The patellar tendon connects the quadriceps muscles, the tibia or shinbone, and the patella or kneecap. Because activities such as running and jumping require frequent use of the knee joints, athletes need to strengthen the area around the patellar tendon to minimize the risk of developing an injury.
If you are just recovering from a case of patellar tendonitis, also known as jumper's knee, start with a series of low-impact exercises designed to help rehabilitate the area and increase flexibility. Begin with a hamstring stretch, which involves placing the foot of your injured leg on an elevated object, such as a stool, and leaning forward; when you're performing the exercise properly, you should be feel it in the back of your thigh. Progress to the quadriceps stretch, pulling the ankle of your injured leg behind you while standing upright. You may find it helpful to have a wall or doorframe nearby to act as a support.
Next try to regain strength. At this point, it may be too early to put too much strain on the muscles. Limit your exercises to leg lifts, which only use the weight of the leg itself. Recline on the ground and turn to one side, such that your injured leg is facing upwards; lift the leg up, then lower it back down. Once you've completed a set of side lifts, lie with your back on the ground and repeat the exercise.
As you start to feel your strength returning, incorporate more of your body's weight through a series of squat exercises. Start with the step-up, placing the foot of your injured leg on a small step or box and using the leg to push your body up and lower it back down. Perform variations of the leg squat. Use a wall for support and bend your legs as far as is comfortable. You may not be able to bend very far at the beginning, but over time you will grow more flexible. Incorporate hand weights to increase the difficulty.
Move on to a one-legged squat, where you will place all of your body's weight on the injured leg. Do not rush your recovery, however, or you may injure yourself all over again.