Changed Temporal Structure of Neuromuscular Control, Rather Than Changed Intersegment Coordination, Explains Altered Stabilographic Regularity after a Moderate Perturbation of the Postural Control System

Abstract

Sample entropy (SaEn) applied on center-of-pressure (COP) data provides a measure for the regularity of human postural control. Two mechanisms could contribute to altered COP regularity: first, an altered temporal structure (temporal regularity) of postural movements (H1); or second, altered coordination between segment movements (coordinative complexity; H2). The current study used rapid, voluntary head-shaking to perturb the postural control system, thus producing changes in COP regularity, to then assess the two hypotheses. Sixteen healthy participants (age 26.5 ± 3.5; seven females), whose postural movements were tracked via 39 reflective markers, performed trials in which they first stood quietly on a force plate for 30 s, then shook their head for 10 s, finally stood quietly for another 90 s. A principal component analysis (PCA) performed on the kinematic data extracted the main postural movement components. Temporal regularity was determined by calculating SaEn on the time series of these movement components. Coordinative complexity was determined by assessing the relative explained variance of the first five components. H1 was supported, but H2 was not. These results suggest that moderate perturbations of the postural control system produce altered temporal structures of the main postural movement components, but do not necessarily change the coordinative structure of intersegment movements.

Adolescent Awkwardness: Alterations in Temporal Control Characteristics of Posture with Maturation and the Relation to Movement Exploration

“…Adolescents may control task-relevant movement components in a rather reliable way; however, redundant components show alterations leading to the observed variability. Results are further in line with previous studies investigating leg dominance [36,37,52], sensory perturbation [48], or dual tasking [39] and its effect on postural control, presenting some but not all PM k to be affected. Although adolescents are suggested to heavily rely on visual information [13], no differences could be observed between the eyes-open and eyes-closed trial.…”

“…The scores represent the posture vectors in the new PC k -basis and are obtained through a basis transformation of the original data onto the new basis. Therefore, the scores can be interpreted as "principal positions" PP k (t), since they are a representation of positions in posture space [36,38,42,48,49]. The principal position PP k (t) together with the eigenvector PC k define one (the k-th) component of the whole postural movement.…”

“…To perform further analyses with an analogue and subject-specific variable, we calculated the relative variances rVAR k from PP k (t). The rVAR k quantify how much each PM k contributed to the whole postural variance for each trial [34,48]. The variable rVAR k was evaluated to identify differences in movement strategy and movement dimensions between the trials and participants (Hypothesis 1).…”

Should the Minimal Intervention Principle Be Considered When Investigating Dual-Tasking Effects on Postural Control?

“…"Movement dimensions" in this context relate to the degrees of freedom in the human body, enabled by joints between the segments [26,27] and to the coordinative patterns that emerge in the control of these degrees of freedom. A suitable approach to evaluate human postural control is to analyze kinematic data using principal component analysis (PCA), which reveals different movement strategies [28][29][30][31]. In an unconstrained bipedal stance with eyes open, the most dominant movement component is the anterior-posterior ankle sway (ankle strategy) with an approximately 70% overall share of the postural variance [29,[31][32][33].…”

“…A suitable approach to evaluate human postural control is to analyze kinematic data using principal component analysis (PCA), which reveals different movement strategies [28][29][30][31]. In an unconstrained bipedal stance with eyes open, the most dominant movement component is the anterior-posterior ankle sway (ankle strategy) with an approximately 70% overall share of the postural variance [29,[31][32][33]. Research investigating postural control by measuring muscle activity using electromyography [34] or joint torques [35] support the ankle strategy as the dominant coordinative pattern in the bipedal stance.…”