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Review

Assessment of Limb Imbalance in Professional Soccer Players

by
Adrián Moreno-Villanueva
1,2,
Alejandro Soler-López
1,
Jose Carlos Cuartero-Martínez
1 and
Jose Pino-Ortega
1,3,*
1
Faculty of Sports Sciences, University of Murcia, 30720 San Javier, Spain
2
Faculty of Health Science, University Isabel I, 09003 Burgos, Spain
3
BIOVETMED & SPORTSCI Research Group, Department of Physical Activity and Sport, Faculty of Sport Sciences, University of Murcia, 30720 San Javier, Spain
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(4), 1875; https://doi.org/10.3390/app15041875
Submission received: 12 December 2024 / Revised: 30 January 2025 / Accepted: 1 February 2025 / Published: 11 February 2025
(This article belongs to the Special Issue Advances in Sports Science and Movement Analysis)
Browse Figure
Review Reports Versions Notes

Abstract

:
Although it has been found that soccer produces limb imbalance, it has not been rigorously determined how to evaluate it in soccer players or which low-cost tests are the most effective for its analysis. Therefore, the objective of this systematic review was to identify and examine the evidence and evaluations of limb imbalance produced in professional soccer players. A systematic search was conducted in three databases (PubMed, Web of Sciences, and Scopus) to identify relevant studies published before 23 May 2022. Of the 2364 studies identified initially, only 12 articles were included in the systematic review. The results revealed that injury risks can be detected in professional soccer players through the YBT (Y Balance Test). The PSLR (Passive Straight Leg Raise) test, as well as the evaluation of the ROM (range of motion) in movements of adduction and internal hip rotation, seem to be two reliable tests to detect imbalances in the flexibility of the extremities. The FMS (Functional Motion Screen) test is inversely related to the performance in jump tests; thus, its combination can help to detect asymmetries in power generation. Finally, strength assessment tests in soccer players can negatively alter the flexibility values of agonist/antagonist muscles. Therefore, it is advisable to monitor both strength and flexibility tests synergistically to obtain a comprehensive evaluation.

1. Introduction

The concept of limb imbalance is about the comparison of the performance of one limb in relation to the other and has been extensively researched in recent years [1,2]. Sports in which a greater number of sporting actions are performed with the dominant leg could lead to this imbalance [3]. Limb imbalance is common in soccer, as players often favor one leg for kicking and cutting skills. Moreover, the high training and competition volumes throughout the season contribute to this imbalance [4,5,6]. Many of the skills involved in soccer training and competitions require soccer players to frequently repeat the execution of unilateral and asymmetric movements (e.g., defensive actions, changes of direction, and ball striking) [5,7,8]. Over time, these movements can lead to differences in strength, power, and range of motion (ROM) due to loading patterns and coordination of movement [2,9]. Although injuries have a multifactorial origin, the limb imbalance produced is a potential risk factor for injury in soccer players, especially related to hamstring injury or injuries sustained during landing, both phenomena of great incidence in soccer [10,11].
Conceptually, numerous classifications have been established to quantify this limb imbalance. These include dominant and non-dominant limb [12], strongest and weakest limb [2,13], right and left [14], bilateral and unilateral asymmetry (i.e., asymmetries between limbs or between the antagonist and agonist muscles of the same leg, respectively) [1], and injured and non-injured limbs [15], although they are sometimes just defined as the kicking limb = dominant, versus the stance limb in kicking = non-dominant. However, this variety of classifications has considered that there is no single way to quantify limb imbalance between the lower limbs to date, with the exception of considering a percentage difference of one limb relative to the other [16].
In research, lower limb imbalance has been examined across a wide range of physical qualities, including strength [17], power [18], changes of direction [19], leg flexibility or stiffness, and dynamic balance [20,21]. These qualities are assessed through various tests. Muscle strength is evaluated using isokinetic dynamometry (hip and knee strength, Nordic curls, and hip abductor and adductor eccentric strength) [22,23], isometric squats, and mid-thigh pull-ups [24,25]. Functional performance is measured with change of direction tests and jump tasks (e.g., countermovement and single-leg jumps) [26]. Flexibility and dynamic balance are assessed with tests like the Y Balance Test and straight leg raise tests [20,27,28]. All of the above methods have been shown to be sensitive in identifying limb differences in the athlete and non-athlete population, and they have been shown to be a more practical and economical alternative to the data derived from force platforms, which have a high economic cost and are difficult to transport for fieldwork. In addition, it has been argued that limb imbalance may be a product of the time spent competing in the same sport [3]. While it is logical to assume that it is desirable to minimize these differences, it is not yet clear whether this has an actual measurable effect on physical or athletic performance [16,29].
Sport training increases the likelihood of limb imbalance [30]. It has been shown that playing a sport as well-known and practiced as soccer has led to limb imbalance [24]. The most recent reviews are based on studying the effects of limb imbalance on performance in sports [16,29], identifying the limb strength characteristics of the dominant and non-dominant legs in soccer players [31], understanding the imbalance produced in quadriceps and hamstring ratios in soccer players [32], and even identifying whether limb imbalance increases the risk of injury in sport [33]. However, there has been no consensus or systematic review of which tests to use and how to assess limb imbalance in soccer players. Therefore, the aim of this systematic review was to identify and analyze tests and assessments of limb imbalance in professional soccer players using tools or materials that are easy to transport and use on the field.

