Athletes were instructed to fill out their diary on a daily basis. Weekly appointments were made with every school class to
improve study compliance. An athlete was considered compliant (3rd inclusion criteria, see above) if he/she had completed his/her personal sports diary for at least 80% of the observation period and doing so with a relative delay of no longer than 2 weeks to avoid recall bias. All uploaded data relative to sport participation were corroborated with regard to the schedule of the sport school and the respective sport federation. When uncertain information was identified, a direct verification was made with the athlete or, if necessary,the school staff and trainers to ensure the highest quality of data. Recorded information on sports injuries was systematically cross-checked and verified regarding completeness by a member of the investigating team, present daily on site. Active assistance was provided by the physical therapists responsible for the
training of injured athletes at the sport school and the national trainers, which lead to a complete data set for sports injuries,
regardless of athlete compliance to data uploading.