Functional Training

Basic anatomy of the core and involved muscles

Recently, core training has become one of the hottest topics in sports conditioning, general fitness and even rehabilitation. The popularity of core stability training is warranted, as it provides many benefits to the athlete including enhanced coordination performance and reduction of injury. Unfortunately, many athletes and exercise professionals are unclear on the actual muscles that comprise the core and even less sure of the method to train them. This article aims to complement the information provided on this website by providing additional basic information on the core and muscle types.Before a trainer can truly manipulate core stability training in the athletes favor, it is important to be able to answer several questions concerning muscle types and the anatomy of the core.

What is the difference between a stabilizing muscle and a mobilizing muscle?

A stabilizing muscle is typically one that spans a single joint and therefore is anatomically designed to provide a high degree of stability to a specific area of the body. Stabilizing muscles are sometimes referred to as phasic muscles. It is likely that some phasic muscles operate in a feed forward manner  the muscle is activated before movement even begins. This has been demonstrated by studies performed on the electrical (EMG) activity of the transversus abdominis muscle in individuals free of back pain. Mobilizing muscles are typically larger and more powerful, spanning several joints and causing gross movement of the body; an example is the large erector spinea muscles of the spine causing extension. This type of muscle is sometimes referred to as a tonic muscle. It is crucial that stabilizers work efficiently and are strong enough to anchor a part of the body to allow the stronger and more powerful tonic muscles to literally pull off the structure. For example, recall Jandas flagpole analogy of the spine in our article dealing with Lower Back Pain. Stabilizing muscles need to anchor the shoulder girdle (shoulder blade and collarbone) to the trunk and spine, which in turn, must be anchored by the stabilizers of the lumbo-pelvic-hip complex (LPHC). If the stabilizers are weak or work inefficiently, the body will attempt to compensate by substituting other less ideal muscles. This has the effect of altering the mechanics of the joint/body part leading to muscle imbalances, posture deviations, less efficient and powerful movements and eventual injury. The power of an athlete is built on a foundation of muscle strength. Likewise, strength is built on a foundation of both dynamic and static stability. The systematic progression from stability to strength to power must be followed otherwise it is like trying to fire a cannon from a canoe.

What is the core of the body and where is it located?

In this discussion and hereafter, the word core is a collective term referring to the stabilizing muscles of certain parts of the body. Theoretically, one can view the body as having two cores; one located in the lower body and one located in the upper body. The true or lower core of the body is where the center of gravity is located and as mentioned previously, where all movement begins. It is located approximately in line with the umbilicus (belly button) or slightly below and can also be considered the bridge between the lower body and the upper body. The lower core is composed the musculature that stabilizes the LPHC and the upper core is comprised of muscles that stabilize the shoulder girdle. The upper core is located in the middle and upper back between the shoulder blades or scapulae. It should be remembered that muscles do not work in isolation during functional movements, so although we discuss the presence of two cores we are actually referring to stabilizing muscles that in effect operate as one unit due to the systematic operation of the kinetic chain and neuromuscular motor patterns.

What anatomy comprises the lower core?

Quite likely the number one response to this question is the abdominal muscles. While this may be partially true, the abdominals are only one group of muscles that make up the core. The core of the lower body consists of the stabilizing muscles of the lumbo-pelvic-hip-complex (LPHC). The name implies the anatomy involved, so therefore muscles that lend stability to the pelvic girdle and lower/lumbar spine are of primary importance. These muscles include:

the abdominals  especially the transversus abdominis and to a lesser degree the internal oblique

the deep paraspinal (laying right next to the spine) muscles called the multifidi

the gluteals (maximus, minimus and especially the medius).

Other muscles that are thought to contribute to core stability but to a lesser degree are the quadratus lumborum and the iliopsoas (hip flexor) muscles. These muscles serve to anchor and stabilize the LPHC to transfer forces from the lower extremities to the upper extremities and to provide a stable base for the mobilizing muscles attached to it to pull off. (see article on Lower Back Pain for a detailed description on the operation of the lower core)

What anatomy comprises the upper core?

