A similar study was conducted in collaboration with the Technical Sector of the Italian Soccer Federation during the 1990 World Cup (26). The design of this study consisted of a questionnaire filled by the physicians of the teams involved in the World Cup; information was collected on traumas occurred from the quarter finals to the finals of the World Cup. There were 106 injuries during the matches, with an average of 3 injuries per match, 1 event every 30 minutes (26).
Another cohort was assembled during the season 2003–2004, consisting of 1,041 professional soccer players from the 2 Italian major Leagues; 743 of the 785 subjects available the day of the interview (94.6%) answered an epidemiological questionnaire; the risk of injuries and their severity according to several variables were assessed (24). Only conditions that required a stop form playing for at least 1 day were recorded in this study. One hundred fifty-seven players suffered 177 major injuries during the game season 2002–2003; 139 of them suffered only 1 injury. From the analysis of the self-reported number of hours per week of activity, the players were estimated to have undergone 356,337 hours of activity, 338,258 practice hours, and 18,079 game hours; the incidence rate was 0.5 injuries per 1,000 hours, 0.19 injuries per 1,000 hours of training, and of 5.53 injuries per 1,000 hours of matches.
A recent study published by the Medical Assessment and Research Center at FIFA reported injury incidence during the final phases of the 2002 World Cup. In this study, the physicians of all participating teams reported all the injuries after each match on a standardized injury report form. There were 171 injuries in 64 matches, with an incidence rate of 2.7 injury per match, or 81 lesions per 1,000 match hours (17).
In summary, several articles have provided data on injuries in soccer players (2,3,12,19,22); however, the variation in the methodology of study design and conduct, in the injury classification, and the diversity of the main objectives of the studies make it difficult to draw firm conclusions (4,15,21). In addition, the populations included in the studies vary from young professionals, women, nonprofessional players, adult professionals, where the etiology of the injury may differ because of the background characteristics of the players (13,18,20).
Very little is published on the risk factors that predispose soccer players to injuries. We have attempted to group the factors possibly predisposing the players to injuries into 2 groups: external and personal factors (Table 3).
Among the external factors, the number of official matches, the presence of games, and of other official commitments within the week (in addition to the week-end matches), a quick start of the game season without the proper preparatory training time, have been hypothesized as possible risk factors (28,26).
To support some of these hypotheses with actual data, we have analyzed the study conducted on a major team observed for 5 years (28). There were no significant difference in the number of injuries occurred during the matches or during the training nor differences according to the role of the player. Injuries occurred with the same frequency in the first or second half of the match; a higher number of injuries were recorded when the team was in a forward phase rather than when it was in a defensive phase of the match. Elite players were more exposed to injuries than other members of the team.
The analysis of the questionnaires collected in 2003 from the cohort of Italian professional soccer players (24) suggests that players who were injured during the season had played a nonsignificant higher number of games in comparison with players who suffered no injuries during the same season (23.2 matches vs. 21.2; p = 0.08).
At a multivariate logistic analysis, the number of matches and a history of previous injuries were associated with a lower risk of injury (Table 4). Role, age, body mass index (BMI), hip-to-thorax ratio had no significant association with injury. The type of tissue affected and the type of injury were significantly associated with the duration of the stop.
Other external factors that could play a relevant role in injuries occurrence but that are difficult to measure are psychological tension and stress connected to the importance of the various games, the expectations of the public and the fans, the presence of media at the match.
Technical aspects to take into account are the increased speed of the matches and the consequent changes in the quality and quantity of the training methodologies. New tactics more often include simultaneous pressing in various areas of the field, a request for more offside positions, double cover, and the confinement of complex actions in a small section of the field which translates into having many players concentrated in a small space. This increases the chances of collisions, contrasts, and impacts.
Last but not least is the need for fair play among the participants in a match, for severe arbitration that punishes aggressive behavior in order to protect the players' physical integrity.
