Determination of the Degree of Dynamic Stability of the Foot in Single-leg Support in Relation to the Foot Posture Index in Judokas
Conditions: Postural Balance, Foot Posture, Sports Injuries, Athletic Performance
Sponsor: Fundación Universidad Católica de Valencia San Vicente Mártir

STUDY PROTOCOL WITH STATISTICAL 
ANALYSIS PLAN 
 
 
Official Study Title: 
Determination of the Degree of Dynamic Stability of the Foot in Single-leg 
Support in Relation to the Foot Posture Index in Judokas 
 
 
NCT Number: To be assigned 
 
Document Date: January 26, 2023 
 
Ethics Committee Approval: 
Catholic University of Valencia San Vicente Mártir 
Protocol Code: UCV/2022-2023/111 
 
 
Principal Investigator: 
Juan Carlos Parada Souto 
Catholic University of Valencia San Vicente Mártir 
Faculty of Medicine and Health Sciences 
Valencia, Spain 
 
Co-Investigator: 
Raúl Gallego Estévez 
Catholic University of Valencia San Vicente Mártir 
Faculty of Medicine and Health Sciences 
Valencia, Spain 
 
 
 
 
 
 
 

ABSTRACT 
Background 
Judo is the most practiced individual sport in Spain, with approximately 97,000 
licenses. One of the fundamental aspects of standing judo consists of knocking 
down an opponent to make them fall on their back. Maintaining good balance is 
essential not only for adequate sports performance but also to avoid possible 
injuries. However, studies describing the dynamic stability of judokas are very 
scarce, and they do not provide specific or detailed data. Therefore, through this 
work, we aim to update and increase knowledge about the stability of judokas. 
Hypothesis 
Judokas who present a neutral foot determined by the Foot Posture Index-6 (FPI-
6) will have a greater degree of dynamic stability in single-leg support during the 
specific techniques of their sport, being able to adapt to different sporting 
situations during practice, compared to those who present a pronated or supinated 
foot. 
Objectives 
Primary Objective: To analyze the degree of dynamic stability through the Y 
Balance Test (YBT) in judokas according to the type of foot they present, 
determined by the FPI-6. 
Secondary Objectives: 
1. To analyze the relationship between the modification of dynamic stability 
and different sociodemographic variables. 
2. To relate injury history with stability in the lower limbs. 
3. To determine if there are significant differences in dynamic stability 
regarding the habitual support foot in the development of specific sports 
techniques. 
 

Methods 
This is a cross-sectional observational study with quantitative methodology 
conducted on judokas from the Galician provinces of A Coruña and Pontevedra. A 
sample of 45 participants will be selected. The dynamic stability of participants will 
be compared through the Y Balance Test in relation to the type of foot determined 
by the Foot Posture Index. 
Expected Outcomes 
The study will provide data on dynamic stability in judokas according to foot 
posture type, contributing to understanding biomechanical factors that may 
influence sports performance and injury risk in this population. 
Keywords: Judo, lower limb, stability, Foot Posture Index, Y Balance Test, 
dynamic stability, sports biomechanics 
 
 
 
 
 
 
 
 
 
 
 
 

1. INTRODUCTION 
1.1. Theoretical Framework 
1.1.1. History of Judo 
Judo, or "the gentle way" in Japanese, is a martial art and Olympic sport that 
includes standing fighting (tachi-waza) and ground fighting (ne-waza)[1]. It was 
born at the end of the 18th century by Jigoro Kano in Japan. He began his journey 
in martial arts practicing ju-jitsu, but due to his thinness and lack of strength, he 
saw his sports practice limited. This led him to modify the techniques of this sport 
to take advantage of the opponent's strength more efficiently and better adjust to 
his physical condition, thus creating judo. 
Judo entered the men's Olympic program in 1964 as a demonstration sport and 
officially in 1972. It was not until 1992 that it began to form part of the women's 
Olympic agenda [1]. It is the 6th most practiced sport in Spain with 97,000 licenses 
(2020 data), and almost 9,000 in Galicia alone, making this sport one of the most 
practiced in the country. 
1.1.2. Development of Judo 
It is a sport practiced by more than 10 million people worldwide, where two types 
of competitions are held: individually through combat and in pairs with kata. 
Individual competition consists of 4-minute combats, where two situations can be 
found during the dynamics: standing judo and ground judo. The combat begins 
standing, and due to the evolution of the fight (opponent's takedown or fall of 
judokas on the mat), it can continue on the ground. Each time the combat is 
stopped (due to lack of continuity, sanctioning one of the competitors, or reviewing 
some situation), it will resume with standing judo. 
The objective in standing judo is to knock down an opponent of the same weight 
category, causing loss of balance through grips, displacements, and offensive 
and/or defensive actions. In ground judo, the judoka must try to control the 

opponent's body for a certain time or make them give up through segmental control 
(strangulation or dislocation) [2]. 
If no score is achieved in the regulatory time, golden score time begins, where the 
first to score wins the combat. 
When speaking of standing judo techniques, four groups are differentiated: 
• Te-waza: Arm techniques where the objective is to unbalance the opponent 
by leveraging through the shoulder/arm. 
• Koshi-waza: Through the hip, the opponent is lifted with the objective of 
making them lose contact with the ground. 
• Ashi-waza: Leg techniques, where the takedown is performed through leg 
movements (divided into sweeps, reaps, and blocks). 
• Sutemi-waza: So-called sacrifice techniques, where the tori (judoka 
executing the technique) must throw themselves to the ground for the uke 
(judoka on whom the technique is performed) to fall on the mat. 
The circle of equilibrium is the area in which the judoka's posture can be disturbed 
and they will always be able to return to their initial position. When performing a 
judo technique, the first step the tori takes is an unbalancing through arm and body 
movement on the uke to take them out of this circle of equilibrium. Once this 
unbalancing has been carried out, it is the moment when the tori performs the 
technique to throw the uke[2]. 
Scoring in standing judo depends on the contact of the opponent's back with the 
mat when a technique is performed. If the contact is with the complete back, an 
ippon is achieved (10 points) and the combat is automatically won; however, if the 
contact is not with the entire back but with a part of it, a waza-ari is achieved (1 
point). Two waza-aris from the same judoka become an ippon. 
Initially, judo competitions did not distinguish by weight, creating a disadvantage 
for lighter judokas. With the evolution of judo, competitions now differentiate by 
age, weight, and sex. 

