Position thighs prone on large pad and lower legs under padded bar. Place barbell on back of shoulders and grasp bar to sides.
Lower body by bending waist until fully flexed. Raise or extend waist until torso is parallel to legs. Repeat.
Adjust lower leg brace so pressure is evenly distributed on thigh pad. Begin with body weight and add additional weight gradually to allow lower back adequate adaptation. Maintain barbell's position on back of shoulders when upper body is lowered.
Do not pause or bounce at bottom of lift. Do not lower weight beyond mild stretch throughout hamstrings and low back. Full range of motion will vary from person to person. Although articulation of waist is emphasized, some hip extension may accommodate movement. Also see Barbell Hyper-extension and Barbell Back Raise.
Synergists (see comments)