I have been in sport for the last 45 years. (Boxing, MMA, Karate Budo Kay Karate Do Jiujitsu. Black belt.) I have been using at least 39 different one's abdominal muscles belt, I honesty they don't last at all. Why? one has the charging feature it's not batteries are on USB port, with all that been said they don't hold charge as strong enough to do the job. Most important safety, sometimes in the very begging of buying the unit it shows too strong and good to do the job but one week later one day I start jumping because it feels so wrong that almost burn my belly, I fallowed all the safety instructions but still not working the way it should be, I could not returned it either so frustrating.. The next brand that i bought the problem was that only goes to 19 speeds, but I don't feel nothing at all on my abs. so useless.
I bought 3 more on Temu.com, they since to be working for about 3 weeks then right after to the garbage, I was trying to fix it, I even put some masking tape to cover some of the current connections but still no luck. But your product Abdominal Muscle best EM37 that's the best unit I ever had, 40 speeds, really strong, I can tell my whole-body sweating after 44 minutes with 2 sections. Easty to use, comfortable, easy to operate, since has batteries it is a lot of stronger and last longer too, better for Longers workout, I have tried twice today I took a look in the mirror unbelievable only 44 minutes using the device. I would recommend to all my colleges family and friends. Really great price only $65 dollars not bad at all. Thanks, Beurer