"Ab Sonic stimulates the nerves that make your muscles contract. Combine the use of the Ab Sonic Fitness Belt with a healthy lifestyle and diet to achieve a firmer and sexier body." That is the advertising slogan for Ab Sonic. But the reason I purchased it was for the muscle relaxation advantage. It works like a tens unit and sends light electrical impulses into the muscle. The idea is that it will work cramps and tension out of the muscle through stimulation. Well, in a word, it works. I used it and it did make the muscles in my back loosen and relax ... yeah !!! However, it takes a bit of trickery to find the right intensity setting by pushing a button and finding the right combination of blinking led lights. It is sleek and compact and not uncomfortable to wear. However, be careful wearing it because just a slight touch to one of the buttons can change the setting and give you quite a jolt. The 'belt' is a very cheesy piece of elastic with Velcro on it that takes more than two hands to get wrapped around you and stuck together while being careful not to touch a button and change your setting. There is a sticker on the inside of it that says 'do not remove' however, it is right next to wear you place the contact gel and is already starting to peel up on the edges. It operates on a flat round battery that came with my unit, which is great, because I'm not sure where to buy another battery like this one and I'm pretty sure when I find it that it won't be cheap. The idea is great for releiving muscle tension and it only makes sense that it would be beneficial for toning muscle. But, investing in a better made, sturdier product for a little more money is a better idea. I feel like penny wise and pound foolish on this item. If your gonna buy one be smart and buy a well made one that is easy to set, durable and will last. The Ab Sonic is none of those things.