Rectus Abdominus

Anatomy Text

Proximal attachment  - From the pubic crest and the pubic symphysis.

Distal attachment - Fifth to seventh costal cartilages, and the inferomedial costal margin and anterior aspect of the xiphoid process of the sternum.

Innervation - Ventral primary rami of T7 to T12.

Blood supply - Muscular branches from the superior and inferior epigastric arteries.

Primary actions

1. Flexion of the thoracic spine when acting bilaterally

Agonists: none

Antagonists: iliocostalis cervicis, iliocostalis thoracis, iliocostalis lumborum, longissimus cervicis, longissimus thoracis, spinalis thoracis, semispinalis cervicis, and semispinalis thoracis

Internal oblique, external oblique, and psoas major assist with flexion of the thoracic spine.

2. Flexion of the lumbar spine when acting bilaterally

Agonists: none

Antagonists: iliocostalis lumborum, longissimus thoracis, and spinalis thoracis

Internal oblique, external oblique, and psoas major assist with flexion of the lumbar spine. Secondary action

3. Assists with forced expiration

Agonists: serratus posterior inferior and transversus abdominis

Antagonists: serratus posterior superior, levatores costarum breves, and levatores costarum longi

Internal oblique and external oblique also assist with forced expiration. Gross motor movement

Rectus abdominis is involved in many common daily activities as well as in some specific exercises, such as:

1. Sit ups - Sit ups can be accomplished in a variety of ways, for example, with bent or straight knees or as a crunch (simultaneous rising of the trunk and flexion of the hip). This animation demonstrates bent knee sit ups, which decrease the activity of the hip flexors and places greater emphasis on the abdominal muscles. The internal and external obliques are also active when performing sit ups, but have been excluded from this animation in order to
allow better demonstration of the other muscles.

Flexion of the cervical spine: sternocleidomastoid (anterior fibers)

Flexion of the trunk: rectus abdominis

Extension of the trunk: psoas major

Flexion of the hip: iliacus, rectus femoris, and sartorius

2. Walking upstairs

3. Standing jump forwards

4. Standing jump upwards

Common injuries/pathologies

Muscle strain, muscle spasm, and myofascial pain syndrome.

Notes

Due to the unique nature of the rectus abdominis, spasm of one section of the muscle can occur without spasm in the other sections. This spasm may be quite alarming to the patient due to its visual appearance, although it is usually of little consequence.

Abdominal surgery often necessitates cutting between the two rows of the rectus abdominis, in the fascial area called the linea alba. Exercise and any sitting-up movements as well as coughing and other activities that increase intrathoracic pressure will be difficult and potentially painful until the tissues are well healed. Care must be taken to protect the incision line during healing, yet stretch the rectus abdominis and linea alba to retain the length of the soft tissue and allow a fully erect posture upon recovery.