Although it is advocated that end-users are engaged in developing evidence-based injury prevention training to enhance the implementation, this rarely happens. The € Implementing injury Prevention training ROutines in TEams and Clubs in youth Team handball (I-PROTECT)' uses an ecological participatory design incorporating the perspectives of multiple stakeholders throughout the project. Within the I-PROTECT project, the current study aimed to describe the development of holistic injury prevention training specifically for youth handball players through using knowledge from both end-users (coaches and players) and researchers/handball experts. Employing action evaluation within participatory action research, the cyclical development process included three phases: research team preparation, handball expert-based preparation and end-user evaluation to develop injury prevention training incorporating both physical and psychological perspectives. To grow the knowledge of the interdisciplinary research team, rethinking was conducted within and between phases based on participants' contributions. Researchers and end-users cocreated examples of handball-specific exercises, including injury prevention physical principles (movement technique for upper and lower extremities, respectively, and muscle strength) combined with psychological aspects (increase end-user motivation, task focus and body awareness) to integrate into warm-up and skills training within handball practice. A cyclical development process that engaged researchers/handball experts and end-users to cocreate evidence-based, theory-informed and context-specific injury prevention training specifically for youth handball players generated a first pilot version of exercises including physical principles combined with psychological aspects to be integrated within handball practice.