What is the main action of the rectus abdominis muscle?
a. rotation of the trunk.
b. flexion of the trunk.
c. extension of the trunk.
d. lateral flexion of the trunk

Flexion of the trunk.

Explanation:

Rectus abdominis muscle is also known as abs. This muscle is separated by linea alba. This is a flat muscle that extend the length of abdomen.

The rectus abdominis muscle helps in the flexion of the long trunk. This is an important postural muscle and also helps in the flexion of the lumbar spine. This muscle is also involved in the process of breathing.

Thus, the correct answer is option (b).

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