Original research
Injury risk factors in young soccer players detected by a multivariate survival model

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Abstract

Soccer is a popular game practiced all around the world by teenagers. However, despite being a relatively safe sport, muscle-strain injuries during competitive matches are common compared to other team-sports. Few studies, to date, have investigated risk factors for soccer injuries using a multivariate survival model (e.g., Cox regression). The aim of this study was to use a multivariate survival model to investigate factors associated with an increased risk of thigh muscle strains, in young soccer players. A multivariate Cox regression was used to evaluate survival probability predictors for thigh muscle strains. 84 young male soccer players (16.4 ± 1.6 years) were followed for a season. Baseline tests were performed for body size, body composition, endurance, flexibility, and jump height from both a static position (SJ), and with a countermovement (CMJ); the percentage difference between the two types of jumps was also calculated (ΔJH). Cox regression result (hazard ratio; C.I. 95%) showed that: previous injuries (2.80; 1.19–6.54), ΔJH (0.79; 0.71–0.87), and stature (1.17; 1.06–1.25) were significantly correlated to thigh-strain survival probability. This study confirms that previous injuries are an important risk factor. However, we also report that a negative ΔJH and an elevated stature increased the probability of thigh strain. This could be explained by poor player coordination, influencing jumping ability, which may be even more evident in tall young players.

Introduction

Soccer has a higher injury rate compared to other team sports such as rugby, basketball, and football.1, 2 Several studies have investigated the etiology, type, location, and incidence of injuries in soccer.3, 4 Other studies have determined the potential intrinsic (person-related) or extrinsic (environment-related) risk factors.5, 6 However, while this information is valuable, few studies to date have investigated risk factors for soccer injuries in young soccer players using Cox regression, one of the statistical approaches recommended by the Union of European Football Associations (UEFA).7

Despite the fact that soccer is the team sport with the highest participation rates by teenagers and pubescents in the world,8 there are few multivariate studies to date that have evaluated risk factors for injuries in this population. Such studies are essential as risk factors during this stage of development, which is characterised by large physiological changes in the musculoskeletal and neuromuscular systems, may differ from those of adults. Furthermore, differences in training methods, match duration and seasonal periods, compared to adults, could modify the injury probability. It has previously been reported that the incidence of injury in young soccer players increased with age, and that the risk was greatest in the elite division.9 While not previously investigated in young soccer players, Hägglund et al.10 observed that adult players injured during one season have an increased risk of injury in the following season.

A further challenge, when comparing studies that have investigated risk factors for injury in soccer players, is the use of different definitions of an “injury”. Previous studies have often used a “time-loss” definition of injury, meaning that injury is one that causes absence from soccer participation.7 However, some authors have recommended a specific tissue injury classification,11 as this avoids the subjective components of the time-loss definition. A tissue injury diagnosis may be the most objective method to determine whether or not an injury has occurred. For a specific assessment of muscular strains, an ultrasound evaluation of muscular damage could be utilised to determine the injury severity.12 The importance of a specific evaluation of muscular strains is highlighted by the high incidence of this injury (31%) compared to other injuries, such as ligament sprains (18%) and contusions (20%), in adult soccer players.13

Thus, the aim of the present study was to examine which factors (time played or spent in training, age, competition level and experience, body size, playing position, jumping ability, aerobic fitness, flexibility or previous injuries) could be identified as risk factors for muscular strains in adolescents, using a multivariate survival model. This data is important as the early identification of risk factors, followed by regular monitoring, could help team physicians and trainers to identify young soccer players at high risk who need to be placed in preventative training programs.

Section snippets

Methods

All players, from three different age-categories of the ChievoVerona young soccer teams: CA (18–17 years old); CB (16–15 years old); CC (14–13 years old), who participated in the Italian national elite tournament, accepted the invitation to participate in this study. All participants and their parents were informed about the purpose of the study; all relatives of the players gave their informed consent to participate and the ethical committee approved the study design.

A total of 96 players, 33

Results

In the first 40 days of intensive training and non-competitive matches (pre-season period) only 5 players incurred a muscle injury (i.e., a thigh strain). The Italian juvenile soccer competitive season is divided in two parts: The first part ended 170 days after the base line assessments; in that period 14 players incurred a thigh strain. In the second part of the competitive season, 171–300 days from the baseline evaluations, 8 thigh strains were recorded (Fig. 1). During the entire season 27

Discussion

The main finding of this study was that, during a soccer season (pre-season + competitive season), there was no significant effect of exposure to training and matches on thigh-strain probability. However, we report for the first time that previous injuries, a low ΔJH, and an elevated stature all contributed to a multivariate model to predict grade II thigh strains in young soccer players.

In order to accurately interpret our results, some methodological factors must be considered. The main

Conclusion

Injuries in juvenile soccer teams are a major problem, and previous studies have observed that the injury rate is higher when compared to other team sports.1 As young elite soccer players showed as great an incidence of thigh strains as previously reported in adult players, risk factor determination is also very important in these age groups. In the present study, previous injuries, a low ΔJH and an elevated player stature all contributed to predict grade II thigh strains in young elite soccer

Practical implications

  • A newly proposed test, percentage difference between squat jump and counter movement jump, may help to identify players at a higher risk of thigh injuries.

  • While additional research is required, it may be prudent to provide more coordination training to taller players.

  • Regular monitoring of percentage difference between the squat jump and the counter movement jump, stature, and previous incidence of injury, may help to identify high-risk players who need to undertake preventive training so as to

Acknowledgments

We appreciate the help of: physical therapist, coaches, and physical trainers of ChievoVerona soccer team.

This project was not supported by external financial assistance.

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