Sit on the floor with your legs extended in front of your body. Place your hands or a rolled towel under the affected knee. Keep your leg straight, and contract your quadriceps muscle (just above the knee). This should make your kneecap move toward your body and make your thigh tighten. Hold for a count of 10 seconds. Release and rest.
Repeat 10 to 15 times (1 set). Perform 3 sets.