Analysis of the postural stabilization in the upright stance using optimization properties

Poststroke consequences upon optimization properties of postural sway during upright stance: a cross-sectional study

BACKGROUND

The understanding of human postural control has advanced with the introduction of optimization process modeling. These models, however, only provide control parameters, rather than analytical descriptors of optimization processes. Here, we use a newly developed direct (pattern) search algorithm to investigate changes in postural optimization process in poststroke individuals.

OBJECTIVE

This cross-sectional study investigated the optimization properties of postural stability during upright standing in poststroke individuals.

METHODS

Twenty-nine poststroke and 15 healthy age-matched individuals underwent posturography with a force platform while standing for 60 s for acquisition of center-of-pressure data. Poststroke individuals were grouped depending on their weight-bearing (WB) pattern and their balance capability assessed through Berg Balance Scale (BBS). The optimization properties of postural stability were computed assuming the minimization of postural sway as cost function.

RESULTS

The asymmetric WB poststroke group showed larger convergence rate toward the local minimum of postural sway than the symmetric WB group. Additionally, the low-balance capability group exhibited smaller values for averaged local minima and global minimum of postural sway coordinates compared with high-balance capability group. Significant correlations were found for BBS and the local minima and global minimum (Pearson's r ranged 0.378-0.424, P < 0.05).

CONCLUSIONS

In summary, the optimization properties describing postural dynamic stability, steadiness, and global reference are altered in poststroke individuals with asymmetric WB pattern and low-balance capability.

Recurrence Quantification Analysis of Center of Pressure Trajectories for Balance and Fall-Risk Assessment in Young and Older Adults

The prevalence and impact of balance impairments and falls in older adults have motivated several studies on the characterization of human balance. This study aimed to determine the ability of recurrence quantification analysis (RQA) measures to characterize balance control during quiet standing in young and older adults and to discriminate between different fall risk groups. We analyze center pressure trajectories in the medial-lateral and anterior-posterior directions from a publicly available static posturography dataset that contains tests acquired under four vision-surface testing conditions. Participants were retrospectively classified as young adults (age< 60, n=85), non-fallers (age≥60, falls=0, n=56), and fallers (age≥60, falls≥1, n=18). Mixed ANOVA and post hoc analyzes were performed to test for differences between groups. For CoP fluctuations in the anterior-posterior direction, all RQA measures showed significantly higher values for young than older adults when standing on a compliant surface, indicating less predictable and stable balance control among seniors under testing conditions where sensory information is restricted or altered. However, no significant differences between non-fallers and fallers were observed. These results support the use of RQA to characterize balance control in young and old adults, but not to discriminate between different fall risk groups.

EVALUATION OF POSTURAL BALANCE INDICATORS IN HEALTHY INDIVIDUALS

OBJECTIVE

The aim: To determine and generalize the indicators of stabilometry in healthy individuals for their further use as a control group in studies of pathologies of the musculoskeletal system.

PATIENTS AND METHODS

Materials and methods: The study was conducted on a stable platform with biofeedback TYMO (Tyromotion). 30 male and female patients aged 18-25 years participated in the study. The following indicators were studied : distance traveled, medial-lateral deviation, anterior-posterior deviation, area of the statokinesiogram (COF), average speed, feedback system, Romberg index. Stabilometry was performed in a bipodal position, standing, in four functional positions: on a hard surface with eyes open and closed, on a soft surface with eyes open and closed.

RESULTS

Results: The reference values of the stabilometric parameters: the traveled distance, medio-lateral deviation, anterior-posterior deviation, the area of the statokinesiogram, the average speed, the feedback system, the Romberg index in healthy individuals aged 18-25 years were determined . When evaluating the feedback system, it was established that the visual component was 34% (32.0; 36.0), the vestibular 34% (32.0; 35.0), the somatosensory 33% (30.0; 36.0). The reflex-driven index was 0.55 (0.46, 0.62), the central nervous system (CNS)-driven index was 1.55 (1.25, 1.89) . The Romberg index M1/ M2 was 0.94 (0.78, 1.07), M2/M3 was 0.98 (0.86, 1.10).

CONCLUSION

Conclusions: The obtained indicators of movement in the sagittal plane, the area of the statokinesiogram, the average speed of movement, the feedback system (visual, vestibular, proprioceptive (somatosensory) components), the Romberg index (RI) can be considered reference values for healthy individuals aged 18-25 years .

Reliability and robustness of optimization properties for stabilization of the upright stance as determined using posturography

Diagnostic value of static posturography depends on its methodological features, measurement properties, and on computational methods that extract meaningful information from the postural sway i.e. the center-of-pressure (CoP) displacements. In this study, we assessed the reliability and robustness of the postural system based on the optimization properties of the CoP signal: descending, local and global stability, and convergence. For the analysis, we used CoP data from 146 participants (104 [71%] female, age 46 ± 23 years, body mass index 23.6 ± 3.4 kg/m²) recorded while standing quietly on a foam surface without visual input. Reliability was estimated using the intraclass correlation coefficient from a single (ICC_2,1) and averaged (ICC_2,3) measurements. Robustness was assessed through main and interaction effects for the signal duration (60, 30 s), sampling frequency (100, 50 Hz), and lowpass filtering cutoff frequency (10, 5 Hz). The observed reliability depended on the use of average or single measurements as it was excellent for the stability property (ICC_2,k ≥ 0.772); excellent-to-acceptable (ICC_2,3 ≥ 0.540) or excellent-to-unacceptable (ICC_2,1 ≥ 0.281) for the descending property; and excellent-to-unacceptable (ICC_2,3 > 0.295; ICC_2,1 > 0.122) for the convergence property. Robustness analysis showed large main effects of signal duration (ω² ≤ 0.834, p < 0.001), sampling frequency (ω² ≤ 0.526, p < 0.001), and the lowpass filter cutoff frequency (ω² ≤ 0.523, p < 0.001) on the optimization properties; but all two-way and three-way effects varied from medium to trivial. Reliability is thus excellent to acceptable for deriving the descending, stability, and convergence properties from the average of three measurements. Those optimization properties are robust to the interaction but not the main effects of methodological sources of variation of posturography.