Plantarflexion and frontal-plane ankle strength are associated with dynamic balance in youth male soccer athletes: a cross-sectional study

Abstract

Background

Ankle strength is essential for dynamic stability and athletic performance. However, its specific relationship with commonly used functional tests remains underexplored in youth athletes. Understanding these associations may inform more targeted training approaches and injury prevention strategies. This study aimed to investigate whether isokinetic ankle strength is associated with performance in three widely used functional tests, the Modified Star Excursion Balance Test, the Side Hop Test, and the Weight-Bearing Lunge Test, in youth male soccer players.

Methods

Twenty-six male soccer players (mean age: 18.56 ± 0.61 years) underwent isokinetic strength assessments, including plantarflexion, dorsiflexion, inversion, and eversion, and performed the Modified Star Excursion Balance Test, the Side Hop Test, and the Weight-Bearing Lunge Test. Limb symmetry was confirmed through paired t-tests, allowing the use of bilateral averages. Pearson correlation coefficients and Least Absolute Shrinkage and Selection Operator regression models were applied to examine associations and predictive capacity.

Results

Significant correlations were found between plantarflexion, inversion, and eversion torque and performance in the Modified Star Excursion Balance Test, with the strongest associations observed for the posteromedial, posterolateral, and composite scores (r = 0.70–0.81, p < 0.001). Performance in the Weight-Bearing Lunge Test was positively associated with plantarflexor torque (correlation coefficient = 0.54, p = 0.004), while dorsiflexor strength showed no significant correlation (p = 0.172). LASSO regression models retained plantarflexor torque (β = 0.078) and frontal-plane torques (inversion: β = 0.054; eversion: β = 0.028) as variables associated with the mSEBT composite score. For the Weight-Bearing Lunge Test, plantarflexor (β = 2.078) and dorsiflexor torque (β = − 0.463) were retained as variables associated with dorsiflexion angle. No strength variables were retained in the model explaining variance in Side Hop Test performance.

Conclusion

Ankle strength, particularly in plantarflexion and frontal-plane movements, plays a key role in dynamic balance and mobility but appears to be less associated with agility-focused tasks such as the Side Hop Test. These findings support the incorporation of strength training targeting multiplanar ankle control and highlight the importance of neuromotor training to enhance agility in youth athletes.

Background

Ankle function is a critical component of athletic performance, especially in youth athletes involved in sports that demand cutting maneuvers, jumping, and rapid changes of direction. During adolescence, ongoing musculoskeletal development, particularly the enhancement of ankle strength and stability, plays a pivotal role not only in optimizing athletic performance but also in reducing the risk of future injuries. Previous studies have highlighted the importance of targeted strength and balance training in improving ankle function and overall physical performance in young athletes [1, 2]. Additionally, recent evidence demonstrates that ankle dorsiflexion range of motion is directly associated with sprinting and jumping performance in young athletes, reinforcing the functional relevance of ankle mobility for sport-specific tasks during youth athletic development [3].

Ankle strengthening through resistance exercises, proprioceptive training, and isokinetic interventions has been shown to improve muscle performance and reduce the risk of injuries such as ankle sprains [4–6]. Isokinetic dynamometry provides a reliable and objective assessment of muscular strength across key ankle movements, including dorsiflexion, plantarflexion, inversion, and eversion. It may serve as a reference standard for evaluating the muscular readiness of athletes [7]. Moreover, deficits in ankle strength have been consistently associated with chronic ankle instability, impaired postural control, and reduced functional capacity in both athletic and clinical populations [8, 9].

The modified Star Excursion Balance Test (mSEBT) is a practical field-based assessment and a widely validated measure of dynamic postural control, with standardized procedures established by the consensus review of Gribble et al. [10]. Alongside the mSEBT, other practical field-based assessments, such as the Side Hop Test and the Weight-Bearing Lunge Test, are commonly employed to evaluate dynamic balance, agility, and ankle mobility [11, 12]. These tests are low-cost and time-efficient, with increasing relevance for performance monitoring, injury risk screening, and rehabilitation in athletic populations [13]. Nevertheless, despite their widespread use, the extent to which performance on these tests reflects underlying ankle muscle strength, particularly among youth athletes, remains insufficiently explored.

Previous research has suggested that dynamic balance is influenced by age, biological maturation, and sport-specific training exposure [14, 15]. Moreover, the integration of proprioceptive and strength-based interventions has demonstrated improvements in performance on dynamic balance tests, reinforcing the relevance of ankle muscle strength in functional assessments [2, 16]. Studies have also demonstrated that invertor and evertor strength may be especially important for maintaining frontal plane control, which is critical during high-demand functional tasks [17, 18].

