Context Although considerable cross-sectional evidence exists regarding the association between sport specialization and injury, sport-specific, prospective research is lacking. Similarly, sport specialization is associated with impairments in sleep and subjective well-being in youth athletes, but it is unknown whether this increases the risk of illness.

Objective To determine the relationship between sport specialization status and in-season injury and illness risk in elite female adolescent soccer players.

Design Prospective Cohort Study

Setting Pre-season evaluation of maximal aerobic capacity (VO2max) and sport specialization, and in-season self-reporting of daily training load (session-rating of perceived exertion), injury and illness resulting in lost sport participation time.

Participants 80 female youth soccer players (ages 13-18) from a local youth soccer organization.

Main outcome measures Sport specialization status, injury and illness incidence during two 4-month competitive soccer seasons. Athletes were considered specialized if they participated in soccer exclusively versus multiple sports during the year. Mixed effects logistic regression models were used to individual injury and illness (yes/no) during the study period, using sport specialization, age, and training load as fixed effects and individual athlete as a random effect.

Results Specialized (n=46) athletes did not differ from non-specialized (n=34) athletes with respect to age, preseason physical activity, VO2max or in-season training load (all p>0.05). No difference was seen in the proportion of individuals from each group that reported an in-season injury (specialized = 19% v 17%, p=0.83) or illness (40% v 38%, p=0.82). After adjusting for age and training load, the individual injuries (OR= 0.86 [0.26, 2.8], p=0.81) and illnesses were not significantly predicted by specialization (OR= 1.06 [0.45, 2.5], p=0.89).

Conclusions After adjusting for age and training load, sport specialization status was not associated with in-season injury or illness risk in elite female soccer players.

Key points

Prior research regarding the associations between sport specialization and health outcomes has been primarily cross-sectional and failed to account for the confounding role of training load.

Among elite adolescent female soccer players with similar pre-season physical activity levels in-season training loads, sport specialization was not associated with injury or illness incidence across two competitive seasons.

Dr. Watson serves as the Chief Medical Adviser for the Elite Clubs National League

This study was partially funded by the Young Investigator Award from the American Medical Society for Sports Medicine

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Approval for the study was provided by the Health Sciences Institutional Review Board at the University of Wisconsin (2014-0373)

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

Data are available upon reasonable request to the authors