1.1.3. Equipment 
Practice is carried out with the judogi, attire for judo practice. It consists of a thick 
cotton jacket (uwagi), pants (shitabaki), and a belt (obi). When competing, to avoid 
referee confusion, one will wear a white judogi (the traditional color) and another 
will wear a blue one. The belt indicates the athlete's degree of learning, with the 
white belt being the first and the highest being the black belt (1st DAN) [1]. 
1.1.4. Benefits of Judo 
One of the main objectives of promoting a healthy lifestyle is increasing the level of 
physical activity that citizens regularly practice, with the aim that these habits 
positively influence the physical and psychological condition of the population [5]. 
The sedentary lifestyle is one of the problems that most concern the childhood 
stage; children increasingly perform less physical activity and spend more time in 
front of multimedia screens. To reverse this situation, the WHO (World Health 
Organization) recommends daily activity to maintain children's psychophysical 
health [6]. 
The main benefit of judo is that it is a sport that can be practiced at any age. Its 
practice at early ages (between 4 and 12 years) has a more recreational function, 
where the pressure to achieve objectives is much less or nonexistent compared to 
adult ages, which makes the risk of injury diminished [6]. 
The practice of martial arts has a large number of benefits. On one hand, there is 
an improvement in physical condition, common to the vast majority of sports, 
necessary for good development of sports activity and performance improvement. 
Various studies affirm that this practice improves the teaching of self-control, self-
esteem, increases positive response to physical challenges, and induces greater 
emotional stability, self-confidence, and assertiveness. It has also been shown to 
improve concentration in children and self-awareness, as well as cognitive self-
regulation [7]. 

These benefits are related to increased levels of certain hormones, such as oxytocin 
during sports practice, which increases motivation, empathy, or recognition of 
emotions, essential for both physical and mental growth of athletes [8,9]. Through 
the practice of judo or other martial arts, an increase in levels of immunoglobulin 
A, cortisol, or testosterone is generated, although these are subject to a 
psychological factor [10]. 
1.1.5. Biomechanics of Judo 
 
Success in sport depends on athletes' ability to achieve and maintain high levels of 
perceptual, psychological, cooperative, and conditioning decision-making during 
competition. Martial arts are cooperative, conditional, and complex, and are based 
on a variety of skills (i.e., strength, power, aerobic endurance, agility) and aptitudes 
(i.e., coordination and perceptual decision-making) [2]. 
During combats, judokas perform great physical efforts that require great muscular 
strength, optimal range of motion of joints, and maintaining different postures to 
attack or defend. These skills require postural stability, not only for greater sports 
performance but to avoid injuries due to lack of balance [13]. 
The biomechanics of judo will be conditioned by the technique that will be carried 
out, where both extremities can perform the same movement or one the opposite 
of the other, although both will always be coordinated. 
A large number of factors can influence an athlete's stability during the execution 
of a specific task of their sport, among which biomechanical and anthropometric 
factors, control of the progression of the center of mass in a dynamic or static 
situation, and the support surface stand out. For this, athletes use different 
movement strategies to stabilize themselves when initiating a voluntary action, 
reacting to perturbations caused by unexpected external forces, or anticipating a 
destabilizing force. All these actions are controlled by the central nervous system, 
giving greater influence to information from visual, vestibular, and proprioceptive 

receptors, and executing a musculoskeletal response adapted to the characteristics 
of the situation [2]. 
Postural control is essential in combat sports, especially in those where grip is 
fundamental (such as judo, sambo, or Olympic freestyle wrestling), because success 
in these sports is based mainly on preserving the center of mass within the base of 
support that changes continuously, so that from a stable position specific skills can 
be executed and cause the opponent's loss of balance. Voluntary regulation of the 
center of gravity in a determined direction is essential both when performing an 
attack and a defense [2]. 
The judoka's stability is in continuous change during a combat due to rapid changes 
in the center of gravity as a consequence of the opponent constantly trying to 
disturb the judoka's balance to knock them down; in turn, the judoka is also moving 
their center of mass continuously to try to attack their opponent. This generates 
modifications in the judoka's base of support, causing them to combine bipodal 
support with single-leg support to achieve greater balance [13]. 
In judo, stability will be conditioned by the tractions and thrusts exerted by the 
upper limb in all directions (antero-posterior, medio-lateral, supero-inferior, 
rotational, and their variations). These perturbations performed on the upper 
extremity cause the athlete to change their habitual support strategy, where these 
alterations must be cushioned by the trunk and lower limbs [2]. 
Although all body musculature is trained in judo, the core is one of the structures 
that must be most trained. It is formed by the lumbopelvic complex, the spine, hips 
and pelvis, proximal lower limbs, and abdominal structures. Its training will 
improve the ability to control trunk movement over the pelvis and leg to allow 
optimal production, transfer, and control of force and movement to the terminal 
segment integrated into specific activities [14]. 
Core strengthening will not only improve the sports level, through improved 
balance during attack and defense, but will also reduce the risk of injuries and 
improve the judoka's body posture both at the sports level and in daily life. Core 

training is included in injury prevention programs such as anterior cruciate 
ligament rupture, given that dynamic movement of the trunk and hip joint 
biomechanically affects the knee joint during physical activities. Neuromuscular 
control deficits in the trunk and hip joint could increase the risk of anterior cruciate 
ligament injury [15]. 
Within all this complexity, it should be indicated that stability in the confrontation 
depends on the interaction between the judokas, their position during sports 
activity, and their communication through the grip, reaching situations where the 
body's center of gravity can be located outside the base of support of one or even 
both judokas [2]. 
1.1.6. Epidemiology of Judo 
As a result of the literature review, it was not possible to adopt a standardized 
definition of either injury or its severity. As a MeSH term, injuries are defined as 
damage inflicted on the body with direct result of an external force, with or without 
interruption of structural continuity. However, during the Olympic Games, any 
alteration in which an athlete received medical attention for a recent injury or a 
new injury after full participation was included as injuries, including injuries in 
competition or during training [1]. 
To protect athletes' health, the International Olympic Committee initiated and 
developed an injury and illness monitoring system during the Beijing 2008 and 
London 2012 Olympic Games, where the most common and serious injuries would 
be collected. The objective was to identify the main sports alterations to ensure new 
knowledge about injury trends over time to thus form the basis for future research 
on injury mechanisms and finally develop injury prevention programs [1]. 
The lower extremity is the body region that suffers the most injuries in sport in 
general terms [16], with the ankle being the joint most likely to suffer damage 
(around 50% of sports injuries correspond to the tibioperoneal-astragalar mortise), 
followed by cerebral concussions and anterior cruciate ligament injuries [17]. 

