Football skills and risk of injury

The data on the relationship between football skills and risk of injury in football are equivocal.3 15,–,20 In youth football, Emery et al3 found no association between the risk of injury and the dynamic balance, vertical jump height, and endurance of female and male players 12–18 years of age. In male youth football, Le Gall et al19 reported no difference in the overall risk of injury between players acquiring a professional contract and those who did not. Yet, a higher risk of moderate and major injuries was found in the non-professionals, while the professionals sustained more injuries to the lower extremity, contusions to the lower leg, minor injuries and re-injuries. The latter results are supported by Severino et al,20 who in 11- to 12-year-old males found that injured players were better at ball juggling, dribbling, agility and anaerobic performance.

It is difficult to suggest reasons for the higher risk of injury in the skilled players compared with their less skilled teammates. Previously, it has been argued that technically skilled players may be less injury-prone due to their ability to efficiently control and pass the ball before being challenged by the opposing player.24 Likewise, tactically skilled players may be protected from injury, because they possess the ability to recognise potentially hazardous situations before they occur, and thus avoid them.25 Although these theories intuitively seem valid, they do not account for the fact that skilled players have more ball possession and consequently are more exposed to tackles and other duels.19 25 26 This rationale is reflected by our findings; players skilled in ball receiving, passing and shooting, and decision-making when in ball possession, experienced a threefold risk of contact injury. In our analyses, we have corrected for exposure, estimated as the number of hours of match and training exposure. In this way, the fact that skilled players are more likely to be selected for games has been adjusted for. However, highly skilled players are most likely also more involved in the game, more prone to tackles and foul play, and hence, at greater risk of injury than their less skilled counterparts. Although generally not feasible in youth football, notational analysis tools27 provide the opportunity to record whether skilled players are more involved in game situations that entail a higher risk of injury, such as tackles.

Previously, it has been shown that the risk of injury in young female amateur players increases by 12% for every successive year of participation in organised football.6 Moreover, previous injuries, as well as symptoms from previous injuries, make the player more susceptible to re-injuries.3 6 28 Although these factors were not recorded in the current study, one possible scenario is that compared to their less skilled teammates, the skilled players not only played more football during the season but also started playing football at an earlier age. Furthermore, key players may experience higher external pressure or be more motivated to quickly return to play after an injury. Inadequate rehabilitation and premature return to play may increase the risk of exacerbations or re-injuries29 and may thus lead to a higher injury risk in skilled players.

Methodological considerations

In this study exposure was recorded individually, and not on a team basis. Individual exposure takes censorship into account, such as abbreviated lengths of follow-up for reasons other than injury (eg, illness, moving, quitting the sport).30 Furthermore, we adjusted the analyses for playing time which can vary greatly among players. The individual exposure demonstrated that the high-skilled players had a higher match and training exposure than their less skilled teammates. However, since match exposure was a dichotomous variable (participation yes/no), it remains possible that the low-skilled players not only played fewer matches but also were on the field for a lower proportion of the match. This may have lead to an overestimation of match exposure and an underestimation of injury risk among the low-skilled players.

Injury recorders, who were blinded to group allocation, interviewed the injured players based on a standardised injury questionnaire as soon as possible after the weekly registration form was received. Even so, there is a possibility that injuries may have been overlooked by the coaches. However, given the individual activity logs kept by the coaches and the time-loss injury definition,22 we think it is unlikely that injuries would go unreported. Thus, our method should ensure good reliability and validity of the injury and exposure data.

The main limitation of the study is that the recording of skills was conducted retrospectively, 2 months after the recording of injuries was completed. This may add uncertainty as to whether a player's level of skill is a possible cause or a consequence of the injury,30 and may be a limitation if the skill assessment of the coach was influenced by his/her knowledge of the player's injury status. However, we believe this to be unlikely, as the purpose of the assessment they were asked to make was not explicitly linked to the study purpose. There is also an obvious advantage of recording the level of skill retrospectively; it allows for an overall assessment of the players' performance throughout the course of a complete season. Nevertheless, skill is not a static variable and potential change in the different skill attributes of the players during the season was not accounted for. In future studies, it would be advisable to measure the skills before the injuries occur and follow-up with prospective repeated assessments throughout the season.

Another limitation is that the skill assessment approach was not validated. In future studies, the use of established tests for passing,31 32 shooting,32 dribbling33 and physical performance34,–,36 should be considered. Nevertheless, football is a complex sport where performance is determined by a wide range of technical, tactical and physiological skill attributes. It is questionable whether performance in football can be assessed strictly using objective testing,37 and the qualitative assessment of a coach can therefore be useful.

The majority of the coaches were volunteers such as parents and their level of education and experience as football coaches was not recorded. Different interpretations of the skill attributes may have affected the inter-rater reliability of the skill assessment. Furthermore, a test–retest procedure of the coaches' skill assessment would have been useful to evaluate the intra-rater reliability. However, 84% of the players were assessed equally in ball receiving and dribbling; two technical skill attributes assumed to be related. By contrast, only 63% of the players were assessed equally in the less-related skill attributes heading technique and speed/agility. This exemplifies our findings of a consistent logical relation between attributes, which strengthens the reliability of the coaches' skill assessment.

Half of the players performed an injury prevention programme throughout the study. The risk of injuries overall, overuse injuries and severe injuries was reduced in these players.11 However, this did not bias the current results, as no interaction was found between the implementation of the injury prevention programme and the association between the players' level of skill and their injury risk.

Implications

Considering the limited knowledge about football skills as a potential injury risk factor in football, our findings need to be confirmed by subsequent studies in youth football, as well as in adult cohorts. Furthermore, by implementing actual game play measures (match statistics) in future research we can ascertain whether skilled players actually are more involved in game situations that entail a higher risk of injury. The disproportionate high risk of contact injuries in players who excel in youth football does in any case seem to warrant injury prevention to focus more on the injuries occurring from tackles and contact situations. Stricter interpretation of the fair play rules and better refereeing may be important means to protect the ‘Messis’ and ‘Martas’38 of tomorrow from career-ending injuries and allow them to hone their skills throughout adolescence to achieve their optimal potential in adulthood. Previously proposed measures to prevent contact injuries include modification and enforcement of the Laws of the Game, the referees' interpretation of the rules, as well as the coaches' and players' attitudes towards fair play and high-risk game situations.39,–,42 To our knowledge, no risk factor studies or preventive measures specifically aimed at contact injuries have been implemented in female youth football. However, it has been shown in international female tournaments that the decision of the referee does not reflect the injury risk of sliding-in tackle.43 Thus, it seems unreasonable to expect referees on a lower level to make correct decisions based on a subjective judgment of injury risk.

The current results also suggest that skill level should be addressed as a possible confounder in studies on other risk factors for injury. However, because skill level was registered in relation to the skill level of teammates, our findings might not be valid within populations consisting of multiple teams or leagues. Teams in female youth football are often characterised by large variations in skill level, larger than on the senior level and in male football. Thus, we do not know if the results can be generalised to both sexes or other age groups.