Association of core muscle strength and endurance with chronic ankle instability- A cross-sectional study

Abstract

Purpose

Chronic Ankle Instability (CAI) often leads to debilitating, long-term consequences, and deficits in core muscle strength and endurance may contribute to the persistence of CAI. The current study aims to investigate the association between core strength and endurance with CAI.

Methods

A total of 128 participants were enrolled, including 64 participants with CAI and 64 participants without instability. Ankle instability was evaluated using the Cumberland Ankle Instability Tool (CAIT). Core strength was assessed using a pressure biofeedback device, and endurance was assessed using the McGill Trunk Endurance Battery. Between group comparisons were conducted using the Mann–Whitney U test. Pearson correlation and multiple linear regression analyses were performed to identify key predictors of CAIT, including the interaction effects.

Results

The CAI group revealed significantly lower endurance in trunk flexors (p = 0.003, r = 0.31) and extensors (p = 0.011, r = 0.26). No significant difference was observed in core strength (p = 0.954). CAIT scores were significantly associated with left lateral flexor endurance (r = 0.28, p = 0.012). The regression model indicated that left lateral flexor endurance showed a trend towards significance (β = 0.074, p = 0.055), suggesting a potential association rather than a definitive predictive role. An interaction effect (p = 0.054) suggested that this relationship may differ by group.

Conclusion

Lateral trunk endurance may play a role in functional ankle stability. These findings suggest that incorporating core endurance training into rehabilitation programs for CAI may be beneficial; however, further research is required to confirm these relationships.

Keywords

chronic ankle instability ankle sprain core strength core endurance

Introduction

Chronic ankle instability (CAI) is considered one of the most prevalent conditions among athletes and physically active individuals.¹ Approximately 70% of individuals who experience an acute ankle sprain may develop CAI, suggesting a significant risk of long-term instability and disability following the initial injury.² CAI is characterized by recurrent episodes of ankle sprain and a persistent perception of instability, which can severely affect individuals’ physical activity performance and overall quality of life, including activities of daily living (ADLs).³ CAI’s complex and multifactorial nature highlights the critical need for comprehensive assessment and management strategies.⁴

Although the underlying pathomechanisms of CAI are complex, conventional models have primarily identified ligament laxity and proprioceptive deficits as peripheral contributors. However, recent evidence has emphasized that proximal impairments-such as deficits in core muscle strength may contribute to the development and persistence of CAI.^5,6 This paradigm shift aligns with kinetic chain theories, which postulate that insufficient trunk muscle strength can significantly affect lower limb mechanics, leading to recurrent injury and sensorimotor impairments.

Despite the growing research interest in exploring the relationship between core muscle strength and ankle injuries, the current literature presents conflicting evidence. Some studies have demonstrated a weak correlation between core strength and the presence of CAI in collegiate athletes.⁷ In contrast, other researchers have identified reduced core strength in female athletes with CAI when compared with healthy controls.⁸ Likewise, differences have also been observed in trunk flexor/extensor core endurance ratios and in endurance ratios between dominant and non-dominant lateral trunk flexor, as assessed using McGill’s core tests between athletes with and without CAI. However, the predominant focus of these studies was on the female athletic population, limiting the generalizability of the findings to male athletes or other populations.⁶

A recent quasi-experimental study suggests a potential therapeutic role of core muscle strengthening in individuals with CAI. An 8-week core stability training program has been shown to significantly improve ankle dorsiflexion range of motion, proprioception, and muscular torque in athletes with CAI.⁹ However, existing evidence in this domain has been constrained by small sample sizes, limited population diversity, and a predominant focus on intervention outcomes rather than on examining the underlying associations.^6–9

Currently, there is limited research exploring these associations in diverse, region-specific populations such as young Indian adults, who may present with variations in biomechanical patterns and physical activity levels. Furthermore, existing studies have primarily explored general core strength with inadequate focus on lateral trunk endurance which is an essential element for postural control and movement stability. Given the conflicting evidence in the current literature, the present study aims to determine the association between core muscle strength and endurance with CAI, as well as to compare the same between individuals with CAI and healthy control participants.

