1. Introduction
Judo is a very popular and commonly practiced martial art and Olympic sport of Japanese origin [
1] with more than 20 million judokas worldwide [
2]. It is observed that 79% of judokas suffer or have suffered an injury lasting more than 3 weeks[
3]. Of all the injuries recorded, the most serious is the anterior cruciate ligament (ACL) rupture[
2]. The ACL rupture affects with a time loss of 3-12 weeks in 10%, 3-6 months in 26%, 6-9 months in 32%, 9-12 months in 18% and more than 12 months in 14% of the injured judokas. Regarding the post-injury sport level, 32% reached the same level, 39% slightly reduced, 24% quite reduced and 5% gave up judo [
2]. It is especially important to note that ACL injuries can lead to the development of osteoarthritis and/or joint instability, which can affect sports practice as well as work or daily life [
4].
According to multiple literature sources, the mechanism of ACL injury is knee collapse in knee valgus [
5,
6,
7,
8,
9,
10,
11,
12,
13]. Dynamic knee valgus is a multiplanar movement pattern of the lower extremity, potentially composed of a combination of femoral adduction and internal rotation, knee abduction, anterior tibial translation, external tibial rotation and ankle eversion [
7,
9].
The origin of ACL injury is multifactorial and is largely caused by neuromuscular deficits in structures such as the core, hamstring and quadriceps muscles, hip abductors and external rotators, decreased ankle dorsiflexion and hip mobility [
7,
8]. Of all these there are differences between men and women, which can lead to a dynamic valgus of the knee and, consequently, to the risk of ACL injury [
7,
8,
10,
11,
12,
13,
14,
15,
16,
17,
18,
19,
20,
21,
22,
23]. A study developed by Hewett et al. [
7] demonstrate that men and women exhibit different activation and muscle recruitment strategies at the hip and knee joints.
In judo, the most common mechanism of suffering an ACL tear is through direct contact (70.1%), or indirect contact (20.1%), unlike other sports such as basketball, where the injury usually occurs without contact, in movements such as braking, jumping or pivoting [
5]. It has also been seen that most cases occur when the injured judoka is attacked (67.4%), especially in those techniques in which the leg is used as a fulcrum to knock the opponent down, such as osoto-gari (18,6%) (
Figure 1), harai-goshi (11.6%) (
Figure 2), kosoto-gari/gake (14%) (
Figure 3) or kouchi-gari/gake (9.3%) (
Figure 4) although also when counterattacking (18.6%) (
Figure 5) or when attacking (14%), with the tai-otoshi technique (11.6%) (
Figure 6) being of note [
5,
24].
It has been observed that more injuries occur when judokas fight between judokas of different laterality (kenka-yotsu), i.e. right-handed vs left-handed, than when they are of the same laterality (ai-yotsu), right-handed vs right-handed or left-handed vs left-handed (
Figure 7) [
1,
2]. It is speculated that the higher risk of injury in kenka-yotsu is due to a greater likelihood of being counter-attacked, a common situation of suffering an ACL tear [
3,
24].
In a study of ACL injuries in soccer [
25], researchers examined 107 case videos of 134 Italian men's professional soccer matches over 10 years. They found that 44% of injuries were non-contact, 44% were indirect contact, and 12% were direct contact. Four main injury situations were identified: pressing and tackling, tackling, regaining balance after a kick, and landing from a jump. Knee valgus loading was the primary injury pattern in all situations (81%). Most injuries (62%) occurred in the first half of matches, with peaks at the start and end of the season.
Under a physiologic load in a position commonly assumed in sports, women tend to position their entire lower extremity and activate muscles in a manner that could increase strain on the anterior cruciate ligament [
26].
Therefore, the main objective of the present study was to detect the possible existence of a differences in movement patterns among elite judokas according to their sex, in order to identify those athletes with a higher risk of ACL injury.
4. Discussion
The main objective of the present study was to detect the possible existence of a differences in movement patterns among elite judokas according to their sex, in order to identify those athletes with a higher risk of ACL injury.
Firstly, no differences were observed between sexes in the Single Leg Squat test, neither in the dominant nor in the non-dominant leg. Furthermore, no differences were observed between men and women in the different hip external rotation tests of both lower limbs and in the Lunge test bilaterally. On the other hand, in the hip internal rotation tests, differences were observed between men and women, both in the dominant and non-dominant leg.
With regard to the SLS test, no differences were observed between men and women in either the dominant or non-dominant lower limb. It should also be noted that the prevalence of obtaining a positive test in this test is quite low, 8.7% for the dominant and 26.1% for the non-dominant. If the data is analyzed in more depth, it can be observed that of all the judokas, a large number obtained at least 1 positive in one of the items assessed in the SLS test (in the dominant leg 60.9% and in the non-dominant leg 82.6%). If only 1 positive in these items, the overall test result is negative, so it is of great importance to note the high rate of positives in these aspects in isolation. This data is of great interest as it may support the high prevalence of ACL injury in judo.
If we analyze the positivity of the test between both legs, we observe a higher positivity of some of the items and of the SLS test in the non-dominant leg, which is of great importance since this is the support leg in monopodal support techniques. In addition, more ACL injuries occur in bouts between judokas with opposite laterality and with techniques such as osoto-gari or harai-goshi in which the attacked judoka receives the attack on the non-dominant leg [
5].
