Over the years buzz words in fitness create extensive press and popularity. One phrase in particular, core strength, continues to gain traction. Understanding the musculature and functionality of core strength is beneficial for building well-rounded exercise programs.
Structurally
For a more complete understanding of core strength let’s first review some basic anatomy. Structurally the body is divided into two skeletons, the axial and appendicular. The axial skeleton is comprised of the skull, vertebral column and rib cage. The appendicular skeleton contains the upper and lower limbs and bony structures that support them. (See visuals on the links)
This separation of the body into two structural components enhances the importance both play in the functioning of the body. While the arms and legs provide incredible movement capabilities, the vertebral column supplies the central supporting pillar.
Movement of the upper extremities, the lower extremities, or both in any type of activity entails the transmission of internal and external forces to the central supporting column, of the body, the vertebral column.
Mark D. Grabiner “Kinesiology and Applied Anatomy”, 7th Edition
The second structural component to highlight is the three-dimensionality of the body. The body can be divided into the sagittal plane, coronal plane and transverse planes. Simply stated you can divide the body into right and left halves, front and back segments, top and bottom sections respectively.
The diversity and complexity of movement that the body can perform, positively correlates to the 360-degree structure. This is important to remember when we talk about core strength because it combines all three of the above mention planes of movement. It is not solely about the front area of the body.
Broadly speaking, core strength involves any and all of the muscles that enable and support the central supporting column, as well as adjacent bony structures. What does that mean in practical terms? That means your spine (vertebral column), hip and gluteal areas because of their proximity and connection to your spine.
It does not include the shoulder and knee joint areas. While there are a variety of muscles that connect the shoulder area to the torso, this is not considered the core of the body. Similarly certain muscles in the upper thigh area have functions in both the hip and knee joints but the primary movers of the knee are not main participants in core strength.
In many fitness and Pilates circles the line of demarcation for core strength ends right about the breast line on the top border and about mid-thigh for the bottom line. You can also think about it like a three-dimensional rectangle box in the middle of your body from your chest to mid-thigh.
Now let’s get that body moving. The torso can bend forward, backward, sideways and rotationally. The hip joint can move forward, extend backward, sideways, towards the midline of the body and rotationally. Those actions of the spine and hip are essentially what comprise core strength movement capabilities.
Vertebral Column
Let’s break that down in muscular terms. The primary muscle that enables the torso to bend forward or flex the spine is the rectus abdominis. For pure sideward motion or lateral flexion of the torso the quadratus lumborum muscle is primary. The transverse abdominis, sits like a belt around the waist, is a primary stabilizer of the pelvis and thoracic area of spine.
For diagonal flexion of the torso the internal and external abdominal obliques are activated. For extension or backward bending of the spine, the erector spinae and various back extensors are incorporated. The prime movers in spinal rotational are the rotatores muscles with support from the transversospinalis group.
The transverse abdominus, internal and external abdominal obliques and rectus abdominus constitute the abdominal muscles. Respectfully listed from deepest to most superficial. In addition to the actions listed above they assist in abdominal compression and help with intra-abdominal pressure (IAP).
IAP is associated with elimination of wastes and reduces the load on the lumbar vertebra. In other words, if a cylinder (your torso) does not have a balanced IAP then the distribution of weight (loads) is unequal. This means that when you attempt an action like picking up a heavy suitcase the forces acting on the body will be uneven. The most common result a lower back injury.
Generally speaking, the deep muscles of the vertebral column are primarily involved with posture. While those more superficial and possibly even palpable, often perform larger gross motor skills. According to Gray’s Anatomy the latissimus dorsi and trapezius are the most superficial back muscles, while the transversospinalis muscle group lie deepest.
“These deep muscles of the spine form an essential part of the network of postural muscles that maintain erect posture. They not only aid in bending and rotation of the spine—in other words, in active movement—but also in maintaining the support of the vertebral column.”
Theodore Dimon Jr. “Anatomy of the Moving Body”
Beyond the diversity of muscle names and actions is the three-dimensionality of movement involved in true core strength. Popular magazines and advertisements often portray core strength as simply “six-pack” abdominals. This depiction then incorporates only one muscle the rectus abdominus. Hopefully this post will demonstrate there is a whole lot more to the core!
Caveat
Maintaining the integrity of the curves of the spine is vital for all the muscles related to the spine, pelvic girdle and hip joint areas. As this is a whole topic on itself I will devote an additional blog post on that issue. Bear in mind though that any and all training should respect the natural curves of the spine.