Materials and methods

The present analytical cross-sectional study was conducted in tertiary care hospitals connected to Kasturba Medical College, Mangalore and aimed to explore the association between core muscle strength and endurance with CAI. The study was approved by the Institutional Ethics Committee of Kasturba Medical College, Mangalore (IEC KMC MLR-01/2023/22) and was registered with the Clinical Trial Registry of India (CTRI/2023/08/056445). The study was conducted from January 2023 to January 2024.

The total sample size was determined to be 128 participants, comprising of 64 patients with CAI and 64 without, assuming a 95% confidence level (Z_1-α/2 = 1.96), 80% power (Z_1-β = 0.84), a pooled standard deviation (S) of 30, and a clinically significant difference (d) of 15. Patients with CAI were included in the study if they met all of the following criteria: age between 18 and 45; a history of at least one acute ankle sprain associated with inflammation and impaired physical activity; the most recent sprain occurring at least months prior to enrolment; at least two episode of giving way, recurrent sprains, or persistent feeling of ankle instability; and a Cumberland Ankle Instability Tool (CAIT) score of ≤24.¹⁰ A single previous ankle sprain without ongoing instability was not considered sufficient for inclusion in the study.

The control group participants were age matched with the cases and included if they had no history of previous ankle injury or sprain and a score of >24 on the CAIT. Exclusion criteria for both groups included history of previous surgeries involving lower extremity musculoskeletal system (bone, ligaments, and/or nerve injury); any acute lower limb injury (sprain, strain, or fracture) within the past 3 months; abdominal surgery or hernia repair within the last 8 weeks, or a history of hypertension, cardiac issues, or hernia.

The study participants were recruited using convenience sampling method. Patients with CAI were identified and screened based on the predefined eligibility criteria. Bystanders of the cases with CAI were approached and screened for inclusion into the control group. All the study participants were informed about the purpose of the study and a written informed consent was obtained before enrolment. Demographic data were collected from all the study participants, and the clinical assessment was conducted by a qualified physiotherapist. Strengthening the Reporting of Observational studies in epidemiology (STROBE) flowchart of the study subjects is shown in Figure 1.

Figure 1.

STROBE flow chart of study participants.

Outcome measures

Self-reported ankle instability was evaluated using the CAIT.¹⁰ Core muscle strength was assessed using a pressure biofeedback unit,¹¹ while core muscle endurance was assessed using McGill’s torso endurance test battery.¹² The evaluation order was randomized using simple randomization technique (chit method) to minimize the influence of one assessment over another.

1. Core muscle strength assessment

Participants were positioned in prone position, with feet off the plinth and with their arms beside the trunk. The lower edge of the inflatable cell was positioned in the centre of the abdomen at the level of the anterior superior iliac spines (ASIS) (Figure 2(a)). The individuals were shown how to perform an abdominal drawing-in movement to selectively contract their Transverse Abdominus. The cuff was inflated to a baseline pressure of 70 mm Hg and changes in the pressure readings were recorded (Figure 2(b)). Readings were taken at the beginning and end of a 10-s contraction (timed using a stopwatch), over three consecutive contractions. Participants were divided into two groups based on the mean value obtained. 4–10 mmHg was considered good core strength and anything below four was considered as poor core strength.

2. Core muscle endurance assessment

Figure 2.

(a) and (b). Core strength assessment using a pressure biofeedback device.

McGill’s torso endurance test battery

Standardized testing protocols were followed for each of the test battery components to assess core muscle endurance. This test battery includes three components: the trunk flexor endurance test, the trunk lateral flexor endurance test, and the trunk extensor endurance test.

(A) Trunk flexor endurance test

The participant was seated with the hips and knees bent to 90° (aligning the hips, knees, and second toe), leaning against a board positioned at a 60-degree incline with their arms crossed over the chest (Figure 3). The support was moved back by 10 cm, and they were asked to hold this position for as long as possible, with the duration of the hold being noted. Deviation from the neutral spine, such as the shoulders rounding or an increase in the low-back arch indicates termination of the test.

Figure 3.

Trunk flexor endurance test.

