Strengths and limitations
time-loss, injuries
One major strength of this trial was the active comparison group representing real-world implementation of IPEPs. Other strengths were the use of structured validated self-report weekly questionnaires to players and coaches in combination with physiotherapist-collected data enabling detection of injuries and complaints irrespective of time-loss or medical attention and with cross-validation from different sources.Some limitations should be mentioned. First, even though we met the a priori decided sample size, the low participation rate and the high pandemic-related dropout of teams and players must be considered. It is likely that the most motivated teams and players entered the study, which should be taken into account when considering compliance and external validity of findings. Participation rate among male players was particularly low and the dropout rendered unequal sex distribution between groups, and we therefore sex-adjusted all analyses. Ideally, programme effects should have been evaluated in men and women separately, but due to the small sample, sex-separated data are only presented descriptively. Second, the prolonged pre-season and shortened competitive season, and matches played without spectators due to the pandemic, limit the possibility of comparing injury rates with other samples. Importantly, the situation was the same within the three study arms and should have negligible impact on comparisons of injury rates. Third, we were forced to adapt the adductor programme due to the pandemic by adding two alternative adductor exercises. This complicates comparisons with studies using the original Adductor Strengthening Programme.