2. Materials and Methods

2.1. Search Strategy

A systematic review was performed in accordance with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta Analyses) guidelines for performing systematic reviews in sports science [34]. A systematic search of three databases (PubMed, Web of Sciences, and Scopus) was performed to identify articles published prior to 23 November 2024. The PICO (Patient, Problem, or Population; Intervention or Exposure; Comparison, Control, or Comparator; Outcome/s) design was used to provide an explicit statement of the state of the question.
The search was focused on studies about the assessment of limb imbalance in soccer. Three main groups of words were established: (1) population: “football”, “soccer”; (2) intervention: “assessment”, “assessing”, “evaluation”, “method”, “protocols”, “test*”; (3) outcomes: “imbalance”, “asymmetry”, “symmetry”, “bilateral”. Words from different groups were combined to extract as many items as possible by adding Boolean markers. Clusters of keywords (population, intervention, and outcome) were connected with OR within each cluster, and AND was used to combine the three groups: (football OR soccer) AND (assessment OR assessing OR evaluation OR method OR protocols OR test) AND (symmetry OR imbalance OR asymmetry OR symmetry OR bilateral). Additionally, the reference lists of the studies retrieved were manually searched to identify potentially eligible studies not captured by the electronic searches.

2.2. Screening Strategy and Study Selection

When the authors had completed the search (A.S.L., A.M.V., and J.P.O.), they compared the results among themselves to ensure that the same articles were identified. Then, one of the authors (J.C.M) downloaded the main data from the articles (title, authors, journal, date, and databases) and put them onto an Excel spreadsheet (version 16.78, Microsoft Excel, Microsoft, Redmond, WA, USA). Duplicate articles were automatically removed. The remaining articles were screened and checked by two authors independently (A.S.L. and J.C.M) against the inclusion and exclusion criteria (Table 1). Possible discrepancies in the inclusion and exclusion of articles were resolved with the intervention of a third investigator (A.M.V.). Moreover, relevant articles not previously identified were also screened in an identical manner, and further studies that complied with the inclusion-exclusion criteria were included and labelled as ‘included from external sources’.

2.3. Quality of Studies

Two authors (A.M.V and J.P.O) performed the methodological assessment of the studies eligible for inclusion using the PEDro scale. Among the articles included in this systematic review (n = 12), three were rated with a quality score of 4/11, four of 5/11, and five of 6/11. A high score was not found because most of the articles are observational in nature, precluding randomization and blinding in the sample. No studies were excluded for poor quality. There were also no discrepancies in the evaluation criteria of the selected articles—two by the two authors responsible for said task.

2.4. Data Analysis

The studies selected for this review focused on several critical aspects relevant to the research objectives. Specifically, these aspects included the anthropometric characteristics of the participants (such as sex, age, weight, and height), the details of the assessment protocols (including the place of intervention, the asymmetry evaluated, measurement variables, and the tests and tools used), and the results obtained from the assessments. Finally, the conclusions drawn were rooted in scientific rigor and objectivity, offering valuable insights into the analysis of the data’s unique patterns and casuistry.

3. Results

3.1. Identification and Selection of Studies

A total of 2364 (i.e., PubMed: 588, Web of Sciences: 1128, Scopus: 650) original articles were initially retrieved from the mentioned databases. These studies were then exported to the reference management software (Zotero 7.0), and duplicates (1068 items) were automatically removed. Thus, a total of 1296 original articles were found. After this, a total of 1279 articles checked by title and abstract were excluded. In addition, two articles from additional sources were included. The remaining nineteen articles were checked in full text, leading to the exclusion of seven articles: three for not specifically analyzing the professional group, two for not having professional players, one for not adapting to the objective of the study, and one for not having the text available. A total of twelve articles met all the inclusion criteria and were finally included in the qualitative synthesis. All the steps followed for the selection of the articles are presented in Figure 1.

