It has been thought, that the back muscles mostly consist of type 1 muscle fibres, to maintain an upright position. However, the back muscles also have to function as movement muscles.
The back muscles can be divided into global and local muscles and deep or superficial; the thoracic erector spinae has been considered a global muscle, whereas the lumbar erector spinae and multifidus have been considered local muscles. There is also a functional differentiation between these muscles into deep and superficial muscle layers. It has been suggested that there is a difference in fibre typing of these muscles.
It has previously been argued that the type 1 fibre is to be more affected by pain and immobilization than type 2 fibres.