Fibromyalgia is a common rheumatic disease characterized by widespread musculoskeletal pain, tenderness, fatigue, sleep disorders, cognitive and somatic complaints. Patients often suffer many somatic and psychological symptoms which contributes negative effect on the health- related quality of life, physical performance and physical activity. Recently, the European League Against Rheumatism presented evidence based recommendations for the management of the fibromyalgia. Accordingly, prompt diagnosis and patient education is required for optimal management. A graduated approach with the aim of improving health-related quality of life should be followed. It should focus first on non-pharmacological modalities and the only "strong for" evidence-based recommendation was the use of aerobic and strengthening exercise. Aerobic exercise with moderate intensity (60 to 70% of age-adjusted predicted maximum heart rate (maxHR)) with a frequency of two or three times per week for at least 4 to 6 weeks for a reduction of symptoms is recommended in the management of fibromyalgia. Low-intensity aerobic exercise (<50 % maxHR) is founded ineffective. In recent years, high intensity interval training (HIIT) is used as popular instead of moderate intensity continuous exercise training (MICT) in cardiac rehabilitation units. It is found superior to moderate intensity exercise in improving cardiovascular fitness as increases maximal oxygen consumption (VO2max). The investigators hypothesis is that 6 weeks of five weekly sessions of HIIT will show superior effect reducing the impact of fibromyalgia and improving pain degree, functional capacity and health-related quality of life in women with fibromyalgia compared to MICT.

Fibromyalgia is a common rheumatic disease characterized by widespread musculoskeletal pain, tenderness, fatigue, sleep disorders, cognitive and somatic complaints. Patients often suffer many somatic and psychological symptoms which contributes negative effect on the health- related quality of life, physical performance and physical activity. Recently, the European League Against Rheumatism presented evidence based recommendations for the management of the fibromyalgia. Accordingly, prompt diagnosis and patient education is required for optimal management. A graduated approach with the aim of improving health-related quality of life should be followed. Pharmacotherapy is only recommended for severe pain and sleep disturbances. It should focus first on non-pharmacological modalities and the only "strong for" evidence-based recommendation was the use of aerobic and strengthening exercise. Aerobic exercise with moderate intensity (60 to 70% of age-adjusted predicted maximum heart rate (maxHR)) with a frequency of two or three times per week for at least 4 to 6 weeks for a reduction of symptoms is recommended in the management of fibromyalgia. Low-intensity aerobic exercise (<50 % maxHR) is founded ineffective. In recent years, high intensity interval training (HIIT) is used as popular instead of moderate intensity continuous exercise training (MICT) in cardiac rehabilitation units. It is found superior to moderate intensity exercise in improving cardiovascular fitness as increases maximal oxygen consumption (VO2max). While the moderate intensity continuous aerobic exercise program lasts 30 to 60 minutes, HIIT contains 4-6 cycles of 1-4 minutes with a maximum effort and lasts approximately 20 minutes in total. Therefore, another advantage of HIIT is the need for a shorter time to achieve similar or greater effects compared to MICT. The investigatorshypothesis is that 6 weeks of five weekly sessions of HIIT will show superior effect reducing the impact of fibromyalgia and improving pain degree, functional capacity and health-related quality of life in women with fibromyalgia compared to MICT. Therefore, the aim of this study is to assess the effects of HIIT versus MICT on pain, functional capacity and quality of life in women with fibromyalgia.

Inclusion Criteria:

• Subjects diagnosed according to the American College of Rheumatology 2016 diagnostic criteria for fibromyalgia.

Exclusion Criteria:

• History of comorbid inflammatory rheumatic/ connective tissue diseases
• History of cardiovascular or musculoskeletal problems that could prevent them to participate in an exercise program.

female sex