Rectus abdominis

Function

Where the muscle sits

The rectus abdominis is a pair of long, straight muscles that run the length of the trunk¹. They lie toward the middle of the front wall of the abdomen¹. Each one starts low, at the pubic crest and the pubic symphysis¹. These are the ridge along the top of the pubic bone and the joint where the two pubic bones meet. Each one ends at the xiphoid process, the lower tip of the breastbone, and at the cartilages of the fifth to seventh ribs^2,7.

At the pubis, the attachment is shared with muscles of the inner thigh⁸. This was seen in 10 dissected halves of the pelvis⁸. The aponeuroses (flat, sheet-like tendons) of the rectus abdominis and the small pyramidalis muscle were attached to the pubic crest⁸. There they blended with the aponeurosis of two inner-thigh muscles, the gracilis and adductor brevis⁸. Together they formed one shared sheet, attached across the front and underside of the pubis⁸.

What wraps around it

Each muscle is wrapped in its own rectus sheath, a covering of connective tissue¹. Where the left and right sheaths meet in the midline, they form the linea alba, a white band of tough fibre¹. To each side, the belly wall has three flat muscle layers: the external oblique, the internal oblique and, deepest, the transversus abdominis¹.

The sheath is built from the aponeuroses of those three flat muscles, and its make-up changes along the muscle’s length⁹. In the upper abdomen, the main part of the front layer is the external oblique’s aponeurosis, which attaches to the linea alba¹⁰. The pattern as it is usually described:

Flat muscle’s aponeurosis	Above the navel	Some centimetres below the navel
External oblique	Passes in front of the muscle9	Passes in front of the muscle9
Internal oblique	Splits, with one layer in front of the muscle and one behind9	Passes in front, without splitting9
Transversus abdominis	Stays behind the muscle9	Moves to the front, from a level that varies between people9

How cross bands divide it

Three bands of collagen, a strong rope-like protein, run across each muscle and split it into segments¹. These bands are called tendinous intersections¹. In one cadaver study, 30 of 32 bodies had three pairs of these bands, and 2 had four pairs¹¹. Most bands did not pass through the whole thickness of the muscle¹¹. Of 168 bands checked, 18% did¹¹.

In four cadavers, the 8th, 9th, 10th and 12th intercostal nerves (nerves that run between the ribs) supplied the eight segments of the muscle¹². Small nerve branches crossed the tendinous intersections to reach the segments next door¹².

What it moves

The rectus abdominis is the prime mover for flexing the spine, which means bending it forward, as in sitting up¹. A study of six men recorded the muscle with fine wires inside it¹³. During a hard push against a closed throat, called a Valsalva manoeuvre, the men also pushed the trunk forward or back¹³. Rectus abdominis activity rose sharply when the men strained to bend forward and fell when they strained to bend back¹³. Transversus abdominis activity stayed about the same¹³.

In these six men, during repeated Valsalva manoeuvres, peak pressure inside the belly tracked the activity of each abdominal muscle recorded except the rectus abdominis¹³. The authors concluded that the transversus abdominis appears to be the muscle whose activity most consistently follows that pressure¹³. In trunk rotation, a study’s background describes the rectus abdominis as working on the side opposite the turn, as the external oblique does¹⁴.

In these six men, during repeated Valsalva manoeuvres, peak pressure inside the belly tracked the activity of each abdominal muscle recorded except the rectus abdominis.

Breakdown

Strains in racket and throwing sports

Strains of the rectus abdominis are described as common injuries in competitive tennis players, and ones that hold players back³. A 2007 report gives the accepted mechanism³. First the muscle on the non-dominant side is overloaded while being stretched, during the cocking phase of the serve³. A forced contraction of that same side follows³.

Studies in tennis and handball point to one side and to the lower part of the muscle^4,7:

• Tennis: ultrasound of 61 professional players found scar tissue in the muscle in 18, or 29.5%⁴. Each scar sat on the side of the non-dominant arm, and 16 of the 18 lay below the navel⁴.
• Handball: in five elite players with a torn rectus abdominis, four tears were on the side opposite the throwing arm⁷. Each of the five tears lay below the navel⁷.

Whether uneven muscle size plays a part is not settled^4,15. The authors of the ultrasound study concluded that uneven growth of the muscle appears to be a risk factor for injury there⁴. An MRI study of eight professional male players found the two sides differed in size¹⁵. Its authors said it remains to be found out whether this imbalance raises injury risk¹⁵.

A gap between the two muscles after pregnancy

Diastasis recti is a condition in which the two rectus muscles sit an abnormal distance apart along their length⁹. It is acquired rather than present from birth, and it comes without a defect in the fascia, the connective tissue between them⁹. The studies below are of women during and after pregnancy, and their findings describe that group^5,16.

A cohort study followed 300 first-time mothers from pregnancy to one year after birth⁵. A gap was counted when at least two fingerbreadths could be felt⁵. The share with a gap changed like this⁵:

Time point	Share of women with diastasis recti
21 weeks of pregnancy	33.1%5
6 weeks after birth	60.0%5
6 months after birth	45.4%5
12 months after birth	32.6%5

In that group, women with and without the gap did not differ significantly in the risk factors studied⁵. Women who reported heavy lifting at least 20 times a week had about twice the odds of the gap (odds ratio 2.18)⁵.

