How should we train the pectoralis major?

What information do we need?

We can use the research literature to enhance our training programs if we search for information about the gross anatomy, regional anatomy, and internal moment arm lengths of a muscle, in addition to its working sarcomere lengths, and susceptibility to muscle damage. Each of these factors provides information that is useful for different reasons (read more).

  • Regional anatomy describes the way in which a muscle divides into several internal regions, and this tells us whether we are going to need multiple exercises to train the muscle.
  • The internal moment arm lengths of a muscle determine its leverage on the joint, and therefore its contribution to a joint moment, relative to other agonist muscles. This allows us to see where peak force in an exercise joint range of motion needs to be, to target one muscle within a group (or one region of a muscle). We can alter the point where peak force occurs by our exercise selection and by our choice of external resistance type.
  • The working sarcomere lengths describe the lengths of the sarcomeres inside a muscle over its joint angle range of motion. It allows us to see if the muscle can experience (1) active insufficiency (and so will be trained poorly by exercises involving peak forces at very short muscle lengths), and (2) stretch-mediated hypertrophy (and so will be trained more effectively by exercises involving peak forces at very long muscle lengths).
  • The susceptibility of a muscle to damage is how easily a muscle is damaged by a workout. It is affected by: (1) muscle fiber type proportion, (2) its level of voluntary activation, and (3) the working sarcomere lengths of its muscle fibers. The amount of muscle damage that a muscle experiences after a workout is the main determinant of the frequency (and volume) we can use for training it, and it also influences our choice of exercises (single-joint vs. multi-joint, single-limb vs. multi-limb, and full vs. partial range of motion).

Anatomy

The pectoralis major is a relatively large, fusiform (within each region), and heavily-segmented muscle that originates on (1) the medial half of the clavicle, (2) the lateral side of the sternum, and (3) the anterior sides of the upper six ribs. Its three origins can be used as reference points to subdivide the muscle into clavicular (upper), sternal (middle), and costal (lower) regions. Although they have different origins, each region inserts in a fairly similar place on the upper, lateral side of the humerus.

N.B. Antagonist to the latissimus dorsi

The pectoralis major is commonly considered to be a key antagonist of the latissimus dorsi, which mainly carries out shoulder extension and adduction. Yet, only the clavicular (upper) region of the pectoralis major is an antagonist for all of the primary movements of the latissimus dorsi, because it carries out shoulder flexion and abduction. The lower (costal) region is actually a synergist most of the time, as it carries out shoulder extension and adduction. The middle (sternal) region is sometimes an antagonist and sometimes a synergist, because it performs shoulder flexion and adduction.

Practical implications

Regional anatomy

Anatomically and biomechanically, the pectoralis major can be subdivided into clavicular (upper), sternal (middle), and costal (lower) regions. Even so, the lower two regions (sternal and costal) are often described in research as a single, sternocostal region. Yet, neither subdivision may be strictly accurate, as up to seven subdivisions of the sternocostal region have been identified on the basis of detailed anatomical analysis.

Practical implications

Internal moment arm lengths

The most well-known role of the pectoralis major is to perform shoulder horizontal flexion (bringing the arms together in front of the face, in the transverse plane). This is a movement that is used in the pec deck exercise and in dumbbell flys. Depending on the technique used, it can also feature in the bench press. However, if the elbows are positioned close to the body with a narrow grip bench press variation, the joint action starts to look more like sagittal plane shoulder flexion, instead of transverse plane horizontal flexion.

#1. Shoulder horizontal flexion

When moving the shoulder at shoulder height in the transverse plane, many muscles are involved. The pectoralis major and anterior deltoid are the main horizontal flexors, and the subscapularis plays a smaller role. The posterior deltoid, infraspinatus, supraspinatus, and teres minor are the main horizontal extensors up to 120 degrees of shoulder horizontal flexion, although the teres major and latissimus dorsi take over beyond this point.

