The World Health Organization (WHO) defines mental health as, "a state of well-being in which a person realizes his or her capabilities and is able to cope with the normal stresses of life, to work productively, and to contribute to his or her community".1 In 2019, one in eight people in the world (equivalent to 970 million people) suffered from a mental disorder; the most common are anxiety and depressive disorders, which in 2020 increased significantly due to the COVID-19 pandemic; initial estimates show a 26 % and 28 % increase in anxiety and major depressive disorders in just one year.2 The WHO definition is in line with the interest in knowing the psychosocial impact that can influence the process of preparation and competition of athletes, because mental health is a fundamental component of the culture of excellence in sport.3 The WHO estimates that millions of people in the world are suffering from common mental disorders, and in the sports context they are related to different specific aspects of sports practice, such as the management of popularity, withdrawal, or injuries, these being one of the variables with a greater association to mental disorders.4 Adverse life events, together with injuries or surgeries related to long recovery periods are associated with symptoms and mental disorders for both active and former athletes.5

A large part of the mental health disorders and symptoms refer to stress, anxiety, depression, addictions or sleep disorders.6,7 In addition, it is important to bear in mind that the COVID-19 pandemic has caused an unprecedented global crisis, with drastic changes in the living conditions and mental health of people,7 including obviously the athlete population. Thus, the prevalence of pathologies and mental disorders has increased not only in the general population, but also in athletes, in addition, the inability to be active because of the disease has brought different types of consequences and sequelae, both physical and mental.8,9

Several researchers have focused their attention on the mental health of athletes and on the positive consequences of physical exercise.10,11 Sport is often associated with health-related aspects, although it also involves a high risk of injury for those who practice it, whether in maintenance physical activities, school competitions or professional sport.12 In addition, the relationship between stress and other psychological variables was found to increase the risk of injury.13

Consequently, the scientific literature shows the great importance that psychological factors have on both the risk of injury and recovery from injury.14,15 During an athlete's sports career, several mental health indicators are manifested, including generic and sport-specific stress factors that can increase the risk of mental health symptoms and disorders. In Goutterbarge's study,16 it is pointed out that athletes can face 600 different stress factors, such as adverse life events, conflicts with the coach, professional dissatisfaction, which can lead to psychological pathologies. Other studies on mental health problems in athletes have focused on sport-specific phenomena, such as injuries, retirement or performance, or on the prevalence of these in different contexts.17

The practice of sports, especially professional or elite sports, is immersed in a context of great competitiveness and performance demands, which can favour the appearance of certain mental disorders, or high levels of anxiety, stress or depression.18 Authors such as Murillo,19 mention that there is a need for more research on psychological aspects and how they affect the athlete's performance, or how certain sporting factors favour the appearance of stress, anxiety or depressive symptoms, such as sports injuries.18,20 In this sense, greater awareness of mental health disorders in elite sport has led to a significant increase in research.17

From a mental health perspective, researchers studied stress as a relevant variable in its association with sports injuries. Stress cannot only affect sports performance, but also the quality of life of the athlete.21,22 It is also one of the most studied psychosocial factors in the sports field due to its association with vulnerability to sports injury.13,23–27 It is the psychological variable that received the most attention since the publication in 1988 of the Andersen and Williams Sports Injury Stress Model,28 pointing out that in potentially stressful situations, athletes can manifest a stress response that increases muscle tension, which, in turn, hinders motor coordination, reduces flexibility and alters attentional capacity.29 Researchers have shown that sport at all levels of performance exposes the athlete to high levels of stress and anxiety,30 although in competition the maximum demand required and the presence of others can significantly increase the levels of competitive stress, anxiety, and the existence of significant changes in mood states. In addition, there are "risk profiles" or "vulnerability profiles" that amplify these levels of stress and anxiety.31 The stress and injury model of Andersen and Williams,28 proposes anxiety as a personality variable, which can act as an antecedent and influence between stress response and injury. Some studies32 show anxiety as one of the most important variables in the possible occurrence of injury. Anxiety is a mental health indicator that related to sport has a negative effect on its practice, since it leads to a higher risk of injury or delays the rehabilitation of the same.

