Hi there. I'm 43, 5'2", 125 lbs. I recently started a new exercise regimen which includes mostly walking on an incline, and simple muscle toning. This morning I noticed a knot-like lump at the base of my hamstring. Could I have injured it and not known? It isn't well defined as for shape, but feels to be about the size of a half dollar. I did injure the knee on this side in a car accident (cracked patella), but it's been over 20 years... so while it may be relevant history, I don't believe it's related. Thanks in advance.