In the sexual realm, we tried several areas such as breasts including nipple area. If the nipples are EXTREMELY sensitive, I advise to avoid that area directly and work on the area surrounding them. Inner thighs are also very good places to explore with this as is the bottom of the buttocks. For muscle massage instead of using for sexual stimulation play, any muscle area is good but I would avoid facial areas. Always start on the very lowest settings and increase slowly. If anyone has a history of medical problems relating to heart or seizures, I advise speaking with their doctor first as a normal precaution.