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In the last post we covered four key, well-known, yet superficial muscles of the back and arms. In this post, we’ll delve a little deeper into the musculature to discuss four other key muscle/muscle groups which lie deeper to these muscles.

Erector Spinae: You may not know them by name, yet they are one of the most distinguishable muscle groups of the back. Located on either side of the spine, the Erectors are a densely layered group of muscles that run from the hip bone to the back of the head. Their mound shape appearance creates a natural trough between the spine and the closest of their muscle fibers. You can see a segment of them on the right side of the back where the superficial muscles have been reflected in the image below. Although they are partially hidden beneath the Trapezius and the Lats, they are still considered a superficial muscle group because there is yet another layer of spinal muscles beneath them!

There are three layers to the Erector Spinae (not distinguishable in the image below):

Spinalis, Longissimus and Iliocostalis — the former being closest to the spine and the latter being farthest away. As a whole, the Erectors are a postural muscle group helping to keep your spine erect and providing balance for the upper body. Their main function is to laterally flex the spine to either side and extend the back bilaterally. They’re also involved to some extent in actions involving forced exhalation, such as coughing and sneezing.

Rotator Cuff Muscles: There are four individually named muscles that comprise the rotator cuff muscles. Each one originates and covers an area of the scapula and attaches to the very top of the Humerus in the shoulder joint. Each muscle performs its own action, which helps to mobilize the shoulder and arm. The three visible rotators in the image below are: Supraspinatus, Infraspinatus and Teres Minor. The fourth rotator cuff, Subscapularis, is located on the front side of the scapula and is therefore not visible.

1. Supraspinatus: Hidden beneath the upper fibers of the Trapezius, Supraspinatus helps to abduct the shoulder and stabilize the shoulder joint.

2. Infraspinatus: Below Supraspinatus and partially hidden beneath the lower fibers of the Trapezius, is Infraspinatus. This muscle is capable of performing several actions.

  • Lateral rotation of the shoulder
  • Adduction of the shoulder
  • Extension of the shoulder
  • Horizontal adduction of the shoulder
  • Stabilizer of the shoulder joint

That’s quite a workload for one muscle. Its key action however is lateral or outward rotation of the shoulder. Without this action, you would not be able to raise your arm above your head!

3. Teres Minor: Although similar in name and in close proximity to Teres Major, Teres Minor is a complete synergist to Infraspinatus. That is, it basically assists Infraspinatus in all its actions.

4. Subscapularis: This last rotator cuff muscle covers the front side of the scapula. Due to its placement, only a small portion of the muscle is truly accessible and palpable along its lateral border. This muscle is an antagonist to Infraspinatus. It medially rotates the shoulder and stabilizes the shoulder joint.

Back Muscles

Rhomboids: Located between the medial border of the scapula and the upper thoracic vertebrae are the Rhomboids. Named for their geometric shape, they are segmented into major and minor fibers but perform the same actions.

  • Adduction of the scapula (moving it closer to the spine)
  • Elevation of the scapula
  • Downward rotation of the scapula
  • Stabilizer of the scapula

Actions that require moving the shoulder and arm back behind the body, such as throwing a ball or rowing a boat, can easily over tax these muscles. The military stance with the spine erect, chest forward, and the shoulders back, require the Rhomboids to fully engage.

Levator Scapula: This next key muscle originates on the side of the cervical spine and twists its way down to attach itself on the upper portion of the scapula. Levator Scapula is mostly hidden under other muscles but is easily palpable and accessible. You may not have heard of this muscle by name, but when it spasms it will prevent you from turning your head to the side. This is another muscle which is capable of performing several actions.

  • Elevation of the scapula
  • Downward rotation of the scapula
  • Lateral flexion of the head/neck
  • Rotation of the head/neck to the same side

 As a pair they help to extend the head and neck back. This is one of those muscles that can be easily over taxed and cause a lot of issues for many people. It’s most vulnerable action is elevation of the scapula. People who are prone to anxiety, emotional distress, or high levels of stress may find their shoulders held up high, forcing this muscle to be in a perpetual state of contraction. Other factors such as poor postural habits, side sleeping without proper support, craning the head and neck, or even heavy backpacks can all cause trouble for this muscle.

Joe Azevedo is a New York State/NCBTMB Licensed Massage Therapist, ARCB Certified Reflexologist, and an Advanced Reiki Practitioner. He is a graduate of the Swedish Institute and is the owner and founder of Brooklyn Reflexology.