The only bone attachment of the shoulder girdle to the rest of the trunk is via the clavicle (collarbone) at the sternoclavicular joint (joining the clavicle to the sternum). All other attachments of the shoulder girdle to the trunk are via muscles. These muscles act to both move and stabilize the shoulder girdle and provide a stable base for the mobilizing muscles that cause arm movement (deltoids) to pull off. Therefore, the effective and powerful control of the arm is directly dependent on the effective muscular stabilization of the shoulder girdle. The primary stabilizing muscles of the shoulder girdle that make the upper core are the serratus anterior and the middle and lower trapezius. As mentioned in a rehabilitation article on this site, sometimes weakness or poor control of these muscles can eventually lead to shoulder impingement.

How do the cores of the body work?

In our article on lower back pain we described in detail the proposed drum formingaction of the stabilizing muscles of the lower core. The transversus abdominis (TA) is proposed as the key stabilizing muscle of the lower core due to its horizontally running fibers and its attachment to the lower back. The TA is a stabilizer in the true sense of the word because its primary function is to stabilize. The muscles that make up the upper core however are a little different however. Since there are no actual joints to move or stabilize the scapula, the muscles themselves must accomplish both actions by forming force couples. Force couples are a difficult concept to explain and visualize, but here is a very basic overview. A force couple is created when two muscles on opposite sides of a body part fire and pull simultaneously. The forces balance each other out and cause rotation of the body part about its axis. For example, to abduct (raise directly to the side) the shoulder, the scapula must rotate upwards. This is accomplished by the simultaneous action of the serratus anterior muscle pulling the scapula forward on the thorax toward the chest, and the inward (toward the spine) pull of the trapezius. This force couple causes the scapula to rotate around an axis within the body of the scapula. As mentioned previously, the stabilizing muscles must also fix the scapula to the spine and thorax to allow the mobilizers to work effectively.

How do the cores of the body work during functional movements?

Recall in a previous article, we discussed that during functional (sports specific and everyday) movements; forces generated from muscles in the lower extremities are transferred progressively up a system of levers (joints) called the kinetic chain. Therefore forces from the legs are transferred via the lower core and spine, to the upper core then the extremities. So technically, the stabilizing muscles that comprise the two cores of the body actually work together – synchronized through programmed motor patterns from the brain to work together as one to stabilize the kinetic chain to enable force generation and power transfer. For example, consider a baseball pitcher throwing a fastball. The powerful and bulky mobilizing muscles of the legs generate large forces against an immovable object (the earth) these forces are transferred up the kinetic chain to the arm and eventually the baseball. Since the stabilizing muscles of the upper core are connected to the trunk and spine, their effectiveness is directly dependent on that of the lower core stabilizers. The adage youre as strong as your weakest link holds a great deal of truth and implies, that if the stabilizers comprising the lower core are weak, total body strength and power will be minimized even if the upper core is strong. It should be clear then that all the stabilizing musculature must be of sufficient strength and work efficiently to allow the links of the kinetic chain to work efficiently for maximal expression of power.

Why is it important to concentrate on strengthening the stabilizer musculature?

Unfortunately phasic muscles are prone to weakness and lengthening while tonic muscles have a tendency to strengthen and tighten. This is probably due to both anatomical and physiological differences in the muscles themselves. Since tonic muscles typically cross multiple joints, there is a greater potential for them to shorten and become tight. Tonic muscles tend to dominate in instances of fatigue while phasic muscles tend to fatigue themselves and become less active. Also, phasic muscles tend to have a higher threshold of neural activation than do tonic muscles; therefore these two muscle types can be viewed as resistors in an electric circuit (nervous system). Phasic muscles are considered as having high resistance, while tonic muscles have a low resistance. Typically an electric current will flow the path of least resistance, therefore the tonic muscles will be facilitated and simultaneously rob the phasic muscles of some of their nerve activation stimulus. Specific training of the stabilizing muscles results in their improved activation by the central nervous system, thus automatically increasing their strength. This also has the effect of lowering their resistance and decreasing the dominance of the tonic muscles.

In conclusion, this article has highlighted the anatomy and locations of the key stabilizing muscles in the body. The purpose of this article was to allow the reader a better understanding of the motivation behind core and stability training. As will become increasingly obvious in Part 2 of this series of articles, core training is much more than performing abdominal crunches or performing strange movements on an exercise ball or balancing on a wobble board; it may if fact be the most important form of training an athlete will ever do.

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