I came across a post of a dancer with her hind knee flexed against the wall in her split. They were also using a band to pull that same flexed knee down. This front split drill, forces the hip into extreme hip extension on that hind leg with the pelvis being driven anteriorly excessively. Problem #1 : When the pelvis tips forward, naturally the femoral head shifts forward in the socket. If pushed excessively, this really stresses the hip capsule long-term wise,it could also h