Youth soccer athletes represent a population with particularly high relevance for investigating ankle strength and functional performance. During adolescence, soccer participation involves frequent sprinting, cutting, single-leg landings, and rapid changes of direction, all of which place substantial mechanical demands on the ankle–foot complex. Previous research has shown that ankle dorsiflexion mobility, plantarflexor capacity, and frontal-plane control are associated with sprint speed, change-of-direction ability, and lower-limb alignment in youth soccer players [12, 16]. Moreover, ankle sprains are among the most common injuries in this cohort, and deficits in strength, proprioception, and dynamic balance are well-established contributors to injury risk [6, 9]. These factors justify the importance of examining how ankle muscle strength relates to functional performance specifically in youth soccer athletes.

Despite the widespread use of the Modified Star Excursion Balance Test, the Side Hop Test, and the Weight-Bearing Lunge Test in athletic monitoring and rehabilitation, their specific relationship with isokinetic ankle strength has not been systematically examined in youth soccer athletes. To our knowledge, no previous study has simultaneously investigated whether strength in multiple ankle planes, plantarflexion, dorsiflexion, inversion, and eversion, is associated with performance across these three widely used functional tests within this athletic population. This gap limits the ability of clinicians and coaches to infer underlying neuromuscular capacities from accessible field-based assessments.

Therefore, the aim of this pilot cross-sectional study was to examine the associations between isokinetic ankle strength and performance on the Modified Star Excursion Balance Test, the Side Hop Test, and the Weight-Bearing Lunge Test in youth male soccer athletes. To date, no study in youth soccer athletes has jointly examined isokinetic ankle strength in four planes together with performance in the mSEBT, Side Hop Test, and Weight-Bearing Lunge Test, nor applied LASSO regression to identify the most relevant predictors among these variables. We hypothesized that plantarflexion and frontal-plane strength (inversion and eversion) would show stronger associations with dynamic balance tasks, whereas dorsiflexor strength would demonstrate weaker relationships, and agility performance (Side Hop Test) would be less dependent on isolated ankle strength.

Methods

Study design

This cross-sectional study was approved by the Human Research Ethics Committee of the Santa Catarina State University (CAAE: 64790922.7.0000.0118), in accordance with the Declaration of Helsinki, and was conducted at the Center for Health and Sports Education. All procedures were performed in a single session under standardized environmental and methodological conditions to minimize variability and ensure consistency in data collection.

Participants

Twenty-six male youth soccer athletes aged between 18 and 20 years, recruited from a professional-level training program, voluntarily participated in the study. Eligibility criteria required participants to have at least two years of competitive soccer experience and to engage in a minimum of eight hours of training per week. Athletes were excluded if they had sustained any lower limb injury within the preceding six months, undergone orthopedic surgery involving the lower extremities, reported pain during assessment, or were unable to complete all testing procedures. Additional exclusion criteria included any known neurological, vestibular, or metabolic conditions that could impair balance or muscle function.

Data collection procedures

Upon arrival at the laboratory, athletes completed a structured demographic assessment during which age, height, body mass, and dominant lower limb (defined as the preferred kicking leg) were recorded. Each participant’s field position, defender, midfielder, or forward, was also documented. Before any procedures were conducted, participants signed both the Free and Informed Consent Form and the Consent Form for Photographs, Videos, and Recordings. Informed consent was obtained from all individuals included in the study, ensuring that they were fully aware of the research procedures and their rights. After the functional and strength assessments, we verified whether dominant and non-dominant limbs differed across all bilateral variables. Paired t-tests were conducted for the Side Hop Test, all mSEBT directions, the Weight-Bearing Lunge Test, and all isokinetic torque measures. No significant differences were found for any variable (all p > 0.05). Based on this verification, bilateral averages were used in all subsequent correlation and regression analyses.

Participants subsequently performed a standardized warm-up consisting of five minutes of cycling at a cadence of 60 ± 5 revolutions per minute, with the workload adjusted to one watt per kilogram of body weight, following established protocols to ensure physiological readiness prior to neuromuscular testing [19].

