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Article

Original Research Shank–Forefoot Alignment Correlates Positively with Hip Kinematics During the Single Leg Squat in Professional Football Players: A Cross-Sectional Study

by
José Roberto de Souza Júnior
1,2,*,
Glauber Marques Paraizo Barbosa
3,
Maikon Gleibyson Rodrigues dos Santos
2,4,
Leonardo Luiz Barretti Secchi
5,
Graziela Vieira da Silva
1,
Thiago Vilela Lemos
3 and
João Paulo Chieregato Matheus
2
1
Centro Universitário do Distrito Federal, Campus Sede, Brasília 70390-045, DF, Brazil
2
Universidade de Brasília, Brasília 70919-970, DF, Brazil
3
Moving Fisioterapia, Goiânia 74000-000, GO, Brazil
4
Centro Universitário Estácio, Brasília 72035-509, DF, Brazil
5
UNIGRUPOFAEF Centro Universitário, Itapeva Campus, Itapeva 18412-000, SP, Brazil
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(22), 12054; https://doi.org/10.3390/app152212054
Submission received: 23 March 2025 / Revised: 4 June 2025 / Accepted: 13 June 2025 / Published: 13 November 2025
(This article belongs to the Special Issue Applied Biomechanics for Sport Performance and Injury Rehabilitation)
Versions Notes

Abstract

Optimal lower limb biomechanics are crucial for movement efficiency and injury prevention in football players. The single-leg squat serves as a valuable assessment tool for neuromuscular control, providing insight into movement patterns and potential imbalances. Deficits in hip strength, ankle mobility, and foot alignment can significantly influence biomechanics, leading to compensatory movements and increased joint stress. Identifying and addressing these factors through targeted training can enhance performance and reduce the risk of injury. This study aimed to examine the relationship between hip and ankle/foot mobility, strength, and alignment with hip kinematics during the single-leg squat in football players. A cross-sectional study assessed 25 professional football players. Measurements included isometric strength of the hip abductors and external rotators, ankle dorsiflexion range of motion, and shank–forefoot alignment. Hip kinematics during the single-leg squat were analyzed using Inertial Measurement Units, and Pearson’s correlation coefficient was applied (p < 0.05). Shank–forefoot alignment showed moderate to strong correlations with contralateral pelvic drop (r = 0.44; p = 0.035), hip adduction (r = 0.42; p = 0.036), and hip internal rotation (r = 0.51; p = 0.009) during the single-leg squat. These findings highlight the importance of foot alignment in movement control, reinforcing its relevance for injury prevention strategies in football players.

1. Introduction

Professional football leagues require prolonged periods of intense competition, demanding high levels of physical and technical training to maintain performance throughout the season [1]. Both official matches and training sessions involve complex unilateral and bilateral movements, including jumping, acceleration, deceleration, changes in direction, and direct physical contact. As a result, football shows the highest incidence of sport-related injuries, reaching 7.1% [2].
The injury incidence rate among professional football players ranges from 2.4 to 9.4 injuries per 1000 h of exposure [1]. Male players present a rate up to 40% higher than female players. Injuries during matches occur nearly ten times more frequently than in training [3], and men are 4.82 times more likely to be injured [4]. A previous study reported 3944 injuries across 1546 matches, resulting in a rate of 2.6 injuries per match [5]. The most commonly affected anatomical regions include the thigh, knee, ankle, hip, and groin, with a predominance of muscle and ligament injuries [3].
Recent research has highlighted the role of biomechanical factors in football-related injury occurrence [6]. Video-based analyses have demonstrated that the dynamic knee valgus is frequently observed during ACL injuries in football players, being present in 81% of the cases analyzed [6,7]. This pattern is typically characterized by excessive contralateral pelvic drop, hip adduction, and femoral internal rotation [7,8]. Functional movement assessments, such as the single-leg squat (SLS), have been widely used to evaluate hip biomechanics. Studies indicate that individuals with poor SLS performance exhibit greater hip adduction angles and increased knee projection angles [9]. This test is low-cost, easy to administer, and shows high accuracy in identifying biomechanical deficits that may predispose athletes to injuries, including ACL tears [9].
Although the association between dynamic knee valgus and ACL injuries is well established, the mechanisms leading to excessive valgus remain multifactorial and not fully understood. Factors such as neuromuscular control, joint mobility, anatomical alignment, and muscle strength may interact in complex ways, influencing movement patterns [6,7].
Despite this known association, few studies have explored the underlying factors contributing to excessive frontal and transverse plane motion during tasks such as squatting, jumping, and running. In particular, the biomechanical pathways through which distal alignment, such as shank–forefoot alignment, influences proximal joint mechanics remain insufficiently understood. Altered forefoot mechanics can modulate tibial rotation and foot pronation, which are biomechanically coupled with knee and hip movements, potentially increasing proximal joint stress and contributing to injury risk [10]. Therefore, this study aims to determine whether hip strength, ankle mobility, and shank–forefoot alignment are associated with hip kinematics in the frontal and transverse planes during the single-leg squat in football players. We hypothesize that reduced hip strength and ankle mobility, combined with forefoot varus alignment, will be associated with increased contralateral pelvic drop, hip adduction, and hip internal rotation during the single-leg squat.