How the gap relates to pain

Findings on back pain are mixed^5,16,17,18:

• In a cohort of first-time mothers, 30.3% had a gap over 30 mm at 12 months after birth¹⁷. They had worse back pain than women without it, but no significant difference in leaking urine¹⁷.
• In two other cohorts, of 300 and 84 first-time mothers, low back and pelvic pain did not differ significantly with or without the gap^5,16.
• In a survey of 177 women within two years of giving birth, a self-reported gap went with belly discomfort and early urinary urgency¹⁹. It showed no significant link with low back pain or pelvic girdle pain¹⁹.
• A systematic review of 13 studies found that 5 linked the gap with low back pain and 8 did not¹⁸. It called for better studies¹⁸.

Recovery

What size studies found after training and in athletes

MRI studies measured the muscle’s volume, its whole size, after one Pilates programme and in professional players compared with inactive men^6,15,20:

Group measured	Rectus abdominis volume
9 inactive women, after 36 weeks of Pilates	21% more than before training6
15 professional male soccer players	26% more than 6 inactive men20
8 professional male tennis players	58% more than 6 inactive men15

In eight professional tennis players, the muscle was 35% bigger on the side of the non-dominant arm than on the dominant side¹⁵. The six inactive men showed no difference between sides¹⁵.

In eight professional tennis players, the muscle was 35% bigger on the side of the non-dominant arm than on the dominant side.

Coming back to sport after a tear

In the five elite handball players with torn rectus abdominis muscles, each followed the same recovery programme⁷. They took 16 to 22 days to return to play, 18.2 days on average⁷. At follow-up 15 months later, no player showed signs of a new tear or lasting discomfort⁷.

How the gap changes after birth

In 84 healthy first-time mothers measured by ultrasound, it was found in 100% at 35 weeks of pregnancy and in 39% at 6 months after birth¹⁶. A review notes that the gap often narrows on its own early after birth²¹. It puts this down to the effects of hormones²¹.

Connections

The muscles around it

The erector spinae, the group of long muscles beside the spine, makes up most of the muscle of the back¹. It is the main muscle for straightening the spine, the opposite of what the rectus abdominis does¹. In 10 healthy people bending slowly forward and back, the six trunk muscles recorded included the rectus abdominis²². Flexors and extensors worked together around a neutral spine posture, more so with a 32 kg mass added to the torso²². A model linked this to keeping the low back stable²².

What exercise studies show

Studies using EMG, a recording of the electrical activity in a muscle, show how hard the rectus abdominis works in different exercises^23,24. Exercise pages that load it: plank, hollow hold, side plank, glute bridge hold, farmer’s carry, deadlift, overhead press. In the plank, position changes altered its activity^25,26:

• Compared with crunches: in 18 adults, face-down exercises including the plank on toes gave rectus abdominis activity similar to the crunch and bent-knee sit-up²³.
• Feet raised: in 24 young adults who did recreational gymnastics, raising the feet on wall bars gave higher activity than the usual plank²⁵.
• Long lever and pelvis tucked: in 19 people, a longer plank with the pelvis tilted back raised upper rectus abdominis activity²⁶.
• Unstable supports: unstable devices raised activity in the surface trunk muscles as a group in 12 adults²⁷. Rectus abdominis activity peaked in 16 men with feet in rings and elbows on a half-ball²⁸.
• Drawing the belly in: in 20 people, this did not significantly change rectus abdominis activity, though it raised activity in other trunk muscles²⁹.

Studies of other exercises also recorded the muscle^30,31:

Exercise	What the study found for the rectus abdominis
Two-leg raise, held	More activity than the plank, in 18 active women24
Leg lift held on the back	More activity with the pelvis tilted back than tilted forward, in 16 men32
V-sit	No difference from the plank detected, in 30 adults33
Side plank	More active on the lower, weight-bearing side, except in the rotational side-bridge, in 25 people34
Rotational side-bridge	Highest of four side-bridge exercises, at 43.9% of its hardest possible effort, in 25 people34
Glute bridge hold	Lower relative activity than the obliques, in 30 students35
Single-leg glute bridge	On an unstable surface or with the hip moved out to the side, more activity than the standard bridge, in 15 adults36
Farmer’s carry	More activity walking with two dumbbells than standing still with them37
Suitcase carry	More activity on the side holding the weight than when standing still, but not on the other side37
Deadlift	More activity with a lifting belt than without30
Dumbbell shoulder press	About 81% less activity seated than standing, in 15 men31
Row	No significant difference between one-arm and two-arm rows, in 15 trained men38

Sources

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Every source the library cites

Changes

• September 30, 2026 Revised. Corrected the upper attachment to the fifth to seventh rib cartilages and the xiphoid process; the earlier textbook table was misaligned.
• September 29, 2026 Added a figure showing where it sits, links to the exercise pages that load it, and tighter wording in a few places.
• September 29, 2026 First published.