Additionally, it has been my experience as a trainer and educator that back extension and rotational movements receive too little attention in core strength training. I believe this among other factors help contribute to the high prevalence of back pain in the US.
The statistics below demonstrate the frequency of back pain in the US, taken from the American Chiropractic Association.
- About 80% of adults in the U.S. have been bothered by back pain at some point
- 50% all working Americans admit to having back pain symptoms each year
- Back pain is one of the most common reasons for missed work
Pelvic girdle and hip joints
As a reminder the core runs from the breast line to just below the pelvis and hip joints, or rather, upper mid thigh. The actions of the hip joint are flexion, extension, lateral flexion (abduction), drawing towards the midline of the body (adduction) and rotation, both internal and external.
Similar to the vertebral column there is great diversity and combinations of movements connected with the pelvis and hip areas. The pelvis plays a crucial role in posture, support and locomotion on two feet.
As cited in the first quote at the start of this post transfer of weight is significant both in the pelvis and vertebral column areas. The pelvis transfers weight of body down through the legs to the ground. It also works in reverse, absorbing shock or forces from the legs to the spine.
So let’s look with a broad brush at the muscles connected to these two areas. Remember we are looking more at what concerns the moving body. For time purposes I have not presented detailed explanation of the ligaments even though they provide vital needed structural support to the whole body.
Hip flexion
The psoas major participates in flexion of the hip and lateral rotation as well as some flexion of the spine. Its adjacent partner the psoas minor is a weaker flexor of the lower lumbar spine. Noteworthy for individuals with back issues is that the psoas major particularly through its insertion on the lumbar spine can “pull” on the lower lumbar back if inactive or not properly trained.
The iliacus differs from the two psoas muscles in that it originates on the ilium or inner surface of the wing of the pelvis (what you feel as your hip bones). It flexes and laterally rotates thigh as well as flexes both the spine and pelvis, dependent on cite of origin.
In many circles these three muscles are often combined in language labeled as the iliopsoas. This is due to their combined and narrowing ending (insertion) point on the top of the thighbone or femur. Thus, they begin separately and end as one unit, with hip flexion as the primary movement.
One additional muscle involved in hip flexion is the sartorius. It is the longest muscle in the body and is called the “tailor’s muscle.” It works also in combination to flex, abduct and laterally rotate the hip and flex the knee. Think of a dancer in a “turned out” passé position of the leg.
Hip extension and abduction
When we think of hip extension the best example might be of a dancer with his leg in the arabesque position. This is lifted and stretched behind the dancer’s body. Thus, hip extension requires the large muscles of the gluteal area, particularly gluteus maximus.
This gluteus maximus also laterally rotates the hip and is involved in abduction (lateral flexion). The next gluteal muscle is more towards the lateral side of the body, gluteus minimus. Its action is to abduct the leg and also for medial (inward) rotation.
Then wedged in between the maximus and minimus is situated the gluteus medius, thus, its name of in the middle. This muscle is involved also in abduction as well as both internal and external rotation of the hip. In some circles the gluteal muscles combined are labeled the “gluts.”
Abduction requires lifting the leg in a lateral (sideways) flexion motion, is seen in fewer activities than flexion or extension. However, the actions of stabilization of both the pelvis and the legs can be connected to these same muscles. Particularly when standing on one leg or more balance type movements.
Gluteus medius and tensor facia latae are the prime movers in abduction. There is participation from gluteus minimus and maximus, as well as rectus femoris (of the quadriceps) and sartorius.
Hip Adduction
The adductor or groin muscles draw the leg towards the midline of the body. A good way to remember the terminology is as the leg moves closer to the center line of the body, one could interpret this as “adding” to the total body.
The adductors are five thick and fan-like muscles. Names include adductor magnus, adductor longus, adductor brevis, pectineus, and gracilis. Due to their fan-like nature and the fact they cover a large surface area of the femur they are vulnerable to injury. They attach the inner pelvis to the inner (medial) side of the thigh.
Gymnast, dancers and sprinters often suffer from groin injuries. The first two due to the nature of a position called the splits. Sprinters and hurdle runners from explosive actions that demand adductor strength and flexibility.
Lateral hip rotation
There are six deep muscles of the hip associated with external (lateral rotation). A good analogy is to think of these like the rotator cuff in the shoulder, only these six muscles support the hip joint.