2. Methods

2.1. Study Design

This cross-sectional study was conducted in accordance with the STROBE [11] (Strengthening the Reporting of Observational Studies in Epidemiology) guidelines and was approved by the Ethics Committee for Research Protocols Analyses of the University’s Ethics Committee (CAAE: 23389019.6.0000.5076). Informed consent was obtained from all participants in accordance with the Declaration of Helsinki and applicable national regulations.

2.2. Participants

The study was performed with a convenience sample of professional football players that played at the national level. Participants who were selected were football players, older than 18 years, with no lower limb injuries, and no history of surgery in the lower limbs in the 12 months prior to the evaluation. The recruitment was made through direct communication with the football team. Players were excluded if they presented any current lower limb injury or condition that could affect functional performance or biomechanics, had a history of chronic musculoskeletal or neurological disorders affecting the lower limbs, were undergoing rehabilitation or had activity restrictions at the time of data collection, or failed to complete the assessment procedures in accordance with the study protocol.

2.3. Procedures

2.3.1. Hip Abductors Isometric Strength

The isometric strength of the hip abductors was measured using a handheld dynamometer (MicroFET2®), positioned 5 cm proximal to the medial malleolus of the tested limb. Participants were placed in a side-lying position with the tested limb on top, fully extended, and the contralateral limb flexed for support. The pelvis was stabilized by the examiner to minimize compensatory trunk movements. Three maximal voluntary isometric contractions (MVICs) of 5 s each were performed, with 30 s rest intervals between repetitions. All assessments were conducted individually and supervised by the same trained examiner to ensure consistency. Standardized verbal encouragement was provided throughout each trial. The peak force value from the three repetitions was recorded in kilograms-force (kgf) and used for analysis, representing the participant’s maximum isometric strength capacity. Only the dominant limb was included in the analysis. For the strength assessments, the dominant limb was defined as the answer to the question “what limb do you choose for kick a ball?” [12].

2.3.2. Hip External Rotators Isometric Strength

The isometric strength of the hip external rotators was assessed using the same handheld dynamometer (MicroFET2®), which was also positioned at 5 cm proximal to the medial malleolus of the tested limb. Participants were seated with hips and knees flexed at 90°, with their feet unsupported. The tested limb was stabilized by the examiner to prevent hip abduction or pelvic rotation during testing. Similarly to the previous test, three 5 s MVICs were performed with 30 s rest intervals. All measurements were performed in isolation and administered by the same experienced examiner to ensure standardization. The highest force value among the three trials was recorded in kgf and used in the analysis, reflecting the participant’s peak isometric strength of the hip external rotators.

