Structural changes in postural sway lend insight into effects of balance training, vision, and support surface on postural control in a healthy population

Abstract

Postural sway was assessed [via center of pressure (COP) 95% elliptical area (EA), path length (PL), normalized path length (PL(n)) and sample entropy (SEn)] in four conditions of bipedal upright stance [compliant (Foam) vs. non-compliant (Hard) with eyes-open (EO) vs. eyes-closed (EC)] prior to, and immediately following, a six-week balance training intervention in a group of healthy adults (N = 26). The intervention was comprised of nine exercises progressed in difficulty based on the subjective assessments of individual competency. Results showed that EA and PL were increased, while PL(n) and SEn were decreased, in EC and Foam stance conditions (collapsed across effects of balance training). Interpretations were that restricted vision and a compliant surface represented constraints to postural control that caused increases in the amount (PL) and area (EA) of sway, but decreases in its coordinative twisting/turning (PL(n)) and temporal complexity (SEn). It was argued that these changes might represent compensatory adaptations in effort to maintain postural control given the demands of the imposed constraints. Balance training caused no change to EA, but did result in decreased PL, PL(n), and SEn for stance conditions performed on the Foam (either EO or EC). These changes were interpreted to reflect improved postural control, potentially through the learned adoption of a more deterministic postural control strategy that is uniquely defined by the constraints imposed on upright stance by the compliant surface.

Control Mechanisms of Static and Dynamic Balance in Adults With and Without Vestibular Dysfunction in Oculus Virtual Environments

“…Note that the comparison of values is made possible, although the assessment was done in 2 separate studies, because we processed the signal in the same manner in the 2 studies (down-sampling by 2, no smoothing applied) [26] and used the same parameters to calculate SampEn (r, m) [27]. Our findings are in agreement with previous studies on environmental constraints [7,8]: regularity increases (ie, SampEn decreases) when participants are standing on a compliant surface compared with a stable floor and when visual complexity increases (ie, dark vs light, larger sway of stars compared with minimal sway). In fact, the effect of the support surface on regularity was so dominant that any between-group differences vanished when participants were standing on the stability trainer.…”

“…Within static stance tasks, increased DP is equated with poor postural steadiness and reflects lower balance performance [7]. Indeed, in our study, we found moderate to excellent correlations between increased DP on the stars scene and decreased self‐reported balance confidence.…”

Altered Visual and Feet Proprioceptive Feedbacks during Quiet Standing Increase Postural Sway in Patients with Severe Knee Osteoarthritis

“…During these conditions, pain intensity was positively correlated with balance impairments, revealing an important role of pain in postural adjustments of obese KOA patients when the environment poses sensory challenges. There are indications that, in healthy subjects, the dynamic sensory reweighting can be optimized via specific training program and enhance balance in altered environments [58]. Therefore, rehabilitation procedures aiming to train sensory reorganization processes, optimizing the time used to solve the sensory conflict and the motor response and decrease pain, may lead to improvements in balance and reduce risk of falls in obese KOA patients.…”

Using Entropy Measures to Characterize Human Locomotion

“…Entropy measures have been successfully used to characterize standing balance [26][27][28], speech signals, and even somewhat predict epileptic seizures and heart attacks [17]. While a direct link between entropy and the sta bility of human walking cannot be proven, given its invariance to initial conditions, connection to Lyapunov exponents and success in diagnosing other biological systems, the construct validity of entropy is quite plausible.…”