Pectoralis major tendon

Function

Where the muscle starts and ends

The pectoralis major is the biggest and highest muscle on the front of the chest wall¹. It is thick and shaped like a fan, and it forms the front wall of the armpit¹. It has two heads, or parts, named for where they start¹. These are the clavicular head, from the clavicle (collarbone), and the sternocostal head, from the breastbone and rib cartilages¹.

Its fibres start from a wide base¹:

the front of the inner half of the clavicle (collarbone)¹
the front of the sternum (breastbone)¹
the first seven costal cartilages, which link the ribs to the breastbone¹
the breastbone end of the sixth rib¹
the aponeurosis, a flat sheet of tendon, of the external oblique muscle, the outermost flat muscle on each side of the abdomen¹

From this base, the muscle ends on the humerus (upper arm bone)¹. It attaches to the outer lip of a groove in the humerus called the bicipital groove¹. The pectoralis major is one of two axial muscles, based on the trunk, that cross the shoulder and move the humerus⁸. The other is the latissimus dorsi, the broad, triangular muscle of the lower back⁸.

Engraving of the right chest and arm from the front. The pectoralis major fans from the clavicle and sternum and converges into a flat tendon that passes under the deltoid to attach to the upper humerus, beside the biceps brachii and coracobrachialis. — Pectoralis majorHenry Vandyke Carter, in Henry Gray, Anatomy of the Human Body (1918), Fig. 410. Public domain, via Wikimedia Commons. (source, Public domain)

What each part of the muscle does

A study of 8 arms from body donors measured the leverage each shoulder muscle has for moving the arm⁹. The upper, clavicular fibres were among the best at flexion, which raises the arm forward⁹. The middle and lower fibres were among the best at adduction, which pulls the arm in toward the body⁹.

The sternocostal head is described as having 2 to 7 separate segments¹. In 11 preserved donor bodies, the clavicular head was uniform, while the sternal head had 6 or 7 segments². In each of the 11, the lowest sternal segment folded forward into a trough holding the underside of the segment above².

How the tendon meets the bone

The footprint is the patch of the humerus that the tendon covers³. Two donor studies measured it:

Donors studied	Footprint length, top to bottom
14 arms, fresh-frozen	75 mm long and about 7 mm wide³
8 male bodies, fresh-frozen	81.4 mm in total¹⁰
Same 8, sternal head alone	42.1 mm¹⁰
Same 8, clavicular head alone	56.6 mm¹⁰

In the 14 arms, tendons from both the clavicular and sternal heads were found in each one³. The clavicular head’s tendon was generally the shorter of the two³.

How studies describe the tendon’s build

Studies have described the tendon’s structure near the bone in different ways^2,3,4. Each finding below is what one study reported:

Two layers. In 11 preserved donor bodies, the tendon had a longer front layer and a shorter back layer, joined along their lower edge². This study noted no twisting of the muscle or the tendon².
One layer. In 14 fresh-frozen donor arms, examined with scans, dissection and a microscope, the enthesis, where tendon joins bone, was a single layer³. It was rich in fibrocartilage, a tough, fibrous kind of cartilage, and no true tendon layers were found there³.
Two tendons. From ultrasound scans, made with sound waves, of 46 volunteers, the authors concluded that the muscle ends in two distinct tendons⁴. One comes from the sternal and abdominal parts; the other, the deltopectoral tendon, joins a tendon inside the deltoid⁴.

Breakdown

Where the tendon tears

A tear can sit at the bone, at the musculotendinous junction where muscle turns into tendon, or in the muscle belly⁷. Studies differ in which site was most common^6,7,11:

Study	Where tears sat
112 published cases, pooled	Most were complete tears at the humerus¹¹
Review of surgical repairs, where type was given	Complete tears at the attachment were most common, at 75%⁶
102 people at one hospital (tears confirmed on MRI, a detailed scan)⁷	60.4% at the junction, 34.9% at the bone, 4.7% in the belly⁷

In the 112 pooled cases, injuries at work more often sat at the musculotendinous junction¹¹. In the review of repairs, both heads tore together in 74% of cases that named the head⁶. The sternal head tore alone in 26%, and the clavicular head alone in one case⁶.

