Back Musculature of The Human Body
This article provides an in-depth exploration of the various muscles in the human back, which play a crucial role in the structural and functional integrity of the body. We will examine each back muscle in detail, including their origins and insertions, to help understand their mechanical and anatomical roles. We will also explore the isolated functions of these muscles, revealing how each contributes uniquely to movement and posture.
Moreover, we will examine how these muscles work together to enable complex and coordinated movements. We will also delve into the aspect of innervation, explaining the intricate neural connections that govern and fine-tune muscle responses. This comprehensive overview is designed to cater to a wide audience, from medical professionals and fitness enthusiasts to anyone curious about the sophisticated network of muscles that make up the human back.
Defining Terms
Origin – The fixed attachment point of a muscle. This is typically the end of the muscle that attaches to the more stationary bone in a pair of bones being moved by that muscle. The origin is generally proximal, meaning closer to the center of the body, or on the more stable part of the skeletal structure.
Insertion – The insertion point of a muscle is where it attaches to the bone and is the part that moves during muscle contraction. This part of the muscle is usually located far from the center of the body, and moves towards the muscle’s origin when it contracts. Understanding the insertion point is important in determining a muscle’s function in movement and leverage, as it influences the direction and force of the movement produced by the muscle contraction.
Isolated Function – The term “isolated function” refers to the specific action a muscle performs when it contracts independently, without the influence of other muscles. Understanding this concept is crucial for comprehending the primary role of each muscle in movement, as it highlights the muscle’s unique ability to produce a particular movement at a joint. The study of isolated functions is often used to understand muscle imbalances, rehabilitation needs, and design targeted exercises for strengthening or stretching a specific muscle.
Integrated Function – The coordinated action of muscles is crucial during complex movements and requires them to work in concert with other muscles and body systems. Isolated function, which focuses on a muscle acting alone, is not enough to fully understand bodily movements. Integrated function, on the other hand, emphasizes how muscles function together in groups, providing a more holistic view of bodily movements. This concept is essential to comprehend how muscles contribute to overall body mechanics, stability, and efficiency during everyday activities and sports.
Innervation – the supply of nerves to a muscle, which enables the muscle to receive and respond to neural signals. This connection is crucial for muscle activation and control, as it allows the nervous system to regulate muscle contractions, both voluntary and involuntary. Innervation is a key aspect in understanding how muscles function, their responsiveness to stimuli, and their role in movement and sensation.
Concentric – refers to a type of muscle contraction in which the muscle fibers shorten as they contract. This occurs when a muscle generates enough force to overcome resistance, resulting in the movement of body parts towards each other. A common example of a concentric contraction is the upward movement during a bicep curl, where the bicep muscle shortens to lift the weight. Concentric contractions are integral to many types of physical activities and exercises, playing a key role in building muscle strength and movement.
Eccentric – refers to a type of muscle contraction where the muscle lengthens while under tension. This occurs when a muscle gradually controls or resists the movement caused by an external force, like gravity. Eccentric contractions are often associated with controlled lowering or decelerating actions, such as lowering a weight during a bicep curl or descending stairs. They play a crucial role in activities requiring controlled movements and are significant in muscle strengthening and injury prevention.
Isometric – refers to a type of muscle contraction where the muscle generates force without changing its length. During isometric exercises, the muscle neither shortens (as in concentric contractions) nor lengthens (as in eccentric contractions), but tension is still produced. Common examples include holding a plank position or maintaining a squat. Isometric contractions are essential for stabilizing joints and maintaining posture, and they are often used in rehabilitation and strength training programs.
Superficial Erector Spinae
The superficial erector spinae muscle group is a combination of three muscles, including the iliocostalis, longissimus, and spinalis muscles. They are subdivided based on the vertebrae to which they attach. All the muscles of the superficial erector spinae originate from a common point, which is the iliac crest of the pelvis, sacrum, and spinous and transverse processes of T1–L5.
