Knowing the major muscle groups (Pt2)
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.
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.
