Question
I did Martial Arts for a number of years, but while I was stretching I felt a pop on the inside of my thigh on my left leg which gave a degree of pain but more so late. This has stopped me from being able to stretch to the same degree ever since, and if I do try I get an extremely tight and painful pulling sensation from the back of my knee to my groin. This happened some yrs ago but I am still unable to stretch without this pain. Can you please advise on what could have happened and what I can do (if anything) that may help?

Answer
Without an actual hands on, it is difficult to diagnose.  But, you could have heard the actual muscle pop, leading to a tear.  Or, there is a distortion of the fascia, which could lead to the inability to stretch normally.  I would suggest an approach using myofascial release, ultrasound, and low level laser.  If there is no change fairly quickly, I would suggest you see your PCP for further testing.