Fibromyalgia syndrome (FMS) is a chronic disease characterized by widespread body pain and tenderness in specific points, which may be accompanied by sleep disturbances, depression, fatigue, cognitive symptoms such as memory problems and attention deficit, and somatic symptoms such as irritable bowel syndrome and constipation. The prevalence of FMS has been found to be approximately 2%. It is more frequently diagnosed in women between the ages of thirty and fifty . It is more common in individuals with low socioeconomic status and education level. Its etiology is not fully known. Genetic and some environmental factors are thought to be influential. Central sensitization, autonomic nervous system dysfunction, immune system dysregulation, intestinal microbiota changes, hypothalamic-pituitary-adrenal (HPA) axis and endocrine system disorders are implicated in the pathogenesis (5; 6; 7; 8). FMS diagnostic criteria were first established in 1990 by the American College of Rheumatology (ACR).

According to these criteria, FMS is diagnosed based on the presence of widespread pain and tender points in the body.

In 2010, the ACR updated the diagnostic criteria by adding the Widespread Pain Index and Symptom Severity Scale. Currently, the 2016 ACR classification criteria are used in the diagnosis of FMS. These criteria consider the presence of pain for at least 3 months, the widespread pain index which assesses the presence of pain in 5 different areas of the body, and the symptom severity scale which assesses fatigue, waking up without rest, and cognitive symptoms. In these criteria, a diagnosis of fibromyalgia can be made independently of other diagnoses; the presence of fibromyalgia does not rule out the presence of other diseases.

The treatment approach for FMS is multidisciplinary. It is considered both non-pharmacological and pharmacological. Non-pharmacological treatment consists of patient education, lifestyle modification, cognitive behavioral therapy, and exercise. Pharmacological treatment includes tricyclic antidepressants, selective serotonin reuptake inhibitors, serotonin norepinephrine reuptake inhibitors, and pregabalin. The aim of the study is to evaluate muscle strength, muscle power, muscle thickness, vitamin D levels, and sleep quality in individuals with and without fibromyalgia syndrome, and to identify possible risk factors.

In individuals diagnosed with FMS, existing somatic and cognitive symptoms and chronic pain negatively affect the quality of life, sleep quality, work capacity, and productivity of patients. There are studies showing that patients have reduced muscle strength and power compared to the normal population. It is thought that accompanying vitamin D deficiency may deepen fibromyalgia symptoms. In light of this information, considering the importance of enabling individuals diagnosed with FMS in the community to continue to lead an active and pain-free life, the importance of clinical studies on this subject is increasing. The aim of our study is to evaluate muscle strength, muscle power, muscle thickness, vitamin D level, and sleep quality in individuals with and without fibromyalgia syndrome, to calculate possible risk factors, to determine the differences between the two groups, and to contribute to the literature with these data.Muscle tissue assessment is done by measuring functional and structural parameters.

Functionality is assessed by measuring muscle strength and muscle power. For structural measurement, muscle mass and muscle thickness should be considered. To draw a meaningful conclusion, all data must be evaluated together.Computed tomography (CT), magnetic resonance imaging (MRI), bioelectrical impedance analysis (BIA), dual energy X-ray absorptiometry (DEXA), ultrasonography (USG) and anthropometric measurements can be used to assess muscle mass and thickness .Although CT and MRI are gold standards, they are not used in clinical practice.

They are used in scientific research BIA provides information about body structure by taking advantage of the conductivity difference of tissues. It is affected by variables such as nutritional and hydration status, skin temperature, and physical condition. Therefore, it is difficult to establish standards for measurements.

DEXA calculates the difference between the absorption amounts of two different X-rays at low doses from tissues and provides information about body composition. It is frequently used, especially in the diagnosis and follow-up of osteoporosis. Compared to CT, it involves less radiation exposure and is less expensive.

