Which muscle is responsible for trunk flexion?

The rectus abdominis is the primary muscle responsible for trunk flexion. This muscle is a long, flat muscle located in the anterior wall of the abdomen and extends along the length of the abdomen from the pubic bone to the sternum. When the rectus abdominis contracts, it pulls the ribcage and pelvis together, effectively bending the trunk forward. This action is crucial for various movements, such as sitting up from a lying position, bending forward, and performing activities that involve lifting or reaching.

While the transversus abdominis and the oblique muscles play important roles in stabilizing the core and rotating the trunk, they are not primarily responsible for flexing the trunk. The transversus abdominis functions mainly to compress the abdominal contents and provide support to the spine, while the obliques assist in lateral bending and rotation. Therefore, the rectus abdominis stands out as the muscle directly involved in trunk flexion.