Postural Control Deficits During Static Single-leg Stance in Chronic Ankle Instability: A Systematic Review and Meta-Analysis

Abstract

Context:

Postural control deficits arising from injured ankles are central to chronic ankle instability (CAI) and its persistent symptoms. This is usually measured by recording the center of pressure (CoP) trajectory during static single-leg stance using a stable force plate. However, existing studies have produced conflicting results on whether this mode of measurement adequately reveals the postural deficits in CAI.

Objective:

To determine whether postural control during static single-leg stance is impaired in CAI patients when compared with uninjured healthy controls.

Data Sources:

Literature databases, PubMed, Embase, Web of Science, Cochrane Library, Scopus, CINAHL, and SPORTDiscus, were searched from inception to April 1, 2022, using ankle-, injury-, and posture-related terms.

Study Selection:

Two authors independently performed the step-by-step screening of article titles, abstracts, and full texts to select peer-reviewed studies investigating CoP trajectory during static single-leg stance using a stable force plate in CAI patients and healthy controls. A total of 13,637 studies were reviewed, and 38 studies (0.003%) met the selection criteria.

Study Design:

Meta-analyses of descriptive epidemiological study.

Level of Evidence:

Level 4.

Data Extraction:

CoP parameters, sway directions, visual condition, and numerical data (means and standard deviations) were extracted.

Results:

The injured ankles of CAI patients had higher standard deviations of sway amplitude in both anterior-posterior and medial-lateral directions (standardized mean difference [SMD] = 0.36 and 0.31, respectively) under conditions of open eyes than controls. Higher mean sway velocity in anterior-posterior, medial-lateral, and total directions (SMD = 0.41, 0.37, and 0.45, respectively) with closed eyes was also found.

Conclusion:

CAI patients had deficits of postural control during static single-leg stance, and these deficits were identified by the CoP trajectory. Further methodological explorations of CoP parameters and corresponding test conditions are required to enhance the sensitivity and reliability of postural deficit assessments in CAI using force plates.

Lateral ankle sprains are among the most prevalent sports-related injuries, occurring up to 7 times per 1000 person-years in emergency department visits.^22,24 Although ankle sprains are often dismissed as being relatively innocuous and expected to recover spontaneously, over 40% of patients develop chronic ankle instability (CAI) and suffer from lifelong residual symptoms, including repetitive sprains and a persistent sensation of the ankle “giving way.” ¹⁶ Prolonged joint instability may also lead to post-traumatic intra-articular lesions and significant loss of work productivity.^22,70

Dozens of therapeutic strategies exist but are not successful due to complex mechanism underlying CAI.^12,70 The greater exploration of contributory factors could advance the clinical management of CAI.

Postural control is defined as the spatial control of body position in relation to stability and orientation. ⁵² The human body is inherently unstable, and the musculoskeletal and neural systems must both be regulated precisely to maintain an upright stance and prevent falls. ⁵⁵ Impaired postural control is a characteristic of CAI that has received a great deal of research attention.^49,74 Freeman et al ¹⁴ introduced the concept of functional ankle instability in the mid-1960s based on the diminished ability of CAI patients to maintain the single-leg stance (Romberg test). Subsequently, most updated theoretical models have highlighted postural deficits as a crucial determinant of CAI and its persistent symptoms.^22,25 However, despite numerous reports of different measuring strategies for postural control, no consensus has been reached regarding a standard for CAI-specific postural deficits.

The center of pressure (CoP) trajectory during static single-leg stance is measured using a stable force plate and is the usual method for assessment of postural control in CAI studies.^39,49 The CoP is the point where body mass is concentrated, and parameters derived from the CoP trajectory are used to indicate postural deficits (ie, larger CoP sway, worse postural control). ⁵⁵ However, controversy exists as to whether postural deficits arising from unstable ankles are revealed through this test.^39,74 Several systematic reviews conducted between 2009 and 2016 have tried to summarize CAI-related postural deficits, but the paucity of original studies and lack of standardization in testing methodologies have made the results inconclusive.^{1,26,39,46,67} In theory, different parameters and directions of CoP sway could reflect different postural characteristics and any reduction of visual input could intensify the difficulty in controlling posture.^39,49 The current study includes subgroup meta-analyses that address the nature of CAI-related postural deficits during static single-leg stance and clarify variations in testing methodologies to enhance knowledge regarding laboratory- and clinic-based CoP measurements for CAI patients.