Functional performance testing commenced with the Modified Star Excursion Balance Test, which evaluates dynamic postural control [10, 20]. The mSEBT was performed according to the standardized procedures and recommendations described by Gribble et al. (2012) [19], who established consensus guidelines for its administration and interpretation. Previous research has shown that the mSEBT has excellent reliability, with intra- and inter-rater ICC values generally between 0.83 and 0.96 across all directions [21]. Athletes performed three trials in each of the anterior, posteromedial, and posterolateral directions for each limb, with reach distances normalized to leg length. The average of the three valid trials in each direction was used for analysis (Fig. 1). A rest interval of 120 s was provided between maximal attempts within the mSEBT. Additionally, a 300-s (5-min) rest period was allowed between the mSEBT, the Side Hop Test, and the Weight-Bearing Lunge Test to account for the transition time required for explanation, demonstration, and setup of each test, ensuring adequate recovery. Subsequently, athletes completed the Side Hop Test, a functional agility task that involves rapid lateral movements (Fig. 2).

Fig. 1.

Application of the Modified Star Excursion Balance Test

Fig. 2.

Side Hop Test setup and execution

Each participant performed 28 consecutive lateral hops on one leg over a 30-cm line. Following the rationale described in previous studies examining the Side Hop Test, where initial and final hops are often excluded to minimize the impact of acceleration and deceleration phases [11, 22]. The Side Hop Test demonstrates excellent convergent validity (ICC = 0.93–1.00) and excellent reliability, with reported intra- and inter-rater ICC values ranging from 0.92 to 1.00 [23]. We recorded the time from hops 4 through 24. Although this specific hop-count window represents an adaptation of prior protocols rather than a direct replication, it follows the established principle of analyzing the middle section of the trial to improve measurement consistency and reduce performance variability.

Following the agility tests, ankle dorsiflexion range of motion was assessed using the Weight-Bearing Lunge Test. During this test, athletes stood facing a wall with one foot positioned in a lunge stance and advanced the knee forward until maximum tibial inclination was reached without heel lift. Tibial inclination was measured in degrees using a digital inclinometer application (Measure App, Apple iPhone 13) positioned along the tibial shaft, and the highest value obtained from three valid trials was recorded for each limb (Fig. 3) [24, 25]. The Weight-Bearing Lunge Test has demonstrated good inter- and intra-rater reliability, with reported ICC values ranging from 0.80–0.99 and 0.65–0.99, respectively [26].

Fig. 3.

Application of the Weight-Bearing Lunge Test

All functional tests were administered by the same examiner using standardized protocols to minimize measurement variability. Familiarization trials were submaximal and intended only to ensure correct technique; therefore, they were not suitable for calculating intra-rater reliability within this study.

Ankle muscle strength was assessed using an isokinetic dynamometer (Biodex System 4 Pro, Biodex Medical Systems, Shirley, NY, USA). The velocity of 30°/s was selected because it is widely used for assessing peak concentric torque of the ankle musculature, providing a reliable measure of maximal force production with minimal momentum contribution. This angular velocity has demonstrated excellent test–retest reliability for dorsiflexion, plantarflexion, inversion, and eversion [27, 28] and is commonly adopted in studies evaluating ankle strength in athletic populations. Each athlete performed five submaximal familiarization repetitions followed by five maximal efforts for each movement. The highest peak torque value from each movement was selected and normalized to body weight, being expressed as peak torque/body weight percentage (%BW), to allow for interindividual comparison. Participants were positioned seated with the hip at approximately 85–90° of flexion and the knee at 30° of flexion. The trunk, pelvis, and tested limb were stabilized using straps to minimize compensatory movements. The foot was secured to the dynamometer footplate, and the rotational axis of the dynamometer was carefully aligned with the anatomical axes of the talocrural joint for dorsiflexion and plantarflexion, and the subtalar joint for inversion and eversion (Fig. 4). These standardized procedures ensured consistent positioning across all strength measurements.

Fig. 4.

Isokinetic dynamometry assessment – Biodex™ System 4 Pro

The sequence of assessments was fixed as follows: Modified Star Excursion Balance Test, Side Hop Test, Weight-Bearing Lunge Test, and isokinetic strength testing. This order was established to minimize fatigue effects on strength performance and to ensure that neuromuscular assessments were conducted prior to high-intensity efforts.

Statistical analysis

All statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS) version 20.0 (IBM Corp., Chicago, IL, USA) and R version 4.3. Descriptive statistics, including means and standard deviations, were calculated for all continuous variables, while categorical variables were presented as absolute and relative frequencies. The Shapiro–Wilk test was employed to assess the normality of data distributions. Depending on the distribution, appropriate parametric or nonparametric tests were applied for group comparisons. Because no significant differences were found between dominant and non-dominant limbs in any bilateral measure (all p > 0.05), bilateral averages were used in the correlation and regression analyses.