We have close to 320 pairs of muscles in the human body. That means we have a staggering 640 named muscles in total throughout the body! Up until the 18th century however, muscles were not given a nomenclature but assigned a number as a way of identifying them. Two anatomists by the name of William Cowper and James Douglas are credited for changing this.

Some muscles are better known within the context of a group, such as: the rotator cuff muscles, the hamstrings, and the quadriceps. But in fact, each of these muscle groups contain four individually named muscles. While it’s not important to know every named muscle in the body, there are key muscles and muscle groups that everyone should be familiar with. The first part of this article will focus on four of the key muscles depicted in the diagram. We’ll cover these superficial and easily accessible muscles first before delving into the slightly deeper layers of muscle beneath them in part two.

Back Muscles

Trapezius: One of the most superficial of the upper back muscles. The “traps” as they’re often referred to are a flat, shawl-like muscle that cover the back of the neck, tops of the shoulders, and middle of the back. When you place your hands on top of someone’s shoulders to give them your best shoulder rub, you’re predominantly grasping the upper fibers of the trapezius. The word “trapezius” is Greek for “small table,” which reflects its four-cornered shape (the right trapezius in the diagram has been removed to show the deeper layers). The muscle is segmented into upper, middle and lower fibers, each capable of performing several actions. All segments of the muscle perform retraction of the shoulders as their main function.

The upper fibers perform:

  1. extension of the head and neck
  2. lateral flexion of the head to the same side
  3. rotation of the head and neck to the opposite side
  4. elevation of the scapula
  5. upward rotation of the scapula/arms

The middle fibers perform:

  1. stabilization of the scapula

The lower fibers perform:

  1. depression of the scapula
  2. upward rotation of the scapula/arms

The upper traps play a big role in supporting the weight of the head and neck during all its movements. So poor postural habits that keep the head and neck pitched forward can greatly over-tax these muscles. The middle traps are strong stabilizers of the scapula when we have our arms out in front of us.

Deltoid: Much like the trapezius, the deltoids are also a segmented muscle which cover the outer shoulder like a cap. The name comes from the Greek letter “delta” which resembles the shape of a triangle. The deltoids have an anterior, lateral, and posterior set of fibers. It’s for this reason that they’re usually referred to in the plural form, “deltoids.” Also like the traps, each segment is capable of several actions. All fibers, especially the lateral fibers, perform abduction (moving the arm up and away from the body) as their main function.

The anterior fibers perform:

  1. flexion of the shoulder
  2. medial rotation of the shoulder (moving the arm into the “handcuff” position)
  3. horizontal adduction of the shoulder (with the arm out in front, moving the arm across the front of the body to the opposite side)

The posterior fibers perform:

  1. extension of the shoulder
  2. lateral rotation of the shoulder (with the elbow bent, moving the arm into a “stop sign” position)
  3. horizontal abduction of the shoulder (with arm out in front, moving the arm away from the body)

Triceps Brachii: As the name implies, the triceps have three individual heads: long, medial & lateral. Each of these heads originate on a different part of the arm but ultimately converge into a thick tendon at the elbow. Since they’re the only muscle found at the back of the upper arm, they’re the muscle solely responsible for straightening out the elbow (extension). The head closest to the body, the long head, is also capable of extending the arm back and moving it in close to the body (adduction).

Latissimus Dorsi: The “Lats” as they’re commonly referred to are the broadest of the back muscles. Their name translates into “broad back muscle.” In bodybuilders, well-developed Lats will give the trunk a “V” shaped appearance. Considered a superficial and easily accessible muscle, the Lats originate along the low back, then fan upwards along the sides of the trunk where they insert into the upper arm. Surprisingly, the Lats do more to move the arm than they do the back. Their main functions include:

  1. extension of the arm/shoulder
  2. adduction of the arm/shoulder
  3. medial rotation of the arm/shoulder

Another muscle worth noting along with the Lats is muscle called Teres Major. The muscle originates along the outside of the scapula and then blends in with the Lats to attach at the same point. Teres Major which translates into “big, round muscle” is often referred to as “Lat’s little helper,” as it’s a complete synergist with the Lats — that is, it performs the exact same movements. Although the Lats do perform one vital function, which Teres Major does not: forced exhalation. Due to its placement, its broad muscle fibers can compress the trunk to aide in quick respiration. The best way to remember their collective actions however is to think of them as the “handcuff muscles.” In order to get your arms behind your back as if to be arrested, both the Lats and Teres Major must contract.

Joe Azevedo is a New York State/NCBTMB Licensed Massage Therapist, ARCB Certified Reflexologist, and an Advanced Reiki Practitioner. He is a graduate of the Swedish Institute and is the owner and founder of Brooklyn Reflexology.

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