Methods

Study Design

The systematic review with meta-analysis was designed and carried out in accordance with the reporting guidelines of Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA). ⁵¹ The study protocol has been registered at the International prospective register of systematic reviews (CRD42022307076).

Search Strategy

A systematic literature search was conducted independently by 2 of the authors using 7 electronic databases: PubMed, Embase, Web of Science, Cochrane Library, Scopus, CINAHL, and SPORTDiscus, from inception until April 1, 2022. The search strategy consisted of keywords and synonyms that combined the following strings with ‘AND’: (1) ankle-related, (2) injury-related, and (3) posture-related. Search terms within each string were combined with ‘OR’. The full search strategies are presented in Appendix 1 (available in the online version of the article). Reference lists of articles chosen for inclusion were also checked manually. Mendeley Desktop Version 1.19 (Mendeley Ltd.) was used to remove duplicates and manage records.

Inclusion Criteria

Inclusion criteria were as follows: (1) investigations of postural control using measurements of CoP trajectory during static single-leg stance by stable force plate; (2) comparisons of injured ankles of CAI patients with control ankles of healthy participants without a history of ankle injury; (3) peer-reviewed, full-text, English-language publications. Studies restricted to between-side comparisons among patients were excluded due to evidence of bilateral impairments in unilateral CAI.^39,77

Given the controversy surrounding CAI-specific CoP parameters and test conditions, 3 authors with experience in kinesiology, orthopaedics, and physiatrics agreed a consensus on parameters of CoP sway as follows: (1) 4 categories of CoP parameters (sway amplitude, sway velocity, sway area, and time-to-boundary [TTB]); (2) 2 visual conditions (eyes open and eyes closed); (3) 3 sway directions were acknowledged (anterior-posterior [AP], medial-lateral [(ML], and total directions). ⁴⁹ Detailed definitions and interpretations of these CoP parameters are summarized in Table 1.

Table 1.

Definition of the included CoP parameters

Names	Definitions	Common Meanings for Postural Control
(1) Sway amplitude	Absolute value of distance between points
Range of amplitude	Maximal CoP amplitude along the trajectory (any 2 points)	Higher = worse
Mean amplitude	Averaged CoP amplitude from the center or axis of the trajectory	Higher = worse
SD of amplitude	SD of CoP amplitude from the center or axis of the trajectory	Higher = worse
(2) Sway area	Area formed by CoP trajectory
	Commonly defined by ellipse covering 95% of CoP trajectory, or rectangle sized by the range of amplitude in AP and ML axis	Higher = worse
(3) Sway velocity	Absolute value of instantaneous velocity of CoP movements
	Averaged CoP velocity (mean velocity), equal to the movement path “length” divided by test duration	Higher = worse
(4) TTB	Time for CoP to reach the foot boundary if it continued on its trajectory at instantaneous velocity
Absolute TTB	Minimal minima of TTB	Lower = worse
Mean TTB	Averaged minima of TTB	Lower = worse
SD of TTB	SD of minima of TTB	Lower = worse

AP, anterior-posterior; CoP, center of pressure; ML, medial-lateral; SD, standard deviation; TTB, time-to-boundary.

The International Ankle Consortium (IAC) standards were generally applied throughout this meta-analysis with the exception of some studies that predated the publication of this standard. ¹⁶ These standards are more general than those in previous reviews of CAI. All patients included had ankle sprain histories and ≥1 typical CAI symptom ( “giving way”, recurrent sprains, and self-reported feelings of instability).^56,77

Article Selection and Data Extraction

Two authors independently reviewed the articles and extracted data. Unresolved disputes were discussed with the senior author, and a consensus was reached. Step-by-step screening of article titles, abstracts, and full texts and removal of duplicates was performed. The following information was extracted: demographic characteristics (age, sex), sample size, details of test methodology (test devices, sampling/cut-off frequency, times and duration of trials, test conditions, and CoP parameters with sway directions), and numerical data (means and standard deviations). The 95th percentile ellipse was the preferred definition of sway area where >1 measurement was reported and sway velocity was preferred over sway length since the relationship between these 2 quantities was multiplied by the duration of trials.^8,55 In the event that numerical data were confusing or not fully reported, corresponding authors were contacted by email (6 emails were sent and 2 authors provided the data required).

