Good posture looks good. Good posture is when the body's weight is distributed evenly in front and behind the central line of gravity. Exercises for how to improve posture include both stretching and strengthening, with the aim of restoring balance wherever abnormality and imbalance have crept in. 

The imaginary line of gravity passes down pretty well through the centre of the L4 vertebra. This is pivotal in dictating the postures of both upper and lower body. Importantly, the centre of gravity also passes just behind the hip joint and just in front of the the knee joint, making it easier to stand on the leg without it buckling. 

Deviations in Perfect Posture are Myriad

There are many variations in over-all posture of the body although to a large extent the stage set by what is going on lower down, in the lumbar area. This in turn, is invariably is dictated by what’s going on in your legs, even your feet. You can read more here about Good Posture Starts from the Feet Up 

A lordotic, or over-arched, lower back usually goes hand in glove with tight hip flexors and lower back muscles (see figure on the right below). The weak lower belly and low-tone butt muscles help create a sway back, with the belly-out-the-front.  

A kyphotic, or humped-out-the-back, lower back is the other variation of lumbar spine posture - and this is usually associated with weak tummy (again) and tight hamstrings (see centre figure below) that tilt your pelvis back. 

The Basic Exercises for Posture Explained

Exercises for posture involve both the pelvis and the core. It’s never an overnight fix. Improvement takes focus, perseverance and concentrated effort. You can read here about the Best Lower Abs Strengthening Exercises.

Strangely, or not so strangely, both the lordotic and kyphotic lumbar postures predispose to a stooped or slumped upper body - and with it, the most recognisable image of ‘poor posture’.  You can read here about Exercises For Posture for The Upper Back.

Poor posture usually benefits from lower back strengthening that builds up both core and deep spinal muscles. The Lower Back Strengthening video above talks about why you may feel weak through the midriff so that you can't hold yourself up. Here, Sarah goes through the right exercises to build up the internal strength of your lower torso with 5 graduated strengthening exercises.

Exercises for Posture Using the BackBlock for The Lower Back

Lying there passively draped backwards over the BackBlock under the sacrum gradually stretches out tight hip flexors, while at the same time allowing the spinal segments in the over-arch of the lower back to translate incrementally backwards towards the floor, thus flattening or 'paling out' the curve. At the same time, the tight structures of the lower back that go with this posture are gradually stretched. 

Different dynamics are at work in the too-stooped lumbar spine on the BackBlock, where the distractive forces are more directed at prizing open the front the vertebral interspaces, stretching the front of the very contracted disc wall and the super-strong anterior longitudinal ligament.

Read here about Exercises for a Hunched Upper Back

Here's some more simple reading on the static dynamics of sitting and proper ergonomic seating