Iliocostalis: Lumborum Division
Origin
Common image
Insertion
Inferior border of the ribs 7-12
Isolated Function
Concentric action – Spinal extension, rotation and lateral flexion
Integrated Function
Eccentric action – Spinal flexion rotation and lateral flexion
Isometric action – Stabilizes the spine during functional movements
Innervation
Dorsal rami of thoracic and lumbar nerves
Iliocostalis: Thoracis Division
Origin
Common origin
Insertion
Superior border of the ribs 1-6
Isolated Function
Concentric action – Spinal extension, rotation and lateral flexion
Integrated Function
Eccentric action – Spinal flexion, rotation and lateral flexion
Isometric action – Stabilizes the spine during functional movements
Innervation
Dorsal rami of thoracic nerves
Iliocostalis: Cervicus Division
Origin
Common origin
Insertion
Transverse processes of c4-c6
Isolated Function
Concentric action – Spinal extension, rotation and lateral flexion
Integrated Function
Eccentric action – Spinal flexion, rotation and lateral flexion
Isometric action – Stabilizes the spine during functional movements
Innervation
Dorsal rami of thoracic nerves
Longissimus: Thoracis Division
Origin
Common origin
Insertion
Transverse processes of T1-T12 and ribs 2-12
Isolated Function
Concentric action – Spinal extension, rotation and lateral flexion
Integrated Function
Eccentric action – Spinal flexion, rotation and lateral flexion
Isometric action – Stabilizes the spine during functional movements
Innervation
Dorsal rami of thoracic and lumbar nerves
Longissimus: Cervicus Division
Origin
Common origin
Insertion
Transverse processes of C6-C2
Isolated Function
Concentric action – Spinal extension, rotation and lateral flexion
Integrated Function
Eccentric action – Spinal flexion, rotation and lateral flexion
Isometric action – Stabilizes the spine during functional movements
Innervation
Dorsal rami of cervical nerves
Longissimus: Capitis Division
Origin
Common origin
Insertion
Mastoid process of the skull
Isolated Function
Concentric action – Spinal extension, rotation and lateral flexion
Integrated Function
Eccentric action – Spinal flexion, rotation and lateral flexion
Isometric action – Stabilizes the spine during functional movements
Innervation
Dorsal rami of cervical nerves
Spinalis: Thoracis Division
Origin
Common origin
Insertion
Spinuous processes of T7-T4
Isolated Function
Concentric action – Spinal extension, rotation and lateral flexion
Integrated Function
Eccentric action – Spinal flexion, rotation and lateral flexion
Isometric action – Stabilizes the spine during functional movements
Innervation
Dorsal rami of thoracic nerves
Spinalis: Cervicus Division
Origin
Common origin
Insertion
Spinuous processes of C3-C2
Isolated Function
Concentric action – SPinal extension, rotation and lateral flexion
Integrated Function
Eccentric action – Spinal flexion, rotation and lateral flexion
Isometric action – Stabilizes the spine during functional movements
Innervation
Dorsal rami of cervical nerves
Spinalis: Capitis Division
Origin
Common origin
Insertion
Between the superior and inferior nuchal lines on occipital bone of the skull
Isolated Function
Concentric action – Spinal extension, rotation and lateral flexion
Integrated Function
Eccentric action – Spinal flexion, rotation and lateral flexion
Isometric action – Stabilizes the spine during functional movements
Innervation
Dorsal rami of cervical nerves
Quadratus Lumborum
Origin
Iliac crest of the pelvis
Insertion
12th rib and transverse processes L2-L5
Isolated Function
Concentric action – Spinal lateral flexion
Integrated Function
Eccentric action – Decelerates contralateral lateral spinal flexion
Isometric action – Stabilizes the lumbo-pelvic-hip complex
Innervation
Spinal nerves (T12-L3)
Transversospinalis: Thoracis Division
Origin
Transverse processes of T12-T7
Insertion
Spinuous processes of T4-C6
Isolated Function
Concentric action – Produces spinal extension and lateral flexion; extension and contralateral rotation of the head
Integrated Function
Eccentric action – Decelerates lateral flexion of the spine, flexion and contralateral rotation of the head
Isometric action – Stabilizes the spine
Innervation
Dorsal rami C1-T6 spinal nerves
Transversospinalis: Cervicus Division
Origin
Transverse processes of T6-C4
Insertion
Spinuous processes of C5-C2
Isolated Function
Concentric action – Produces spinal extension and lateral flexion and extension and contralateral rotation of the head
Integrated Function
Eccentric action – Decelerates lateral flexion of the spine, and flexion and contralateral rotation of the head
Isometric action – Stabilizes the spine
Innervation
Dorsal rami C1-T6 spinal nerves
Transversospinalis: Capitus Division
Origin
– Transverse processes of T6-C7
– Articular processes C6-C4
Insertion
Nuchal line of occipital bone of the skull
Isolated Function
Concentric action – Produces spinal extension and lateral flexion and extension and contralateral rotation of the head
Integrated Function
Eccentric action – Decelerates lateral flexion of the spine and flexion and contralateral rotation of the head
Isometric action – Stabilizes the spine
Innervation
Dorsal rami C1-T6 spinal nerves
Multifidus
Origin
Posterior aspect of the sacrum and processes of the lumbar, thoracic and cervical spine
Insertion
Spinuous processes 1 to 4 segments above the origin
Isolated Function
Concentric action – Spinal extension and contralateral rotation
Integrated Function
Eccentric action – Spinal flexion and rotation
Isometric action – Stabilizes the spine
Innervation
Corresponding spinal nerves
Latissimus Dorsi
Origin
Spinous processes of T7-T12, iliac crest of the pelvis, thoracolumbar fascia and ribs 9-12
Insertion
Inferior angle of the scapula and interubercular groove of the humerus
Isolated Function
Concentric action – Shoulder extension, adduction and internal rotation
Integrated Function
Eccentric action – Shoulder flexion, abduction, external rotation and spinal flexion
Isometric action – Stabilizes the lumbo-pelvic-hip complex and shoulder
Innervation
Thoracodorsal nerve (C6-C8)
Conclusion
Upon conducting a thorough examination of the back muscles, we have discovered their complexity and crucial role in the human anatomy. Our understanding of their specific origins and insertions, as well as their isolated and integrated functions, has deepened. This has given us a better understanding of how these muscles work together to support movement, posture, and stability. The exploration of innervation has highlighted the intricate link between the nervous system and muscular function, further emphasizing the sophistication of back muscles in bodily mechanics.
This knowledge is not only valuable for medical and fitness professionals but also for anyone interested in the inner workings of the human body. In conclusion, it’s evident that the back muscles, with their diverse functions and intricate coordination, are fundamental to our daily lives, enabling us to move, lift, and maintain posture with remarkable efficiency and strength.
References
National Academy of Sports Medicine. NASM Essentials of Personal Training. Jones and Bartlett Publishers; 7th edition (Jan. 4, 2021)
National Academy of Sports Medicine. NASM Essentials of Corrective Exercise Training. Jones and Bartlett Publishers; 2nd edition (Jan. 13, 2021)