(B) Trunk lateral endurance test

The participant was on his or her side with extended legs, aligning the feet in a tandem position (heel-to-toe). The hip was lifted off the ground, with both the legs extended and with the elbow of the lower arm positioned directly under the shoulder using the forearm to support the body (Figure 4). The duration of hold was noted and any deviation such as hips dropping downward or shifting forward or backward to maintain balance will result in termination.

Figure 4.

Lateral endurance test.

(C) Trunk extensor endurance test

The participant was in prone position with the iliac crests at the edge of the table and the lower legs anchored with either a strap or the body weight of the examiner (Figure 5). Duration of hold was noted and if the chest falls below horizontal the test was terminated.

Figure 5.

Trunk extensor endurance test.

Statistical analysis

All analyses were performed using IBM SPSS Statistics (Version 29.0) and R (Version 4.3.1), with statistical significance set at p < 0.05. Categorical variables were summarized using frequencies and percentages. Continuous data were assessed for normality; normally distributed data were reported as mean ± standard deviation (SD), and non-normally distributed data as median and interquartile range (IQR). Group comparisons for categorical variables were conducted using the Chi-square test, while the Mann–Whitney U test was used for non-normally distributed continuous variables. Effect sizes for group differences were reported using rank-biserial correlation (r). Pearson’s correlation coefficients were calculated to examine associations between CAIT scores and core variables and visualized in a heatmap. Furthermore, a multiple linear regression model was developed to assess whether core strength and endurance predicted CAIT scores, with model fit assessed using R² and adjusted R². Multicollinearity was evaluated using variance inflation factors (VIF). An interaction term (Group × Left Lateral Flexor Endurance) was added to explore whether group status moderated the association. Group was coded as 1 = CAI and 0 = Control.

Results

A total of 128 participants were included in the study, with 64 participants each in the CAI group and the control group. The mean age of participants in the CAI group was 22.73 ± 1.93 years and in the control group was 21.89 ± 1.69 years. Among the 128 participants, females comprised 78.1% of the CAI group and 70.3% of the control group. In the CAI group 40 participants (62.5%) reported instability on the right ankle, while 24 participants (37.5%) reported it on the left ankle. Table 1 summarizes the baseline demographic and clinical characteristics of both groups.

Table 1.

Demographic and clinical characteristics of participants.

Variable	Experimental group (n = 64)	Control group (n = 64)
Age (years)	22.73 ± 1.93	21.89 ± 1.69
Gender (female)	50 (78.1%)	45 (70.3%)
Gender (male)	14 (21.9%)	19 (29.7%)
Affected leg (right)	40 (62.5%)	0 (0.0%)
Affected leg (left)	23 (35.9%)	0 (0.0%)
CAIT score	17.09 ± 5.22	28.28 ± 1.52
Core strength value (mmHg)	3.64 ± 1.68	5.86 ± 8.06
Core strength (good)	28 (43.8%)	27 (42.2%)
Core strength (poor)	36 (56.2%)	37 (57.8%)
Core endurance - flexors (sec)	117.72 ± 76.85	177.09 ± 125.63
Core endurance - extensors (sec)	66.48 ± 33.69	87.72 ± 44.42
Core endurance - right LF (sec)	42.95 ± 30.46	48.05 ± 26.89
Core endurance - left LF (sec)	41.25 ± 25.16	49.95 ± 28.38

Values are presented as mean ± standard deviation (SD) for continuous variables and number (percentage) for categorical variables. CAIT: Cumberland ankle instability tool. *LF: lateral flexor; right LF and left LF refer to trunk lateral flexor endurance (in seconds) on the right and left sides, respectively.

Group comparisons of core strength and endurance

Table 2 demonstrates the findings of the Mann–Whitney U test analysis comparing core strength and endurance variables between the CAI and control groups. Notably, trunk flexor endurance (p = 0.003, r = 0.31) and extensor endurance (p = 0.011, r = 0.26) were significantly lower in the CAI group, with moderate effect sizes. No significant differences were found in core strength (p = 0.954, r = −0.01). Left lateral flexor endurance approached statistical significance (p = 0.053, r = 0.20), suggesting a small effect. Group differences in core strength and endurance are summarized in Table 2 and illustrated in Figure 6.

Table 2.

Group comparison of core strength and endurance variables.

