Cheerleading Reporting Information Online (RIO), an Internet-based injury surveillance tool for collecting cheerleading exposure and injury data, has been described in detail previously [10]. All US cheerleading teams with a designated reporter were eligible to participate. Excluded from the study were impromptu teams formed by friends who got together to cheer for neighborhood sports teams. A convenience sample was used because there is no comprehensive or authoritative list of all cheerleading teams in the United States that can be accessed to aid in sampling the cheerleading population. Participants were recruited via e-mail, flyers, advertisements in cheerleading magazines and newsletters, and at cheerleading-related events.