BACKGROUND: 81% of adolescent girls in the UK are not currently meeting the daily physical activity (PA) guidelines1 (60 minutes per day2) and are therefore at an increased risk of multiple health issues. Commonly cited barriers to PA include lack of time, perceived lack of competence and monotony3. High intensity interval training (HIIT) has been found to have equal benefits to traditional exercise in significantly less time and often in a more enjoyable format4. Numerous adolescent exercise interventions are created solely by exercise scientists, are not successful in long-term adherence and lack follow-up. Therefore, this study is critical to learning what protocol is preferred by adolescent girls, in order to inform the development of a HIIT intervention and optimise participant adherence. Therefore, this is the first study of a series which aims to develop and trial a home-based HIIT programme for inactive adolescent girls. This qualitative study has two main objectives, (1) obtain detailed feedback on a proposed HIIT programme and (2) to understand adolescents perceived facilitators and barriers towards PA. The results will inform the development of a HIIT protocol and the promotion strategy of the intervention. METHODS: 45 inactive adolescent girls, recruited from 5 secondary schools and 2 youth clubs in Liverpool and Dublin, will participate in semi-structured focus groups, guided by the Youth Physical Activity Promotion model. Adolescents will also complete demographic questionnaires and self-reported PA questionnaires. Focus groups will be transcribed verbatim and analysed using thematic analysis to identify key themes. RESULTS: As this study is still ongoing final results are not yet available but will be presented for the first time at the Future Physiology 2019 conference. Preliminary results show that choice in PA is a vital element of participation for adolescent girls, both inside and outside of school. A common theme which emerged in all focus groups was the girls self-perceived incompetence for PA in the presence of others and the time barrier of homework, especially among older adolescent girls.The participants felt that home-based HIIT would be an exciting and acceptable form of exercise that they would adhere to, provided they had individualised regular support. They express the importance of having “normal” girls of varying shapes and sizes lead the instructional videos and that air-brushed fitness models with perceived unattainable physiques promoted by the media add to society’s pressure of girls looking and behaving a certain way. CONCLUSION: We hope that by listening to the feedback and opinions of adolescent girls we can develop a home-based HIIT intervention that is feasible, enjoyable and something that they can stick to for life, thereby decreasing the associated health risks of inactivity.