Effect of Specific Versus General Hamstring Stretch on Clinical Outcomes in Patellofemoral Pain Syndrome (PFPS)

Inclusion Criteria: * Anterior or retropatellar knee pain lasting at least three months * Pain reproduced by at least two functional tasks: squatting, kneeling, prolonged sitting, stair climbing, hopping or running * Pain intensity of ≥3 on a Visual Analog Scale * positive active knee extension test (inability to achieve greater than 160° of knee extension with the hip at 90° of flexion) * Body mass index (BMI) \< 30 Kg/m² and \> 18Kg/m² Exclusion Criteria: * Previous knee surgery * History of knee pathologies, such as meniscal injury' ligament injury, or knee osteoarthritis * Psychological, cardiovascular' or neurological disorders * Dizziness or fainting while doing exercises, pregnancy, or any contraindications to exercise * Physical therapy treatment in the last 3 months