Here is a re-post of one of Simon’s popular blog posts about relieving back pain.

Most modern adults tend to have very stiff middle backs (usually from about the tenth thoracic vertebra (T10) to the fourth lumbar vertebra (L4). This region (T10-L4) is stuck in a slight forward bend (spinal flexion) in many modern adults. These people usually do most of their bending backwards (spinal extension) from the very lowest part of the mobile spine at junction between the fifth lumbar vertebra and the first sacral vertebra (L5-S1). L5-S1 is usually located about 2 centimetres below the top of your hips (iliac crests).

Please read more here.