3.2. Methodological Quality

The overall methodological quality of the cross-sectional studies is assessed using the PEDro scale, as shown in Table 2. Scores range from 4 to 6, reflecting differences in study rigor based on criteria such as random allocation, blinding, and follow-up. These scores highlight the variability in methodological quality across the studies.

3.3. Study Characteristics

Twelve articles were analyzed, of which four assessed limb imbalance using flexibility tests [27,36,37,42], four using lower limb power and other physical qualities [35,39,40], two by testing strength and various physical qualities [22,38], and the remaining two investigated limb imbalance by dynamic balance testing [20,28].
Four studies assessed asymmetry with flexibility tests, three focusing on asymmetry [27,34,35] and one on both types [36], with only one showing no significant changes [34]. In power and physical tests, three of four studies found significant asymmetry [38,39]. Two studies on strength tests found no significant asymmetry [22,40]. Lastly, two studies on dynamic balance tests found asymmetry, with one showing no significant changes [20]. Finally, of the twelve studies reviewed, three additionally used expensive and/or difficult-to-transport measuring devices, such as contact platforms [35] and isokinetic dynamometers [38,39]. On the other hand, the remaining authors employed more practical and affordable devices, such as encoders [39], the functional motion screen (FMS) [35,40,42], video cameras [35,38], boxes or benches [35,38], a Y Balance Test (YBT) platform [20], the modified Star Excursion Balance Test (mSEBT) [28], a tape measure [28,38,39,40], goniometers [22,36,37,39,40], inclinometers [22,27,39], and handheld dynamometers [22,39] that allow for greater practicality in the research setting (Table 3).

4. Discussion

The purpose of the systematic review was to synthesize and critically and objectively analyze the evaluation tests used for the assessment of limb imbalance in professional soccer players, mainly using materials or tools that are easily transportable and applicable in the field. The main findings revealed that injury risks can be detected in professional soccer players through the YBT. In addition, the PSLR test, as well as the evaluation of the ROM in movements of adduction and internal rotation of the hip, seem to be two reliable tests for detecting imbalances in the flexibility of the extremities. On the other hand, the FMS test is inversely related to the performance in jump tests. Therefore, its combination can help to detect asymmetries in the power generation of soccer players. Finally, strength assessment tests in soccer players may negatively alter the flexibility values of agonist/antagonist muscles. Therefore, it is advisable to conduct synergistic monitoring of both types of tests to ensure a balanced evaluation.

4.1. Tests Measuring Dynamic Balance

The dynamic balance represents the ability to perform an action while maintaining or restoring a stable position and plays an important role in soccer, as it requires strength, adequate range of motion, proprioception, and neuromuscular control to complete actions such as kicking, passing, dribbling and defending [43]. Therefore, a dynamic balance test should be performed in order to identify soccer players at risk of lower limb musculoskeletal injuries [44,45].
In the present study, two papers were found [20,28] that tried to assess limb imbalance through dynamic balance tests. To this end, Ates et al. [20] used the YBT to assess limb imbalance in the anterior, posteromedial, and posterolateral planes, taking into account the position of each player on the field of play. In this study [20], there were no significant differences in the anterior, posteromedial, and posterolateral scores among the positions of each player’s group. The YBT has been widely used to identify potential risks of injury in team sports by other researchers [46], demonstrating its reliability and efficacy in a rigorous manner. In addition, the YBT allows discriminating athletes at risk of suffering a lower limb injury due to limb imbalance since it requires balance, lower limb strength, and flexibility [47]. Therefore, we can determine that the YBT would be useful to detect the risk of injury in professional soccer players, but we cannot consider it a valid test to measure limb imbalance among positions in professional soccer because there is no study that makes this distinction. On the other hand, Onofrei et al. [28] used the mSEBT, verifying that this test showed acceptable sensitivity in detecting limb imbalance in professional soccer players. However, since the study was carried out only on athletes with no previous history of injuries and in a single period of the season, future studies are needed to expand information related to the mSEBT. Furthermore, it is important to bear in mind that the tests analyzed in the present study focused on healthy adult professional soccer players. In this respect, it is necessary to clarify the potential of both dynamic balance tests to provide information that will help coaches and trainers prevent injuries resulting from limb imbalance.
In summary, the YBT appears to be a useful tool for assessing injury risk in professional soccer players. However, it may not be sensitive or valid enough to detect differences between playing positions. Future research should focus on confirming its utility in evaluating limb imbalances in professional soccer players, which is in line with the purpose of assessing test measures for asymmetry.

