I do not understand how you comfortably do EMS on your quads with a flexed knee. If you sit in a chair and strap your ankles to the chair, the chair may break. If you sit in a chair and immobilize your foot against the wall, it will be difficult to keep your butt on down on the chair. Not to mention shearing the hell out of your knee. Given this, is it safest to just do it with the knees maximally extended? Do you have any video examples of somebody who has a high level of strength doing maximal EMS on the quads with a flexed knee?