Muscles Acting on Trunk

Question 1

Rectus abdominis

Answer 1

Origin- pubic crest & symphysis; Insertion- xiphoid process & costal cartilages
(runs vertically- your 6 pack muscles)
Action- flexes and rotates trunk

Question 2

External Oblique

Answer 2

Origin- lower 8 ribs; Insertion- aponeurosis to linea alba (runs down midline of abs)
Note- fibers run diagonal, in direction of “hands in pocket”

Action- flexes and laterally rotates trunk

Question 3

Internal oblique

Answer 3

Origin- lumbar fascia (CT sheet over lower back) & iliac crest; insertion- linea alba & lower 4 ribs
(runs a perpendicular to external obliques, but deep)
Action- flexes and laterally rotates trunk

Question 4

Transversus abdominis

Answer 4

Origin- inguinal ligament & lumbar fascia; insertion- linea alba & pubic crest
(deepest abdominal muscle- fibers run horizontally)
Action- compresses abdomen (coughing, defication)