Acceptance and Commitment Training (ACT) aims to build and strengthen psychological flexibility processes among athletes and improve their performance, well-being, and mental health. Meta-analyses and systematic reviews show that acceptance-based and mindfulness-based interventions might be effective in achieving these goals (Bühlemayer et al., 2017; Noetel et al., 2019; Ptáček et al., 2023), but none of the meta-analyses, or systematic reviews differentiate the developmental phases of participants within included studies. Youth athletes' context undoubtedly differs from adult athletes. When using contextual-based approaches (such as ACT) with youth, practitioners must consider contextual and developmental factors (i.e., metacognition and language, identity development, cultural influences, social dynamics, and others). In this regard, we argue that the evidence base of ACT among adult athletes cannot be used to guide practitioners working with youth. At the same time, youth athletes make up a substantial part of the population of competitive athletes facing the pressure of known demands of the sporting environment. Thus, there is a need to differentiate the evidence base based on the developmental phases of athletes. The presented project aims to address these issues. We aim to: (i) complete the systematic review of ACT in youth sport; (ii) develop an evidence-informed, web-based training program for Czech and Norwegian adolescent athletes.

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