All six lateral rotators originate on the pelvis and attach to the femur (upper thigh bone) at the greater trochanter. They are piriformis, quadratus femoris, gemellus superior, gemellus inferior, obturator internus and obturator externus. In combination with the previously mentioned iliopsoas they balance the hip joints to the spine.
Some individuals may have incurred familiarity with the deep rotators particularly piriformis. This muscle can often become aggravated and thus contribute to issues involving inflammation of the sciatica nerve, layman’s terms “sciatica or piriformis syndrome.” Another good reason to keep all the core strength muscles in motion with regular balanced training.
Upper thigh muscles
OK, take a big breath, we are almost there on this long anatomy excursion. If you have made it this far, congratulations! Last but not least the muscles of the upper thigh; these include the hamstrings, quadriceps muscle group and groin muscles (adductor group mentioned above).
Remember that the bottom border of core strength is mid-thigh, thus the inclusion of the upper thigh muscles. Core strength does not involve the actions of the knee joint. The hamstrings and quadriceps muscle group participate in both hip and knee joint actions.
The hamstrings are the muscles on the back (dorsal) side of the thigh or femur bone. They include the semimembranosus, semitendinosus and biceps femoris. Their basic function is hip extension and knee flexion.
On the opposite side of the thigh are the big quadriceps muscles, as the name implies they are a four-headed group. Rectus femoris, vastus lateralis, vastus medius and vastus intermedius. Knee extension is the primary function of the quadriceps muscles.
The names simply reflect their placement on the body, rectus femoris is the most superficial or above the others. Underneath vastus lateralis is on the outer (lateral) side of the leg, medialis the innermost (medial) side of the femur and intermedius between lateralis and medialis.
It is the rectus femoris that is officially in most circles the only true member of core strength of the quadriceps muscles. It is the only one of the four to cross at the hip joint. The other three quadriceps muscles primarily extend the knee and do not cross the hip joint.
Caveat
Grabiner’s work in “Kinesiology and Applied Anatomy” states that 22 muscles act on the hip joint. He points out that there is a critical ratio of quadriceps to hamstrings strength that the muscles should adhere to for lower injury rates. In practical terms these means maintaining strength needs a total body emphasis and not simply “stretching” one side or either bulking one side is recommended.
“Two factors that can aid in reducing hip or thigh injuries are related to reducing the imbalance of strength between antagonistic sets of muscles and maintaining flexibility.”
The brilliance of Pilates
The original classical system of Pilates is designed in such a manner as to challenge the core muscles from a variety of positions with diverse pieces of equipment. In a general sense the individual performs exercises on his back, side lying, face down, upside down and in numerous other combinations of these positions.
In addition to the various body postures the equipment provides additional means of challenging and training the core. The Pilates equipment such as reformer, Cadillac, wunda chair, guillotine and barrels offer unique opportunities to work the core muscles from spine to hip and train them for efficient use in daily life. Simply stated core strength is the optimization of the body to do its daily tasks with grace and ease.
“Our interpretation of physical fitness is the attainment and maintenance of a uniformly developed body with a sound mind fully capable of naturally, easily, and satisfactorily performing our many and varied daily tasks with spontaneous zest and pleasure.”
Joseph Pilates “PILATES’ Return to Life Through Contrology”
The bottom line is that unless you activate, utilize and consistently maintain all of the core muscles weaknesses and imbalances will occur. These can be simply a part of the natural aging process, inactivity patterns, and by acute or chronic conditions. The diversity of exercises in Pilates allows for imbalances in the body to regain their mobility and strength through the deliberate and precise method of the system.
Classical Pilates is taught as Joseph Pilates intended to regain and rebalance through the brilliance of movement. As Power Pilates teachers state “movement heals.” It is not therapy it is a workout pure and simple.
Obviously as a certified Pilates instructor I believe in the method. At the same time I understand there are excellent teachers and other methods that have proven beneficial. However, Pilates is the one I know both from the prospective of an injured dancer and as a middle-aged exercise enthusiast.
One last word on the spine
The vertebral column has in my opinion four main requirements. These highlight why it is so vital to the integrity and sustainability of our bodies that core strength is maintained. This demands intelligent comprehensive and consistent use of all the muscles and more.
- Be structurally flexible
- Withstand tension, compression, bending and torsion forces
- Protection of nerves and blood vessels from damage even during movement
And last but certainly not least
4. Function a Lifetime!
