Athletes can avoid tendonitis by increasing exercise intensity and frequency slowly over time. Proper strengthening and stretching of the quadriceps and hamstrings muscles may also help.
Exercises to try:
Straight leg raise: Lie flat on the floor with one knee bent and the other knee straight. Raise the straight knee off of the floor about 10 inches, tightening your quadriceps. Hold this position for 5 seconds and then relax. Repeat three sets of 10.
Quadriceps stretch: Lie face down on a flat surface. Bend one knee and grab the same ankle behind your back. Keep the thigh flat and you should feel a stretch in the front of the thigh (this is the quadriceps). Hold for 30 seconds.