Around 20% of hospital emergencies correspond to sports injuries, of which judo 
is the martial art that collects the most, in which 56% of athletes have suffered at 
least one, where the highest percentage of injuries focuses on the elbow and 
shoulder, followed by karate and wushu, where the main injuries found are ankle 
sprains and joint injuries[18]. 
The prevalence of injuries in judo varies depending on the study. At the Beijing 
2008 and London 2012 Olympic Games, there was a prevalence of 11.2-12.3% of 
injuries in more than 380 participants, although other studies increase this 
prevalence to 23-29% or 1.18 injuries per year in each athlete. These discrepancies 
are due to the different levels of judokas who participated in the studies and the 
definition of injury used in each of them. There is no consensus regarding a higher 
prevalence of injuries in relation to sex or the moment of injury (training or 
competition) [1]. 
The body regions most affected by injuries are the hand/fingers, knee, and shoulder 
in that order. As previously explained, these values depend on the definition used 
in the studies and the level of judokas; therefore, some studies identify finger 
injuries as the most frequent in competition due to gripping in combats, and others 
do not include them as injuries. In children, injuries focus on the shoulder, ankle, 
and elbow in that order. There are no differences in the causes of injuries between 
sexes [1]. 
85% of injuries occur in standing judo compared to ground judo, mainly because 
more time is spent in this part of the combat, where the grip struggle constitutes 
one of the main risk factors (finger injury is described as the most frequent in some 
studies). The fall is the situation that comprises the most injuries, around 70%, 
associated with the risk that judokas assume to not fall with their back and thus 
lose the combat; also, the lack of ability to fall is associated with an increase in both 
acute and chronic injuries [1]. 
As previously indicated, there are no significant differences in the cause of injuries 
in relation to sex or age; however, women have a higher injury prevalence in ground 
judo. Loss of balance when throwing the opponent also constitutes one of their 

main causes. These reasons are common to males between 10 and 19 years; from 
20 years on, the fall constitutes the main risk factor for them. Seoi Nage techniques 
(leverage applied with variable arm) are the techniques with the highest risk of 
shoulder and knee injury, with incorrect technique being the main injury 
mechanism [1]. 
Knee injuries, such as anterior cruciate ligament rupture or sprains, are mainly 
caused by leg techniques such as O Soto Gari, where the violence with which the 
techniques are performed also influences. Ankle injuries correspond in most cases 
to sprains of the external ligaments caused by varus torsion [1]. 
Compared to other Olympic wrestling sports, judo has a shorter injury recovery 
time than others like taekwondo, although longer than boxing or freestyle wrestling 
[1]. 
Several studies have been conducted that highlight that functional taping is the 
most effective method to prevent injuries in sport along with orthopedic elements 
[19], a prevention method carried out by a large number of judokas. But this means 
has several disadvantages: not only does it limit the range of motion of the joint, 
but it increases the mechanical demand on the rest of the proximal joints, 
increasing the risk of injuries on them [20]. 
One of the main areas of greatest risk when applying an ankle taping is the knee; 
fixation of the tibioperoneal-astragalar (TPA) joint increases tension on the triceps 
surae (gastrocnemius and soleus), generating greater knee valgus, thus increasing 
the probability of suffering an injury to it [21]. 
Both proprioception training and muscular strength training of the lower 
extremities improve athletic performance and raise the skill level of athletes in 
maintaining posture in taekwondo. Therefore, the application of these methods in 
taekwondo training programs has a positive effect on improving competitive 
performance in these athletes. In particular, the findings confirm that conscious 
effort to perform the posture with the load applied on the forefoot is related to 

maintaining balance when performing the posture at the single-leg level [22]. Due 
to the similarity of both sports, this condition can also be applied to judo. 
Due to the presence of all the threats that the judoka's stability must face in a 
combat, it is not surprising that examination of postural care in judo generates 
great interest. Previous studies indicate a relationship between the ability to 
maintain posture and the sports performance achieved in a competition, with 
performance evaluation based on ranking criteria and levels of activity and 
competitive effectiveness. When cohorts of judokas were compared with control 
groups that did not practice physical activity, it was observed that judokas obtained 
better results by relying more on proprioceptive information. It is this reliance on 
vestibular and proprioceptive information that makes these athletes obtain greater 
stability than in other sports such as dance or swimming [23-25]. 
1.1.7. Foot Posture Index 
Variations in foot posture influence lower extremity function and therefore can 
generate a greater predisposition to suffer overuse injuries [26]. Overuse is defined 
as excessive force repeatedly applied over a tissue, making it unable to cope with 
mechanical stress through natural mechanisms of physiological adaptation or 
tissue repair [27]. This mechanical stress on tissues, of repetitive nature but always 
below their rupture threshold, leads to the development of a type of injury known 
as overuse injuries [28]. 
The Foot Posture Index (FPI-6) is a tool used both clinically and in research. It has 
been used in studies to determine the biomechanical factors causing neuropathic 
ulcers in diabetic patients, to determine inclusion and exclusion criteria, or to 
associate sports injuries with foot types [26]. 
The FPI-6 is a validated test that allows determining the postural index of the foot 
in a quick, simple, and reliable way through palpation and visual inspection of 6 
items: palpation of the talar head, supra and inframaleolar curvature, relaxed 
calcaneal position in support, navicular prominence, congruence of the medial 

longitudinal arch (MLA), and the degree of adduction/abduction of the forefoot 
relative to the rearfoot [29]. 
Each of these parameters is assessed on a 5-point scale, ranging from -2 to +2, with 
-2 corresponding to a high supination position, 0 a neutral position, and +2 a 
maximum pronation position. The FPI-6 value is given by the sum of all the values 
obtained, providing values between -12 and +12; these measurements must be 
performed on both feet. Those feet with an FPI-6 from -12 to -5 will be classified as 
highly supinated, from -4 to -1 as supinated, from 0 to +5 as neutral, from +6 to +9 
as pronated, and from +10 to +12 as highly pronated [29,30]. 
According to Cheung RTH et al. [30], a meta-analysis studying the efficacy of 
external controls for overpronation, foot pronation involves multiple joint 
movements in the rearfoot and midfoot, which are necessary for optimal movement 
and shock absorption during the initial and mid-phase of gait; however, people 
with excessive foot pronation are vulnerable to injuries both distally (metatarsal 
pathologies or fasciopathies) or proximally (patellofemoral pain) in the lower 
extremity. 
Although the evidence is not conclusive, MLA characteristics have been discussed 
as possible factors contributing to overuse injuries of the lower extremity. Feet with 
a higher MLA have less shock absorption capacity, associating this characteristic 
with a higher incidence of ankle injuries, bone injuries (mainly in tibia or femur), 
or on the lateral side of the lower extremity. Conversely, a decreased MLA is more 
prone to relate to soft tissue injuries and on the medial side of the lower extremity 
[31]. 
High positive values on the FPI-6, which classify the foot as a pronated foot, are 
related to overuse pathologies in the lower extremity and the appearance of 
osteoarthritis in the knee [32]. 
Those feet considered supinated through the FPI-6 will have altered stability, 
where the presence of an elevated arch height and increased ankle inversion force 
are related to a decrease in postural stability in single-leg support [33]. 