On the other hand, it is important to consider the relationships between the different psychological variables as indicators of mental health, mainly stress, anxiety and depression. Authors such as Gouttebarge5 identified that the prevalence of mental disorders in high performance athletes ranges from 16 % to 34 %, with anxiety and depression being the most common complications. Rice33 considers that anxiety is directly related to depressive symptoms or their diagnosis, and even concludes that athletes under 25 years of age tend to have the highest level of anxiety. Reese34 reports that injuries can affect the mental health of athletes by triggering depression and anxiety. He also adds that sports injuries can lead to imbalance and discomfort in athletes' lives even after the injury, and this physical disability prevents them from succeeding in their sport.

Another relevant indicator of mental health is the quality of the athlete's sleep. It plays a crucial role in physical and cognitive performance and is an important factor in reducing the risk of injury.35 Research indicated that injured athletes reported worse sleep quality than non-injured athletes, and also showed a close relationship with fatigue.36 Therefore, if athletes do not evidence a correct rest, it will not be possible to improve or avoid an injury. According to Copenhaver and Diamond,37 people with sleep deficiency are at greater risk of acute illness, traumatic sports injuries and the development of chronic diseases.

In athletes, sleep is the most effective and natural way to favour and accelerate recovery processes; during sleep, cells are regenerated through the elimination of metabolic waste from the brain, which protects against fatigue.38,39 On the other hand, Halson,40 points out that sleep for high performance athletes is an essential method for optimal recovery and is considered a factor that directly affects sports performance. Athletes' sleep should be regulated, and training programs should be adjusted to their circadian and homeostatic rhythms. Alterations in sleep quality can affect performance and increase the risk of injury. The aim of this study is to review the existing scientific literature that relates mental health with sports injuries, considering these either as an antecedent of mental health disorders or because of mental health deficits.

Study eligibility was determined in two steps. In step 1, a total of 63 potentially relevant citations were collected. Fifteen of these were eliminated for duplicity, leaving a total of 44 citations. In step 2, exclusion criteria were applied and 9 of the citations were eliminated, then the full-text studies were assessed and reviewed. The verification of the articles resulted in the elimination of 10 more citations for not having significant results due to small samples and/or lack of concordance.

Accordingly, this systematic review includes 25 original studies that provide evidence on mental health in sport and its relationship to sports injuries.

Table 2 shows the most relevant aspects of the included review studies.

As can be seen in Table 2, there are 7 systematic review studies, 3 of which also include meta-analyses, 1 narrative review study and 4 literature review studies. Among the most relevant findings we find that; injuries can increase the risk of mental health problems and adverse behaviours. Mental health indicators (anxiety, depression, sleep and stress) can lead the athlete to a greater occurrence of injuries and obstructs and delays their rehabilitation. Furthermore, we can affirm that sports injuries and mental health have a bidirectional relationship in the rehabilitation process, and this premise gives us enough information to prove it scientifically and to be able to establish prevention strategies, identifying and recognizing mental health problems in the athlete and/or developing treatment and intervention programs so that during the injury the athlete is not predisposed to suffer from a mental health disorder.

Table 3 shows the most relevant aspects of the empirical studies included in the review of reviews.

As can be seen in Table 3, there are 5 cross-sectional studies, 2 correlational studies, 1 cross-sectional-correlational study, 1 prospective study, 1 qualitative descriptive study and 3 unclassified studies. Among the most relevant findings we find that stress, anxiety and depression are positively related to the number of injuries and that this incidence is more prevalent in competition, since its problems cause disorders in the mental health of the athlete. We also observed that the higher the level of stress, the higher the risk of more serious injuries. As well as sleep, which plays a crucial role in reducing the risk of injury and should be addressed with preventive psychological intervention.

The aim of the present study was to review the existing scientific literature that relates mental health to sports injuries, considering the latter either as an antecedent of mental health disorders or as a consequence of mental health deficits. Specifically, firstly, to determine which are the most relevant mental health indicators in relation to injuries; secondly, to determine the relationship between mental health indicators and the vulnerability to injury of the athlete; and finally, to determine the relationship between the injury suffered and its rehabilitation process with the mental health indicators of the injured athlete.

From a general perspective, the literature confirmed with a large amount of evidence that there is a close, multifaceted and significant relationship between mental health and physical performance. After conducting the present systematic review, the relationship between mental health and sports injuries56,57 is significantly observed in athletes.

From what was analysed in the reviews, 5 of them do not indicate the data collection system, as well as the sample (2) and/or the statistical test used (9), so some deficiencies can be observed in these articles.

