In most cases, when landing on the knees, the torso leans forward. There will be no back pain in this case. In some cases when landing on the knees or on one knee, the torso, shoulders and the arm opposite the knee that just hit the ground are swung backwards. In this case, the upper and lower back muscles and the torso may jerk or twist upon impact. Also in this case, one falls backwards instead of forwards. And as a result, the backward “twist” will bring on subsequent back pain.