Which statement best describes the action of the longissimus thoracis?

Which statement best describes the action of the longissimus thoracis?

• A. Flexes the spine
• B. Extends the spine and assists in lateral flexion
• C. Rotates the pelvis
• D. Elevates the ribs

Answer: (C)

Longissimus thoracis is part of the erector spinae and mainly keeps the back upright by extending the vertebral column. When both sides contract, it lengthens the spine to produce extension; when it contracts on one side, it bends the trunk laterally toward that side. It does not rotate the pelvis, and rib elevation isn’t a function of this muscle (rib elevation is done by other muscles like the intercostals and serratus posterior). So the best description is that it extends the spine and assists in lateral flexion.

Longissimus thoracis is part of the erector spinae and mainly keeps the back upright by extending the vertebral column. When both sides contract, it lengthens the spine to produce extension; when it contracts on one side, it bends the trunk laterally toward that side. It does not rotate the pelvis, and rib elevation isn’t a function of this muscle (rib elevation is done by other muscles like the intercostals and serratus posterior). So the best description is that it extends the spine and assists in lateral flexion.