4.2. Tests Measuring Flexibility

The high-intensity demands of the movements required in soccer could lead to overloading joints and muscles, generating sport-specific adaptations that would cause deficiencies in the normal range of motion of muscles such as the quadriceps or hamstrings during soccer activities and that, therefore, may produce a notable risk of injury [48]. Poor flexibility is a risk factor for hamstring strain injury and is still considered a major risk factor for injury by professionals working in premier league soccer clubs [49]. Therefore, soccer teams include hamstring flexibility assessments in preseason testing to identify players who are more susceptible to hamstring strain [50].
In the present study, four papers were identified that investigated asymmetry using flexibility tests [27,36,37,42]. Manning and Hudson [37] found significant differences (p < 0.001) in hip abduction and internal rotation ROM, with asymmetry observed between limbs in soccer players. Specifically, these parameters showed increased hip abduction ROM and decreased hip internal rotation ROM in one limb compared to the contralateral limb. It can be concluded that the assessment of asymmetry in soccer players is more effective when measuring hip ROM than measuring the knee and ankle joints. This may be because the hip is one of the important lower body joints used during instep strikes in soccer [51]. In contrast, López-Valenciano et al. [36] assessed asymmetry by measuring the ROM of the ankle, knee, and hip joints. In this study [36], no significant changes in asymmetry were found. This may be because they only evaluated soccer players, which tends to homogenize decompensations located in the lower limbs. Furthermore, in this study [36], they did not use a control group; hence, the data were compared between the soccer players analyzed. Future research should investigate whether this imbalance does not occur due to soccer practice. It would therefore be advisable to conduct a study in which we observe whether this imbalance occurs in other kick dominant running team sports such as Australian Football, Gaelic Football and Rugby.
Another study [27] assessed hamstring flexibility by measuring ROM using the ASLR and PSLR tests, specifically examining right/left asymmetry in hamstring flexibility. They compared the results from both tests and concluded that the PSLR was a more suitable measure for detecting hamstring flexibility asymmetry than the ASLR. The ASLR test does not accurately assess hamstring flexibility in soccer players due to the involvement of other muscle groups [52]. Therefore, the ASLR test is a more complex task than the PSLR test, and poor scores do not necessarily indicate only a hamstring flexibility deficit [27]. Consequently, the PSLR test seems to be a test that analyzes hamstring flexibility in a more individualized way. Therefore, the use of the PSLR is recommended instead of the ASLR, although its application requires more time; hence, it is not as practical in this regard. Finally, Zalai et al. [42] analyzed flexibility using the FMS test, a tool to assess functional mobility and postural stability in different non-locomotion settings [53]. In this case, the FMS test was found to have adequate sensitivity to assess the functional consequence (on flexibility) of a previously sustained lower limb injury. During the examination period, injured players had lower FMS scores than non-injured ones. When analyzing the FMS scores and injuries on the basis of additional aspects, it was found that the players who did not have injuries typically achieved better FMS scores in their average results than their injured peers, though this difference was not significant in terms of the variables [42]. Therefore, the FMS test can be useful to assess the limb imbalance that occurs in soccer players, especially if the players have recently suffered a previous injury or have a serious injury history; although the pre-learning nature of the test could interfere with the measurement of limb imbalance in the FMS, as has occurred in subsequent investigations in balance tests [54,55].
In conclusion, it appears that the assessment of limb imbalance can be reliably performed with the PSLR test, as well as by measuring ROM in hip abduction and internal rotation movements. However, further research is needed to determine whether these tests and the FMS test are sufficiently sensitive for the detection of limb imbalance among healthy soccer players, i.e., in the absence of a control group.

