Maturity status and injury risk in youth soccer players.

OBJECTIVE: To investigate the association of relative skeletal age and other risk factors with injury in elite schoolboy footballers (soccer players).
DESIGN: Prospective cohort study, with players participating for varying numbers of years.
SETTING: Manchester United Football Club Academy, 2001 to 2007. PARTICIPANTS: Players were recruited to the club by scouts. At intake, the boys were medically screened to ensure they could be fully involved in the training and games program. Computerized medical records for the boys were maintained for the entire study period. The investigation included boys 9 to 16 years of age. Numbers varied between 98 and 144 per year (mean n/y = 130) over 6 years. Overall, 292 players were represented in the sample. Mean drop out per season was 21%. ASSESSMENT OF RISK FACTORS: Each year consenting players had a radiograph of the left wrist and hand for the assessment of skeletal age (SA), using the Fels method. Eighty-five players had at least 1 radiograph and 12 players had 6 radiographs, 1 in each year of the study. Early and late maturers were those with an SA >1 year older or younger, respectively, than their chronologic age (CA). Information on demographics, height and weight, playing and training times, and position played was collected. MAIN OUTCOME MEASURES: The main outcome measure was the relation of maturity status to the occurrence of injuries. MAIN
RESULTS: For the total sample across all the age groups the incidence of injuries was 1.44 per 1000 hours of training (n = 244 injuries), and 10.5 per 1000 match hours (n = 169 injuries). The mean number of injuries per season was 79.3, with a mean loss of 12.5 injury days per player per season. Boys aged <14 years were most vulnerable. Most injuries resulted from overuse rather than from trauma. Most common injury type and location were, respectively, soft tissue and knee joint. Mean SA for the total sample was in advance of mean CA (12.08y vs 11.74y; P < 0.05). Injury incidence did not differ significantly among late, normal, and early maturing players (1.4, 1.5, and 1.8, respectively) when training time, playing time, height, and playing position were statistically controlled as covariates (P = 0.73). However, results of general log linear analysis of mean data over the 6 seasons indicated a relationship between injury occurrence and training time, match-play time, and the CA-SA difference (P < 0.05). The 3 variables together explained 48% of the variance in injury incidence. Position played, foot dominance, and mean height gain were not related to injury occurrence.
CONCLUSIONS: Maturity status and time spent in match play and training were significant predictors of injuries in 9- to 16-year-old elite male soccer players.