Since 2005-2006, I've been a big proponent of hip mobility. So much, that at the time, I developed a DVD product just on the topic. Before working with golfers, I had learned that the more freedom there is at the hip joint, the more the workload shifts to the hips and glutes, rather than the lumbar spine. Years ago, I suffered chronic low back pain from incorrect squatting, useless leg presses, and overall poor posture. Through my own corrective exercise studies and working with more sedentary clients that sat all day; I learned how to incorporate corrective drills to move the hips more independently from the torso. The more mobile the hips became, the less stress was experienced by the lower back. Essentially, the lower back muscles were spared during heavy lifting sessions and the force production was generated by the stronger hips and glutes. The erectors of the lower back still came into play during triple extension movements, but they weren't the primary movers that you typically see in individuals with poor posture (sway back or kyphotic).
In this article I wrote for Mike Robertson a while back, I explain that movement is produced within our body's system of levers. In order to initiate movement, stop it, or change the speed of it, we have to brace one part of the body to allow the intended segments to move in the manner that we desire. The ground is used intentionally and extensively in sports and daily life. For the drill above, the upper and lower body segments are dis-associated from each other by means of stability and mobility. In the stable segment, the torso is braced by way of core stability. The ground or surface becomes a major player in the next video, because we change the segments that are mobile and stable.
In the T-Spine Dis-association Drill above, the lower body "grabs" the floor and braces to separate the torso from the lower body. These two drills are the premise to an effective golf swing and were introduced by Dr. Greg Rose for Titliest years ago.
Remember, you want to dis-associate the two segments. At first, your rotation will be very slight and possibly minimal. Continue this drill at least everyday for approximately 2 minutes 2-4 times a day. Within a few weeks, you should begin to see a "swiveling" effect between your bottom half and top half. This process can be made quicker with regular foam rolling and massage therapy to increase tissue suppleness.