The Flex Belt Flex System Abdominal Toning Belt, Black Ultimate Toning Technology Intense Abs Workout Maximum Core Strength Toning, Firming and Strengthening Ab Muscles In a 6 week clinical trial, 100% of users reported firmer, more toned abs and a 72% increase in abdominal muscle endurance (core strength) when used 5 times per week for 6 weeks. Kindly refer the user manual attached below for troubleshooting steps and instructions.