The VertiMax Hip Flexor Harness set which comes with a “left leg” and “right leg” harness is used to connect resistance bands to the back of the knee and thus apply load to the hip flexor when lifting the foot off the ground. Hip Flexor Harnesses come in two sizes (each size is color coded as shown below) to suit a wide range of athletes from 4'7″ up to 7' tall. A waist belt is required to hold the harnesses in place when training. Requires VertiMax Waist Harness belt*