Koyama K et al. [34] studied how judo affects foot structure. It was found that after 
specific judo training, the foot arch was lower compared to a healthy population of 
the same characteristics who did not practice judo, with judokas presenting greater 
strength in the toe flexor and also superior foot arch dynamics. In this way, it was 
possible to affirm that specific judo training can affect force generation capacity, 
morphological structure, and foot arch function. 
1.1.8. Dynamic Stability 
From the biomechanical point of view, balance arises from the interaction of 
external forces acting on the body and internally generated movements to prevent 
falls and maintain body posture [35]. 
When speaking of stability, we must speak of two different types: postural stability 
and dynamic stability. The first is defined as the ability to remain close to a desired 
body position, without falling or taking a step (i.e., maintaining balance), under 
brief perturbations of external forces and spontaneous changes in intrinsic body 
states [36]. 
Dynamic stability is known as the ability to conserve a stable static condition on a 
base of support after a dynamic transition (i.e., after a movement). Since judo is a 
sport in which continuous displacements and variations of the center of gravity are 
performed, this study will focus on performing an analysis of dynamic stability. 
Work on postural control and balance is fundamental to avoid falls and decrease 
the risk of pathologies, affecting both the childhood and adult stages [37]. 
Postural control requires maintaining an upright posture, requiring correct motor 
behavior. Maintaining this depends on the integration of sensory inputs from the 
vestibular, visual, and proprioceptive systems; if one or more of these components 
are compromised, muscles are activated to reduce oscillations and maintain 
postural balance [38]. 
Proprioceptive sensory receptors, located in the skin, muscles, joints, tendons, and 
ligaments, are responsible for sending the information provided by these structures 

to the central nervous system. This information is complemented by that provided 
by the visual system and vestibular system to maintain balance and body position. 
For this reason, when an injury occurs, the mechanoreceptors of the affected region 
can be damaged and cause some tissues to lose their function and thus reduce their 
proprioceptive capacity [39]. 
The main cause of falls in the population is lack of balance, generated by lack of 
postural control that increases with advancing age by presenting less postural 
stability (hunched posture, greater muscular coactivation, and postural sway). An 
improvement in posture of an ascending character (i.e., improving stability and 
balance of the lower extremity initially) can decrease excessive muscular 
coactivation and thus improve balance not only in older adults but in the general 
population, including athletes [40]. 
In medical evaluations, postural control analyses are recurrent to assess injury risk, 
initial injury deficits, and the level of improvement after intervention for an injury. 
This postural control is necessary to maintain during statics and during movement. 
Musculoskeletal pathological conditions of the lower extremities are generally 
associated with deficits in postural and neuromuscular control [41]. 
Dynamic stability allows expected movement around a base of support, such as 
jumping or moving to a new location and immediately attempting to maintain 
posture or perform the movement without compromising the established base of 
support [41]. 
One of the tests that has gained notoriety in clinical settings and research is the Star 
Excursion Balance Test (SEBT), a dynamic stability test tool for rehabilitation in 
which, through a series of single-extremity squats, the unsupported extremity is 
used to reach maximum distance at 8 different points designated on the ground. 
The objective of this test is for the individual to establish a stable base of support 
on the posture extremity in the middle of the test grid and maintain it through a 
maximum reach excursion in one of the prescribed directions [41]. 

This test is used to determine the extent of an injury in the lower extremity, in 
which the patient is asked to perform the test while in single-leg support on the 
affected extremity to maintain balance, finding a deficit in reach distances, 
indicating a limitation in dynamic stability associated with the pathological 
condition [41]. 
Patients and athletes suffer injuries both for the first time and of a repetitive nature, 
so physicians must identify injury risk and determine if patients have recovered a 
level of dynamic and postural control that minimizes injury risk when they return 
to sports practice. Dynamic stability tests such as the SEBT or Y Balance Test (YBT) 
can help determine if the patient possesses optimal or symmetrical values of this. 
This test can be used as a marker of normalization of neuromuscular control for 
return to play after an injury [41]. 
As just mentioned, these tests can be used to identify individuals at higher risk of 
injury and reduce future sports injuries. By requiring strength, flexibility, 
neuromuscular control, core stability, wide range of joint mobility, balance, and 
proprioception for its performance, it is an excellent test for pre-participation 
physical and clinical examinations, since finding any of these components defective 
would cause a defective test [41]. 
A study carried out on soccer players by Yu N et al. [39] concludes that through the 
combination of proprioceptive training with ankle muscular strength training, 
dynamic and static stability can be improved and thus decrease the risk of ankle 
injuries in players. They also indicate that the stability of martial arts athletes 
decreases in the antero-posterior direction. 
1.2. Study Justification 
Through the literature search carried out for this study, no research has been found 
that relates dynamic stability of the lower limb in judokas with the type of foot they 
present. Although there are multiple studies about injuries in this sport or foot 
posture and its relationship with injuries, they do not analyze how the type of foot 
influences the balance of athletes. 

Balance and stability are essential for good sports performance and injury 
prevention, especially in a sport like judo where continuous changes in the center 
of gravity and the base of support occur. Understanding how foot posture affects 
dynamic stability could provide valuable information for: 
• 
Improving training programs 
• 
Developing specific injury prevention strategies 
• 
Optimizing sports performance 
• 
Guiding orthopedic interventions when necessary 
This study aims to fill this gap in the scientific literature and provide practical 
information for coaches, podiatrists, and sports medicine professionals working 
with judokas. 
Additionally, the Y Balance Test has proven to be a reliable and valid tool for 
assessing dynamic stability in various sports populations, but its application and 
normative values in judokas remain limited. This study will contribute to 
expanding the knowledge base about dynamic stability assessment in this specific 
population. 
 
 
 
 
 
 
 
 

2. HYPOTHESIS 
2.1. Conceptual Hypothesis 
Judokas who present a neutral foot determined by the FPI-6 will have a greater 
degree of dynamic stability in single-leg support during the specific techniques of 
their sport, being able to adapt to different sporting situations during practice, 
compared to those who present a pronated or supinated foot. 
2.2. Statistical Hypotheses 
Hypothesis H1 (Primary): 
• Null hypothesis (H0): There is no relationship between foot posture type 
(determined by FPI-6) and dynamic stability (measured by YBT). 
• Alternative hypothesis (H1): There is a relationship between foot 
posture type and dynamic stability. 
Hypothesis H2 (Secondary 1): 
• Null hypothesis (H0): There is no relationship between dynamic stability 
and sociodemographic variables (sex, age, weight category). 
• Alternative hypothesis (H1): There is a relationship between dynamic 
stability and sociodemographic variables. 
Hypothesis H3 (Secondary 2): 
• Null hypothesis (H0): There is no relationship between injury history 
and lower limb stability. 
• Alternative hypothesis (H1): There is a relationship between injury 
history and lower limb stability. 
Hypothesis H4 (Secondary 3): 
• Null hypothesis (H0): There are no significant differences between the 
habitual support foot and the non-habitual support foot in the development 
of specific sports techniques. 

• Alternative hypothesis (H1): There are significant differences between 
the habitual support foot and the non-habitual support foot in the 
development of specific sports techniques. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
3. OBJECTIVES 
3.1. Primary Objective 
To analyze the degree of dynamic stability through the Y Balance Test (YBT) in 
judokas according to the type of foot they present, determined by the Foot Posture 
Index-6 (FPI-6). 
3.2. Secondary Objectives 
1. To analyze the relationship between the modification of dynamic stability 
and different sociodemographic variables (sex, age, weight category). 
2. To relate injury history (neck, back, hip, or rest of the lower extremity) with 
dynamic stability in the lower limbs. 
3. To determine if there are significant differences in dynamic stability 
regarding the habitual support foot (dominant foot) versus the non-habitual 
support foot (non-dominant foot) in the development of specific single-leg 
sports techniques. 
 
