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Rectus abdominis
The strap of muscle running from the pubic bone to the ribs that folds the trunk forward.
Latin name: Musculus rectus abdominis. In plain English, the straight abdominal muscle, the six-pack. It is filed here under core, breathing and pelvic floor.
Reference information, not a diagnosis. Where a symptom is described below, it is there so you can describe your own more precisely to a clinician — not so you can name what you have.
Where it is
Rectus abdominis is a pair of vertical straps running up the front of the abdomen either side of the midline, separated by the linea alba — the white line of connective tissue where the aponeuroses of the flat abdominal muscles meet. Three or more fibrous bands cross each strap horizontally, the tendinous intersections, and it is these that carve the muscle into the blocks people call a six-pack. The number of blocks is inherited, not earned.
The whole muscle sits inside the rectus sheath, formed by the aponeuroses of the external oblique, internal oblique and transversus abdominis wrapping around it. Below a line roughly midway between the navel and the pubis, all three aponeuroses pass in front of the muscle, which is why the back of the sheath is deficient in the lower abdomen.
| Feature | Detail |
|---|---|
| Origin | Pubic crest and pubic symphysis |
| Insertion | Xiphoid process of the sternum and the costal cartilages of ribs five to seven |
| Nerve | Anterior rami of the thoracoabdominal nerves T7-T11 and the subcostal nerve T12 |
| Main actions | Flexion of the trunk, posterior tilt of the pelvis, and raising intra-abdominal pressure with the other abdominal muscles |
What it does
Its mechanical action is simple: it shortens the distance between the ribs and the pubis. That happens two ways — curling the chest toward the pelvis, as in a sit-up, or tilting the pelvis toward the chest, as in a hanging knee raise. It also resists the opposite movement, which is what it is really doing in a plank or an overhead carry: stopping the ribs flaring and the lower back arching.
Whether the blocks are visible has almost nothing to do with how strong the muscle is and almost everything to do with the layer of subcutaneous fat over it, which is determined by overall energy balance rather than by abdominal exercise. Training the muscle makes it thicker and stronger. It does not selectively remove fat from above it; spot reduction does not work that way.
Exercises that load it
| Exercise | Category | Muscles the exercise library lists |
|---|---|---|
| Sit-ups | Core | Abdominals, hip flexors |
| Plank | Core | Deep core, shoulders, glutes |
| Mountain climbers | Conditioning | Core, hip flexors, shoulders |
| Burpees | Conditioning | Whole body |
Curling movements load it in shortening, plank-type positions load it isometrically, and anything that resists the trunk being pulled into extension — an overhead carry, a rollout, a heavy overhead press — loads it hardest of all. There is no need to choose: a mixture of trunk flexion and anti-extension work covers the muscle better than either alone.
How it is lengthened
Any controlled backward bend lengthens it: lying face down and pressing up onto the forearms, or a supported bridge over a ball. Keep the movement spread through the whole spine rather than hinging at one point in the lower back, and stop well short of pinching. For most people the abdominal wall is not short, and this is more useful as a counter-movement after a lot of flexion work than as a corrective.
When it goes wrong
| Problem | What it typically feels like | Usual setting |
|---|---|---|
| Diastasis recti | A visible ridge or gap along the midline when curling up, with a soft doming above the navel | Common in and after pregnancy, and seen in people who have gained abdominal weight quickly |
| Abdominal muscle strain | A sharp local pain in the belly wall on curling, coughing or sneezing | A sudden maximal trunk effort, or a big jump in abdominal training volume |
| Rectus sheath haematoma | Sudden severe abdominal wall pain with a tender lump, sometimes after coughing | Uncommon; more likely on anticoagulant medication, and needs medical assessment |
Abdominal pain that is severe, constant, worsening, or accompanied by fever, vomiting, or a hard rigid belly is not a muscle question — seek medical care the same day. A lump in the abdominal wall or groin that appears on straining should be examined for a hernia.
Nothing on this page is a treatment plan. If a problem is limiting what you do, is not improving, or is getting worse, the right next step is an assessment by a doctor or a physiotherapist who can examine you.
Sources: descriptive anatomy from Gray's Anatomy of the Human Body, 20th US edition (1918), which is in the public domain; Latin names follow Terminologia Anatomica, published by the Federative International Programme for Anatomical Terminology. Nerve root levels are the conventional ranges taught from those sources and vary between individuals and between textbooks. Exercise cross-links use the TempoLife exercise library. Checked 2026-09-06.
Frequently asked questions
Do sit-ups burn belly fat?
No. They train the muscle underneath. Where the body loses fat from is not controlled by which muscle you work, and abdominal fat responds to overall energy balance and activity rather than to abdominal exercises.
Why do I have four abs and someone else has six?
The number of visible blocks depends on how many tendinous intersections you inherited and how symmetrical they are. It is anatomy, not training.
Is a plank better than a sit-up?
They do different jobs. A plank trains the abdominal wall to resist movement; a sit-up trains it to produce movement. Most people benefit from both, and the choice matters much less than doing something consistently.
Nearby in this reference
Abdominal obliques
The side abdominal muscles that twist the trunk
Transversus abdominis
The deepest abdominal layer, a corset around the waist
Diaphragm
The dome of muscle that does your breathing
Pelvic floor
The sling of muscle at the base of the pelvis
Deltoid
The cap of the shoulder
Rotator cuff
The four small muscles that hold the shoulder in its socket
All 34 body parts · Exercise library · Body map
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