How the tendon tears

In the 112 pooled cases, rupture happened most often in sport: weight training, weight lifting or wrestling¹¹. In those injuries, the arm was typically raised out to the side and rotated outward¹¹.

A donor study copied a bench press to look for the reason¹². The short lower fibres stretched out of proportion to the others during the last 30 degrees of lowering the arm¹². The authors concluded that these fibres are at a mechanical disadvantage at the end of the eccentric phase¹². That is the lowering phase, when the muscle works while it lengthens¹². They concluded that heavy loads on these fully stretched fibres cause rupture¹².

What people were doing

The bench press stands out in reviews of ruptures^5,6:

In one review of repairs, the bench press caused 49% of ruptures, contact sports 8%, and weight lifting 7%⁵.
In another review of repairs, the bench press and other weight lifting caused over 70% of ruptures where the cause was given⁶.
Of 365 published cases of pectoralis major injury (1822 to 2010), the authors reported 48% during weight training¹³.

Three-quarters of those 365 cases were from the last 20 years of that span¹³. In the 102 people seen at one hospital, the causes were⁷:

Share of people (%). Bars start at zero; the table below gives each value with its source.

Cause	Share of people
Weightlifting	66.7%⁷
Trauma	17.6%⁷
Sport	10.8%⁷
Manual labour	4.9%⁷

One bench press article lists pectoralis major rupture among injuries reported with the lift¹⁴. It adds that high-quality data on specific bench press injuries are lacking¹⁴.

Who it happens to

Almost everyone in these studies was a man, and the average age was about 30^5,6,7,15:

Group studied	Who they were
330 surgical repairs in 63 articles	100% men, mean age 30.4, range 18 to 74⁶
536 repairs in 18 studies	One woman⁵
291 US military patients who had surgery	100% men, mean age 30.5¹⁵
102 people at one hospital	98.1% men⁷

Among US active-duty military from 2012 to 2014, surgically repaired ruptures occurred at 60 per 100,000 person-years¹⁵. Person-years count people times the years each was followed, so 100,000 person-years could be 100,000 people for one year. Rupture was linked with serving in the Army, junior rank, and ages 25 to 34¹⁵.

What is known about anabolic steroids

Anabolic steroids are drugs related to the hormone testosterone. Some studies report how many patients used them^5,7:

In a review of 18 studies, 11% of patients (48 of 425) reported using them⁵.
At one hospital, 5 of the 102 people (4.8%) confirmed current use⁷.

The review notes that several studies have linked steroid use with a higher chance of this rupture⁵. In its own pooled data, the authors judged steroid use not to look like a major factor⁵. They could not compare outcomes by steroid use, and they note that use may be under-reported⁵. In a case series of six male bodybuilders, the authors suggested steroids may play a part by pushing lifting goals too high¹⁶.

Recovery

Return to sport after surgical repair

The figures below are outcomes in the groups each study followed^5,17. Going back to any sport and going back at the same level gave different numbers⁵:

Group followed	What the study reported
149 patients in 10 studies	Pooled results suggest about 90% returned to sport, a mean of 6.1 months after surgery⁵
128 patients in 8 studies	74% returned to their earlier level of sport⁵
24 competitive athletes, mostly bodybuilders	21 returned; 6 reached the same level with under 10% strength loss⁵
44 men, followed a mean of 51 months	97.7% returned at some level; 50.0% at the same or higher intensity¹⁷
214 US military patients, 12 months or more	95.3% returned to military duty¹⁵

In 44 men, 43 went back to sport at some level, but 22 went back at the same or a higher intensity¹⁷. In the same group, 17 men (38.6%) reported some apprehension, or unease, that affected their weight lifting¹⁷.