Quality and Risk of Bias Assessment

The standards of each evaluative criterion were determined by all authors, and assessments were performed independently by L.Y. and Z.J. and discussed with the senior author in the event of disagreement. The epidemiological appraisal instrument was used to assess study quality.^15,29 The Cochrane standardized bias tool for cross-sectional studies was used to evaluate potential confounders. ²⁹ Publication bias due to the lack of studies with small sample sizes and negative outcomes was assessed by Egger’s test. ²⁸

A rating scale based on the IAC standard was used to assess the variability of ankle instability criteria. ¹⁶ CAI patients should meet the following criteria: (1) ≥1 significant ankle sprain; (2) the significant sprain occurred ≥12 months previously; (3) the significant sprain resulted in pain, swelling, and interrupted desired physical activity for ≥1 day; (4) no ankle injury during the previous 3 months; (5) ≥1 of the following 3 symptoms should be present: (5.1) ≥2 episodes of the ankle ‘giving way’ in the previous 6 months, (5.2) or ≥2 sprains to the same ankle, (5.3) or self-reported ankle instability confirmed by a validated questionnaire. ¹⁶ Each item was scored as “Reported and achieved the standard”, “Reported but the standard not achieved,” or “Not reported.” ¹⁶

Inter-rater agreements for quality and risk of bias assessment were estimated based on the kappa value (κ). The R package Visualizing Categorical Data Version 1.4-8 (http://www.r-project.org) was used to calculate the unweighted κ for risk of bias (yes/no) and weighted κ for study quality and CAI criteria (ordered 0/0.5/1 points) with κ > 0.8 indicating almost perfect agreement.

Statistical Analysis

Meta-analyses were performed using Stata Version 16 (Stata Corp LP) for studies with similar CoP parameters (Table 1) and visual conditions (eyes open or eyes closed), and subgroups were divided by sway directions (AP, ML, total). The comparability of outcomes with different units was clarified by use of standardized mean difference (SMD) of Cohen’s d effect sizes between injured ankles and controls with 95% CIs to present differences between groups.^9,21 A greater SMD indicated higher patient outcomes with 0.2 to 0.5 indicating a small, 0.5 to 0.8 a moderate, and >0.8 a large effect size (clinical meanings, Table 1).^9,21 Considering the heterogeneity of test methodologies and CAI criteria among the studies, the random-effects model was used to pool the results. The presence of heterogeneity was evaluated by I² statistics and I² ≥75% indicated considerable heterogeneity, requiring cautious interpretation. ⁵³ Sensitivity analysis was performed by removing 1 study at a time to estimate the impact on the pooled result from >2 studies. If a significant result turned out to be an insignificant one, the pooled result would be considered unstable, requiring cautious interpretation.

Results

Study Selection and Characteristics

A total of 13,637 eligible unique publications were identified by electronic and manual searches, and 38 studies met the inclusion criteria (Figure 1). Further details, including sample size, age, sex, force plate devices with test frequency, foot conditions, and CoP parameters, are presented in Appendix 2 (available online).

Figure 1.

Flow chart of the systematic review selection process.

Quality and Risk of Bias Assessment

A total of 1166 agreements were achieved for quality assessment by the epidemiological appraisal instrument tool (weighted κ = 0.90). Most studies clearly described study design and properly reported findings. For the risk of bias assessment, 259 agreements were achieved (unweighted κ = 0.89). All studies enrolled representative samples of CAI patients and uninjured healthy controls and utilized force plates to measure the CoP trajectory during static single-leg stance. Rating scales for quality and risk of bias assessments are presented in Appendix 3 (available online).

A total of 256 agreements were achieved in the assessment of CAI patient variability (weighted κ = 0.96). All studies required patients to have a history of ankle sprains, but only 9 studies met the recommended severity. A total of 10 studies stipulated that the initial sprains had to have occurred ≥12 months before the study and 23 completely excluded injuries occurring in the previous 3 months. All studies mentioned symptoms of instability but 10 did not achieve IAC standards. Detailed IAC standard rating scales are presented in Appendix 4 (available online).