 
 
 
 
 
 
 

4. MATERIALS AND METHODS 
4.1. Bibliographic Search Criteria 
The bibliographic search was conducted during the first week of work. It aimed to 
gather all available information on lower limb stability during sports practice in 
judo. To collect the maximum available information, no temporal limits or 
publication type limits were applied; regarding language, only articles in Spanish 
or English were included. 
The search strategy included the following databases: 
• PubMed/MEDLINE 
• Scopus 
• Web of Science 
• SPORTDiscus 
• Google Scholar 
Search terms used: 
• Judo AND (stability OR balance) 
• Judo AND (lower limb OR lower extremity) 
• Judo AND injuries 
• Foot Posture Index AND (stability OR balance) 
• Y Balance Test AND athletes 
• Dynamic stability AND martial arts 
4.2. Study Design 
4.2.1. Type of Design 
Cross-sectional observational study with quantitative methodology. 

On January 26, 2023, the Research Ethics Committee of the Catholic University of 
Valencia approved the conduct of the study "Determination of the degree of 
dynamic stability in single-leg support in relation to the Foot Posture Index in 
judokas" with project code UCV/2022-2023/111. 
4.2.2. Study Setting 
The study will be carried out in judo centers in the Galician provinces of A Coruña 
and Pontevedra, Spain. 
4.2.3. Study Population 
Federated judokas who train regularly in judo clubs in the provinces of A Coruña 
and Pontevedra. 
4.2.4. Study Period 
Recruitment period: February 1, 2023 to February 15, 2023 
Data collection period: March 1, 2023 to May 23, 2023 
Total duration: Approximately 4 months 
4.2.5. Selection Criteria 
4.2.5.1. Inclusion Criteria 
Participants must meet ALL of the following criteria to be included: 
1. Federated judokas (holding a valid judo federation license) 
2. Age between 10 and 40 years 
3. Training at least 2 hours per week 
4. At least 1 year of federated experience in judo 
5. Willing to participate and sign informed consent (or parental consent for 
minors under 18 years, with assent for those 14-17 years old) 
4.2.5.2. Exclusion Criteria 

Participants will be excluded if they present ANY of the following: 
1. Current lower limb injury that prevents normal sports practice 
2. Lower limb surgery in the last 12 months 
3. Neurological pathologies affecting balance or coordination 
4. Vestibular disorders 
5. Visual impairments not corrected by lenses that affect balance 
6. Inability to understand or follow study instructions 
7. Refusal to sign informed consent 
8. Pregnancy (for female participants) 
9. Use of orthopedic devices (orthoses, braces) during judo practice that 
cannot be temporarily removed for testing 
4.2.6. Sample Size 
The sample size was determined using the GPower software (Erdfelder, Faul, 
Buchner, 1996), using as reference a similar study by Cote KP et al.[45] to identify 
the true difference in dynamic stability score means in the 3 foot types. 
Sample size calculation parameters: 
• Statistical test: ANOVA (one-way) 
• Effect size (f): 0.40 (medium effect) 
• Alpha (α): 0.05 (significance level) 
• Power (1-β): 0.95 (95% power) 
• Number of groups: 3 (neutral, pronated, supinated foot) 
Calculated sample size: 42 participants 
Adjusted for expected losses (15%): 45 participants total (15 per group) 

Distribution: 15 participants with neutral foot, 15 with pronated foot, 15 with 
supinated foot. 
Although the sample size is estimated over the total population of Galicia that 
practices judo, only those participants who meet the inclusion criteria will be 
included in the study. 
4.2.7. Establishment of Variables and Measurement Methodology 
4.2.7.1. Sociodemographic and Anthropometric Variables 
Age: 
• Type: Quantitative continuous 
• Unit: Years 
• Measurement method: Self-reported from identification document 
Sex: 
• Type: Qualitative dichotomous 
• Categories: Male / Female 
• Measurement method: Self-reported 
Weight: 
• Type: Quantitative continuous 
• Unit: Kilograms (kg) 
• Measurement method: Weight category in which they compete. For non-
competing participants, current weight will be recorded. 
• Categories according to Sub-21 and absolute category (see Table 1 in 
Introduction) 
Height: 
• Type: Quantitative continuous 

• Unit: Centimeters (cm) 
• Measurement method: Standard stadiometer measurement 
Leg length: 
• Type: Quantitative continuous 
• Unit: Centimeters (cm) 
• Measurement method: Distance from anterosuperior iliac spine to the most 
distal area of the tibial malleolus, measured with tape measure 
4.2.7.2. Podiatric Variables and Variables Related to Sports 
Practice 
Training frequency: 
• Type: Quantitative continuous 
• Unit: Hours per week 
• Measurement method: Self-reported 
Federated time in sports practice: 
• Type: Quantitative continuous 
• Unit: Years 
• Measurement method: Self-reported, verified with federation records when 
possible 
Foot posture: 
• Type: Qualitative ordinal 
• Categories: Highly supinated (-12 to -5), Supinated (-4 to -1), Neutral (0 to 
+5), Pronated (+6 to +9), Highly pronated (+10 to +12) 
• Measurement tool: Foot Posture Index-6 (FPI-6) 

• Measurement method: Clinical assessment by trained podiatrist using 
standardized FPI-6 protocol 
Dominant foot: 
• Type: Qualitative dichotomous 
• Categories: Right / Left 
• Measurement method: Determined as the habitual support foot in single-leg 
techniques (uchi-mata, harai-goshi, etc.) 
Dynamic stability: 
• Type: Quantitative continuous 
• Unit: Percentage (%) 
• Measurement tool: Y Balance Test (YBT) 
• Measurement method: Normalized composite score calculated as: [(Sum of 
three reach distances) / (3 × leg length)] × 100 
Injury history: 
• Type: Qualitative dichotomous 
• Categories: Yes / No 
• Specification: Location (neck, back, hip, lower extremity), type of injury, 
context (training, physical test, competition) 
• Measurement method: Self-reported questionnaire 
• Timeframe: Injuries in the last 12 months 
4.3. Data Collection 
4.3.1. Constitution of the Work Team 
The work team consists of two podiatrists: 
1. Juan Carlos Parada Souto 

o Master's student in Sports Podiatry at the Catholic University of 
Valencia (UCV) 
o Principal investigator 
o Role: Data collection, FPI-6 assessment, YBT administration 
2. Raúl Gallego Estévez 
o Teaching and Research Staff (PDI) at UCV with research profile in 
podiatric pathology 
o Role: Study director, methodological supervision, data analysis 
4.3.2. Request to Judo Centers 
Judo club directors located in the Galician provinces of A Coruña and Pontevedra 
will be contacted and the purpose of the study explained. If they accept to 
participate in the study, they will send a communication to their federated athletes 
inviting them to participate. 
Contact will be made through email using a standardized invitation letter that 
includes: 
• Study objectives and relevance 
• Procedures and time commitment required 
• Ethical approvals obtained 
• Contact information for questions 
4.3.3. Recruitment of Participants 
Judo centers that accept to participate in the study will provide a list of their 
federated judokas who accept to participate. These judokas will contact the 
principal investigator through telephone or email, previously provided. 
The club directors will be informed of the possibility of scheduling an appointment 
to attend the training center with interested athletes. 

