Post pictures of your favourite backs, even your own.
Three major muscle groups that make up your back are:
The Latissimus Dorsi is the large flat triangular muscle that runs down the sides of your back and is responsible for extending, rotating and pulling your arm in to your body.
The Erector Spinae is made up of three muscles that run from your neck down to the bottom of your spine and is involved in extending your spine. In other words it helps you stand up straight.
The Rhomboids sit between your shoulder blades and are responsible for rotating, elevating and retracting the shoulder blades.