Measure	Case median (IQR)	Control median (IQR)	p-value	Effect size (r)
Core_Strength_Value	3.33 (2.00–4.83)	3.33 (2.00–5.50)	0.954	−0.01
Flexors	100.50 (65.75–160.25)	153.00 (80.00–219.75)	0.003	0.31
Extensors	64.50 (44.00–89.25)	79.00 (56.00–109.50)	0.011	0.26
Right_LF	37.50 (21.75–55.25)	41.00 (26.25–64.25)	0.120	0.16
Left_LF	35.00 (24.00–52.75)	46.50 (26.75–64.25)	0.053	0.20

Values are presented as median (interquartile range). Statistically significant values (p < 0.05) are presented in bold. p values computed using Mann–Whitney U test. Effect size are reported as rank-biserial correlation (r). An r value of 0.1–0.3 indicates a small effect, 0.3–0.5 a moderate effect, and >0.5 a large effect.

Figure 6.

Group-wise comparison of core strength and trunk endurance variables Boxplots compare chronic ankle instability (CAI) and control groups across five measures: (a) Core strength (mmHg) showed no significant difference, (b) Trunk flexor and (c) extensor endurance were significantly lower in the CAI group (p = 0.003 and p = 0.011, respectively). (d, e) Right and left lateral flexor endurance showed non-significant trends favouring controls. Plots include medians, interquartile ranges, and individual data points.

Regression analysis

As shown in Table 3 and visually depicted in Figure 7, CAIT scores were positively correlated with all core muscle measures, with the strongest bivariate correlations observed for left lateral flexor endurance (r = 0.28) and trunk extensor endurance (r = 0.28). Moderate inter-correlations were also noted among predictor variables, especially between right and left lateral flexors (r = 0.79) and between left lateral flexors and extensors (r = 0.53), suggesting potential shared neuromuscular control mechanisms.

Table 3.

Summary of correlation and regression analysis for CAIT score.

Predictor	Pearson r	β coefficient	p-value (β)	VIF
Core strength	0.20	0.039	0.734	1.39
Trunk flexors	0.23	0.009	0.135	1.34
Trunk extensors	0.28	0.022	0.203	1.55
Right lateral flexors	0.18	−0.041	0.216	2.74
Left lateral flexors	0.28	0.074	0.055	3.23

Pearson r represents the strength of the bivariate correlation between each core variable and the CAIT score. β Coefficients, p-values, and VIFs are derived from the multiple linear regression model predicting CAIT score.

Figure 7.

Pearson correlation matrix of CAIT score and core muscle variables CAIT score showed positive correlations with all core measures, with the strongest associations observed for left lateral flexor (r = 0.28) and extensor endurance (r = 0.28). High inter-correlations were noted between lateral flexors (r = 0.79) and between extensors and left lateral flexors (r = 0.53). Warmer colours indicate stronger correlations (Pearson’s r).

A multiple linear regression model was subsequently constructed to assess the combined influence of these variables on the CAIT score. The overall model was statistically significant (F (5,122) = 3.67, p = 0.004), explaining 13.1% of the variance (adjusted R² = 0.095). Among all predictors, only the left lateral flexor endurance approached significance in predicting CAIT score (β = 0.074, p = 0.055), suggesting a potential association with ankle instability severity rather than a definitive predictive role. All variance inflation factors (VIFs <3.5) indicated acceptable levels of multicollinearity. These findings suggest that while CAIT score shares weak-to-moderate linear relationships with multiple core variables, left-sided lateral core endurance may play a more prominent role in explaining functional ankle stability outcomes.

Although a greater proportion of participants reported right-sided ankle instability, the association with trunk endurance was observed for the left lateral flexors. This asymmetry may reflect proximal compensatory neuromuscular adaptations rather than a strictly side-matched trunk response.¹³

In addition, an interaction model was constructed to examine whether the association between left lateral flexor endurance and CAIT score differed by group (CAI vs control) (Table 4). The overall model was statistically significant (F (4,123) = 76.76, p < 0.001), with an adjusted R² of 0.705, indicating strong explanatory power. The main effect of the group was highly significant (β = −13.16, p < 0.001), confirming that individuals in the CAI group had substantially lower CAIT scores. The interaction term (Group × Left Lateral Flexor Endurance) approached statistical significance (β = 0.052, p = 0.054), suggesting a trend towards a stronger positive relationship between lateral flexor endurance and ankle function in the CAI group compared to controls. Neither core strength nor left lateral flexor endurance alone were significant when controlling for interaction effects. These findings suggest that group membership may moderate the relationship between core endurance and ankle stability, emphasizing the need for group-specific interpretation in clinical rehabilitation planning.