4.3. Tests Measuring Power with Flexibility

Jumps occur frequently during match play, and asymmetry is a natural by-product of competing in a single sport over time [56]. In this respect, the continuous and recurrent execution over time of a gesture that involves a maximum expression of force in the shortest possible time can cause the limb imbalance generated to be of greater magnitude [57]. Therefore, it would be prudent to minimize limb differences in dynamic balance and optimize ankle range of motion for better jumping and change of direction performance [16]. A variety of jump tests have been shown to be valid and reliable measures for quantifying limb asymmetry [58]. Additionally, significant differences in jump height have been observed between limbs, with a limb imbalance of around 10% between the injured and uninjured limbs [18].
To our knowledge, there are no studies that have worked on power in isolation. However, studies were found that analyzed power with flexibility [35,59]. The power–flexibility relationship is of vital importance for efficient ball striking [60]. On the one hand, Kraus et al. [35] used the Landing Error Scoring System (LESS) to assess both unilateral differences between agonist and antagonist muscle groups and limb imbalance during the execution of a high jump [35], finding that worse landing mechanics were obtained (p < 0.001) for soccer players when jumping higher. In turn, they used the FMS test to assess flexibility, concluding that flexibility in the FMS test could limit landing mechanics. However, in the studies by Sannicandro et al. [40], who also analyzed jumping power alongside flexibility, they found that the assessment of unilateral and limb imbalance obtained through the FMS test showed a negative relationship with respect to jumping ability. Therefore, [40] showed an inverse relationship between the score obtained in the FMS tests and the limb imbalance produced in the jumping tests (p < 0.01). This could be due to the fact that the soccer players developed an improved stretch capacity in their musculature, producing a more developed flexibility in their lower limbs, which would help them to improve their jumping mechanics and, therefore, provide them with a greater capacity to reduce the limb imbalance observed in these jumps. There is currently no scientific evidence for this; thus, more research should be carried out on professional soccer players to see if this hypothesis holds true.
From another perspective, Read et al. [50] analyzed the relationship of power to other qualities, such as flexibility and strength. Power was assessed through countermovement jumping (CMJ) with one and both legs. Unilateral imbalance was assessed through strength testing, while limb imbalance was measured through knee, hip, and hamstring ROM. In this regard, differences in strength tests (p < 0.05) were observed between limbs, highlighting the presence of asymmetry in strength among soccer players [50]. It is important to note that such differences in strength may contribute to limb imbalances in soccer players [61,62]. In turn, Read et al. [39] also concluded that jumping tests showed no relationship to limb imbalance in flexibility and strength tests. Therefore, more research is needed to relate the asymmetry of flexibility and strength to jumping tests. On the other hand, there were differences between the jumping and strength variables (p < 0.05); it was found that the group with very high asymmetry in the jumping tests had lower scores in the isokinetic strength test. This may be because soccer players with lower knee extensor and flexor strength would have been more likely to show high limb imbalance in jumping [63].
In summary, better scores on the FMS tests seem to produce less asymmetry in the jumping tests. On the other hand, it was also determined that limb imbalance in flexibility and strength did not affect jumping performance, requiring future research to corroborate that greater asymmetry does not prevent reduced jumping performance.

4.4. Tests Measuring Strength

Soccer requires players to perform repeated moderate and high-intensity movements, such as sudden accelerations and decelerations, rapid changes of direction, and jumping and landing tasks, situations in which players are involved in the struggle to maintain possession or to win the ball [64]. Muscle flexibility, joint stiffness, and the ability to generate muscle strength are essential for soccer performance [65]. Specifically, appropriate flexibility and strength of the hip muscles are necessary to allow proper hip and knee movements, generating the power required for soccer practice [66]. It also requires hip muscle strength to absorb and generate energy and provide stability in the lower limbs and trunk during different actions produced on the soccer pitch [60]. Therefore, an assessment of limb strength imbalance is crucial to detect muscle imbalance in professional soccer players.
Two studies were found that assessed limb imbalance through strength testing [22,38]. On the one hand, Ocarino et al. [22] found greater torque in the external rotators (measured through a handheld dynamometer) and less flexibility in the iliopsoas and rectus femoris (measured using the modified Thomas test [67]) of the dominant leg compared to the non-dominant leg (p < 0.01). This reinforces the conclusions drawn from previous studies [65,68], highlighting the importance of addressing hamstring flexibility to facilitate optimal knee flexion and hip extension. It is important to note that reduced iliopsoas flexibility would likely restrict hip extension rather than flexion, while reduced rectus femoris flexibility could limit knee flexion when the hip is extended or restrict hip extension when the knee is flexed. On the other hand, Ostenberg et al. [38] concluded that data obtained from strength tests and functional jumping tests were not comparable and should not be used interchangeably. They emphasized the need for further development and validation of specific functional performance tests, suggesting that extrapolating data from only a strength or power test would not reflect real-world conditions.
In summary, when assessing strength imbalance together with other qualities, differences in strength values and bilateral flexibility imbalance between the dominant and non-dominant legs of the soccer players were established. Therefore, hamstring flexibility work in professional soccer players will be of great importance in achieving positive functional synergies with strength development.
This systematic review is not without limitations. First, only articles written in English were included; hence, some equally valid articles in different languages might have been excluded. Second, all the articles except one were composed of male subjects; hence, the data cannot be extrapolated to the female population, with different conditioning factors than those of men. Lastly, the heterogeneity in the study procedures and objectives of the selected investigations, as well as their sample space, which may be somewhat scarce (12 articles), make it difficult to reach universal conclusions.

