- External rotation strength and internal rotation range of motion did not improve
- Training dosage possibly insufficient or inappropriate exercises
- Unclear which factors are responsible for the protective effect of the programme
A prevention programme of the Oslo Sports Trauma Research Centre (OSTRC) which proved to be effective to prevent shoulder injuries in a randomised and controlled trial (RCT) conducted among 660 handball players in 2017  did not lead to significant improvements in external rotation strength and internal rotation mobility of the shoulder. Unfortunately, the factors that determine the effectiveness of the programme remain unclear. This was concluded by an international research group which randomly assigned 57 adolescent male and female handball players to two groups and let one of these two groups perform the prevention programme for 18 weeks.