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Background: The prevalence of falls among the older population underscores the imperative of comprehending human adaptations to gait perturbations. Dual-belt treadmills offer a controlled setting for such investigations. The purpose of this study was to examine the effect of the acceleration of one belt of the treadmill during three different phases of the gait cycle on kinematic and kinetic parameters and relate these changes to unperturbed gait. Methods: Twenty-one healthy young females walked on a treadmill in a virtual environment, in which five unexpected perturbations were applied to the left belt at the Initial Contact (IC), Mid Stance (MS), and Pre-Swing (PS) phase of the gait cycle. Data from the undisturbed gait and the first disturbance of each trial were extracted for analysis. Results: All perturbations significantly affected the gait pattern, mainly by decreasing the knee extension angle. The perturbation in the IC phase had the most significant effect, resulting in a 248.48% increase in knee flexion torque. The perturbation in the MS phase mainly affected plantar flexion torque, increasing it by 118.18%, while perturbation in the PS phase primarily increased the hip extension torque by 73.02%. Conclusions: The presence of perturbations in the IC and PS phases caused the most aggressive and significant changes in gait parameters.

Human postural control is commonly assessed by center of pressure (CoP) displacement analysis. However, traditional linear parameters do not provide a complete picture of postural control, so a number of nonlinear analyses have been introduced. One of these is recurrence quantification analysis (RQA), which is used to determine the number and duration of repeated states in a dynamic system. This review aimed to show how the RQA measures look in different groups of subjects when assessing postural stability during quiet standing and how the authors interpret them. Therefore, a systematic review was conducted of papers published from 2000 to February 2023. Searched databases were PubMed, ScienceDirect, and EBSCO. Twenty-eight publications were included in this review. The RQA parameters most commonly found in papers are %DET (determinism), ENT (Shannon entropy), %REC (recurrence), and %LAM (laminarity). %LAM is the most sensitive factor in determining differences in CoP position between different age groups, as it describes motion fluidity. The vision affects the deterministic structure of CoP motions. When the sensory organization test conditions became difficult, CoP variability increased, while the %DET decreased. It was concluded that traditional and nonlinear methods provide complementary and not redundant information for assessing age- and health-related changes in standing balance.

Background: Mediolateral perturbations caused by external pulling and pushing forces can occur in everyday living. Although the loss of balance can appear in all directions, coping with frontal plane perturbations is more challenging. In literature, it is common to compare postural responses between the elderly and the young, but the accurate description of reactions in the young is lacking. This manuscript aims to review all previous papers investigating how healthy young adults deal with mediolateral perturbations in a standing position, including reviewing the methodology, outcomes, and sequence of responses in these studies. Methods: A systematic review was conducted of papers published from 1999 to 2022. The databases searched were PubMed, Google Scholar, ScienceDirect, and EBSCO. Eight publications met the inclusion criteria. Results: There is no consensus on the methodology for conducting this type of research and how to collect the data, as it varies between authors. Many papers lack an accurate description and justification of the magnitude of imposed perturbations. It has been shown that the first joint torque and muscle response on perturbation may not be produced by active and voluntary muscle contraction, but are due to tissue stiffness. Such stiffness-based balance control does not directly involve the CNS and provides an immediate and appropriate corrective response. Conclusions: Postural reactions to mediolateral perturbations are a complicated process that still need further, systematized investigation.