What is Vigorous?

I read the posting by "coco", and now I worry about what is vigorous and what is not. I want to point out that I'm a novice Aneros user, but never used the Aneros massager as a dildo or otherwise manually. However after ending my first or second session, I noticed a small amount of blood on the Aneros device upon removal. I followed the directions and only used my anal muscles to move the massager into motion. So here are my questions. Did I do something wrong, or were my anal contractions far to "vigorous"? Can anything go wrong using only the anal muscles? I'm only 21, and presumably I already have a healthy prostate. I don't want to cause future prostate problems or otherwise damage my reproductive system. I'd appreciate some clarification on this subject. Thanks!

Regards,

Gspotter