Fibromyalgia is a chronic condition characterized by widespread musculoskeletal pain, fatigue, sleep disturbances, and psychological symptoms. Autonomic nervous system (ANS) dysfunction, marked by increased sympathetic and reduced parasympathetic activity, is considered one of its possible mechanisms. Although exercise is recommended in treatment, low motivation and fatigue often limit participation. Therefore, inspiratory muscle training (IMT), which targets the respiratory muscles, is seen as an easy-to-apply alternative.This randomized, controlled, double-blind study will be conducted at Niğde Ömer Halisdemir University Hospital. Fifty-one women aged 18-65 years who meet the 2010/2016 ACR criteria for fibromyalgia will be randomly assigned to three groups: training (30% of maximal inspiratory pressure), sham (0-10%), and control (no training). ANS functions will be assessed using heart rate variability and the COMPASS-31 questionnaire. Pain, sleep quality, fatigue, anxiety, depression, and respiratory muscle strength will also be evaluated. Training will be performed with the Powerbreathe® device twice daily for six weeks.The study aims to investigate the effects of IMT on ANS functions in fibromyalgia and to explore its relationship with symptoms such as pain, fatigue, sleep disturbances, anxiety, and depression.