The knee is surrounded by ligaments, tendons and muscles that act to stabilize the joint. Injuries to any of these structures can lead to an unstable knee joint. In order to increase stability, you will need to strengthen the muscles surrounding the joint including muscles of the hips and thighs. Consult with a medical professional prior to starting any new exercises if you've had a knee injury or suspect one.
The quadriceps muscle is the muscle on the front of the thigh that flexes the hip and extends the knee. The quadriceps tendon attaches the quads to the patella, or the kneecap. Strengthening this muscle increases stability of the knee joint by giving added support and cushioning during daily, as well as sporting, activities. Do a quadriceps setting exercise to isolate the muscle by half-sitting on the floor with your legs extended in front of you. Roll up a small towel and place it underneath one knee such that there is a slight bend in the knee. The heel of the foot should touch the ground. Contract the quadriceps as you push the back of your knee into the towel. Hold for three seconds before relaxing. Repeat 10 times for a total of three sets.
Squats stabilize the knee joint by strengthening the supportive thigh and hip muscles. Perform squats by standing up tall with feet about hip-width apart and arms extended in front of you. Contract the abdominal muscles as you slowly start to lower down into a squat position by sticking your buttocks out. Avoid deep knee bending and extending your knees past your toes, as this can cause knee strain. Perform two to three sets of 10 to 12 reps.
Strong hamstrings will stabilize the knee joint and prevent a muscular imbalance between the quads and hamstrings. Develop the backs of the thighs with hamstring curls. Do this exercise with a theraband for added resistance. Begin by sitting in a chair that is nonmoving or set against a wall. Tie a theraband to a fixed object in front of you such as a table leg or doorknob that is on an even plane with your hips. Tie the other end of the band around your ankle while your leg is extended in front of you. Bend your leg down toward the floor against the resistance of the band. Hold for three seconds before returning to start. Repeat 10 times for a total of two to three sets.
Use caution when using exercise machines to strengthen the muscles around the knee joint. Certain machines, such as the leg extension machine, increase the shearing forces on the patellar tendon. The Huffington Post cites Dr. Joseph Horrigan, director of the Soft Tissue Center at DISC Sports & Spine Center, as saying that the leg extension machine maximizes force to the back of the patella. This can lead to cartilage damage, since the thinnest aspects of the cartilage are found there.