The knee absorbs a lot of impact every time you take a step. This can cause problems in any level of runner, from beginner to elite. There can be a variety of reasons, but usually this is caused by either the patella (tendon on the front of the knee) moving out of place and becoming inflamed, or muscle imbalance in the upper legs. This is one of the more common injuries among runners, hence the name of "runner's knee."
Also helpful: Any exercises that strengthen the quads, glutes, and hamstrings. Try Squats, Hamstring curls on an exercise ball, or if you're really adventuresome Nordic Hamstring Curls.
Foam roll: Foam roll the upper legs (quads, some hamstrings), which often cause knee problems by being too tight.
If the pain becomes too severe, the injury may have developed into patellar tendonitis. This requires more effort to alleviate the pain.
All of the above exercises, and:
Ice: Reduce the inflammation by icing the location 3-5 times a day.
Cross-train: Back off of mileage a lot, and supplement your training with bike or swim workouts.
Specific Injury Resources
For Patellar Tendonitis:
- Stretch the hamstrings and quads multiple times per day, as well as foam rolling and massaging
- Try Eccentric decline squats
- Check this site for more info.