Of all the possible abnormal movement patterns that can be observed and assessed in the SLS test, such as arm flailing, knee valgus and Trendelenberg, the one that can be seen the least in both legs is pelvic instability or Trendelenberg sign (8.7% in the dominant lower limb and 21.7% in the non-dominant). This indicates that there is good control of the core musculature. However, there is a high percentage of judokas with uncontrolled arm movements (17.4 and 34.8% respectively) and dynamic knee valgus (34.8 and 26.1% respectively). From these data it can be assumed that the judoka's stability cannot depend on the arms, since in the usual combat situations in which the ACL injuries usually occur, it is the opponent who attacks, being unlikely to be able to maintain the balance and stability of the attacked knee with a support of the hands on the opponent. On the other hand, it is of utmost importance to highlight the role of knee valgus observed in the SLS test, a movement previously mentioned as being mainly responsible for the ACL injury [
5,
6,
7,
8,
9,
10,
11,
12,
13]. Therefore, it would be of great interest to perform neuromuscular control exercises to stabilize dynamic knee valgus without the intervention of the arms.
The study by Della Villa et al. [
25] found that 90% of ACL injuries involved loading the injured leg, often with a limb on the ground (70%). They stated that proper biomechanics, aligning force vectors for joint stability, were crucial. ACL injuries were the result of mechanical perturbations to the upper or lower body during interactions with opponents, without direct contact with the knee. Hip abduction motion was frequent, resulting in increased hip internal rotation and adduction in most cases, possibly due to an externally oriented knee abduction moment from hip abduction. Injuries were more frequent in the first half of the matches, suggesting that factors other than fatigue played a role, possibly related to hip rotation and myotatic reflexes.
In terms of physical preparation for competition, von Gerhardt et al. [
33] evaluated the efficacy of a specific judo injury prevention warm-up program supervised by a coach on overall injury prevalence, and concluded that the intervention did not significantly reduce the prevalence of overall and severe injuries.
Lambert et al. [
34] found that the type of injury, sport level, treatment method and gender seemed to influence the judoka's psychological preparation and ability to return to sport after injury. However, in the present study no differences were observed between sexes in the external rotation of the athletes participating in the study, neither in the dominant nor in the non-dominant leg. On the other hand, statistically significant differences were observed in the internal rotation of both legs, with the mean range of this movement being lower in men than in women. This difference may be related to the dynamic knee valgus observed as the main mechanism of injury [
5,
6,
7,
8,
9,
10,
11,
12,
13]. As for the hip, this movement involves adduction and internal rotation of this joint [
7,
9].
On the other hand, it is of great relevance to highlight that restrictions in hip mobility may be a risk factor for ACL injury [
21,
22,
31]. Clinical and radiological studies assessing this injury risk have shown an association between decreased hip rotations and the likelihood of previous ACL injury [
22]. In addition, in silico biomechanical simulations and cadaver studies have provided evidence of a mechanism of hip restriction at the ACL, highlighting the importance of internal rotation restrictions. Indeed, the article by VandenBerg et al. [
22] discusses the association of ACL injury risk with hip internal rotation limitation. As hip IR increases, the likelihood of ACL rupture decreases. However, prospective cohort studies are needed to establish that decreased hip mobility is a risk factor for ACL injury, so this may not be sufficient reason to determine that men are at greater risk of ACL injury. However, as mentioned above, it is of great importance to work on the neuromuscular control of the external rotators and hip abductors, which are responsible for braking and stabilizing the knee towards valgus collapse. If they do not exercise their function, they could lead to increased ligamentous tension and thus an increased risk of ACL injury [
7,
9,
10,
15].
Finally, the data obtained in the Lunge test was analyzed. This test also does not show different results between men and women in both dominant and non-dominant lower limbs. Although the averages of both legs were higher in the male gender, these differences were not statistically significant, so neither can we show a disparity in the risk of ACL injury between the sexes due to ankle dorsiflexion restriction.
As already noted, there is no biomechanical factor that is really a demonstrable cause to conclude that, as in other sports such as basketball, handball, volleyball or football, the risk of ACL injury is higher in women than in men [
5,
6,
7,
35]. This is probably due to the way in which they occur. In all the sports mentioned above, the majority of ACL injuries occur in non-contact actions such as changes of direction, braking and jumping. Based on these results, neuromuscular training methods were developed to reduce the risk of non-contact ACL injuries. Due to the characteristics of judo as a martial art, a non-contact mechanism is not the main cause of ACL injuries and a neuromuscular training approach may not be suitable for prevention [
5]. As developed by Koshida et al., the occurrence of ACL injury is more common in movements where the leg is used as a fulcrum, when the injured judoka is attacked and when the judoka is on the opposite side of the body [
5]. Therefore, the difference observed between both sexes in other sports may not be extrapolated to judo [
36]. Deficits in postural control and neuromuscular function of the knee and hip are highly predictive of the risk of a second ACL injury after return to sport following ACL reconstruction [
7,
37]. Rehabilitation programs aimed at reducing functional asymmetries prior to return to sport after ACL reconstruction may be necessary to more safely reintegrate these patients into sport [
7,
37].
In our study we have assessed mobility and activation of the lower limb joints, observing limitation in hip internal rotation that could modify the force vectors in the entire lower limb, increasing the risk of injury. Impaired hip rotation ROM is commonly associated to lower extremity pathology [
38]. The influence of central descending reflexes in improving hip mobility has been demonstrate [
39]. Due to the contribution of the sensorimotor cortex in joint flexibility [
40].
It would be necessary to find and modulate the mobility dysfunctions produced by the central descending reflexes in order to improve neuromuscular activation and therefore joint stability. In this way, the judoka would be as well repaired as possible to respond and protect himself from the opponent's impacts.
4.1. Limitations and Strengths
This study also presents a series of limitations, such as the proportion between both sexes and the number of participants because they are elite athletes.
In addition, no data was collected on previous injuries because they were competing at a high level and thus be able to assess the possible dysfunctions that they could create.
This would have been of great interest as a previous ACL injury significantly increases the likelihood of sustaining another ACL injury. Even so, significant differences were only found in hip internal rotation.