Pearson correlation coefficients were calculated to examine linear associations between isokinetic ankle strength variables, dorsiflexion angles measured by the Weight-Bearing Lunge Test, and functional performance outcomes from the Side Hop Test and Modified Star Excursion Balance Test. To further explore the relationships between strength and mobility variables, a Least Absolute Shrinkage and Selection Operator regression model was constructed using the glmnet package in R. The model included normalized peak torque values for dorsiflexion, plantarflexion, inversion, and eversion, dorsiflexion range of motion from the Weight-Bearing Lunge Test, and athlete field position (dummy-coded). Ten-fold cross-validation was used to select the optimal penalty parameter (λ), and standardized beta coefficients were interpreted to assess the relative contribution of each variable. Statistical significance was set at p < 0.05 for all analyses.

A post hoc sensitivity analysis was performed using G*Power (version 3.1.9.7, Düsseldorf, Germany) for correlation models. With a sample size of 26 athletes, α = 0.05, and power (1 − β) = 0.80, the minimal detectable effect size was r ≈ 0.52. This indicates that the study was sufficiently powered to detect moderate to strong associations, consistent with the effect sizes observed in our findings.

Results

Sample characteristics

A total of 26 male youth soccer athletes (mean age: 18.56 ± 0.61 years) participated in the study (Table 1). No significant differences were observed between limbs for any variable, including performance on the Side Hop Test, all directions of the Modified Star Excursion Balance Test, the Weight-Bearing Lunge Test, and all isokinetic strength parameters (p > 0.05). As a result, bilateral averages were used in all subsequent analyses to represent overall functional capacity.

Table 1.

Participant characteristics and functional test results

Variable	Mean ± SD	95% CI (lower – upper)
Age (years)	18.56 ± 0.61	(18.31–18.81)
Body mass (kg)	74.38 ± 6.59	(71.72–77.04)
Height (cm)	180.26 ± 6.69	(177.56–182.97)
Years of training	6.38 ± 3.20	(5.09–7.67)
Weight-Bearing Lunge Test (°)	41.96 ± 7.32	(39.00–44.92)
Side Hop Test (s)	7.85 ± 1.64	(7.19–8.51)
mSEBT Anterior (LL ratio)	0.59 ± 0.12	(0.54–0.64)
mSEBT Posterolateral (LL ratio)	0.96 ± 0.18	(0.89–1.03)
mSEBT Posteromedial (LL ratio)	0.95 ± 0.19	(0.87–1.03)
mSEBT Composite (LL ratio)	0.83 ± 0.16	(0.77–0.89)
Plantarflexion peak torque/BW (%)	125.69 ± 30.41	(113.41–137.97)
Dorsiflexion peak torque/BW (%)	47.16 ± 16.64	(40.44–53.88)
Eversion peak torque/BW (%)	44.90 ± 9.52	(41.05–48.75)
Inversion peak torque/BW (%)	43.71 ± 9.84	(39.74–47.68)

Caption: SD standard deviation, CI confidence interval, kg kilogram, cm centimeter, s seconds, LL limb length, mSEBT Modified Star Excursion Balance Test, PL posterolateral directions, PM posteromedial directions, p statistical value

The average time to complete the Side Hop Test was 7.85 ± 1.64 s, while the mean dorsiflexion range of motion, as measured by the Weight-Bearing Lunge Test, was 41.96 ± 7.32 degrees. The bilateral mean peak torques, expressed as peak torque/body weight percentage (%BW), were 125.69 ± 30.41% for plantarflexion, 47.16 ± 16.64% for dorsiflexion, 44.90 ± 9.52% for eversion, and 43.71 ± 9.84% for inversion. For the Modified Star Excursion Balance Test, the reach distances normalized to limb length were 0.59 ± 0.12 in the anterior direction, 0.96 ± 0.18 in the posterolateral direction, and 0.95 ± 0.19 in the posteromedial direction, with a composite score of 0.83 ± 0.16.

Correlations between ankle strength and functional performance

Pearson correlation analyses were performed between isokinetic ankle strength (bilateral means) and performance outcomes in the Side Hop Test, Weight-Bearing Lunge Test, and Modified Star Excursion Balance Test (Fig. 5). Results showed distinct association patterns for each test.

Fig. 5.

