The internal oblique muscles are a pair of flat muscles located on each side of the abdomen. They lie beneath the external oblique muscles and play a crucial role in trunk movement and stability. These muscles help in bending the torso sideways and rotating it, as well as assisting in actions like coughing and sneezing. Originating from the iliac crest and the thoracolumbar fascia, the internal oblique muscles insert into the lower ribs and the linea alba. They are essential for maintaining proper posture and supporting the abdominal organs, contributing to overall core strength and stability.