Discussion

The aim of this study was to use the consensus statement7 methodology to describe the incidence, patterns and risk of injury according to commonly used age groups in a UK Premier League soccer academy.

The English Premier League introduced the Elite Player Performance Plan in 20126 to ‘create more time for players to play and be coached’. Its impact on training load and potential risk of injury from the increased training time, in addition to competitive play has not been assessed until now.

Research has suggested that improved levels of strength, endurance and coordination in older players might give rise to reduced injury levels when compared with younger age groups.27 We did not find this in the current study. Training injury incidence in all players shows similarities to those found within both elite adult (3–6/1000 hours)10 ,12 ,14 ,15 ,26 and elite youth soccer (3.6–7.2/1000 hours).13 ,18 Training injury incidence for the U9–16 players is below that previously reported, possibly suggesting adequate levels of strength, endurance and coordination.

With regard to match injury incidence, we found 80/1000 hours in the U15 players to be higher than all other groups investigated within the current study, as well as elite adult and youth players included in other research.1 ,5 ,14 ,16 ,18 ,20 A possible explanation is that match exposure for U15 players was substantially lower than other groups, explained by the lack of a games programme provided for this age group by the Premier League in the 2012–2013 season. However, while the U16 and to a lesser extent the U15 players had a higher risk and had greater odds of sustaining an injury during a match than training, the U16 players had three times more odds of getting injured in a match rather than training. Interestingly, we found trends indicating that younger players have a higher risk and greater odds of sustaining an injury in training while older players have a higher risk and greater odds of sustaining an injury during matches.

Our findings are in contrast to Malina34 who suggested that boys younger than 14 years of age were at most risk of injury in training and matches. It could be that fewer games put U15 players at a higher injury risk. Fewer games would result in the real-life experience which result in greater levels of muscle strength, power and coordination, also referred to as ‘match fitness’, which might reduce injury risk.20 A lack of match fitness might lead to local muscle fatigue and central brain fatigue,26 ,33 which also might be causative factors for match injuries; such factors are not yet suggested as an area of data collection within the consensus statement.7

An alternative hypothesis is that throughout the season, U15 players were required to play in U16 matches. Younger players being involved in competitive matches where their opponents are older and possibly more skeletally mature and able to cope with higher physical demands might explain a higher match injury incidence in the U15 group. In the current study, the skeletal maturity of the academy players was not tested; further research is needed to determine if grouping players according to this parameter is more relevant than by age. It could also be due to lower skill levels of players that might reduce protection from match-incurred injury.18 Such claims are not evidence based. While this might be a possibility for the results found, further research is necessary. The issue of players playing in multiple age groups is one which has not needed to be addressed in adult research.

Previous authors1 ,14 ,15 ,26 ,33 have suggested posterior thigh muscle strains were the most common injuries in adult soccer. We found the most common injury to be anterior thigh and knee injuries in academy players, suggesting as indicated in previous research,18 that growth-related factors such as hypermobility syndrome, Osgood-Schlatter disease, Severs disease and Sinding-Larsen disease might contribute to the larger number of training injuries. It is possible that growth-related injuries may account for the large number of knee injuries found among youth-level players.

Le Gall et al18 suggested that the U14 age group were the most likely to suffer injuries as a result of training. We found the highest number of injuries in training to be in U12–14 players. They had the second highest injury incidence in training and risk of injury per 100 hours of exposure, second to the U18s. The numbers of hip/groin injuries are noticeably higher within the U12–14 and U15 groups, with injury numbers reducing with advancing age beyond this age group. Recent research has suggested that anterior groin pain in these age groups may be indicative of femoroacetabular impingement, diagnosed via a detailed history, physical examination and radiographs.35

Our results showed a greater number of injuries sustained in training (50%) than matches (32%). The majority of studies suggest that match injuries tend to be the most prevalent within elite soccer.1 ,5 ,10 ,12 ,14 ,16 ,20 ,26 ,33 However, others have reported that injuries occur equally in matches and training,32 while others claim a larger proportion of injuries occur in training than matches.18 The latter suggests that players were subjected to a training intensity beyond physical toleration and lacked injury-avoidance skills as well as strength, endurance and coordination. These variables would need to be quantified and used in conjunction with an injury audit to establish the presence of such a relationship.

In the current study, 17% of injuries were reported from no specified activity. When questioned, players reported the onset of symptoms in the days following training and matches; these were noticeably higher within the U12–14 age group and specifically for the knee. Such findings highlight an injury of gradual onset, and therefore suggest that overuse might be a contributory factor. In order to attribute cause of an injury to a specific session, we suggest that if pain is felt the day after a game, the injury should be recorded as a ‘match injury’, and likewise for training. This might reduce the numbers of injuries categorised as ‘NA’, and provide a more accurate injury profile.

The strengths of the current study are that it is the first of its kind to apply the consensus statement7 methodology to Premier League academy soccer and categorising players according to exposure. Analysis using standard definitions of injury, matches, training, location of injury and incidence will assist in injury prevention within higher incidence groups, and thus maximise the development time for each individual player. Data were not analysed during the season and so changes to minimise injury were not made, based on the findings.

Limitations of the study include multiple staff recording exposure data, possibly introducing a source of bias. Using fewer staff to monitor and record exposure data in future studies would reduce this. External validity could be improved by increasing the number of Premier League soccer academies. However, although overall injury incidence would be identified and differences between clubs observed, its findings would be limited due to the differing training and coaching methods employed as well as types of matches played. Reporting such data may be difficult given the potential barriers to sharing sensitive data between professional soccer clubs. Perhaps a more useful method would be to perform longitudinal research via data collection from the same academy over several seasons, with additional analysis made with regard to player position and injury incidence.

Certain issues arose surrounding the Injury Record Form throughout the course of data collection, and further amendments might be made. First, in response to the question ‘When did the injury occur?’ some injuries were reported in the days following an injury and were incorrectly recorded as ‘NA’. Rewording the section title to ‘When was the injury reported?’ might allow the researcher to ascertain whether the injury was a result of match or training exposure. Second, in the section ‘Indicate type of training or match where injury occurred’, it was initially thought that subdividing soccer training into contact and non-contact would provide specific onset details. However, coaching sessions can involve both aspects and to prevent confusion it might be beneficial to group the two options into ‘football training’.