Quantitative Data Synthesis of CoP Outcomes

Sway Amplitude

Six studies evaluated the range of sway amplitude,^{23,35,44,57,75,79} but no significant differences were observed between groups for pooled results in the AP or ML direction when eyes were open or closed (Appendix 5.1, available online). Mohamadi et al ⁴⁴ evaluated the range of sway amplitude in the total direction and observed a significantly larger range in CAI patients with both closed and open eyes. Six studies evaluated the mean sway amplitude,^{30,38,42,59,60,62} no significant differences were found between groups in the AP or ML direction with either closed or open eyes. A total of 12 studies evaluated sway amplitude standard deviation (SD),^{11,23,31,35,36,38,41,50,60,64,66,75} finding a higher CAI patient SD with small effect when eyes were open in both the AP (SMD = 0.36) and ML (SMD = 0.31) directions, a result that was stable according to sensitivity analysis. However, no significant differences were observed with closed eyes in either the AP or total directions and the significant difference in the ML direction was proved to be unstable when the studies of Knapp et al ³⁵ or Méndez-Rebolledo et al ⁴¹ were removed.

Sway Area

A total of 13 studies evaluated sway area,^{7,27,31,35,36,38,41,43,44,60,61,62,63} with Linens et al ³⁸ reporting both elliptical and rectangular areas, of which the ellipse was included in the meta-analysis (Appendix 5.2, available online). Significantly larger sway areas were observed in patients with eyes open, but the pooled results were not significant when the study of Mohamadi et al ⁴⁴ was removed during sensitivity analysis. Under conditions of closed eyes, small effects of larger sway areas were observed without significant publication bias (SMD = 0.44) in CAI patients and this was not affected by removal of studies, thus proving the stability of the result. However, definitions of areas were extremely heterogeneous and lacked clarity. Four studies defined the area through 95th percentile ellipse,^35,38,61,62 4 studies through the rectangle made by maximum AP and ML sways,^38,43,60,63 and the remaining 6 studies failed to clearly define area calculations.^{7,27,31,36,41,44}

Sway Velocity

A total of 26 studies evaluated mean sway velocity (or length) (Appendix 5.3, available online).^{7,11,17,18,19,20,23,27,30,31,35,36,38,41,43,44,47, 57,58,60,61,62,64,66,71,75} Under conditions of open eyes, small to large differences were observed but the heterogeneity was high in the AP and total directions (I² = 80.1% and 83.6%, respectively). Significant pooled results were proved to be unstable when 1 study was removed in the AP direction,^41,60,75 and 1 in the ML direction.^23,60,64,75 Under conditions of closed eyes, small effects of significantly larger mean sway velocity in patients were observed homogeneously without publication bias in the AP (SMD = 0.41), ML (SMD = 0.37), and total (SMD = 0.45) directions. All pooled results of mean sway velocity with closed eyes also proved to be stable by sensitivity analysis.

Time-to-Boundary

Five studies evaluated the minimum TTB (Appendix 5.4, available online),^{5,23,35,38,40} but no significant differences were observed between groups in the AP or ML directions with eyes open. Pooled results indicated small effects of lower absolute TTB in CAI patients in the AP and ML directions, but both of these effects were unstable, according to the sensitivity analysis that removed the study of McKeon et al ⁴⁰ or Knapp et al. ³⁵ A total of 12 studies evaluated mean TTB.^{5,23,31,32,35,38,40,45,54,68,71,75} Pooled results indicated lower mean TTB in the AP direction with open eyes. But the results were not significant when the studies of Hertel and Olmsted-Kramer ²³ or Wikstrom et al ⁷⁵ were removed. Significant publication bias was also detected (Egger’s P = 0.03). No significant differences were observed in the ML direction with open eyes or in AP or ML directions with closed eyes. A total of 11 studies evaluated the SD of TTB,^{5,23,31,32,35,38,40,54,65,68,75} no significant differences were found between groups in the AP or ML directions with either open or closed eyes.

Discussion

The current analysis synthesized existing evidence regarding the evaluation of postural control by CoP trajectory during static single-leg stance in CAI patients. Our hypothesis that postural deficits did exist was verified. Where meta-analyses could be performed, injured ankles exhibited higher SD of sway amplitude in the AP/ML directions when eyes were open and higher mean sway velocity in all directions when eyes were closed than controls without a history of ankle sprains.