Correlations (r) and p-values between functional tests and isokinetic torque. Caption: WBLT = Weight-Bearing Lunge Test; SHT = Side Hop Test; mSEBT = Modified Star Excursion Balance Test; BW = body weight; %BW = peak torque normalized to body weight percentage; PL = posterolateral directions; PM = posteromedial directions; INV = inversion; EV = eversion; DF = dorsiflexion; PF = plantarflexion; p = statistical value

For the Side Hop Test, moderate positive correlations were observed with most ankle strength variables, including plantarflexion (r = 0.52), eversion (r = 0.48), inversion (r = 0.47), and dorsiflexion (r = 0.39). Since higher Side Hop Test times indicate poorer performance, these positive correlations suggest that greater ankle strength does not necessarily translate into better agility, underscoring the potential influence of neuromotor factors such as coordination and rhythm.

In the Weight-Bearing Lunge Test, only plantarflexor strength demonstrated a meaningful association with dorsiflexion range of motion (r = 0.54), while correlations for eversion, inversion, and dorsiflexion strength were weak (r ≤ 0.24), with dorsiflexion torque showing no relevant association (r = –0.09). These findings suggest that plantarflexor control may play a more prominent role than dorsiflexor strength in facilitating forward tibial progression during weight-bearing dorsiflexion.

Regarding the Modified Star Excursion Balance Test, moderate to strong positive correlations were observed between ankle strength and reach distances across all directions. Plantarflexion strength exhibited the strongest associations, with correlation coefficients of r = 0.81 (anterior), r = 0.77 (posterolateral), r = 0.78 (posteromedial), and r = 0.77 for the composite score. Eversion strength was also significantly correlated with anterior (r = 0.62), posterolateral (r = 0.78), posteromedial (r = 0.71), and composite (r = 0.73) reach distances. Similarly, inversion strength was associated with anterior (r = 0.61), posterolateral (r = 0.74), posteromedial (r = 0.70), and composite (r = 0.73) scores. In contrast, dorsiflexion strength showed weaker correlations across all directions of the Modified Star Excursion Balance Test (r ≈ 0.30–0.35).

These results highlight the relevance of plantarflexor and frontal-plane (inversion and eversion) strength in supporting dynamic balance performance, particularly in the posterolateral and posteromedial directions, which are mechanically more demanding and require greater neuromuscular control.

LASSO regression models

Least Absolute Shrinkage and Selection Operator regression was applied to determine which ankle strength variables, based on bilateral average torque, best explained variance in performance on the functional tests (Table 2).

Table 2.

Least Absolute Shrinkage and Selection Operator regression models for functional test outcomes

Outcome	Predictor	Coefficient (β)	Selected by LASSO?
WBLT	PF	2.078	✓
WBLT	DF	−0.463	✓
WBLT	EV	−0.0
WBLT	INV	0.0
SHT	PF	0.0
SHT	DF	0.0
SHT	EV	0.0
SHT	INV	0.0
mSEBT Anterior	PF	0.076	✓
mSEBT Anterior	DF	0.0
mSEBT Anterior	EV	0.003	✓
mSEBT Anterior	INV	0.03	✓
mSEBT Composite	PF	0.078	✓
mSEBT Composite	DF	0.0
mSEBT Composite	EV	0.028	✓
mSEBT Composite	INV	0.054	✓

Caption: LASSO Least Absolute Shrinkage and Selection Operator, WBLT Weight-Bearing Lunge Test, SHT Side Hop Test, mSEBT Modified Star Excursion Balance Test, INV inversion, EV eversion, DF dorsiflexion, PF plantarflexion

Regarding the Side Hop Test, none of the ankle strength variables were retained in the regression model after penalization, reinforcing the notion that performance in this test is more closely influenced by neuromotor control, coordination, and dynamic balance rather than by isolated ankle muscular strength.

For the Weight-Bearing Lunge Test, two variables were retained in the model: plantarflexion strength (β = + 2.08), which was positively associated with dorsiflexion range of motion, and dorsiflexion strength (β = –0.46), which showed a negative association. These results suggest that greater plantarflexor strength is positively associated with tibial excursion through improved eccentric control, whereas higher dorsiflexor torque may reflect a compensatory or antagonistic mechanism that limits range of motion.

In the case of the Modified Star Excursion Balance Test, strength variables were retained for the anterior direction and the composite score. For the anterior direction, plantarflexion (β = + 0.076), eversion (β = + 0.003), and inversion (β = + 0.030) were retained. The composite score was predicted by plantarflexion (β = + 0.078), eversion (β = + 0.028), and inversion (β = + 0.054). Collectively, these findings confirm that plantarflexor torque is consistently associated with dynamic balance performance, particularly when considered alongside frontal-plane torque contributions from the evertor and invertor muscle groups.