Table 4.

Interaction effect model predicting CAIT score.

Predictor	β coefficient	Standard error	t-value	p-value
Intercept	25.0385	0.9510	26.3200	<0.001
Core strength	0.0039	0.0397	0.1000	0.917
Left lateral flexor endurance	−0.0109	0.0291	−0.3800	0.707
Group (1 = CAI, 0 = control)	−13.1623	1.3594	−9.6800	<0.001
Group × left lateral flexor	0.0523	0.0269	1.9500	0.054

Model statistics: Adjusted R² = 0.705, F (4,123) = 76.76, p < 0.001. Group is coded as 1 = CAI, 0 = control. The interaction term (group × left lateral flexor endurance) examines whether the relationship between endurance and CAIT score differs by group.

Discussion

The present cross-sectional study investigated the relationship between core muscle strength and endurance with chronic ankle instability in a cohort of young Indian adults. Although no significant group difference was found for core muscle strength between groups, the participants of the CAI group demonstrated lower endurance of trunk flexors and extensors compared to the healthy controls.

The regression analysis revealed a positive correlation between left lateral flexor endurance and CAIT scores, suggesting a possible association with CAIT scores compared to other core variables. The documented predominance of left lateral trunk flexor endurance, despite a higher proportion of right-sided ankle instability in the sample, may suggest compensatory neuromuscular adaptations within the kinetic chain.^13,14 During functional tasks, trunk musculature may contribute to postural stability and control of center of mass displacement within the kinetic chain framework.^15,16 Alternatively, this asymmetry may be influenced by limb dominance, movement strategies, or task-specific neuromuscular recruitment patterns.¹⁴ However, given the relatively small effect size and borderline statistical significance, this finding should be interpreted with caution.

The findings of the current study align with the kinetic chain model approach in the rehabilitation of musculoskeletal injuries.^15,16 According to this model, proximal segment function significantly contributes to distal joint stability. It can be postulated that the lateral trunk muscles may serve as mechanical constraints that stabilize the lumbopelvic region. This passive support, in turn, might ease the strain on the ankle and help maintain balance, which could explain their role in imparting neuromuscular control and mitigating the risk or severity of CAI.¹⁷

The present study findings indicate that lateral trunk endurance demonstrated a potential association with CAIT score aligning with existing evidence emphasizing the role of proximal compensations in individuals with CAI. Previous research has demonstrated that individuals with CAI exhibit a greater range of motion and higher angular velocity in the knee, hip, and torso during dynamic balance tasks, indicating that CAI affects not only the ankle but also the stability and movement strategies of proximal joints, including the trunk.¹⁴ In addition, trunk muscular impairments, such as decreased contractility of the transversus abdominis, have been documented in CAI populations, underscoring the role of core muscles in maintaining dynamic stability.¹³ These insights provide a deeper understanding of the mechanisms underlying CAI and the critical role of core muscle strength and endurance in its management.

The findings of correlation analysis revealed moderate positive relationships between CAIT scores and both trunk extensor and left lateral flexor endurance (r = 0.28). This aligns with Barati et al.'s research, which found significant correlations between trunk muscle endurance and static balance, emphasizing the crucial role of core muscle endurance in maintaining stability. Improved trunk muscle endurance, particularly in the lateral muscles, may contribute to better overall balance and potentially mitigate CAI. Analogous to the centre of gravity, the core operates as integrated functional units, reinforcing the significance of core endurance for optimal performance and injury prevention.¹⁸ Incorporating specific trunk endurance exercises into rehabilitation programs for individuals with CAI could enhance balance and reduce ankle instability.¹⁹