2.3.3. Ankle Dorsiflexion Range of Motion

Ankle dorsiflexion was measured using the weight-bearing lunge test (WBLT). An inclinometer was positioned 15 cm below the tibia tuberosity. Participants were placed in front of a wall and were instructed to lunge forward to touch the patella of knee on the wall without lifting the heel off the floor. The angle was collected at the maximum lunge distance from the wall [13]. All measurements were performed and administered by the same experienced examiner to ensure standardization. Three measurements were performed, and the mean was used in the analysis. Ankle dorsiflexion was measured in degrees.

2.3.4. Shank–Forefoot Alignment

The shank–forefoot alignment was measured using a prone position with the foot positioned outside the treatment table. The participant was instructed to sustain a dorsiflexion of 90°. The examiner marked the bisection point between the athlete’s tibial plateaus and between the superior boards of the malleoli. Then the examiner attached a metallic rod that was positioned to follow the direction of the metatarsal heads. Later, he traced a straight line on the skin of the distal portion of the shank, connecting the central marks between the tibial plateaus and malleoli [14]. With the aid of a goniometer, the examiner measured the shank–forefoot alignment as the angle between the bisection of the tibia and the orientation of the metal rod positioned on the metatarsophalangeal region [15]. All measurements were performed and administered by the same experienced examiner to ensure standardization. Varus alignments were reported as positive values and valgus alignments were reported as negative values [16].

2.3.5. Contralateral Pelvic Drop, Hip Adduction, and Hip Internal Rotation During the SLS

The kinematics of the hip in the frontal and transverse planes during the single-leg squat was measured using a 3D movement analysis system with Inertial Measurement Units (IMUs). The myoMOTION® system is an alternative to the Vicon system, considered as the gold standard for analyzing 3D movement. For measuring anatomical angles, a standard error of 0.5° and a correlation coefficient of 0.99 between the systems were observed [17]. The myoMOTION® software (myoMOTION Research Pro, Noraxon USA Inc., Scottsdale, AZ, USA) was used with 9 units positioned on the cervical–thoracic, thoracolumbar, and lumbosacral regions, bilaterally on the lateral part of the thigh and tibia, and on the feet. The data captured by each sensor was interpreted at a frequency of 200 Hz. Participants had to perform three single-leg squats until 60 flexion and then return to the original position [12]. This angle was determined by the examiner and the subjects were informed at the moment of data collection. All kinematic data was collected by the same experienced examiner to ensure standardization. The kinematic angles were collected throughout the movement. The contralateral pelvic drop, hip adduction, and hip internal rotation angles in degrees were considered for analysis.

3. Data Analysis

The SPSS (Statistical Package for Social Sciences), version 26.0 was used to analyze the data. Descriptive statistics were performed with mean, standard deviation, and 95% confidence intervals. Shapiro–Wilk’s test was performed to verify the normality of the data. Pearson’s Coefficient Correlation (r) was calculated to verify the relationship between hip abductors and external rotators isometric strength, ankle dorsiflexion range of motion, and shank–forefoot alignment with the contralateral pelvic drop, hip adduction, and hip internal rotation angles during the single-leg squat. Values between 0.10 and 0.29 were considered as weak correlation, between 0.30 and 0.49 as moderate correlation, and between 0.50 and 1 as strong correlation [18]. A significance level of p < 0.05 was adopted.

4. Results

Twenty-five football players participated in the study. They had a mean age of 25.12 (±4.86) years, a body mass of 79.92 (±10.84) kg, height of 1.80 (±0.08) m, and body mass index (BMI) of 24.51 (±1.47) kg/m2. These general characteristics are summarized in Table 1.
Regarding the primary outcomes, we found moderate to strong positive correlations between shank–forefoot alignment and key hip kinematic variables during the single-leg squat. Specifically, shank–forefoot alignment was significantly correlated with contralateral pelvic drop (r = 0.44; p = 0.035), hip adduction (r = 0.42; p = 0.036), and hip internal rotation (r = 0.51; p = 0.009). These results suggest that greater varus alignment of the forefoot is associated with increased deviations in proximal joint kinematics during functional loading. In contrast, no significant correlations were found between the hip abductor or external rotator strength and the hip kinematic variables assessed during the SLS (p > 0.05). Similarly, the ankle dorsiflexion range of motion was not significantly correlated with pelvic drop, hip adduction, or internal rotation angles during the task. The full descriptive and inferential statistics for these variables are presented in Table 2.