Discussion

The interrelationship between ankle isokinetic torque and functional performance is particularly evident in youth soccer athletes, especially in tasks involving dynamic balance and mobility. The present findings indicate that plantarflexion and frontal-plane torques (inversion and eversion) are strongly associated with performance in the Modified Star Excursion Balance Test, particularly in the posterolateral and posteromedial directions, which demand considerable neuromuscular control and the ability to shift weight effectively.

Dynamic balance

The results are consistent with previous studies indicating that targeted ankle strengthening can enhance dynamic balance, including performance on the Modified Star Excursion Balance Test, in both athletic and clinical populations [29, 30]. Recent investigations in youth soccer athletes have shown that ankle muscle strength contributes meaningfully to multiple performance-related tasks, including balance, sprint acceleration, unilateral landing control, and change-of-direction performance [31–33]. Studies involving adolescent soccer players also indicate that deficits in plantarflexion and frontal-plane ankle strength are associated with poorer dynamic balance and altered lower-limb biomechanics during sport-specific tasks [34, 35]. Additionally, research has demonstrated that youth soccer athletes often present rapid neuromuscular development during late adolescence, making ankle strength particularly relevant for performance monitoring and injury-risk mitigation in this cohort [36, 37]. These findings reinforce the importance of examining ankle strength in youth soccer players and provide context for interpreting the associations observed in the present study.

While dorsiflexion is commonly emphasized in both performance and injury-prevention paradigms, its isokinetic strength showed weaker and sometimes negative associations with balance and mobility metrics in our study. This supports findings from Jo & Kim (2022) [38] and Moreno-Pérez et al. (2019) [39], who argue that dorsiflexor strength contributes more significantly to gait and landing mechanics than to isolated balance performance. Our Least Absolute Shrinkage and Selection Operator regression also retained dorsiflexor torque as a negatively associated variable in the Weight-Bearing Lunge Test performance, reinforcing the biomechanical interpretation that eccentric plantarflexor control plays a more critical role in forward tibial translation during lunge-type tasks [40, 41]. One possible explanation is that athletes with stiffer or stronger dorsiflexors may rely on different movement strategies during the WBLT, limiting anterior tibial translation even when greater range of motion is mechanically possible. Technical execution, familiarity with the movement, and compensatory patterns may also contribute to this inverse association. Additionally, dorsiflexor torque may play a more prominent role in gait and landing mechanics rather than in controlled forward-lean tasks such as the WBLT. Although plantarflexion torque emerged as a positive predictor of dorsiflexion range of motion in the WBLT, this finding should be interpreted carefully. The WBLT is a quasi-static test of maximum weight-bearing dorsiflexion and does not directly reflect eccentric plantarflexor control. Therefore, this unexpected association likely represents a non-causal relationship influenced by individual movement strategies, neuromuscular coordination, or other unmeasured variables such as calf flexibility, ankle joint morphology, or habitual loading patterns. These factors may enable certain athletes to achieve greater anterior tibial translation despite higher plantarflexor strength. We explicitly acknowledge that this association is correlational and not mechanistic, and future studies incorporating muscle–tendon extensibility and dynamic biomechanical analyses are needed to clarify the underlying factors contributing to WBLT performance.

Eversion and inversion torque emerged as consistent variables associated with dynamic balance, particularly in mediolateral control during the Modified Star Excursion Balance Test. These findings echo the work by Isbilir et al. (2015) [42], Lee & Park (2020) [43] and Yoon et al. (2022) [44], who emphasized the role of frontal-plane muscle control in stabilizing the ankle during dynamic tasks. Furthermore, Cao et al. (2019) [45] and Chimera & Larson (2021) [46] suggest that inadequate frontal-plane torque increases the risk of losing postural stability, especially in high-demand sports such as soccer.

Agility

Conversely, agility performance measured by the Side Hop Test revealed a weaker connection with ankle strength metrics. Our regression analysis did not retain any ankle torque variables as predictors of Side Hop Test time, supporting the interpretation that agility performance may be more closely related to neuromotor coordination, reaction time, and rhythm than on isolated ankle muscle strength [47, 48]. This aligns with findings by Sekulić et al. (2014) [49] and Spiteri et al. (2014) [50], who argue that pre-planned and reactive agility are multifactorial abilities requiring sensory processing, perception, and motor planning, rather than mere strength.

