I've managed to find out a way to describe this better:

1. The cramps only occur in the thigh of my left leg.

2. I only get them when sitting down.

3. When they occur, they last for about 5 minutes.

This maynot have anything to do with this, but I also had an operation fo a slipped-apifisus (sp?). Could this have anything to do with the cramps?

Dude, this is all about muscle tension and shit because your body (like everyone else's) tenses up as you masturbate. Remember that the body thinks it is having sex.

Anyway, if they are really painful, frequent, long-lasting, etc. consult a doctor.