Once at the club, the project will be explained to them, resolving any doubts that 
may arise. Interested parties will be provided with: 
1. Information sheet about the research, explaining: 
o Study purpose and procedures 
o Risks and benefits 
o Data confidentiality measures 
o Right to withdraw at any time 
2. Informed consent forms to be signed before participation: 
o Adult consent form (≥18 years) 
o Parental consent form (<18 years) 
o Assent form (14-17 years) 
3. Confidentiality commitment document 
These documents must be signed and delivered before the scheduled appointment 
with their club, at which analysis and data collection will proceed. 
4.3.4. Data Collection and Coding 
General Data Collection 
General data will be collected through a standardized form that includes: 
Section 1: Personal Information 
• Participant code 
• Age 
• Sex 
• Weight / Weight category 
• Height 

Section 2: Sports Practice Information 
• Dominant foot (habitual support foot in single-leg techniques) 
• Shoe size 
• Years federated 
• Hours dedicated to weekly training 
• Competition level (regional, national, international, or non-competing) 
Section 3: Injury History 
• Previous injuries (yes/no) 
• If yes: Location, type, context (training/competition), time since injury 
Foot Posture Assessment (FPI-6) 
The FPI-6 will be administered by a trained podiatrist following the standardized 
protocol: 
Six components assessed (each scored -2 to +2): 
1. Talar head palpation 
2. Curves above and below the lateral malleoli 
3. Calcaneal frontal plane position 
4. Prominence in the region of the talonavicular joint 
5. Congruence of the medial longitudinal arch 
6. Abduction/adduction of the forefoot on the rearfoot 
Assessment conditions: 
• Participant standing in relaxed stance 
• Feet hip-width apart 
• Weight evenly distributed 

• After brief walk to assume natural position 
• Both feet assessed 
Scoring: 
• Total score: Sum of 6 component scores 
• Range: -12 to +12 
• Classification: 
o Highly supinated: -12 to -5 
o Supinated: -4 to -1 
o Neutral: 0 to +5 
o Pronated: +6 to +9 
o Highly pronated: +10 to +12 
Y Balance Test (YBT) 
Test description: 
The Y Balance Test is a dynamic stability test that requires strength, stability, and 
proprioception. It is based on the Star Excursion Balance Test (SEBT) with 
modifications[36,48]. 
Setup: 
• Three lines marked on the mat (tatami) 
• Anterior direction 
• Posteromedial direction (120° from anterior) 
• Posterolateral direction (120° from anterior) 
Test procedure: 
1. Preparation phase: 

o Participant completes their usual warm-up routine with judogi 
o Changes to short athletic pants (or provided shorts) to visualize lower 
extremity 
o Leg length measured bilaterally (ASIS to tibial malleolus) 
o Four familiarization trials performed with each leg 
2. Testing phase: 
o Participant stands barefoot on center of Y 
o Hands placed on hips (to prevent compensations) 
o With opposite foot, reaches as far as possible in each direction: 
▪ Anterior reach 
▪ Posteromedial reach 
▪ Posterolateral reach 
o Toe touch must be light (avoiding balance recovery) 
o Returns to center between each reach 
o Three valid trials in each direction 
o Procedure repeated for both legs 
Trial invalidation criteria (must be repeated): 
• Judoka does not maintain single-leg stance (touches down with opposite 
foot) 
• Does not maintain hand position on hips 
• Does not return foot to center between reaches 
• Uses reaching foot for support/balance recovery 
• Lifts stance foot from center 
Measurement: 

• Reach distances measured from center to furthest point touched 
• Recorded in centimeters for each of three directions 
• Mean of three trials calculated for each direction 
YBT composite score calculation: 
YBT score (\%) = (Anterior + Posteromedial + Posterolateral)
3 × Leg length
× 100
(1) 
Where: 
• Anterior, Posteromedial, Posterolateral = mean reach distances (cm) 
• Leg length = measured from ASIS to tibial malleolus (cm) 
Order of testing: 
• Dominant foot first (habitual support foot in single-leg techniques) 
• Non-dominant foot second 
Rest periods: 
• 30 seconds rest between each of the three directions 
• 2 minutes rest between dominant and non-dominant foot testing 
Data Coding and Storage 
Data necessary to carry out this study will be collected and stored in coded form. 
Each participant's data collection sheet will be assigned a code to which only 
members of the research team will have access; without this code, it will not be 
possible to identify which participant the collected data corresponds to. 
Coding system: 
• Format: JC-XXX (where XXX is sequential number 001-045) 
• Master code list stored separately from data files 
• Only principal investigator and study director have access to code key 

Data storage: 
• Physical forms: Locked cabinet at research office 
• Digital data: Password-protected computer files 
• Master code list: Separate secure location 
• Retention period: 5 years after study completion (per regulatory 
requirements) 
4.3.5. Intervention 
Participants who agreed to participate in the study were scheduled at their training 
center. The steps to follow for the intervention were as follows: 
Step 1: General data collection (10 minutes) 
• Complete participant information form 
• Record sociodemographic data 
• Document training history 
• Record injury history 
Step 2: Foot Posture Index-6 assessment (10 minutes per participant) 
• Participant stands in relaxed stance on tatami 
• Both feet assessed following FPI-6 protocol 
• Scores recorded for each of six components 
• Total FPI-6 score calculated for each foot 
• Foot classification determined (supinated/neutral/pronated) 
Step 3: Y Balance Test preparation (5 minutes) 
• Leg length measurement (bilateral) 
• Participant changes to athletic shorts if needed 

• Y-pattern marked on tatami with tape 
• Belt segments positioned on each of three lines for distance marking 
• Instructions explained and demonstrated 
Step 4: Y Balance Test familiarization (10 minutes) 
• Four practice trials with each leg 
• Feedback provided on technique 
• Questions answered 
Step 5: Y Balance Test measurement (15 minutes) 
• Three valid trials in each direction (anterior, posteromedial, posterolateral) 
• Dominant foot tested first 
• 30-second rest between directions 
• 2-minute rest before non-dominant foot testing 
• Same procedure repeated for non-dominant foot 
• Distances recorded for each trial 
Total time per participant: Approximately 50-60 minutes 
Testing conditions: 
• Conducted on tatami (judo mat surface) 
• Barefoot for YBT 
• After participant's normal warm-up 
• Same time of day when possible (to control for fatigue effects) 
4.4. Statistical Analysis Plan 
4.4.1. Descriptive Analysis 
A descriptive analysis will be performed for all variables recorded in the study. 