The predictive power of plantarflexion torque across Modified Star Excursion Balance Test and Weight-Bearing Lunge Test indicates a stable association with dynamic balance and controlled motion. These results are aligned with previous work reporting that plantarflexor strength is associated with balance performance and contributes to proper biomechanics during landing and anterior tibial excursion [51, 52]. While adequate dorsiflexion capacity remains crucial for injury prevention [53], our data suggest that dorsiflexor strength may not be as critical to balance control as previously assumed.

Inversion torque, in particular, was retained across all directions of the Modified Star Excursion Balance Test and is consistently associated with control of frontal-plane motion, a factor discussed in previous research as relevant for counteracting excessive pronation and maintaining joint alignment during single-leg tasks [45, 54]. Furthermore, our findings encourage integrated strength and proprioceptive training programs that enhance not only sagittal-plane output but also mediolateral ankle stability, which appears to be more relevant for high-level balance performance. The sport-specific relevance of these findings becomes clearer when considering the biomechanical demands of soccer. These relationships are particularly meaningful in the context of soccer, a sport characterized by frequent accelerations, decelerations, single-leg landings, and rapid multidirectional changes. The ankle–foot complex plays a crucial role in shock absorption, propulsion, and maintaining dynamic stability during these high-demand actions [1, 8, 30]. Inadequate strength or control in the plantarflexor and frontal-plane musculature can impair performance in tasks such as sprinting, cutting, and kicking, which rely heavily on neuromuscular precision and lower-limb alignment [1, 15, 30]. Furthermore, ankle sprains remain among the most common injuries in soccer athletes, and deficits in dorsiflexion range of motion, proprioception, and dynamic balance are well-established contributors to injury risk [6, 9, 29, 39, 41]. Thus, understanding how isolated ankle muscle strength relates to functional performance provides important insight for training planning, screening, and prevention strategies in youth soccer players.

Taken together, these findings carry important clinical and athletic implications. For practitioners and strength coaches, prioritizing the strengthening of the plantarflexor, invertor, and evertor muscle groups may yield greater benefits for functional balance than focusing exclusively on dorsiflexor conditioning. Concurrently, agility and quickness training should be rooted in neuromotor development rather than strength enhancement alone. Moreover, the use of analytical tools such as Least Absolute Shrinkage and Selection Operator regression enables more refined interpretation of complex biomechanical data, facilitating evidence-informed training strategies.

The relationship between ankle strength and functional performance in youth soccer athletes is multifaceted. Plantarflexion and frontal-plane torques emerge as key contributors to dynamic balance, while agility performance appears to depend more heavily on neuromotor attributes. A comprehensive training approach that integrates strength development, balance enhancement, and agility-specific drills may represent the most effective strategy for improving performance and reducing injury risk in this population. This is consistent with the understanding that agility incorporates perceptual–cognitive processing, anticipatory skills, and coordination, which are not captured by isolated isokinetic strength assessments. Thus, the weak associations observed here may reflect the multifactorial nature of agility rather than an absence of functional relevance of ankle musculature.

Clinical implications

These findings have important practical implications for training and injury prevention strategies in youth athletes. In applied settings, such as soccer academies, school-based programs, and clinical sports rehabilitation environments, strengthening programs that emphasize plantarflexion, eversion, and inversion may contribute to improved dynamic balance and functional mobility, particularly in tasks requiring multiplanar control, such as those assessed by the Modified Star Excursion Balance Test. Specifically, exercises such as resisted ankle movements with elastic bands, single-leg heel raises on unstable surfaces, and closed-chain frontal-plane control drills may be strategically incorporated into warm-up routines or conditioning blocks. These muscle groups appear to play a critical role in mediating postural stability and controlling movement during high-demand activities involving directional changes and single-leg tasks.

In contrast, agility and rapid motor execution, as assessed by the Side Hop Test, may require different neuromuscular approaches, including plyometric training, rhythm-based drills, and sensorimotor integration exercises. Examples include lateral hop-and-hold drills, reactive hopping tasks with external cues, and multidirectional change-of-direction exercises performed under time constraints. These modalities specifically target coordination, reaction time, and temporal control, which are likely more relevant to optimizing agility performance than isolated strength development. Thus, practitioners should avoid relying solely on strength metrics when designing programs aimed at improving agility-related outcomes.

Furthermore, the absence of significant differences between limbs supports the use of bilateral average values in screening and performance monitoring, suggesting that well-conditioned youth athletes may maintain functional symmetry. In practical terms, this finding supports the feasibility of streamlined assessment protocols during preseason screening or routine monitoring, reducing testing time without compromising interpretability. This symmetry could serve as a protective factor against unilateral overuse injuries and may help establish rehabilitation benchmarks and guide return-to-play decisions, particularly when asymmetries emerge following injury or periods of detraining.

