From what I've read, it is tricky and the vibration cycle/intensity has to be set precisely. There are reported cases of (weekend warrior types?) going gung ho for intense vibratory experience and suffering detached retinas. I'm going to get one of the machines but be very conservative with it. One writer here posted about the recommended 30 hz setting for people with osteopenia and osteoporosis. Also a link to a site explaining that parameter.