Patellofemoral joint problems constitute a significant portion of knee pain and injuries. Among these problems, patellofemoral pain, which is not directly related to an obvious structural abnormality such as ligament rupture, cartilage degeneration or tendinopathy, is characterized by pain in the retro or peri-patellar region, especially during activities such as squatting, running, and climbing stairs. It is a musculoskeletal disorder with a poor long-term prognosis despite treatment and education. In individuals with patellofemoral pain, disturbances in the function of the M. quadriceps femoris muscle, which is necessary for the function and dynamic stability of the knee, have been observed. M. Quadriceps femoris dysfunction, which prevents returning to activities, leads to decreases in physical function and quality of life, increases the risk of re-injury, and contributes to the development and progression of knee osteoarthritis, weakness, and voluntary activation deficiencies that continue after injury and surgery, namely arthrogenic muscle inhibition (AMI). includes. AMI has been associated with edema, inflammation, pain, joint laxity, and structural damage. The relative importance of these factors is not fully understood, but it is generally accepted that AMI results from a change in the discharge of sensory receptors in the damaged knee joint. Abnormal joint afferent discharge can have potent effects on the central nervous system by affecting the excitability of the spinal and supraspinal tracts, which limits M. quadriceps femoris muscle activation. As a result, the ability to produce motor output is affected by changing efferent information to the muscle. Therefore, not only spinal reflex pathways but also corticomotor and intracortical pathways are involved in the neurophysiological mechanism of AMI. In order to reduce chronic M. quadriceps femoris dysfunction, a better understanding of the function of these pathways and the factors affecting the pathways is required. Transcranial magnetic stimulation (TMS) of the motor cortex, which has been used recently to measure changes in the corticomotor excitability of the M. quadriceps femoris associated with chronic knee joint pathology, is a technique that uses magnetic fields to stimulate neural structures such as cerebral cortex, spinal roots, cranial and spinal neurons. It is a non-invasive evaluation method in which responses are recorded with an electromyography (EMG) device. Thanks to TMS, it is possible to evaluate the integrity of motor pathways and to have information about the connections of the relevant brain regions. A limited number of studies using TMS recently in the literature show that after various knee joint pathologies and surgeries, changes may occur in the excitability of the corticomotor pathway of the M. quadriceps femoris and this may affect chronic quadriceps dysfunction. Due to the limited number of studies examining the changes in corticomotor excitability of M. Quadriceps femoris in individuals with patellofemoral pain and the differences in results, it was stated in a meta-analysis study conducted in 2022 that additional studies are needed to provide more information about the changes in corticomotor excitability in order to establish the treatments to be applied to individuals with patellofemoral pain on a neurophysiological basis. In addition, although it is known that the severity of pain varies in different degrees of flexion of the knee joint during active movements and affects the function, a study investigating corticomotor excitability specifically for these degrees could not be found in the literature. In addition, it was observed that the relationship between corticomotor excitability and functional outcomes was not investigated in TMS studies in patellofemoral pain. In the literature, the importance of investigating the factors affecting corticomotor excitability and revealing them clearly has been stated.

It is known that the sense of joint position in the knee is affected in individuals with patellofemoral pain. This affects the functionality of the patients and increases the risk of injury to the knee joint. Proprioceptive force sense plays an important role in supporting the joint by adjusting the tension level of the muscle during weight transfer. However, no studies were found in the literature investigating the sense of proprioceptive force in the knee joint in individuals with patellofemoral pain. Pain resulting from any injury to the body leads to restriction of movement after injury. With the increase in pain perception, the individual thinks that the movement will cause additional pain and re-injury and is afraid to move. Kinesiophobia, which is defined as the fear of re-injury and movement, leads to limitation of activities and leads to decreases in strength, flexibility and physical capacity. Few studies have investigated kinesiophobia in individuals with patellofemoral pain. Few of the studies investigating kinesiophobia in individuals with patellofemoral pain have compared healthy individuals with healthy individuals. For this reason, it was stated that the number of these studies should be increased. Quality of life is defined as an individual's perceptions of goals, expectations, standards and concerns in the context of position in life, the culture and value systems in which live. There are studies showing that there is a decrease in the quality of life in individuals with patellofemoral pain. However, it has been stated that the number of studies on this subject is not sufficient. For these reasons, the primary aim of the study is to compare central neuromuscular involvement in individuals with patellofemoral pain with those of healthy individuals in order to develop comprehensive evaluation and rehabilitation programs for individuals with patellofemoral pain. Investigators' secondary aim is to examine the isometric muscle strength of the M. quadriceps femoris muscle, the sense of muscle strength, knee joint function, quality of life, physical activity and kinesiophobia levels in individuals with patellofemoral pain by comparing them with healthy individuals of the same age and gender.