Pitches and shoes are also important determinants in injuries: The structure of a technical shoe is such as to obtain maximum adhesion to the field during the player's action, with consequent modifications of the physiological mobility of the foot. Soles that favor high adhesion to the field increase the blockage of the various joints of the foot but in doing so they make the knee joint more vulnerable. The simultaneous presence of a very adhesive technical shoe, of a less than perfect condition of the field, together with a faster technical movement of the players greatly increase the risk of injuries.
The composition of the fields where the matches occur should be grass, and the fields should be smooth and regular, without any dangerous structure along the sidelines. Recently, both FIFA and UEFA have evaluated the possibility of introducing synthetic fields, whose characteristics are more advanced technologically and more reproducible across fields than natural grass (7).
Several personal and behavioral characteristics are possible predisposing factors for injuries. Among these there are age and life style factors such as smoking, alcohol, and diet.
Age may influence the strength, resistance, and elasticity of the bones of the muscles and of the connective tissue composing the tendons and ligaments; in addition, aging is accompanied by degenerative phenomenon of the main joints, such as the knee and the ankle. Because of the lack of published data on behavioral risk factors in the literature, the analysis of our data set was performed (24). The results did not suggest an independent effect of age on injuries occurrence (Table 4), probably because the age range of the players is very narrow. However, age may influence the length of time required for a complete recovery after an injury; the relationship between age and time to recovery postinjury has not been addressed by any study to our knowledge.
Smoking and alcohol consumption, 2 factors generally believed to have low prevalence in professional athletes, are instead frequently observed in the cohort of Italian soccer players (Table 5).
Although there are no reliable data on recreational drugs consumption because of the stigmas associated with use, 15.6% of the Italian soccer players reported having ever used drugs, with an additional 6% who elected not to answer this specific question. Our questionnaire investigated how the players spent their free time: The majority of the players (67.8%) reported having at least 1 hobby outside of their soccer activity, and more than half reported at least 2 hobbies.
Physical and Biological Characteristics
The physical aspect of the players has certainly changed over the years, especially in relation to BMI and body composition, and this could affect the players' predisposition to injuries. We performed a comparison of the anthropometric characteristics of 397 A league Italian soccer athletes playing during the season 2007–2008 and of 273 players of the same league playing in 1977–1978 by comparing historical data published by the Panini company (Table 6). Today's players are 4 kg heavier and 4 cm taller on average than how they were 30 years ago but with a similar body mass index. This may indicate that today's athletes have the ability of to develop more power when exercising. The increased muscle strength and the extreme solicitation imposed on the muscular-skeletal system may represent an excessive stimulus for the bones, joints and the surrounding connective structures, thus increasing the risk for acute (rupture of the knee ligaments and or cap) and chronic (tendinopathies, chondropathies) lesions. A major role is played by fatigue and stress, which may influence the appropriate response of the propioreceptor system to stimuli.
The biological characteristics of the player may be relevant factors in increasing the chances of a trauma; for example, the player may carry small, undiagnosed anomalies of the muscular-skeletal system that favor excessive overload of some parts of the system. Examples of this are small differences in the length of the lower extremities, differences in shape between feet, valgus, or varus deformities of the femur-tibia and femur-rotula axes.
Role of Previous Injuries
Having had a previous traumatic event exposes the payer to a higher chance of suffering another injury, mostly because there is never a full anatomic recovery even in the presence of a complete functional recovery. For example, an inflammation of the tendon may be successfully treated and result in a perfectly functional tendon, but the tissue will be less elastic than before the inflammation, thus predisposing the player to future injuries.
The analysis of the cohort of Italian soccer players show that having a history of injury protects the player from having a new injury (Table 4), suggesting the confounding effect of other variables. It is likely in fact that players who suffered injuries may play fewer matches after recovery or may play less strenuously or may undergo less strenuous training sessions to reduce their own risk. Thus, the study of how injuries affect the risk of new injuries in soccer players is very complex and requires more scientific data.
