Question

If you contract just your right erector spinae muscles, what movement will occur?

Answer 1

Erector spinae is one of the major muscle of back & it is a extensor of back.

It is not a single muscle, a group of muscles which runs on either side of back from thw cervical to lumbar region. Each muscle is doing an action depending on their location. Before to see their action should clear about their location.

Erector spinae is composed of three different group of muscles namely

ILIOCOSTALIS - iliocostalis lumborum, iliocostalis thoracis & iliocostalis cervicis

LONGISSIMUS - longissimus thoracis, longissimus cervicis & longissimus capitis

SPINALIS - spinalis thoracis, spinalis cervicis & spinalis capitis

each of them again divided into three sub parts & the name of their sub parts meant by their location.

For example cervical & capitis - cervical or neck region. So muscles of this area will works to neck movements either flexion of forward / side or extension.

Lumborum - lumbar region & costalis means ribs, so we can understand its thoracic region.

FUNCTION:

As above said it is a back extensor. It also does the side flexion.

Now imagine these muscles presents in both sides of the back. So we are having a "pair of muscles" in those parts. For example if taking longissimus cervicis - we are having right & left longissimus cervicis.

If the muscle contracts on any one side, it will provide the movement on same side. If contracts on both side, results in extension.

( understand these terms

Unilateral - one side

Bilateral - both side

Ipsilateral - same side

Contralateral - opposite side)

So a unilateral contraction ( one side) results in side flexion. For example if you are contracting iliocostalis lumborum of right side will results in ipsilateral flexion of lumbar region.

If taking right iliocostalis cervicis results in ipsilateral cervical flexion. For example imagine like you are answering a phone call & mobile is inbeteeen your right shoulder & right ear. Your neck is flexed and same side muscles are working including iliocostalis (some other muslces are also there).

A bilateral contraction is results in back extension. Imagine a erect standing. Its a antigravity position. The back muscles working on either side to maintain the erect postion. So bilateral contraction is required for standing & it results in extenion. To maintain your neck straight also , muscles work on both side.

CONCLUSION:

Contracting right side erector spinae alone results in ipsilateral ( same side) flexion of the vertebral column / back.