I'm not sure where to post this, but I have an interesting problem.

8 months ago, I started doing heavy leg exercises. I'm about 6'1 180, and I usually leg press 450-500 pounds.

A couple months ago, I noticed what appears to be a cyst of some kind under my knee cap. It's smaller than a grape, and hard.

Can this be from trauma caused by the leg presses?

I doubt that it was caused by stress from using the leg press. The cyst may be filled with liquid or it may be a fatty substance. Is it tender to the touch? Is it easily moved or does it seemed "attached" and imobile? I think with questions of health you should go to a doctor to have it checked out.