Hmm...I'm not a hundred percent sure, but when I was still going to therapy my therapist was really pushing for the TENS unit so that I could get the same relief at home as I got at therapy. I know it was a much bigger unit that also had an ultrasound on it (I think I actually saw the same one for sale for about $3000) and it was a combo TENS unit and ultrasound. I guess I just assumed they were using a TENS program since she said it would be the same relief. And it FELT the same...although I wouldn't know if that means anything because different types of stim might feel the same and I wouldn't know the difference. It's a good question for me to ask though.