Back of Knee Soreness the day after...

Question
Hi,
I have been very athletic my entire life (40 yrs).  Gave up basketball about 3 years ago and switched to running.  for the past two years ran about 10-15 miles per week at about 8mpm. for fitness.
Last month upped that to about 20 mpw and did 100 miles in October.  Never any problems with my right knee.  Had my long run Sunday and ran 10.6 miles which is about a mile or so more than my normal long run.  FELT GREAT.  Ran about 8:45/mile...kept my heart rate at 140bpm.  Felt great after the run, Sunday evening felt great, no leg pains at all.
Woke up Monday morning and my right knee was very stiff in the ligaments/tendons behind my knee to the outside.  
Is this a knee problem or a lower ham string problem (Kind of feels like the ligament going into the back of my knee).
Thanks

Answer
I'm in no way a doctor, and I don't think anyone can diagnose an injury online, even if that person is a doctor.  What I can guess at is it is probably a hamstring problem, as soreness at the tendon could be an issue (a ligament connects bone to bone, and you typically can't feel those until they are absolutely torn inside).  Since the problem is to the outside of your knee, it could also be an illiotibal band, or IT band, issue.  This is a large tendon that goes down the side of your leg, and can be disturbed over time if you run long mileages on roads on one side of a banked road.  Say for instance you ran for 10.5 miles all on the right side of a road, your right leg on every step it takes during that run is actually landing longer on the banked road than your left leg is.  So, hips can get off-kilter and muscle stresses get off-kilter, and soreness can hit you later on. If you are looking for general help, I don't know much off the top of my head, but a good resource for taking care of minor running injuries is at http://runnersworld.com

Rick Karboviak