Data collection
groin, training/match, primary injury, Trauma
APPENDIX, OVERUSE INJURY
Players responded to a baseline questionnaire (Supplementary Appendix 1) at the start of the football season including questions about previous (previous season or earlier) and/or present injury in any of the locations ankle, knee, hamstrings, or groin (primary injury outcomes of the randomised trial), if they participated in other sports during the football season, if they performed strength- and/or conditioning training during the football season and questions about injury beliefs, importance of success in sports and training load (response model 7-level Likert scale): “I expect I will sustain an injury sometime during this football season” (extremely likely–extremely unlikely); “What significance does sporting success have for your interest and motivation in sports?” (little importance–great importance); “How do you rate your current total training volume?” (extremely low–extremely high); How do you rate your current total training load (quantity and intensity of training? (extremely low–extremely high); How do you rate your current match load (frequency and time on the pitch)? (extremely low–extremely high); and I have a good balance between training/match load and recovery (strongly disagree–strongly agree).Players responded to weekly questionnaires about occurrence of injury based on the Oslo Sports Trauma Research Center Overuse Injury Questionnaire (OSTRC-O2) [All questionnaires were distributed via online software (esMakerNX3 V 3.0). The baseline questionnaires, with two reminders, were distributed after each team’s acceptance to participate, and weekly questionnaires were distributed on each Sunday evening, with reminders sent to non-responders on Tuesday and Thursday the week after.