The aim of this study was to investigate the effect of progressive muscle relaxation on affective well-being (anxiety and mood), cognitive variables (sustained attention and reaction time), and aggressive behavior in female athletes during menstruation. Forty-five athletes age 18–22 years were randomly assigned to three groups: an experimental group (n = 15) undergoing eight sessions of 30-min progressive muscle relaxation, a breathing group (n = 15) engaging in eight sessions of 30-min deep breathing, and a control group (n = 15) receiving no intervention. The participants were evaluated during menstruation, at baseline, and after the intervention. Results showed significant improvements in mood (