5. Conclusions

The main conclusion drawn from this work is that the YBT seems to be a useful test for detecting injury risk in professional soccer players, but it does not seem to be sensitive or valid enough to detect differences between game positions. On the other hand, the evaluation of the imbalance in the flexibility of the extremities can be carried out reliably with the PSLR test, as well as measuring the ROM in the movements of abduction and internal rotation of the hip. It has also been shown that the FMS test is inversely related to the ability to perform jumps. Therefore, the combination of the FMS test together with the jump test can increase the sensitivity of the latter in search of possible asymmetries. Lastly, it has been shown that lower limb strength tests can increase imbalances in their flexibility agonist/antagonist ratio. Therefore, it is advisable to monitor both manifestations of muscle performance to avoid imbalances.
Future research on the YBT and mSEBT is needed for the assessment of limb imbalance using dynamic balance tests, as no data have been found that clearly indicate that these tests are useful for assessing limb imbalance in professional soccer players. Regarding the flexibility tests that assess limb imbalance, it is highlighted that the PSLR test and the measurement of ROM in hip abduction and internal rotation movements could be used to assess limb imbalance correctly. However, further research is needed to verify whether these tests and the FMS test are adequate to detect limb imbalance when not using a control group. In addition, the assessment of limb imbalance through flexibility tests such as the FMS ASLR is related to a limitation in jump landing mechanics. Also, better FMS test scores tend to produce less asymmetry in jumping tests. On the other hand, flexibility and limb strength imbalance did not affect jumping performance, and further research is needed to confirm this hypothesis. However, when unilateral asymmetry (agonist-antagonist muscles of both legs) and/or bilateral asymmetry (between dominant and non-dominant leg) were evaluated by means of strength and flexibility qualities, differences were obtained between strength values and flexibility imbalance between the dominant and non-dominant legs of the soccer players. This highlights the importance of working on flexibility in the hamstring musculature for professional soccer players.

Author Contributions

Conceptualization, J.C.C.-M. and A.S.-L.; methodology, A.M.-V. and J.C.C.-M.; software, A.M.-V. and J.P.-O.; validation, A.M.-V., J.C.C.-M. and J.P.-O.; formal analysis, A.M.-V. and J.C.C.-M.; investigation, A.S.-L.; resources, A.S.-L. and A.M.-V.; writing—original draft preparation, A.M.-V. and A.S.-L.; writing—review and editing, A.M.-V. and A.S.-L.; supervision, J.P.-O. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Applsci 15 01875 g001
Figure 1. PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) flow diagram.
Figure 1. PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) flow diagram.
Applsci 15 01875 g001
Table 1. Inclusion and exclusion criteria.
Table 1. Inclusion and exclusion criteria.
InclusionExclusion
PopulationThe tests were conducted on healthy, adult, professional-level football players.The tests were carried out on players at youth and/or injured and/or amateur level.
InterventionAssess lower limb asymmetry.
They use low-cost equipment (goniometer, inclinometer, tape measure, video camera, etc.).		They do not assess lower limb asymmetry.
They use expensive equipment (isokinetic dynamometer and contact/force platforms).
OutcomesThey include measures of unilateral asymmetry (agonist-antagonist muscles of both legs) and/or bilateral asymmetry (between dominant and non-dominant leg).They do not include measures of unilateral and bilateral asymmetry.
StudyPeer-reviewed, original, full-text articles written in English.Written in a language other than English or original non-peer-reviewed full-text studies.
Table 2. Assessment of study quality using the PEDro scale.
Table 2. Assessment of study quality using the PEDro scale.
RESEARCH1234567891011Score
Ateş et al. [20]✓ ✓✓✓✓5
Kraus et al. [35]✓ ✓✓✓✓5
López-Valenciano et al. [36] ✓ ✓✓✓✓5
Manning y Hudson [37]✓ ✓ ✓✓✓✓6
Medeiros et al. [27]✓ ✓ ✓✓✓✓6
Ocarino et al. [22]✓ ✓ ✓✓✓✓6
Onofrei et al. [28]✓ ✓✓ ✓4
Östenberg et al. [38]✓ ✓✓ ✓4
Read et al. [39]✓ ✓ ✓✓✓✓6
Sannicandro et al. [40]✓ ✓ ✓✓✓✓6
Sannicandro et al. [41]✓ ✓✓ ✓4
Zalai et al. [42]✓ ✓✓✓✓5
Note: choice criteria (item 1); random allocation (item 2); concealed allocation (item 3); baseline comparability (item 4); blinded participants (item 5); blinded therapists (item 6), blinded assessors (item 7); follow-up (item 8); intention to treat analysis (item 9); between group analysis (item 10); point estimates and variability (item 11).
Table 3. Characteristics of the selected studies.
Table 3. Characteristics of the selected studies.
STUDYSAMPLEASSESSED ASYMMETRYTESTVARIABLESRESULTSCONCLUSIONS
Ateş et al. [20]24 men (Age: 24.3 ± 5.25 years; 75.7 ± 12.2 kg; 1.82 ± 0.02 cm).BilateralY Balance TestDynamic balanceNo significant differences in total score, ANT, PM, and PL (p > 0.05).Field position is not relevant for detecting differences between YBT asymmetries.
Kraus et al. [35]53 men (Age: 23.3 ± 2.1 years)BilateralDS, HS, ILL y ASLRHip, knee, and ankle mobilityNegative correlation *** between landing mechanics and LESS height.

