Deadlift Set-up

Nearly every case of “weak lockout” can be traced back to your starting position. If you start with a rounded back, you will almost certainly have trouble at the lockout. In a rounded position, your hips are closer to a vertical line with the bar. It gives you a mechanical advantage in moving the weight off the floor, but once the bar passes knee level, your knees will be mostly locked and even your hips will be largely complete with their range of motion. However, your back will still be rounded, which means that you have to extend your spine while you’re in this mechanically difficult position.
Contrast that with a person who pulls with a flat back at the start. In the bottom position, the spine is already extended, but it pushes the hips further back—further out of line with the bar path. This means it will be comparatively difficult to get the weight moving off the floor, but once the bar passes knee level, the leverages in the hip and knee improve dramatically. Because the spine is already in a “locked out” position, completing the lift is much easier. In the flat back position, the action of your spinal erectors is mostly isometric. One easy way to improve your lockout is to stop pulling with a rounded back.