Patellofemoral joint problems account for a significant portion of knee pain and disability. Among these problems, patellofemoral pain is not directly related to any obvious structural abnormality and is characterized by pain in the retro- or peri-patellar region, particularly during activities such as squatting, running, and climbing stairs. It is commonly seen in the general population. The current literature highlights the tendency of patellofemoral pain to recur and become chronic despite all treatments. Individuals with patellofemoral pain often experience disorders in the neuromuscular function of the quadriceps femoris muscle, which is necessary for knee function and dynamic stability and is frequently suggested to play an important role in the pathophysiology of the disease. A decrease in the tissue's ability to utilize oxygen during exercise or physical activity may lead to permanent dysfunction of the quadriceps femoris muscle. However, no studies have been found in the literature examining changes in oxygenation of the quadriceps femoris muscle in individuals with patellofemoral pain. Therefore, the aim of this study is to investigate changes in oxygenation of the quadriceps femoris muscle in individuals with patellofemoral pain during various exercises and physical activities by comparing them with pain-free individuals.

Inclusion Criteria:

• 18-40 years of age
• pain around or behind the patella, which is aggravated by at least one activity that loads the patellofemoral joint during weight bearing on a flexed knee (e.g., squatting, stair ambulation, jogging/running, hopping/jumping)
• the pain persist for at least four months, and be rated at ≥ 3/10 on the Numeric Pain Rating Scale (NPRS)
• vastus medialis muscle adipose tissue thickness <20 mm

Pain-free controls were age- and gender-matched, with vastus medialis muscle adipose tissue thickness <20 mm.

Exclusion Criteria:

• a history of joint surgery
• meniscal and/or ligament injuries
• patellar instability, congenital patellar subluxation/dislocation
• any cardiovascular, congenital, or musculoskeletal disorders that could interfere with the assessment

Twenty-one patients with patellofemoral pain and 20 pain-free controls will be conducted at Ankara Medipol University, Faculty of Health Sciences, Physiotherapy and Rehabilitation Department.