This is a compound movement which involves several muscle groups working together to keep the knee and pelvis stable. Core must be activated, glutes and lower back working with quads and hamstrings too. By using a band with this exercise, hip external rotators must also work to prevent knee from rolling in and medial quads such as VMO have to work to maintain knee stability. A great exercise for knee rehab and teaching spinal stability, knee, hip and pelvic stability when training hamstrings and the posterior chain.