Outcomes with and without surgery

A meta-analysis, a study that pools the results of several earlier studies, combined 23 studies of 664 tears, all in men¹⁸. In this meta-analysis, tears that were surgically repaired had significantly better outcomes than tears managed without surgery¹⁸. The repaired tears did better in function, in two kinds of strength test, in satisfaction with appearance, and in deformity at rest¹⁸.

In the same meta-analysis, 14.21% of surgical repairs had a complication¹⁸. That total includes a 3.08% rate of re-rupture, where the tendon tore again¹⁸. An analysis pooling 112 reported cases, all in men, also found significantly better outcomes in people who had surgery than in those managed without it¹¹.

A small series of 12 people with 14 ruptures gives one example¹². On a strength-testing machine, those who had surgery showed peak torque and work comparable to their other side¹². Peak torque is the greatest turning force a muscle produces about a joint. Those managed without surgery showed a marked shortfall in both¹².

Timing of repair

The evidence on when to repair is mixed^6,19. A meta-analysis of 20 studies, covering 384 injuries, all in men, compared acute and chronic repair¹⁹. Acute repair gave significantly better results for function and for satisfaction with appearance¹⁹. It also showed a trend toward more pain-free patients, but that did not reach statistical significance¹⁹.

A systematic review looked at 259 repairs whose timing was reported⁶. Repairs within 8 weeks of injury and later repairs showed no statistically significant difference in outcome⁶. About 90% of each group had outcomes rated excellent or good⁶.

The analysis of 112 pooled cases found that surgery, preferably within 8 weeks, did significantly better than management without surgery or delayed repair¹¹.

Connections

The muscle and its neighbours

The tendon attaches the pectoralis major muscle to the humerus¹. It works beside other muscles that move the arm at the shoulder^8,9:

Latissimus dorsi: the other axial muscle that crosses the shoulder and moves the humerus⁸.
Teres major and the middle and lower latissimus dorsi: with the middle and lower pectoralis fibres, the most effective adductors in 8 donor arms⁹. The teres major is a thick shoulder muscle that runs from the shoulder blade to the upper arm bone.
Anterior deltoid and supraspinatus: with the upper pectoralis fibres, among the most effective flexors in the same study⁹. The anterior deltoid is the front part of the deltoid (shoulder cap muscle), and the supraspinatus is a shoulder muscle.

What studies of the bench press show

The bench press is the lift most often named in these ruptures⁵. Its traditional model counts the pectoralis major, anterior deltoid and triceps brachii as the main movers²⁰. The triceps brachii is the three-headed muscle on the back of the upper arm that straightens the elbow.

A review of 14 electromyography (EMG) studies, which record a muscle’s electrical activity, compared these muscles²⁰. Pectoralis major and triceps showed similar activity, and both were higher than the anterior deltoid²⁰. Related exercise pages: bench press, overhead press.

In 10 elite powerlifters, the sternal part peaked as the bar began to rise and stayed about the same as it went up²¹.
In 19 men, each did the lift three separate ways: full range, upper-half range and lower-half range²². Activity was significantly higher in the lower-half lift than in the full-range lift, at all four recording sites²².
The same men showed no significant difference between the lower-half and upper-half lifts at any site²².

In 30 trained adults lifting 60% of their one-repetition maximum (1RM), each muscle’s activity was compared across five bench angles²³:

Muscle or part	Bench angle where activity was highest or higher
Upper pectoralis major	30 degrees²³
Middle and lower pectoralis major	Flat, 0 degrees²³
Anterior deltoid	60 degrees²³
Triceps brachii, medial head	Similar at each angle²³

The same study found that inclines over 45 degrees lowered the pectoralis major’s muscular performance²³. Grip width made little difference to the pectoralis major in two studies^24,25. A third found the balance with triceps mostly unchanged²⁶:

In 28 men lifting their 6-repetition maximum, pectoralis major activity was similar across grip widths²⁴.
In 12 men holding a still bench press, a narrower grip raised triceps activity²⁵. It lowered activity a little in the sternoclavicular portion of the pectoralis major²⁵.
In 14 men, the balance of pectoralis to triceps activity did not differ by grip, except in untrained men lowering under fatigue²⁶.