Significant correlation * between ASLR with SD and ILL.		Landing mechanics are related to jumping performance.
The length of the ASLR kinetic chain may limit the landing mechanics.
LESSHigh jump and landing mechanics
López-Valenciano et al. [36]82 men (Age: 25.5 ± 5.0 years; 75.0 ± 6.5 kg; 180.1 ± 6.5 cm)Bilateral PHFKF, PHFKE, PHE, PHA, PHER PHIR, PKF, ADFKF y ADFKEROM de PD y PNDNo significant differences (p > 0.05) for PHFKF, PHFKE, PHE, PHA, PHER PHIR, PKF, ADFKF and ADFKEUnilateral training should be considered in sports where training could promote bilateral differences.
Manning y Hudson [37]40 men (Age: 26.3 ± 4.2 years, 74.3 ± 6.2 kg; 179.9 ± 6.5 cm)BilateralPassive hip IR, ER, flexion, abduction and extensionROMLower IR and flexibility *** of football players vs. control groups.

Differences in abduction *** between football players and control group.		Hip ROM in the abduction and IR flexion planes football players is different from that of the control groups.
Medeiros et al. [27]101 men (Age: 21 ± 3 years; 75 ± 9 kg; 179 ± 7 cm)BilateralPSLR Test
ASLR test		Hamstring flexibility by measuring ROMHigher ASLR score values *Better hamstring flexibility stratification of PSLR over ASLR.
Ocarino et al. [22]134 men (Age: 19.42 ± 2.57 years; 74.24 ± 7.69 kg; 180.10 ± 6.91 cm) Thomas testFemoral and iliopsoas flexibilityLess PD flexibility in the iliopsoas and rectus femoris ** versus PND.

Lower hip PD stiffness ** versus PND.

PD has greater external rotator torque ** PND.		No significant differences between limbs in strength, flexibility, and hip stiffness data.
Passive knee ExtHamstring flexibility
BilateralHip rotationPassive hip stiffness
Hip extensor flexors and rotatorsForce
Onofrei et al. [28]73 men (Age: 23.8 ± 5.4 years, 74.6 ± 7.6 kg and 177.7 ± 20.2 cm)BilateralmSEBTDynamic balanceSignificance *** of the mean mSEBT score for PD and PND.
Higher ** asymmetries in mSEBT in PM and PL direction in ANT.
Lower asymmetries predicted 4 cm for ANT and PL *** and PM ** direction.		Flexion is used to measure flexion balance performance in football players.
Östenberg et al. [38]101 females (Age: 20.3 ± 4.1 years; 61.3 ± 7.3 kg; 166.9 ± 4.9 cm) Concentric knee flexion strengthStrengthHigh correlation *** between the single-leg jump and triple jump.
High correlation *** between five functional tests except (vertical jump with single leg raise and vertical jump with square jump).
Significant differences *** when comparing PD with PND in all tests.		Isokinetic endurance and functional tests cannot be used interchangeably.
Lift one legHip and knee extensor strength
BilateralVertical jumpVertical height
Square jumpMultidirectional movements
Horizontal jumpPower measuring distance
Triple jump
Read et al. [39]203 men (Age: 24.4 ± 4.7 years; 71.5 ± 9.3 kg; 175.7 ± 6.6 cm) Knee flexionForceGreater DC asymmetry * in Fcon of Q and Fexc of hip abduction MC and DF.