Interestingly, core strength showed no significant group differences or predictive value for CAIT scores. These findings challenge conventional assumptions that generalized core strength translates directly into distal joint control. Instead, our results highlight the role of dynamic and endurance-based trunk performance over static core strength measures. These findings are consistent with earlier research which showed that general core strength was not a significant predictor. In particular, the study found trunk muscle endurance significantly predicted static balance, suggesting that improving trunk muscle endurance could enhance distal joint control. Hence endurance-based assessment of core stability is more relevant than static core strength measures for functional movement and balance.¹⁸

The findings of non-significant group differences in core strength between individuals with and without CAI may be attributed to a combination of contextual and methodological factors. Given that, both groups primarily consisted of young, health-conscious physiotherapy and medical students and they were likely engaged in regular physical activity. This might have resulted in a higher baseline of core strength for participants of both groups, whereby the detection of a meaningful and clinical difference in core strength between groups is challenging.²⁰ Methodologically, core strength was measured using the abdominal drawing-in manoeuvre (ADIM) with pressure biofeedback, which required participants to maintain proper technique and control of their core muscles during testing. However, inconsistent activation of the transversus abdominis or poor posture may have contributed to the lack of significant group differences.²¹ Strength gains often reach a plateau, or ceiling effect, in individuals who are already physically active and fit, where further improvement is limited despite continued training or neuromuscular adaptation.^22,23 Taken together, these factors might likely contribute to the documented non-significant group differences in core strength.

Strengths and limitations

The strength of the studies lies in the detailed analysis including effect size reporting, multivariable modelling, and interaction analysis.^24,25 Also, reliable and valid assessments were established by using McGill’s endurance test battery and validated core strength tests.¹² The study’s limitations include a relatively small sample size, gender imbalances between groups, insufficient preparation time before testing, and potential fatigue due to successive contractions. Additionally, the cross-sectional design of the study prevents the establishment of a causal relationship between core endurance and ankle instability, and only an association can be identified.²⁶ Therefore, it remains unclear whether poor core endurance and strength contribute to the development of ankle instability or whether individuals with ankle instability tend to have weaker core function. Additionally, the usage of only static endurance tests may not reflect the dynamic control needed in athletic activities.^27,28 Future studies should consider longitudinal designs and dynamic assessments. An asymmetry between left and right lateral trunk endurance was observed, which may reflect compensatory mechanisms or statistical variability. This limits the internal validity of side-specific conclusions.

Clinical implications

The study findings reinforce the clinical relevance of lateral core endurance in the assessment and rehabilitation of individuals with CAI. Conventional rehabilitation programs for CAI primarily focus on balance and proprioception at the ankle level.²⁹ However, integrating lateral trunk endurance training into this framework could enhance proximal control and improve distal joint function. Lateral trunk endurance showed a potential association with CAIT scores, highlighting its possible relevance as a clinical marker. In addition, the documented interaction effects from this study may encourage clinicians to explore group-specific rehabilitation strategies, particularly in populations at high risk for recurrent ankle instability.

Conclusion

The study demonstrated the relevance of trunk muscle endurance, particularly, the role of lateral trunk endurance in individuals with chronic ankle instability. The documented association between core endurance measures and CAIT scores provides critical insight into the potential contribution of proximal factors to ankle function in individuals with chronic ankle instability. However, the side specific findings need to be interpreted with caution due to asymmetry and borderline statistical significance reported in this study. These study findings indicate that integrating core endurance training into rehabilitation programs for CAI may be advantageous. However, further research is required to confirm these relationships.

Footnotes

Acknowledgements

We would like to thank Manipal Academy of Higher Education and all the participants of this study. The authors acknowledge the use of ChatGPT (4.1) to assist in improving the grammar and readability of the manuscript, in compliance with ethical standards.

ORCID iD

Ashish John Prabhakar

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Trial registration

The study was registered with the Clinical Trial Registry of India (CTRI/2023/08/056445).

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29.

McKeon

Donovan

. A perceptual framework for conservative treatment and rehabilitation of ankle sprains: an evidence-based paradigm shift. J Athl Train 2019; 54(6): 628–638. https://doi.org/10.4085/1062-6050-474-17