. CoP frequencies diminished to <0.2 Hz when vision was available on hard support surface. Amplitudes of both GRFs and CoP oscillations decreased in the order ECF > EOF > ECS ≈ EOS. Adaptation had no effect except in ECF condition. Specific rhythms of the GRFs do not transfer to the CoP frequency, whereas the magnitude of the forces acting on the ground ultimately determines body sway. The discrepancies in the time-series of the HGRF and CoP oscillations confirm that the body's oscillation mode cannot be dictated by the inverted pendulum model in any experimental conditions. The findings emphasise the robustness of the VGRF "postural rhythm" and its correspondence with the cortical theta rhythm, shed new insight on current principles of balance control and on understanding of upright stance in healthy and elderly people as well as on injury prevention and rehabilitation.
当一个人直立站立时，平台记录的地面反作用力（GRF）位于控制站立的神经网络与从压力中心（CoP）位移推导得出的身体摆动之间的界面处。它可以分解为垂直（VGRF）和水平（HGRF）向量。很少有研究探讨感觉条件对GRF的调节及其与身体摆动的关系。我们重新审视了24名健康年轻受试者站立90秒时GRF振荡的特征，旨在表征视觉、支撑表面以及对重复试验的适应性可能产生的影响，以及HGRF与CoP时间序列之间的对应关系。我们比较了在固体支撑表面（EOS、ECS）和泡沫上睁眼或闭眼时这些变量的频谱。所有站立试验均按八个一组的顺序重复进行。条件在不同日期随机安排。VGRF、HGRF和CoP的振荡彼此不同，根据其频谱的主导频率（分别约为4Hz、0.8Hz和<0.4Hz），呈现出从VGRF到HGRF再到CoP的低通滤波效应。GRF频率几乎不会随实验条件（包括适应性）而变化。当在坚硬支撑表面有视觉信息时，CoP频率会降至<0.2Hz。GRF和CoP振荡的幅度均按ECF>EOF>ECS≈EOS的顺序降低。适应性除了在ECF条件下没有影响。GRF的特定节律不会传递到CoP频率，而作用在地面上的力的大小最终决定身体摆动。HGRF和CoP振荡时间序列的差异证实，在任何实验条件下，身体的振荡模式都不能由倒立摆模型决定。这些发现强调了VGRF“姿势节律”的稳健性及其与皮质θ节律的对应关系，为当前的平衡控制原理以及对健康和老年人直立姿势的理解提供了新的见解，也为预防损伤和康复提供了新的思路。
