The knees are one of the hardest working joints of the body, and they are a common site of injury, pain and degeneration. Keeping the knees healthy to protect against injury and healing a current knee injury depends on strengthening and stabilizing the muscles that surround the knee and keep it securely in place.

Leg Extensions

The quadriceps muscle group on the front of the thigh is the largest muscle group of the leg and helps to support and stabilize the knee. Weak quadriceps muscles will lead to weakened and impaired knee joints. A leg extension is a simple way to strengthen the quadriceps muscles and stabilize the knee. If you have an injury or are new to exercise, start by sitting in a chair with both feet flat on the floor. Slowly straighten one leg at the knee joint so that the leg extends straight out from the hip. Hold for a one-second count and release. Repeat 15 to 20 times and then switch legs. To make this exercise more challenging, use ankle weights or a leg-extension machine at the gym, gradually increasing the weight as your quadriceps muscles become stronger.

Modified Leg Extension

Another good exercise for strengthening the quads and stabilizing the knee is the modified leg extension. You can do this exercise at home every day and you do not need access to any gym equipment. Sit on a chair facing a wall with your knees about one foot away from the wall. Keep one foot flat on the floor and press the toes of the other foot into the wall and push, as if you are pushing the wall away from you with your foot. You may want to wear shoes for this exercise as it can be hard on the toes. Hold for a five-second count and release. Repeat five to 10 times on each side.

Swiss Ball Hamstring Curl

The hamstrings on the backs of the thighs are another major muscle group that attach to the knee and help stabilize and protect it. Lie on your back on the floor with your feet propped up on a medium-sized swiss exercise ball. Press your heels into the ball and lift your buttocks off the ground as you slowly pull the ball toward you using your hamstring strength. You will need to use your abdominal muscles to help balance your body. This exercise is tricky, so it may take a few tries to get it right. When you have pulled the ball in as close as you can, slowly roll it back out and release your buttocks to the ground. Repeat 12 to 15 times.

Calf Raises

The calf muscle along the back of the lower leg comprises two muscles: The soleus and the gastrocnemius. The gastrocnemius attaches to the knee and acts as a knee flexor. Keeping this muscle strong will help in stabilizing the knee during flexion, or bending, or the knee. An easy exercise to strengthen the gastrocnemius muscle is a calf raise. Stand on the edge of a step on the balls of your feet so that you are looking up the stairs. Allow your heels to hang over the edge and slowly let them drop down below the step so that you feel a stretch down the back of your lower leg. Now, press into the balls of your feet and rise up as high as you can on your toes. Repeat 15 times.