Drugs and Medications
It has been suggested that a heavy use of medications, such as anti-inflammatory and pain killer drugs, may cause the player to participate in a match when he is not yet physically fit for heavy exercise. This may in turn become a strong risk factor for injury. In the prospective study of A league Italian soccer players, we collected self-reported information on medications use. We correlated the number of matches played during the season vs. the reported amount of medications used by the players (Figure 1) and found no significant association.
This result seems to suggest that the use of drug and medications may not be a function of the external pressure to return to play and therefore not associated with new injuries.
The occurrence of injuries in professional soccer players has probably a multifactorial, multifaceted origin; few epidemiologic studies have been published on the topic, and it is not clear yet as to what is the independent contribution of each risk factor to injury occurrence. Differences in study design, methodology for sample recruitment, tools used for data collection, study design that favor retrospective and observational approaches over prospective studies limit the possibility to summarize data from the existing literature.
What appears very clearly is that many important areas of research in sport injuries have not yet been tackled by researchers; we have identified in this article a list of factors that are likely associated with injuries and have discussed the possible basis for each association with the overarching aim of identifying risk factors that can be prevented through appropriate public health interventions.
One of the most surprising findings of this review is the proportion of self-identified smokers and regular drinkers of alcoholic beverages in the Italian A league; one-third of the sample reported to be an “ever” smoker, two-thirds declared to be regular drinker, 15% reported use of recreational drugs. These data are very likely an underestimation of the reality but still suggest that professional players often embrace life style habits that are likely to unfavorably affect the player performance on the short term and can be prevented or reduced through appropriate education by the health professionals.
One concept appeared relevant while reviewing the literature: Professional soccer players are a dynamic cohort who adapted and changed over the years to respond to the new technicalities of professional games. For example, several observations suggest that changes in anthropometric structure occurred over the years as to favor a more muscular and strong typology, which delivers more power under strenuous exercise, thus increasing the chances of injuries especially of the joints and surrounding tissues. Temporal changes in the technical and tactical aspects of the game are among the less studied factors and the most difficult to quantify in an unbiased, systematic way through rigorous epidemiological studies. For example, changes in intensity and speed both during training and during the matches have occurred over the last 10 years and are likely to have substantially contributed to injury incidence and to the type of injuries registered in soccer players. However, objective data on such changes and on how they have influenced injury patterns are lacking and probably difficult to collect. The new playing season often brings new technical staff to the team, for example, a new trainer; this may introduce substantial differences in the training methodology, both in quantity and quality. The result may be an increased number of injuries at the beginning of the season.
Another aspect that needs to be addressed and evaluated as a risk factor for injuries is the high number of matches played by professional soccer players during a typical season. For example, there are 180–200 players in the Italian A league who play the full Italian championship, the European Cup, the matches of the national team, and sometimes the under 21 games. This translates into less time available for appropriate training; the ratio of number of training session per number of matches has been shown to be a good indicator of injuries in soccer players (5,27).
Psychological factors often hard to measure are the high degree of competition among players from the same team, who must compete for being chosen to be in the match rather than in the reserve team. This translates into very demanding, aggressive training sections, where the players feel they have to prove to their coach that they are the appropriate candidates for the next official match instead of 1 of their team mates. The larger number of players present in a team nowadays should theoretically allow for more players turnover and more resting time for each player. In reality, the coach is often more prone to always chose the best players, thus loading few players with the bulk of the work.
Environmental factors that have not been fully addressed by injury research are field conditions and the type of shoes used during training and matches.
This article shows that much research needs to be conducted in the area of injury predictors in professional soccer players. This is the first mandatory step to plan efficacious preventive activities on this population. Meanwhile, some practical applications can be drawn from what is known: personal behavioral risk factors should be recorded by the coach and taken into account because they may impact the player's susceptibility to injuries; the presence of previous injuries should drive the choice of the training; the number of matches played, and the number of previous injuries are not major risk factors for future injuries.
The authors thank the Panini SpA for historical data material. This study is supported by RF 03/232 from the Italian Ministry of Health to ET.
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Keywords:© 2012 National Strength and Conditioning Association
football; epidemiology; trauma; public health; cohort studies