Juvenile Idiopathic Arthritis (JIA) and Familial Mediterranean Fever (FMF), two of the most prevalent pediatric rheumatologic diseases, significantly compromise the physical health of children and adolescents, leading to reduced physical fitness, muscle weakness, and a sedentary lifestyle. This study aims to evaluate the validity and reliability of the International Fitness Scale (IFS) and the Self-Perceived Health-Related Fitness Questionnaire for Children (PHFQ-C) as assessment tools for physical fitness in individuals diagnosed with JIA and FMF. Our hypothesis is that these scales will provide demonstrably reliable and valid data within this patient population. To test this, 98 patients aged 10-18 years, recruited from the Pediatric Rheumatology Clinic at Istanbul Faculty of Medicine, will participate. Their physical fitness will be objectively measured using the FitnessGram Test Battery (assessing aerobic capacity, muscular strength, and flexibility), while the IFS and PHFQ-C will be administered online. Statistical analysis, conducted using SPSS 25.0, will employ Pearson/Spearman correlation for validity and Cronbach's alpha and test-retest Intraclass Correlation Coefficient (ICC) for reliability.

The expected findings will confirm the utility of the IFS and PHFQ-C as practical, economical, and valid instruments for assessing physical fitness in children and adolescents with JIA/FMF. Promoting the widespread use of these scales in clinical settings will facilitate the rapid and convenient evaluation of patients' fitness levels, thereby enabling the development of early, targeted intervention strategies and ultimately contributing to an improved quality of life. Furthermore, by offering a validated alternative to standard test batteries-which are often cumbersome due to requirements for time, specialized equipment, and expert personnel-this work will make a valuable methodological contribution to the existing scientific literature.

Pediatric rheumatologic diseases are a group of chronic inflammatory conditions that affect multiple organ systems and are characterized by periods of flare-ups. These conditions encompass diverse groups of disorders, including inflammatory arthritis, autoinflammatory syndromes, vasculitis, and other autoimmune diseases. While Juvenile Idiopathic Arthritis (JIA) is the most common rheumatologic disease in childhood and adolescence, Familial Mediterranean Fever (FMF) is another major and frequently encountered rheumatologic condition in the pediatric population in Turkey. FMF is an autosomal recessive autoinflammatory disease, typically manifesting in childhood and presenting with recurrent episodes of fever and pain. JIA is defined as a heterogeneous group of rheumatic inflammatory diseases characterized by arthritis of unknown etiology that begins before the age of 16 and lasts for at least six weeks.

These pediatric rheumatologic conditions are often marked by pain, which can lead to limited joint mobility, muscle weakness, and fatigue. Individuals experiencing pain symptoms generally exhibit reduced physical function compared to those who are pain-free. Due to the chronic nature of the disease, frequent attacks, and associated symptoms, individuals with FMF and JIA face significant challenges such as a sedentary lifestyle, physical inactivity, decreased muscle strength, fatigue, low physical fitness, and overall reduced physical function. Several studies have consistently demonstrated low levels of physical fitness in children with JIA and adolescents with FMF.

The evaluation of physical fitness in children and adolescents is crucial for identifying developmental differences and allowing for the early detection of potential health problems that may persist into adulthood. While validated and reliable, current physical fitness test batteries frequently encounter practical barriers during field application, including limitations in space, equipment, time constraints, and the need for specialized personnel. These limitations highlight a pressing need for standardized, easily administered scales to facilitate routine clinical assessment.

Inclusion Criteria:

• Age between 10 and 18 years
• Diagnosis of Familial Mediterranean Fever (FMF) or Juvenile Idiopathic Arthritis (JIA) established by a pediatric rheumatologist at least six months prior
• Voluntary willingness to participate in the study
• Provision of informed consent by both the participant and their parents/guardians
• Ability to ambulate independently, communicate effectively, and comply with the instructions required for the research assessments
• Sufficient literacy to comprehend written instructions and complete study-related materials

Exclusion Criteria:

• Having a history of a mental or psychological problem that would prevent the understanding of questions or compliance with given instructions.
• Medically unstable conditions (history of hospitalization due to heart or lung disease or a disease flare within the 4 weeks prior to the test).
• Having a history of a chronic disease of cardiovascular, orthopedic, neuromuscular, or neurological origin that could affect physical fitness.
• Having a history of trauma affecting the musculoskeletal system within the last 6 months.

It is generally recommended that the sample size for validity and reliability studies be 5 to 10 times the total number of items (30). In light of this information in the literature, and given that the International Physical Fitness Questionnaire (IPFQ) and the Self-Perceived Health-Related Physical Fitness Questionnaire for Children (SPFQ-C) have a total of 14 items, the sample size for our study was determined to be 98 participants. Consequently, we plan to include a minimum of 100 patients diagnosed with JIA or FMF in our study. Participants will be recruited from individuals who are being followed up at the Pediatric Rheumatology Subdivision of the Department of Internal Medical Sciences at Istanbul University Faculty of Medicine and who meet the inclusion criteria.