Quantitative variables will be described as: 
• Central tendency parameters: Mean and median 
• Dispersion parameters: Standard deviation, minimum, maximum, and 
range 
• Normality will be assessed visually (histograms, Q-Q plots) and with 
statistical tests 
Qualitative variables will be described as: 
• Absolute value (n) 
• Percentage (%) 
• Frequency tables and cross-tabulations as appropriate 
4.4.2. Normality Testing 
Shapiro-Wilk test will be used to determine if quantitative variables are 
normally distributed: 
• Applied to samples or subgroups with n < 50 
• Significance level: p < 0.05 indicates non-normal distribution 
Kolmogorov-Smirnov test (with Lilliefors correction) will be used: 
• Applied when comparing two independent samples 
• Significance level: p < 0.05 indicates non-normal distribution 
4.4.3. Primary Objective Analysis 
Research question: Does foot posture type (FPI-6) affect dynamic stability 
(YBT)? 
Groups: 
• Group 1: Neutral foot (FPI-6: 0 to +5) - n=15 
• Group 2: Pronated foot (FPI-6: +6 to +12) - n=15 

• Group 3: Supinated foot (FPI-6: -12 to -1) - n=15 
Dependent variable: YBT composite score of dominant foot (%) 
Statistical procedure: 
1. Normality test: Shapiro-Wilk test for each group 
2. Homogeneity of variances: Levene's test 
o H0: Variances are equal across groups 
o If p < 0.05: Variances are not equal (heteroscedasticity) 
3. Comparison of means: One-way ANOVA 
o H0: No differences in mean YBT scores among the three groups 
o Alternative: At least one group differs 
o Significance level: p < 0.05 
4. Post-hoc tests: If ANOVA is significant: 
o If variances are equal (Levene p ≥ 0.05): Tukey's HSD test 
o If variances are unequal (Levene p < 0.05): Dunnett's T3 test 
o Purpose: Identify which specific groups differ from each other 
o Pairwise comparisons: Neutral vs Pronated, Neutral vs Supinated, 
Pronated vs Supinated 
Interpretation: 
• Significant ANOVA + post-hoc results will determine which foot types differ 
in dynamic stability 
• Effect sizes will be reported using Cohen's d for pairwise comparisons 
• Clinical significance will be interpreted alongside statistical significance 
4.4.4. Secondary Objective 1: Sociodemographic Variables 

Research question: Is there a relationship between dynamic stability and sex? 
Groups: 
• Group 1: Male (n ≈ 37, expected based on judo demographics) 
• Group 2: Female (n ≈ 8, expected) 
Dependent variable: YBT composite score of dominant foot (%) 
Statistical procedure: 
1. Normality test: Kolmogorov-Smirnov test for YBT scores in each sex 
2. Comparison of means: Independent samples t-test 
o H0: No difference in mean YBT scores between sexes 
o Alternative: Mean YBT scores differ between sexes 
o Significance level: p < 0.05 
o Two-tailed test 
3. Effect size: Cohen's d will be calculated 
Note: Other sociodemographic variables (age, weight category, training hours, 
years federated) may be explored using: 
• Pearson or Spearman correlation (depending on normality) 
• Linear regression if associations are found 
4.4.5. Secondary Objective 2: Injury History 
Research question: Is there a relationship between injury history and dynamic 
stability? 
Groups: 
• Group 1: Injury history present (injuries in neck, back, hip, or lower 
extremity in past 12 months) 

• Group 2: No injury history 
Dependent variable: YBT composite score of dominant foot (%) 
Statistical procedure: 
1. Normality test: Kolmogorov-Smirnov test for YBT scores in each group 
2. Comparison of means: Independent samples t-test 
o H0: No difference in mean YBT scores between injury and no-injury 
groups 
o Alternative: Mean YBT scores differ between groups 
o Significance level: p < 0.05 
o Two-tailed test 
3. Effect size: Cohen's d will be calculated 
4.4.6. Secondary Objective 3: Dominant vs Non-Dominant Foot 
Research question: Are there differences in dynamic stability between 
dominant and non-dominant foot? 
Groups: 
• Dominant foot YBT scores (habitual support foot) - n=45 
• Non-dominant foot YBT scores (non-habitual support foot) - n=45 
Design: Paired samples (same participants tested on both feet) 
Statistical procedure: 
1. Normality test: Kolmogorov-Smirnov test for YBT scores of each foot 
2. Comparison of means: Paired samples t-test 
o H0: No difference in mean YBT scores between dominant and non-
dominant foot 

o Alternative: Mean YBT scores differ between feet 
o Significance level: p < 0.05 
o Two-tailed test 
3. Effect size: Cohen's d for paired samples will be calculated 
4. Interpretation: Consider potential order effects (dominant foot always 
tested first) 
4.4.7. General Statistical Considerations 
Significance level: α = 0.05 for all tests (two-tailed unless otherwise specified) 
Missing data: 
• Cases with missing primary outcome data (YBT or FPI-6) will be excluded 
from analyses 
• Missing data for secondary variables will be reported 
• No imputation planned due to small sample size 
Outliers: 
• Will be identified using box plots and z-scores (|z| > 3.0) 
• Outliers will be checked for data entry errors 
• Sensitivity analyses may be conducted with and without outliers if present 
Multiple comparisons: 
• Post-hoc tests will use appropriate adjustments (Tukey, Dunnett) 
• For multiple secondary analyses, results will be interpreted with caution 
• Bonferroni correction will NOT be applied to maintain statistical power in 
this exploratory study, but results will be interpreted conservatively 
Effect sizes: 
• Cohen's d: Small (0.2), Medium (0.5), Large (0.8) 

• Will be reported for all comparisons to assess clinical significance 
Software: All statistical analyses will be performed using IBM SPSS Statistics 
version 22.0 or higher. 
Reporting: Results will follow STROBE (Strengthening the Reporting of 
Observational Studies in Epidemiology) guidelines. 
4.5. Ethical Aspects 
4.5.1. Ethical Approval 
This research complies with the good research practice standards of the 
Declaration of Helsinki. Given that this study collects health data and the tests 
performed are non-invasive, a favorable ethical report was requested from the 
Research and Teaching Ethics Committee of the Catholic University of Valencia. 
Ethics approval obtained: 
• Institution: Catholic University of Valencia San Vicente Mártir 
• Committee: Research Ethics Committee 
• Approval date: January 26, 2023 
• Protocol code: UCV/2022-2023/111 
4.5.2. Data Protection and Confidentiality 
Appropriate measures have been adopted to guarantee complete confidentiality of 
personal data, in accordance with the provisions of: 
• Spanish legislation: 
o Organic Law 3/2018, of December 5, on Protection of Personal Data 
and guarantee of digital rights 
• European legislation: 

o Regulation (EU) 2016/679 of the European Parliament and of the 
Council, of April 27, 2016, on the protection of natural persons with 
regard to the processing of personal data and on the free movement 
of such data (General Data Protection Regulation - GDPR) 
Data protection measures: 
1. Pseudonymization: All data will be collected and stored in coded form 
using unique participant codes (JC-001 to JC-045) 
2. Limited access: Only research team members will have access to the code 
key linking codes to participant identities 
3. Secure storage: 
o Physical documents: Locked filing cabinet 
o Electronic data: Password-protected, encrypted files 
o Code key: Stored separately from research data 
4. Data retention: 5 years after study completion, then securely destroyed 
5. Data sharing: Only de-identified data may be shared for scientific 
purposes with appropriate safeguards 
4.5.3. Informed Consent Process 
All participants will be informed about the characteristics of the research and the 
confidentiality commitment before enrollment. 
Informed consent requirements: 
For adults (≥18 years): 
• Must sign adult informed consent form 
• Must receive copy of signed consent 
• Must receive information sheet about study 