Practical implications

#2. Shoulder flexion (and extension)

When moving the shoulder in the sagittal plane, many muscles are involved. The anterior and middle deltoids, pectoralis major, and supraspinatus are the primary shoulder flexors, while the posterior deltoid, latissimus dorsi, teres minor, and teres major are the primary shoulder extensors. The role of the pectoralis major varies according to the region, as follows:

  • Sternal (middle) region — the sternal region of the pectoralis major also has a shoulder flexor moment arm throughout the joint range of motion, although its moment arm length is far smaller than the clavicular region. Its leverage is very small when the arm is by the side of the body, but it increases rapidly to a low plateau at just 30 degrees of shoulder elevation, declining slightly above 60 degrees.
  • Costal (lower) region —the costal region of the pectoralis major has a shoulder extensor moment arm only when the arm is above 45 degrees of shoulder elevation. Its leverage increases gradually above this point, reaching a low plateau at 90 degrees of shoulder elevation.

Practical implications

#3. Shoulder adduction (and abduction)

When moving the shoulder in the frontal plane, many muscles are involved. The anterior and middle deltoids and two of the rotator cuff muscles (the supraspinatus and infraspinatus) are the primary shoulder abductors, while the pectoralis major, latissimus dorsi, teres major, and subscapularis are the primary shoulder adductors. The role of the pectoralis major varies according to the region, as follows:

  • Sternal (middle) region — the sternal region of the pectoralis major has a moderate shoulder adduction moment arm throughout the joint range of motion. It has least leverage at lower and higher shoulder angles, and displays its greatest leverage at 45 degrees of shoulder elevation.
  • Costal (lower) region — the costal region of the pectoralis major has a moderate shoulder adduction moment arm throughout the joint range of motion. It has least leverage at lower and higher shoulder angles, and displays its greatest leverage at 60 degrees of shoulder elevation.

Practical implications

#4. Shoulder scaption

While biomechanical analyses tend to work in distinct planes of movement (transverse, frontal, and sagittal), many movements involve a combination of these joint actions. Shoulder scaption (scapular plane abduction) is a shoulder movement in which the arm is elevated after first being subjected to approximately 30 degrees of shoulder horizontal flexion. The resulting shoulder elevation task is therefore partway between a shoulder abduction task and a shoulder flexion task, although it has more in common with shoulder abduction than with shoulder flexion.

Practical implications

#5. Bench press variations

Although bench press variations are the most commonly-used exercises for training the pectoralis major, it is actually very difficult to identify the role of the pectoralis major and its individual regions in such exercises, because they often involve elevating the shoulder slightly at the same time as horizontally flexing it. Moreover, what shoulder elevation occurs can either take place near to the sagittal plane (when using a close grip) or near to the scapular or even transverse planes (when using a wider grip). Additionally, when the bench press variations involve a different force direction (such as an incline or a decline bench press), complexity is increased further.

Practical implications

Working sarcomere lengths

The working sarcomere lengths of the pectoralis major have been investigated in a small number of studies, and vary between regions. The sternal (middle) region spans the longest range of working sarcomere lengths, working through the ascending limb, plateau region, and descending limb of the length-tension relationship. The clavicular (upper) region also works on all three parts of the length-tension relationship, albeit to a slightly lesser extent. In contrast, the costal (lower) region starts on the plateau of the length-tension relationship, and extends onto the descending limb, reaching the same maximum lengths as the sternal (middle) region.

Practical implications

Susceptibility to muscle damage

Research has found that the pectoralis major takes longer to recover from a standardized workout than most other muscles, and it has been reported to take a slightly longer time to recover than the triceps brachii, another muscle that is easily damaged. The ability of any muscle to recover from a workout depends upon its (1) voluntary activation percentage, (2) fiber type, and (3) working sarcomere lengths.

Practical implications

What is the takeaway?

The pectoralis major is a relatively large muscle with three regions: the clavicular (upper) region, the sternal (middle) region, and the costal (lower) region. All regions are worked by shoulder horizontal flexion (and also by shoulder internal rotation) but they differ in their contributions to other shoulder movements. This means that the muscle will likely benefit from being trained with several exercises.

Figuring out how strength training works. See more of what I do: https://www.patreon.com/join/SandCResearch

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