The effectiveness of quadriceps strengthening with and without blood flow restriction in the treatment of knee cap pain (patellofemoral pain)

INTERVENTION: The intervention group will perform Low intensity blood flow restriction training on the affected leg only. This group will perform 15 minutes (total) of exercises on the stationary bicycle, leg press and leg extension. These exercises will be performed 3 times per week for 8 weeks. The cycling will be for 5 minutes based at an intensity that the participant considers "light". The blood flow restriction training group will perform exercises at 30 % of their maximum strength for 4 sets. The sets will consist of repetitions of 30, 15, 15 and 15. Each repetition will take 3 seconds, and there will be a 30 second rest between each set. Physiotherapists will prescribe the exercises. The blood flow restriction will be applied using a pneumatic cuff with a handheld sphygmomanometer (width 10cm). The cuff will be applied to the proximal thigh. The cuff will be applied only for the leg press and leg extension exercises and will remain on between sets of exercises, but removed after the exercise is completed (cuff will remain on for approximately 4 minutes for leg press and 4 minutes for leg extension, with a 2 minute break between exercises with the cuff off). Arterial occlusion pressure will be measured with Doppler ultrasound on initial assessment, by placing the ultrasound over the tibial artery at the ankle, and the cuff around the proximal thigh. The cuff will be inflated until the artery is occluded (this process is the equivalent of taking a blood pressure reading). The pressure of the cuff to be used during exercises will be 60% of the arterial occlusion pressure. Participants will tick off which exercises were completed on each session in an exercise log to monitor adherence to the program. CONDITION: Patellofemoral pain PRIMARY OUTCOME: Kujala anterior knee pain scale‐ measures of patellofemoral pain and function. Nil Patellofemoral pain (VAS), worst pain in the past week. 100mm scale. ; SECONDARY OUTCOME: Global rating of change in pain, rated as 1. Much worse, 2. Worse, 3. Same, 4. Improved, 5. Much Improved Isometric quadriceps muscle strength measured with a Humac Dynamometer at 60 degrees of flexion. Patellofemoral pain with daily activity (VAS). Worst pain with squatting, stairs, or prolonged sitting on a 100mm scale. Quadriceps muscle size‐ measured with real time ultrasound as muscle thickness (cm) at the mid thigh and distal thigh. INCLUSION CRITERIA: Pain at the front of the knee for 8 weeks or longer Atraumatic onset of symptoms Pain with any two of running, squatting, prolonged sitting, jumping, kneeling.