For minors (<18 years): 
• Ages 14-17 years: 
o Parental consent required (signed by legal guardian) 
o Minor assent required (signed by participant) 
o Verbal assent confirmed at time of intervention 
• Ages 10-13 years: 
o Parental consent required (signed by legal guardian) 
o Verbal assent from minor confirmed at time of intervention 
Information provided in consent documents: 
• Study purpose and procedures 
• Voluntary nature of participation 
• Right to withdraw at any time without consequences 
• Confidentiality measures 
• Potential risks (minimal: temporary fatigue, mild muscle soreness) 
• Potential benefits (knowledge about their stability, contribution to science) 
• Contact information for questions 
• Ethics committee approval information 
4.5.4. Participant Rights 
All participants have the right to: 
1. Access: Request access to their personal data collected in the study 
2. Rectification: Correct any inaccurate personal data 
3. Erasure: Request deletion of their data (right to be forgotten) 
4. Restriction: Request limitation of data processing 

5. Portability: Receive their data in structured, commonly used format 
6. Objection: Object to data processing for specific purposes 
7. Withdrawal: Withdraw from study at any time without explanation or 
negative consequences 
Exercise of rights: Participants may exercise these rights by contacting the 
principal investigator using the contact information provided in the consent form. 
4.5.5. Risk-Benefit Assessment 
Risks: 
• Minimal risk study 
• Temporary muscle fatigue from YBT testing 
• Minimal risk of fall during balance testing (mitigated by supervision) 
• Potential mild muscle soreness (less than typical training) 
Benefits: 
• Individual: Knowledge about their dynamic stability and foot posture 
• Scientific: Contributing to knowledge about judo biomechanics and injury 
prevention 
• Future: May inform training and injury prevention programs for judokas 
Risk mitigation: 
• Testing supervised by qualified podiatrist 
• Participants complete usual warm-up before testing 
• Testing surface is tatami (cushioned, familiar to participants) 
• Participants can stop testing at any time 
4.5.6. Conflict of Interest 

The research team declares no conflicts of interest. This study is conducted as part 
of an academic Master's thesis and receives no commercial funding. 
4.5.7. Dissemination of Results 
Results will be disseminated through: 
• Master's thesis publication 
• Scientific journal publications 
• Presentations at scientific conferences 
• Summary report to participating clubs and participants (if requested) 
All dissemination will maintain participant confidentiality and report only 
aggregate data. 
 
 
 
 
 
 
 
 
 
 
 
 

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APPENDICES 
Appendices 
This protocol includes a series of appendices that document the ethical approval, 
participant-facing documents, and study instruments used to conduct the research. 
Appendix A. Ethics Committee Approval 
Favorable opinion issued by the Research Ethics Committee of the Catholic 
University of Valencia San Vicente Mártir for the study “Determination of the 
degree of dynamic stability of the foot in single-leg support in relation to the Foot 
Posture Index in judokas” (Protocol code UCV/2022-2023/111). This appendix 
confirms that the study was reviewed and approved in accordance with applicable 
ethical and regulatory standards. 
Appendix B. Information Sheet for Participants and Confidentiality 
Commitment 
Full “Participant Information Sheet and Confidentiality Commitment” describing 
the purpose of the study, eligibility criteria, study procedures, potential risks and 
benefits, data protection measures, and contact details for the research team. This 
document is provided to all potential participants prior to obtaining informed 
consent. 
Appendix C. Informed Consent Form – Adults 
Template of the informed consent form for adult participants (≥18 years), including 
specific items on voluntary participation, right to withdraw, use of data for 
research, teaching and dissemination, access to results, and options regarding data 
retention and destruction. This form is signed by the participant and the 
investigator before any study procedure is initiated. 
 

Appendix D. Informed Consent Form – Minors (Parental Consent) 
Template of the informed consent form for legal guardians of minors participating 
in the study, which mirrors the adult consent structure but is addressed to the 
parent or legal representative. It covers study information, risks and benefits, data 
protection, and explicit authorization for the minor’s participation, as well as 
conditions for withdrawal and revocation of consent. 
Appendix E. Assent Form – Minors (14–17 years) 
Age-appropriate assent form for adolescents, summarizing the study in clear and 
simple language and documenting that the minor has received and understood the 
information, knows that participation is voluntary, and agrees to take part in the 
study alongside the consent given by their legal guardian. 
Appendix F. Letter to Judo Clubs 
Standardized invitation letter sent to judo clubs describing the objectives of the 
study, eligibility criteria, study procedures (Y-Balance Test and questionnaire), and 
organizational aspects for recruitment. The letter requests collaboration in 
disseminating the study information among eligible judokas and provides contact 
details for the research team. 
Appendix G. Participant Information Form (Athlete Data Form) 
Data collection form used to record general participant information, including age, 
sex, weight category, years of federation, weekly training hours, shoe size, 
dominant foot, and detailed injury history (type of injury, side, context—training 
or competition—and recovery time). 
Appendix H. Foot Posture Index-6 (FPI-6) Assessment Form 
Standard FPI-6 scoring sheet used to assess foot posture in both feet. It includes 
the six items (talar head palpation, supra- and infra-malleolar curvature, calcaneal 
position, talonavicular prominence, medial longitudinal arch congruence, and 

forefoot abduction/adduction), each scored from −2 to +2, and provides space to 
record the total score for each foot. 
Appendix I. Y-Balance Test Recording Form 
Form for recording reach distances in the different directions of the Y-Balance Test 
and calculating composite scores for each lower limb. It is used to standardize data 
collection across all testing sessions. 
Appendix J. Coding Sheet (Participant Code Assignment Log) 
Master coding sheet listing the unique identification codes assigned to participants 
and the corresponding fields for recording their personal identifiers. This 
document is stored separately from the research data, in a secure location, and is 
accessible only to the principal investigator and authorized supervisors, in order to 
maintain confidentiality and enable pseudonymization of the dataset. 
Appendix K. Bibliographic Search Strategy 
Description of the electronic search strategy used for the literature review, 
including databases searched and key terms/MeSH headings related to martial 
arts, judo, lower extremity, foot posture, stability, and balance. This appendix 
documents the reproducibility of the background literature search that supported 
the rationale and design of the study. 
Appendix L. Dissemination Plan 
Summary of the planned dissemination activities for the study results, including 
target professional audiences (podiatrists, sports scientists, physiotherapists, and 
judo professionals), candidate national and international journals for manuscript 
submission, and scientific conferences where the findings are intended to be 
presented.