Integrating field-based assessments such as the Weight-Bearing Lunge Test and the Modified Star Excursion Balance Test into periodic evaluations may provide accessible and reliable insights into lower limb function, facilitating more individualized and effective training prescriptions. These tests can be readily administered by coaches, strength and conditioning professionals, and clinicians with minimal equipment, making them suitable for use in both high-performance and community sport settings. Strength and conditioning professionals, coaches, and clinicians are encouraged to adopt multicomponent training strategies that address not only muscular strength but also balance, mobility, and motor control, thereby promoting comprehensive physical development and resilience in youth sports environments.

Limitations and future directions

This study offers valuable insights into the relationship between ankle strength and functional performance in youth soccer athletes. Nevertheless, several considerations should be acknowledged. First, the sample consisted exclusively of male athletes from a single competitive level and age group, which may limit the generalizability of the findings to broader athletic populations. Therefore, the practical recommendations derived from this study should be interpreted primarily within the context of late-adolescent male soccer players with structured training backgrounds. However, this homogeneity also allowed for a more controlled examination of neuromuscular characteristics within a well-defined cohort. Another limitation concerns the sample size (n = 26), which is appropriate for a pilot investigation but restricts the statistical power and the stability of regression-based analyses. Although LASSO regression was selected specifically to mitigate overfitting in the presence of multiple predictors, the possibility of unstable coefficients and inflated predictive relationships cannot be fully eliminated. Therefore, the regression findings should be interpreted as preliminary and hypothesis-generating, underscoring the need for larger validation studies to confirm the predictors identified in the present investigation.

The cross-sectional design precludes causal inference; however, the observed associations provide a strong foundation for future longitudinal or interventional studies. Such designs may help clarify whether targeted ankle strengthening or neuromotor training interventions lead to measurable improvements in functional performance or reductions in injury incidence. Additionally, isokinetic strength was assessed at a single angular velocity (30°/s), which may not capture the full spectrum of functional demands associated with sport-specific movements. Despite this limitation, the chosen protocol represents a widely accepted and reliable method for evaluating peak torque production in both clinical and athletic contexts.

Future research should aim to expand sample diversity by including female athletes and multiple age categories to enhance external validity. Incorporating dynamic strength testing at varied velocities, and combining isokinetic measures with neuromuscular, biomechanical, or cognitive-motor variables, may offer a more comprehensive understanding of performance determinants. Moreover, longitudinal studies and training-based interventions are warranted to determine whether targeted improvements in ankle strength directly translate to gains in balance, mobility, or agility within sport-specific contexts.

Conclusion

In youth soccer athletes, plantarflexion and frontal-plane ankle strength were the variables most consistently associated with dynamic balance, and plantarflexor strength also showed a stable association with dorsiflexion mobility in the Weight-Bearing Lunge Test. In contrast, agility performance demonstrated minimal association with isolated ankle strength. These findings indicate that strengthening plantarflexors, invertors, and evertors may be particularly relevant for balance-oriented tasks, whereas agility development may benefit more from neuromotor-focused approaches. Overall, integrating ankle conditioning with neuromotor training may better support functional performance demands in this population.

Authors’ contributions

All authors gave their final approval and agreed to be responsible for all aspects of the work. RSM, MLM, and RO contributed to the research concept and study design. BCD, VGM, and JCS conducted the literature review and participated in data collection. BCD, VGM, JCS, and RO were involved in data analysis and interpretation, with RO also responsible for the statistical analyses. TBM and RO were responsible for writing the manuscript and reviewing/editing the final draft. All authors read and approved the final version of the manuscript.

Funding

This study was financed in part by the Demand Program, Coordination for the Improvement of Higher Education Personnel (CAPES), Foundation for the Support of Research and Innovation of the State of Santa Catarina (FAPESC), and National Council for Scientific and Technological Development (CNPq).

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This cross-sectional study was approved by the Human Research Ethics Committee of the Santa Catarina State University (CAAE: 64790922.7.0000.0118), in accordance with the Declaration of Helsinki, and was conducted at the Center for Health and Sports Education. Informed consent was obtained from all individuals included in the study, ensuring that they were fully aware of the research procedures and their rights.

Consent for publication

Written informed consent for publication of personal and clinical details, including identifying images, was obtained from all participants prior to their inclusion in the study.

Competing interests

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