5. Discussion

This study explored the correlations between hip strength, ankle dorsiflexion, and shank–forefoot alignment with hip kinematics in the frontal and transverse planes during the single-leg squat (SLS). Moderate to strong correlations were found between increased forefoot varus (via shank–forefoot alignment) and greater pelvic drop, hip adduction, and internal rotation. In contrast, no significant associations were observed for hip abductor/external rotator strength or dorsiflexion ROM. These findings partially support the hypothesis that lower-limb mechanics influence hip motion during the SLS.
A previous study that compared hip kinematics between individuals with neutral alignment and forefoot varus (≥8°) found greater hip internal rotation in the group with increased forefoot varus [19]. Although this finding aligns with our study, the same research did not observe differences in hip adduction, likely due to compensatory trunk and pelvic strategies. Unlike our study, which analyzed intra-individual correlations, these authors conducted group comparisons. Similar results to ours were also described by [20], who investigated the association between hip muscle strength and kinematics during functional tasks and found no significant correlations in asymptomatic individuals, suggesting that this relationship may be dependent on clinical context.
Additionally, a study examining hip and knee angles during a single-leg jump in amateur dancers found that greater hip abduction strength was associated with greater hip internal rotation, while shank–forefoot alignment and ankle dorsiflexion ROM did not correlate with hip or knee movements [21]. This contrasts with our findings, where shank–forefoot alignment correlated with pelvic drop, hip adduction, and internal rotation. Similar discrepancies were observed in other studies, which identified that greater passive ankle dorsiflexion was associated with less thigh internal rotation and pelvic drop during SLS [22]. These findings differ from ours, which found no significant correlations between dorsiflexion range and hip kinematics, possibly due to methodological differences. Importantly, task-dependent factors such as SLS versus jump tasks and individual anatomical differences may influence outcomes. Differences in foot progression and knee valgus have also been identified as a possible factor to explain such variations [23]. Previous studies have shown that different functional tasks, such as the SLS and the step-down, result in distinct hip and trunk activation and kinematic patterns, which may directly influence results [24]. In contrast, Ref. [25] reported that individuals with patellofemoral osteoarthritis exhibited greater hip adduction during the SLS, associated with reduced hip abductor and external rotator strength, suggesting that this relationship may be more evident in clinical populations.
Furthermore, our findings diverge from those of [26], who found no correlation between shank–forefoot alignment and hip movements in the frontal and transverse planes. This difference may stem from the population sample, as their study included both men and women, while ours focused exclusively on male athletes. Previous research has shown sex differences in SLS execution, with women exhibiting greater hip internal rotation and adduction [27,28]. A subgroup analysis considering sex could clarify these variations, especially given the influence of anatomical variables, such as femoral anteversion, on hip motor control [29].
A biomechanical study comparing hip kinematics in three different foot positions in the transverse plane—neutral (0°), adducted (−10°), and abducted (+10°)—found no significant differences in hip adduction or internal rotation [30]. However, altering only the foot position in the transverse plane may not sufficiently impact hip biomechanics as much as forefoot varus does, particularly in a closed kinetic chain, where greater ankle–foot pronation can lead to increased leg and hip internal rotation, hip adduction, and contralateral pelvic drop [31,32].
Moreover, studies using non-linear analytical methods have shown that shank–forefoot alignment, together with proximal factors, contributes to the development of patellar tendinopathy and greater knee projection angles in the frontal plane [12,33]. Our study used a linear correlation approach and identified significant associations between tibia–forefoot alignment and hip movement, reinforcing its usefulness in musculoskeletal assessments.
Previous research linked isometric hip strength to greater knee projection angles in the frontal plane, but did not analyze pelvic drop and hip adduction separately [34,35]. A systematic review highlighted that musculoskeletal factors such as muscle pain, femoroacetabular impingement, fatigue, and stiffness influence performance in squatting tasks [36]. Additionally, muscle fatigue has been associated with increased pelvic drop and hip adduction [37]. Studies on gait have also shown that changes in foot progression angle alter muscle activation patterns and lower limb kinematics, suggesting that distal adaptations may influence proximal control [38]. Similar findings were also reported by [39], who observed lower muscle activation in women with patellofemoral pain during the SLS, even with preserved strength and dorsiflexion, suggesting that neuromuscular activation patterns may not always correlate directly with these variables across all populations. These findings are also in line with those of [8], who observed a relationship between hip strength and dynamic valgus in asymptomatic women. The SLS may not require as much gluteus medius activation compared to other functional evaluations [40], which could explain the absence of significant correlations between hip strength and kinematic factors in our study.
Individuals classified as low performers in the SLS based on a visual assessment scale exhibited greater hip adduction, reduced knee flexion [8], ipsilateral trunk rotation, and dynamic knee valgus [41]. The findings of our study highlight the clinical importance of assessing shank–forefoot alignment in professional football players. The significant correlations observed between this alignment and key hip kinematic variables during the single-leg squat reinforce the role of distal segment positioning in proximal joint control. These results suggest that excessive forefoot varus may contribute to movement patterns associated with dynamic knee valgus, a known risk factor for lower limb injuries such as ACL ruptures [6] and patellar tendinopathy [33].
This study has several limitations that should be considered when interpreting the findings. First, the cross-sectional design does not allow for causal inferences; thus, we cannot determine whether altered shank–forefoot alignment leads to abnormal hip kinematics or vice versa. Second, the small sample size and inclusion of only male professional football players limit the generalizability of the results to other populations, such as female athletes or non-professional players. Third, only the dominant limb was assessed, which may overlook asymmetries that could influence performance and injury risk. Finally, although Inertial Measurement Units provide a valid and practical alternative to motion capture systems, they may still be subject to measurement errors, particularly in dynamic movements.