USG is a radiation-free, low-cost, and easily applicable imaging method. Despite the disadvantage of being person-dependent, it is frequently preferred in musculoskeletal system assessment due to its easy accessibility and repeatability. Although there are different modes and frequencies, brightness (B)-mode USG at a frequency of 1-10 MHz is frequently used in tissue thickness measurement.

Using USG, skin, subcutaneous fat tissue, and muscle thicknesses can be evaluated. By looking at the changes in muscle tissue echogenicity, comments can also be made about the structure of muscle tissue .

Anthropometric measurements; It is done using measurements such as body mass index, waist circumference, hip circumference, calf circumference, and arm circumference. The disadvantage is that it does not provide data on muscle strength and power.

Muscle strength is the work produced by a muscle in a certain period of time as a result of voluntary contraction.

It can be measured by isometric, isotonic, and isokinetic methods. Isometric Method: A level of counter-resistance is applied to the muscle that will prevent movement. The high counter-resistance applied ensures maximum loading of the muscle. However, the measurement is only valid for the position in which the measurement is made. Since there is no displacement or movement during the process, no physical work is produced. Isometric measurements are frequently preferred because they are simple and inexpensive. However, since a large part of daily activities involve movement, the data obtained by the isometric method generally does not reflect the muscle capacity in daily activities. Isotonic method: In this method, certain weights are used throughout the range of motion of the joint. The resistance applied to the joint during movement is high at the end of the range of motion and lower at the midpoints. That is, during isotonic measurement, the tension in the muscle can be maximum in only a small part of the range of motion of the joint. For this reason, it is difficult to evaluate the maximum force produced. Isokinetic method: In this method, the angular velocity of the muscle is kept constant, and the counter-resistance that can be applied is kept at its maximum. In this way, the speed of the automatically increasing muscle power is prevented by applying appropriate resistance, and the power to be expended for acceleration is converted into torque. Thus, at a certain angular velocity, the maximum performance that the muscle can produce throughout the range of motion of the joint can be determined by a dynamic method. Thanks to the different angular velocities selected, information about the performance of the muscle is obtained.

Slow angular velocities are preferred in measuring muscle force. Medium and high angular velocities are used to measure muscle energy capacity, endurance, and strength.

Measurements made with an isokinetic dynamometer are considered a valid method for determining muscle strength and power. For this reason, isokinetic dynamometers are frequently preferred to measure muscle strength and power during rehabilitation and exercise. There are points to consider in order to obtain accurate data. One of these is that the individual to be measured should be familiar with the device and understand the operating protocol. For this, light warm-up exercises are recommended before the measurement. These exercises ensure familiarity with the device and reduce the likelihood of muscle injury. If measurements are to be made at different angular velocities, it is recommended that the individual rest for approximately 20 seconds between different angular velocities. The order of the measurement velocities is also important. Measuring low angular velocities before high angular velocities has been found to be more reliable. Individuals being measured may hesitate to exert their maximum effort due to lack of motivation, therefore verbal motivation should be provided during the measurement.

Inclusion Criteria:

Patient group:

• female gender
• 18-55 years old
• Clinical diagnosis of Fibromyaljia syndrome

Control group:

• female gender
• 18-55 years old
• absence of fibromyalgia syndrome diagnosis

Exclusion Criteria:

• Rheumatological disease, crystal arthropathy, septic arthritis
• Advanced osteoarthritis
• History of major orthopedic surgery (total knee and hip replacement, etc.)
• Neurological disease (Parkinson's disease, multiple sclerosis, cerebrovascular event, etc.)
• Neuromuscular disease (Polyneuropathies, myasthenia gravis)
• Active malignancy
• Advanced organ failure/transplantation

Only female individuals

The case group consisted of 40 volunteer female patients who presented to the outpatient clinic of the university hospital, agreed to participate in the study, were diagnosed with fibromyalgia syndrome, and met the inclusion criteria. The control group consisted of 40 healthy female volunteers who did not have a diagnosis of fibromyalgia syndrome

No decision has yet been made regarding IVD.