i'm in the middle of training for the buffalo marathon (end of may), and did my longest run at the moment yesterday (15 miles). I felt fine, however I've noticed that during my 10+mile runs, my right groin muscle begins to ache, and I find myself having to repeatedly "sit down" and stretch to alleviate the achiness.
This is a very personal question but have you had a vasectomy? I did and the doctor did something that has affected my groin muscles ever since. The good doctor said the groin muscles shouldn't have been affected by this but I never felt such pain before the vasectomy. I just stop for a few minutes and stretch. I have also found that when I reach that same distance again whether it be swimming or running I acquire a threshold and can continue a little bit farther.
I get this pain after sitting/riding on the bike for extended periods of time. Do you think this could be the cause and is just transferred over to your running?