Accepted for Publication: September 30, 2013.
Published Online: January 20, 2014. doi:10.1001/jamapediatrics.2013.4518.
Study concept and design: O’Kane, Neradilek, Polissar, Schiff.
Acquisition of data: O’Kane, Spieker, Levy, Schiff.
Analysis and interpretation of data: O’Kane, Neradilek, Polissar, Schiff.
Drafting of the manuscript: O’Kane, Schiff.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Neradilek, Polissar, Schiff.
Obtained funding: O’Kane, Schiff.
Administrative, technical, or material support: O’Kane, Levy.
Study supervision: O’Kane, Levy.
Conflict of Interest Disclosures: None reported.
Funding/Support: This study was supported by grant R01AR051059 from the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health (Dr Schiff).
Role of the Sponsor: The funding source had no role in the design and conduct of the study; collection, management, analysis, or interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
Additional Contributions: We thank the soccer associations and the players and parents who participated in this study. Christopher Mack, MS, assisted with data management and was paid by the grant from the National Institutes of Health.