Generally, postural control is achieved as a result of peripheral sensory inputs (eg, somatosensory, vestibular, and visual), spinal/cortical processing (eg, sensory integration, motor planning), and corrective motor outputs (eg, muscle reflex, voluntary movement). ⁵⁵ All of these components should combine to meet the demands of both the environmental conditions and functional requirements with precision. ⁵⁵ In cases of CAI, impaired proprioceptive sense, weakened muscle strength, delayed neural reflex, and maladaptive neuroplasticity in the corticospinal tract and cerebellum are all possible source of impairment of the postural control system.^22,72,77 We suggest that a clearer understanding of the pattern of deficits may assist with future investigations of the causes.

CoP Parameters

The efficiency of CoP measurements during the single-leg stance for studies of CAI has been questioned. The previous systematic review conducted by McKeon and Hertel ³⁹ suggested that deficits of static postural control measured by CoP trajectory were subtle in CAI. Wikstrom et al, ⁷⁶ Arnold et al, ¹ and Munn et al ⁴⁶ performed a meta-analysis of pooled balance-related outcomes (including CoP outcomes) to reveal overall deficits in CAI. Hiller et al ²⁶ performed an analysis of pooled sway area and mean amplitude, taking account of whether eyes were open or closed, while sway velocity and other CoP outcomes were not analyzed fully. Focusing on the TTB, Song et al ⁶⁷ recalculated this parameter with respect to visual modulations but did not perform direct between-group comparisons. The most recent review, by Thompson et al, ⁷⁴ analyzed data from the aforementioned reviews but did not subdivide visual conditions, concluding that sway velocity was not altered in CAI. In the current review, performing detailed subgroup analysis highlighted the superiority of the SD of sway amplitude with open eyes and mean sway velocity with closed eyes when detecting postural deficits in CAI.

The range of sway amplitude has traditionally been used to evaluate the ability to limit sway spatially but has been criticized on the grounds of high variability. ⁵² The 2 extremities of CoP trajectory were used to calculate the range of sway amplitude, so even a small perturbation of the test environment (eg, an accidental noise) could lead to large variations in outcome and consequent misinterpretation.^52,55 Mean sway amplitude was introduced to solve this problem but its sensitivity to detect postural deficits in sports injuries has been questioned. Only 2 to 4 studies in each subgroup used it without significant differences being observed.^52,59,60 The SD of sway amplitude was used to assess the stability of CoP distribution with time. Normal postural regulation based on lower-limb proprioceptive and plantar cutaneous sense was thought to limit abnormal distribution.^52,69 The current results show a significantly larger SD of sway amplitude in CAI with eyes open but not with eyes closed. This finding seems to contradict mainstream views that the closed eyes condition would exacerbate postural deficits. ²⁶ We speculated that the relatively lower number of studies under closed eye conditions might increase the susceptibility to effects of individual negative results. In addition, the long test duration used by Kodesh et al ³⁶ (30 s) might exceed the ability even of healthy people to successfully regulate body sway and obscure pathological differences between patients and controls. However, considering the heterogeneous outcomes in studies with relatively long test duration, further controlled studies focusing on test duration are needed to confirm our speculations.

Sway area was estimated to approach an assessment of overall spatial qualities of postural control.^52,60 Pooled results showing significantly larger sway area in CAI patients indicated greater spatial possibilities for the unstable ankles to achieve the risky boundary between stabilizing and spraining.^52,60 However, nearly half the studies failed to clearly define the sway area and its calculation, which made further subgroup analysis unapproachable. Maximal values in the AP and ML axes used to produce estimates of the rectangular area of sway also had the problem of variability, whereas the ellipse area that contained the 95th percentile of CoP points reduced the influence of extremums.^8,55 Only Linens et al ³⁸ calculated both the elliptical and rectangular areas but did not identify either as superior for detection of postural deficits in CAI. The current pooled results indicated homogenous differences between groups according to these various definitions, but a clear description in future CAI studies would improve the comparability of this parameter.

Mean sway velocity assesses temporal qualities of postural control and was believed to be the most widely used CoP parameter.^52,60 The anticipatory reaction of peripheral ankle muscles, which slows the CoP sway is a response likely to be impaired in CAI according to our results.^33,73 The cerebellum has also been shown to participate in the suppression of sway velocity and morphological evidence of cerebellar atrophy in CAI exists.^10,78 Considerable heterogeneities in the pooled results were observed with open eyes and this may be due to the lack of controlled visual conditions, since few studies asked participants to focus on a visual target.^20,23,63 To avoid errors caused by moving objects and uncontrolled visual backgrounds, the utilization of standardized visual targets would be a good addition to future studies under open-eye conditions.

