Abdominal Muscles of The Human Body

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.

 

Rectus Abdominis

Origin

 Pubic symphysis of the pelvis

 

Insertion

Ribs 5-7

 

Isolated Function

Concentric action – Spinal flexion, lateral flexion and rotation

 

Integrated Function

 Eccentric action – Spinal extension, lateral flexion and rotation

Isometric action – Stabilizes the lumbo-pelvic-hip complex

 

Innervation

Intercostal nerve T7-T12 

 

External Oblique

Origin

 External surface of ribs 4-12

 

Insertion

Anterior iliac crest of the pelvis, linea alba and contralateral rectus sheaths

 

Isolated Function

Concentric action – Spinal flexion, lateral flexion and contralateral rotation

 

Integrated Function

Eccentric action – Spinal extension, lateral flexion and rotation

Isometric action – Stabilizes the lumbo-pelvic-hip complex

 

Innervation

Intercostal nerves (T8-T12), iliohypogastric (L1) and ilioinguinal (L1) 

 

Internal Oblique

Origin

 Anterior two-thirds of the iliac crest of the pelvis and thoracolumbar fascia

 

Insertion

Ribs 9-12, linea alba and contralateral rectus sheaths

 

Isolated Function

Concentric action – Spinal flexion (bilateral), lateral flexion and ipsilateral rotation

 

Integrated Function

Eccentric action – Spinal extension, rotation and lateral flexion

Isometric action – Stabilizes the lumbo-pelvic-hip complex

 

Innervation

Intercostal nerves (T8-T12), iliohypogasmic (L1) and ilioinguinal (L1) 

 

Transverse Abdominis

Origin

 Ribs 7-12 anterior two-thirds of the iliac crest of the pelvis and thoracolumbar fascia

 

Insertion

Linea alba and contralateral rectus sheaths

 

Isolated Function

Concentric action – increases intra-abdominal pressure and supports the abdominal viscera

 

Integrated Function

Isometric action – Synergistically with the internal oblique, mulitfidus and deeper erector spinae to stabilize the lumbo-pelvic-hip complex

 

Innervation

 Intercostal nerves (T7-T12), iliohypogastric (L1) and ilioinguinal (L1)

 

Diaphragm

Origin

Costal part – inner surfaces of the cartilages and adjacent bony regions of ribs 6-12

Sternal part – posterior side of the xiphoid process

Crural (lumbar) part: – (1) Two aponeurotic arches covering the external surfaces of the quadratus lumborum and psoas major and (2) right and left crus, originating from the bodies of L1-L3 and their intervertebral discs

 

Insertion

Central tendon

 

Isolated Function

Concentric action – Pulls the central tendon inferiorly, increasing the volume in thoracic cavity

  

Integrated Function

Isometric action – Stabilization of the lumbo-pelvic-hip complex

 

Innervation

 Phrenic nerve (C3-C5)

 

Conclusion

After thoroughly exploring the abdominal muscles, we have come to understand their complexity and vital importance to the human body. We have examined the anatomy of each muscle, including their origins, insertions, and individual functions as well as how they work together. Through this examination, we have learned how these muscles facilitate movement, while also providing stability and protection to our core.

Furthermore, we have discussed the innervation of these muscles, which has revealed the intricate interaction between them and the nervous system. This underscores the significance of abdominal muscles in overall bodily function and health. This knowledge is invaluable not just for medical and fitness professionals but also for anyone interested in the capabilities of the human anatomy. In conclusion, we can see that the abdominal muscles are fundamental to the harmonious operation of our body, highlighting the marvel of human design in their strength and coordination.

 

Reference

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)