Your body should bend at the hips, not in the waist (your buttocks will protrude slightly when you are in this correct posture). The spine is the axis of rotation for the swing, so it should be bent towards the ball from the hips at approximately a 90-degree angle to the shaft of the club. This right angle relationship between the spine and the shaft will help you swing the club, arms and body as a team on the correct plane.
Your vertebrae should be in a straight line with no bending in the middle of the spine. If your spine is in a "slouch" posture, every degree of bend decreases your shoulder turn by 1.5 degrees. Your ability to turn the shoulders on the back swing equals your power potential, so keep your spine in line for longer drives and more consistent ball striking.
Video: Correct golf posture