In reference to the analysis of the empirical articles, the design of the studies (3) is not reported, and in one of them, neither the sample, nor the statistical test (3), nor the data collection. In addition, there is no experimental study, which would help us to analyse a cause-effect relationship of these variables of a primordial nature.

The results indicate that, regarding the objective of determining which are the most relevant mental health indicators in their relationship with injuries, anxiety appears in 8 of the studies, of which the significant relationship with injuries can be observed in 3. Depression appears in 6 of the studies and in 5 of them it appears together with anxiety, which leads us to understand the relationship between the two and their great relevance. Also, stress and sleep quality are very important indicators to consider, since they are closely related to sports injuries. The studies that consider these indicators affirm that we must bear in mind that mental health interferes in athletes and to avoid this, their indicators (anxiety, stress, sleep quality and depression) must be observed and evaluated, since they provide useful information to prevent and intervene in their appearance or reduce the aggravation of the sports injury.58,59 If an athlete is injured, these factors increase, since it has been demonstrated that mental health plays a very important role in the response, rehabilitation and recovery of the athlete's injury.31 Data indicates that identifying stressors early can decrease the rate of injury and illness.60

In turn, in many publications it has been possible to determine how the terms "mental health", "anxiety", "sleep quality", "depression" and "stress" are mentioned by athletes, coaches and family members in the sports environment and in relation to the discomfort of the athlete at the psychological and physical level.35,61 Another fundamental aspect in which both concepts must be contextualized is in the athlete's retirement, as there is high quality evidence to support that a high athletic identity contributes to an increase in mental health symptoms after retirement.62

On the other hand, it has been possible to detect how studies have investigated some of its indicators separately (stress and injuries, anxiety and injuries, sleep quality and injuries, depression and injuries) but not as a whole. It is necessary to observe mental health as a whole and analyse its indicators, since stress leads to anxiety, anxiety can end in depression and all this leads to a bad rest and incorrect recovery due to the lack of sleep quality due to the state of restlessness that the athlete may manifest.

Likewise, the results regarding the objective of determining the relationship between mental health indicators and the vulnerability to injury of the athlete indicate that the prevalence of mental health symptoms and disorders (stress, anxiety, depression, sleep) predisposes the athlete to injury.63

The importance of mental health among athletes is increasingly recognized and appreciated. In Rogers' study64 conclusive results were obtained stating that sports injuries have a negative impact on the mental health of athletes and that mental health can influence and influences sports performance, which is closely linked to the risk of sports injuries, thus creating a complex cycle with an inability to separate physical and mental health. If we allow these disorders to develop, the athlete's vulnerability will be greater, and the athlete will have a greater predisposition to develop the problem.

Similarly, the trend towards early sports specialization is associated with an increased risk of injury and burnout, which have significant implications for mental health.65 The importance of the mental health of athletes cannot be underestimated, so we must work from a multidimensional approach, starting by recognizing that both mental and physical health are related, and that this implication will be reflected in performance, in the number of injuries of the athlete and in his or her recovery in the case of suffering them.

Finally, the results regarding the objective of determining the relationship between the injury suffered and its rehabilitation process with the mental health indicators of the injured athlete indicate that sports injuries and mental health have a bidirectional relationship in the rehabilitation process. Stress is the major indicator in rehabilitation and recovery from injury along with anxiety and depression. It should also be added that the number of injuries increases if these indicators are not addressed in time.

Along the same lines, analysing current studies related to the promotion of mental health, it was observed how emotional distress due to pressure and injury can cause some participants to experience negative results, therefore, mental health guidelines should be considered as an urgent call to action by experts.66 It is paramount that the athlete knows how to manage his or her mental health and has all the necessary information to be able to cope with an injury, not only physically but also psychologically.

It has even been specifically shown that injured athletes have higher rates of anxiety and depression compared to the general population67 and are therefore more at risk of worsening their mental health and worsening their recovery. Consequently, psychological interventions can lead to a reduction of negative thoughts and moods and prevent all this continuous stress from ending up in a state of depression in the athlete.

Finally, tools must be used to recognize the mental health of athletes and facilitate early detection of their symptoms and address them in a loquacious manner. It is highly recommended to treat and work on the injury from a multidisciplinary approach with a good mental health awareness.

This systematic review shows how mental health indicators significantly affect sports injuries, and how their relationship can lead the athlete to an improper recovery or be more exposed to suffer it. Mental health is paramount to the proper development of the athlete and is vital to their performance.