Lower H and Q jump scores * of the highly asymmetric group compared to the other groups in SLCMJ and CMJ.		Asymmetries in the H:Q ratio, ROM, and hip strength do not affect jumping performance.
Hamstring Nordic curl
BilateralAbd and add eccentric hip strength
BKFOROM
Loaded stride
IR
Hamstring flexibility
SLCMJ and CMJJumping
Sannicandro et al. [40]30 men (Age: 22.2 ± 4.6; 74.3 ± 10.1 kg; 176.1 ± 8.7 cm) Jumping testJumping asymmetryNegative correlation between FMS, % lateral, and cross jump asymmetry **.

Correlation between FMS score and CMJ values **.		The FMS test is related to increase CMJ performance and decrease percentage of % functional asymmetry.
Lateral jumpLateral jump asymmetry
BilateralCross jumpCross jump asymmetry
CMJJumping performance
DS, HS, ILL and ASLRHip, knee, and ankle mobility
Sannicandro et al. [41]31 men (Age: 22.2 ± 4.6; 74.3 ± 10.1 kg; 176.1 ± 8.7cm) Jumping testJumping asymmetryNegative correlation between FMS and asymmetries of jump test, lateral, and cross jump **.

Correlation between jump asymmetry and lateral and cross jump asymmetries ***.

High correlation between lateral and cross jump asymmetry *** 		Jumping assessment is useful for assessing strength flexion and asymmetry in football players.
Lateral jumpLateral jump asymmetry
BilateralCross jumpCrossed jump asymmetry
DS, HS, ILL and ASLRHip, knee, and ankle mobility
Zalai et al. [42]20 men (Age: 23.00 ± 3.00 years; 76.75 ± 6.97 kg; 182.25 ± 5.02 cm)BilateralDS, HS, ILL and ASLRHip, knee, and ankle mobilitySignificant differences * between ankle and HS injuries.

Significant differences * of SD with knee and hip injuries.		The FMS shows asymmetries in 40% of the participants.
ADFKE (ankle dorsiflexion with knee extension); ADFKF (ankle dorsiflexion with knee flexion); ANT (anterior); ASLR (active straight leg raise); BKFO (bent knee supine drop); CMJ (countermovement jump); DC (forward); DF (defence); DS (deep squat); H (hamstring); HS (hurdle step); ILL (in-line stride); LESS (landing error scoring system); MC (midcentre); mSEBT (modified Star Excursion Balance Test); PD (dominant leg); PHA (passive hip flexion in abduction); PHE (passive hip flexion in extension); PHER (passive hip flexion in external rotation); PHFKE (passive hip flexion with knee extension); PHFKF (passive hip flexion with knee flexion); PHIR (passive hip flexion in internal rotation); PKF (passive hip flexion with knee flexion); PL (posterolateral); PM (posteromedial); PND (non-dominant leg); PSLR (passive straight leg raise); Q (quadriceps); SLCMJ (single leg countermovement jump). Significant correlations between variables: * p < 0.05, ** p < 0.01, *** p < 0.001.
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Moreno-Villanueva, A.; Soler-López, A.; Cuartero-Martínez, J.C.; Pino-Ortega, J. Assessment of Limb Imbalance in Professional Soccer Players. Appl. Sci. 2025, 15, 1875. https://doi.org/10.3390/app15041875

AMA Style

Moreno-Villanueva A, Soler-López A, Cuartero-Martínez JC, Pino-Ortega J. Assessment of Limb Imbalance in Professional Soccer Players. Applied Sciences. 2025; 15(4):1875. https://doi.org/10.3390/app15041875

Chicago/Turabian Style

Moreno-Villanueva, Adrián, Alejandro Soler-López, Jose Carlos Cuartero-Martínez, and Jose Pino-Ortega. 2025. "Assessment of Limb Imbalance in Professional Soccer Players" Applied Sciences 15, no. 4: 1875. https://doi.org/10.3390/app15041875

APA Style

Moreno-Villanueva, A., Soler-López, A., Cuartero-Martínez, J. C., & Pino-Ortega, J. (2025). Assessment of Limb Imbalance in Professional Soccer Players. Applied Sciences, 15(4), 1875. https://doi.org/10.3390/app15041875

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