6. Conclusions

In conclusion, shank–forefoot alignment was positively correlated with contralateral pelvic drop, hip adduction, and hip internal rotation angles during the single-leg squat in professional football players. Hip strength and ankle dorsiflexion were not correlated with the kinematics of the hip in the frontal and transverse planes. These findings reinforce the hypothesis that distal alignment of the foot may play a contributory role in the neuromechanical control of proximal joints during closed kinetic chain tasks, highlighting the importance of considering foot posture in the assessment and management of lower limb movement patterns.

Author Contributions

Conception and design of the study, drafting the article, and acquisition of data: J.R.d.S.J. Writing assistance, and drafting the article: G.M.P.B. Writing assistance and drafting the article: M.G.R.d.S. Writing assistance and drafting the article: L.L.B.S. Writing assistance and drafting the article: G.V.d.S. Conception and design of the study, writing assistance, acquisition of data, and drafting the article: T.V.L. Conception and design of the study, writing assistance, drafting the article and for important intellectual content and final approval of the version to be submitted: J.P.C.M. All authors have read and agreed to the published version of the manuscript.

Funding

The authors thank the DPI/BCE/UnB for the financial support, in accordance with public call No. 001/2025 DPI/BCE/UnB.

Institutional Review Board Statement

The manuscript complies with the Ethical Principles for Medical Research Involving Human Subjects, as outlined in the Declaration of Helsinki, and was approved by the Ethics Committee for Research Protocols Analyses of the University’s Ethics Committee (CAAE: 23389019.6.0000.5076).