The novel CoP parameter, TTB, was thought to give a quantitative evaluation of the reduced time taken by CAI patients to make postural corrections from the boundary of sprains and give deeper insight into the spatio-temporal characteristics of postural control. ²³ The current pooled results did not fully support this point of view, and significant publication bias was observed among subgroups of this parameter. CoP reflects the center of mass within the foot area in contact with the force plate and movement of it may be greater than movements of body center of gravity. Thus, the true spatial boundary between stabilization and spraining may be narrower than the actual foot length and width.^40,52 We suggest that proper definition of boundaries of TTB would allow more reliable calculation of this parameter.

The precise neurophysiological significance of CoP parameters in either healthy people or in patients with CAI has yet to be fully defined. Moreover, the selection of CoP parameters was determined by availability, and less commonly used ones (eg, the frequency and entropy) were excluded due to the difficulty in performing quantitative analysis given the limited number of studies.^6,54 We feel that there are better CAI-specific CoP parameters and corresponding test conditions yet to be discovered, and further effort is needed to identify them.

Research Implications

The current study is intended to supply reference material to aid selection of CoP parameters and testing conditions during future CAI studies on postural deficits during static single-leg stance. However, it is noteworthy that only small differences were found between groups for the above effects. Whereas the sensitivity and reliability of CoP parameters during static single-leg stance remain to be improved, the static task might not be challenging enough to fully elucidate the postural deficits in CAI. Other test strategies, such as dynamic tasks and artificial perturbations, may enlarge the deficits of postural control and aid detection. ⁷⁴

Clinical Implications

The current review highlights the importance of detailed assessments and targeted interventions to restore stability of the single-leg stance in the clinical management of CAI. The deficits of static tasks were relatively subtle but may contribute to difficulties in accommodating more challenging tasks.^44,57 For example, on distraction of visual attention during daily activities or competitive sports, patients with worse static deficits may be less adaptable to unanticipated postural errors.^44,57 No consensus has been achieved on minimal clinically important differences in CoP parameters,^3,8,55 but this study highlights the potential significance of even small postural deficits in CAI.

Greater targeting of interventions of postural control for CAI patients is necessary, such as single-leg stance training with visual and cognitive constraints.^37,48 Transcranial stimulation of the motor cortex has also achieved satisfying outcomes for CAI patients, and we speculate that this approach may have utility in restoring postural deficits.^4,10,48,78 In summary, we recommend that more work should be undertaken to strengthen formal clinical recommendations regarding management of postural deficits.

Limitations

We acknowledge significant limitations to the present study. First, the cross-sectional design makes it difficult to distinguish between postural deficits present before the initial injury and those occurring during CAI progression. Longitudinal evaluations from the preinjury state to CAI are needed to clarify this point. Second, methodological qualities and study numbers among some subgroups were low, which might influence the reliability of the results and the power of publication bias estimations. ²⁸ This is a common problem in the field of ankle injuries and we hope that future studies will follow official methodological checklists, so that updated reviews will have sufficient high-quality evidence to pool.^2,3 Third, the foot condition and control ankle varied among the studies, and the effects of sampling/cut-off frequency, duration of trials, data preprocessing protocols were not explored due to the paucity of data. Although the previous studies indicated negligible effects of foot condition and leg dominance on static single-leg stance,^13,34 and the forest plots did not reveal impacts of these factors, further methodological studies should be conducted to confirm them in CAI. Fourth, descriptions and definitions of CoP outcomes were extremely varied and sometimes ambiguous among the studies and misclassification remains a risk even though we tried our best to categorize them. ⁵⁴ Fifth, we applied a broader definition of CAI than the IAC standards. We felt that our definition might give our conclusions better external consistency, but IAC standards are needed to allow comparisons among CAI studies.^16,25,70

Conclusion

Postural deficits during static single-leg stance in CAI patients may be evaluated by CoP trajectory, including higher SD of sway amplitude with open eyes and higher mean sway velocity with closed eyes. Further methodological explorations of CoP parameters and corresponding test conditions are needed to enhance the sensitivity and reliability of postural deficit assessments in CAI using force plates.