Runner’s knee, or patellofemoral pain syndrome, is a condition that causes a dull or aching pain around or under your kneecap, according to the American Academy of Orthopaedic Surgeons. This condition can be aggravated by walking up or down stairs or when squatting down or bending your knee for an extended period of time. Treatment for this condition often includes exercises designed to help you build strength and flexibility in your thigh muscles.
Standing Hamstring Stretch
Stand in front of a chair or stool that is about knee height. Place the heel of your injured leg on the stool with your toes pointing toward the ceiling. Lean forward at your waist until you feel a stretch in the back of your thigh. Hold this stretch for up to 30 seconds and relax. Repeat. Be sure that you keep your shoulders positioned directly in line with your hips when performing this stretch.
Standing Quadriceps Stretch
Stand in front of a counter or wall for support. Place the hand of your uninjured side on the wall with your uninjured leg farthest away from the wall. Bend your injured knee and reach down with your other hand and grab your foot around your ankle. Use your hand to pull your ankle toward your buttocks until you feel a stretch along the front of your thigh. Hold this stretch for 15 to 30 seconds and relax. Repeat.
Sit down on the floor with both legs extended in front of you and your toes pointing toward the ceiling. If necessary, you can place a rolled-up towel under the back of your injured knee. Press the back of your knee into the towel by contracting the muscles along the front of your thigh. Hold this contraction for about five seconds and relax. Repeat. You can ensure that you're performing this exercise correctly by placing your hands on the front of your thigh to feel your muscles contract.
Straight Leg Raise
Lie down on your back with your injured leg extended and your toes pointing toward the ceiling. Bend your other knee and place the sole of your foot on the floor. Keep your injured knee straight and lift your heel about eight inches off the floor. Hold this position for a few seconds and use a slow and controlled motion to lower your heel back to the floor. Repeat.
Note – This information has been taken from different internet sources.