High-Intensity Interval Training and Menstrual Health Experience in Primary Dysmenorrhea.

The goal of this study is to evaluate whether a 12-week online supervised high-intensity interval training program can reduce menstrual pain and improve quality of life in women with primary dysmenorrhea. Participants will be divided into two groups: one receiving an educational workshop and the HIIT program, and a control group receiving only the workshop. Additionally, the study seeks to understand the personal experience of these women through weekly health diaries, exploring how the intervention affects their relationship with their bodies and their menstruation. The ultimate goal is to offer new, non-pharmacological evidence-based tools for managing menstrual pain.

This research follows a convergent mixed-methods design integrating a randomized controlled trial with a descriptive qualitative study. Fifty women (aged 18-40) with primary dysmenorrhea will be randomized into two arms: Experimental Group: 12 weeks of online supervised HIIT (2 sessions/week) plus a menstrual health educational workshop. Control Group: Menstrual health educational workshop only. Clinical variables (pain intensity via NRS, quality of life via SF-12, and pain characteristics via McGill Questionnaire) will be collected at baseline, 3 months (post-intervention), and 6 months (follow-up). Simultaneously, all participants will complete a weekly semi-structured digital diary for 12 weeks. These diaries are designed to capture the "thick description" of their menstrual health experience, focusing on the evolution of their relationship with their body and menstruation, perceptions of self-management and empowerment and barriers and facilitators for adherence to the exercise program (in the experimental group). Following the convergent design, quantitative statistical results will be integrated with the thematic analysis of the diaries. This merging of data will provide a holistic understanding of how high-intensity exercise influences not only physical symptoms but also the biopsychosocial perception of menstrual health in young women.

Inclusion Criteria: * nulliparous * primary dysmenorrhea * body mass index between 18 and 30 * menstrual pain \>5 according to the Numeric Pain Scale * exercise \>45 minutes/week * understand Spanish and can freely read and sign the informed consent form Exclusion Criteria: * amenorrhea or cycles \>35 days * secondary dysmenorrhea * pelvic or abdominal surgical intervention * use of hormonal drugs * diagnosed with fibromyalgia, muscoloskeletal injuries or medical comorbidities that prevent them from performing intense exercise * receiving physiotherapy for pelvic floor disorders * intense exercise \>75 minutes/week