Informed Consent Statement

Informed consent was obtained from all participants in accordance with the Declaration of Helsinki and applicable national regulations.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Table 1. General characteristics of the participants (n = 25).
Table 1. General characteristics of the participants (n = 25).
Mean (SD)95% (CIs)
Age (years)25.12 (±4.86)23.19–27.05
Body mass (kg)79.92 (±10.84)75.44–84.40
Height (m)1.80 (±0.08)1.76–1.83
Body Mass Index (kg/m2)24.51 (±1.47)23.90–25.12
Table 2. Relationship between hip abductors and external rotators strength, ankle dorsiflexion, and shank–forefoot alignment with contralateral pelvic drop, hip adduction, and hip internal rotation angles during the single-leg squat (n = 25).
Table 2. Relationship between hip abductors and external rotators strength, ankle dorsiflexion, and shank–forefoot alignment with contralateral pelvic drop, hip adduction, and hip internal rotation angles during the single-leg squat (n = 25).
Contralateral Pelvic Drop (°)Hip Adduction (°)Hip Internal Rotation (°)
Hip abductors strength (Nm/kg)r = 0.14 (−0.33–0.61)
p =0.540		r = −0.07 (−0.52–0.38)
p =0.750		r = 0.03 (−0.42–0.49)
p = 0.869
Hip external rotators strength (Nm/kg)r = −0.09 (−0.54–0.34)
p = 0.658		r = 0.34 (−0.06–0.74)
p = 0.092		r = −0.02 (−0.68–0.14)
p= 0.190
Dorsiflexion ROM (°)r = −0.22 (−0.64–0.21)
p = 0.302		r = 0.11 (−0.31–0.54)
p = 0.590		r = −0.16 (−0.63–0.28)
p= 0.442
Shank–forefoot alignment (°)r = 0.44 (0.03–0.81)
p = 0.035 *		r = 0.42 (0.03–0.81)
p = 0.036 *		r= 0.51 (0.14–0.88)
p= 0.009 *
Abbreviations: (°) = Degrees; ROM = Range of Motion; Nm/kg = Newton x Metter/Kilogram; Statistical test used: Pearson’s Coefficient Correlation. r = 0.10–0.29—weak; r = 0.30–0.49—moderate; r = 0.50–1—strong. * Significance level set at p < 0.05.
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de Souza Júnior, J.R.; Barbosa, G.M.P.; Santos, M.G.R.d.; Secchi, L.L.B.; da Silva, G.V.; Lemos, T.V.; Matheus, J.P.C. Original Research Shank–Forefoot Alignment Correlates Positively with Hip Kinematics During the Single Leg Squat in Professional Football Players: A Cross-Sectional Study. Appl. Sci. 2025, 15, 12054. https://doi.org/10.3390/app152212054

AMA Style

de Souza Júnior JR, Barbosa GMP, Santos MGRd, Secchi LLB, da Silva GV, Lemos TV, Matheus JPC. Original Research Shank–Forefoot Alignment Correlates Positively with Hip Kinematics During the Single Leg Squat in Professional Football Players: A Cross-Sectional Study. Applied Sciences. 2025; 15(22):12054. https://doi.org/10.3390/app152212054

Chicago/Turabian Style

de Souza Júnior, José Roberto, Glauber Marques Paraizo Barbosa, Maikon Gleibyson Rodrigues dos Santos, Leonardo Luiz Barretti Secchi, Graziela Vieira da Silva, Thiago Vilela Lemos, and João Paulo Chieregato Matheus. 2025. "Original Research Shank–Forefoot Alignment Correlates Positively with Hip Kinematics During the Single Leg Squat in Professional Football Players: A Cross-Sectional Study" Applied Sciences 15, no. 22: 12054. https://doi.org/10.3390/app152212054

APA Style

de Souza Júnior, J. R., Barbosa, G. M. P., Santos, M. G. R. d., Secchi, L. L. B., da Silva, G. V., Lemos, T. V., & Matheus, J. P. C. (2025). Original Research Shank–Forefoot Alignment Correlates Positively with Hip Kinematics During the Single Leg Squat in Professional Football Players: A Cross-Sectional Study. Applied Sciences, 15(22), 12054. https://doi.org/10.3390/app152212054

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