As humans, one of our most distinct features is the presence of round mass of muscle located on the posterior aspect of our hips. This muscle mass is commonly known as the gluteus maximus (GM). It provides us with many different qualities. These qualities range from a perceived enhanced physical appearance to proper control of our lower extremities in everyday functional activities and protection from injury.
In the health and fitness industry, the emphasis is generally placed upon its cosmetic qualities, one of the top requests of a client seeking the assistance of a fitness professional. Count the times you have heard the phrase, “I’d like to firm up my butt.” As such, a fitness professional should have a comprehensive understanding of this muscle, how its works, what causes it to work improperly and leads to altered appearance and, most importantly, how to fix it.
The key is to implement a systematic, progressive, integrated training program that compiles all aspects of training into one neat package with a purpose. The beauty of creating a properly integrated training program is that while you are striving to fix the altered appearance of this muscle, you will simultaneously enhance its functional capacity.
This is a very important concept to note. In order to change the characteristics of a muscle (size, shape or strength), you must get the muscle to function properly. This means proper neuromuscular communication. If a proper neuromuscular connection is not established, it will create dysfunctions not only in the specific muscle but also throughout the entire kinetic chain. By addressing the neuromuscular needs of your clients, you will increase their quality of life and help them to achieve their desired goals more effectively, which will ultimately make you a more successful trainer.
Defining Key Terms
Regardless of the goal, all clients must achieve optimal neuromuscular efficiency to ensure the highest level of performance with a minimal amount of breakdown. The NASM defines neuromuscular efficiency as the ability of all muscles in the kinetic chain (agonists, antagonists, synergists, stabilizers and neutralizers) to work together to produce force, reduce force and dynamically stabilize force in all planes of motion.
The kinetic chain is simply defined as the interdependent operation of the soft tissue system (muscle, tendon, ligament and fascia), the nervous system and the articular system. In other words, these three major systems in the body operate together to allow for proper movement patterns to occur (neuromuscular efficiency). A deficiency in any one of these systems will produce faulty recruitment patterns and place an increased demand on tissues in the body. This can further lead to early fatigue and eventual injury.
Therefore, training for any goal must involve a comprehensive understanding of some key aspects of the kinetic chain that are necessary for proper program development. These include functional anatomy and biomechanics, common causes of disruption in neuromuscular efficiency and, most importantly, how to correct them through program design. In the following article, we will address the GM with respect to these key aspects and their impact on performance.
Functional Anatomy and Biomechanics
As seen in Figure 1 below, the GM originates from the thoracolumbar fascia, iliac crest, sacrum, sacroiliac ligaments, coccyx and sacrotuberous ligament. It attaches into the iliotibial tract (IT-band) or fascia lata and the gluteal tuberosity of the femur.
Figure 1. The Gluteus Maximus
Traditional functional anatomy and biomechanics places the emphasis on concentric muscle actions where muscles are viewed as “working” when they shorten or decrease a joint angle. However, this is an isolated view of muscle action and does not demonstrate the integrated functional capacity that muscles must forgo to ensure proper and efficient movement. All muscles operate within a muscle action spectrum consisting of concentric (acceleration), eccentric (deceleration) and isometric (dynamic stabilization) actions. Therefore, both the traditional and integrated function of the GM must be illuminated to demonstrate its importance and contribution to everyday functional movements.
Concentrically, the GM accelerates (produces force) hip extension and assists in the production of hip external rotation and abduction. From a functional biomechanical perspective, this has also been termed supination. This simply means that with the foot fixed (on the ground) the hip, knee and ankle/foot complex will concurrently extend, abduct and externally rotate when producing force or acting in a concentric manner. Therefore, the description of hip extension, abduction and/or external rotation as a separate action is merely for simplicity. With a fixed foot, they will all occur together.
To demonstrate this, simply stand with your feet on the ground and squeeze your glutes, externally rotating your hips. Notice that your knees and ankle/foot complex follow into external rotation.
Some examples of concentric GM actions with the foot unfixed (not on the ground) would be a swimmer’s kicking action or a figure skater extending the leg (hip extension, external rotation and abduction) behind them prior to a jump.
However, in everyday life, we rarely extend, externally rotate or abduct the hip when the foot is not fixed on the ground, and thus supination becomes a much more functional description of how the GM works. Examples of supination occur during walking, running, standing up from a seated position and climbing stairs. In the sagittal plane, the GM exerts a posterior pull on the pelvis and acts to extend the hip by pulling the trunk into an upright position (extension). GM activity increases with increased force production such as walking on an incline, running or sprinting.
Other examples of supination that are more frontal and transverse plane dominant include:
A baseball pitcher who pushes off his back leg, creating abduction and external rotation when throwing a baseball or reaching up and across your body into a cupboard for a dish.
Rotation of the trunk in a standing position, such as swinging a bat or taking groceries out of a shopping cart and putting them into the trunk of a car.
Essentially, any activity that requires triple extension (hip and knee extension and ankle plantar flexion) involves concentric action (supination) of the GM.
Eccentrically, the GM decelerates (reduces force) hip flexion, hip internal rotation and hip adduction prior to and during the single-leg stance phase of gait. From a functional biomechanical perspective, this has also been termed pronation. This simply means that with the foot fixed (on the ground) the hip, knee and ankle/foot complex will concurrently flex, adduct and internally rotate when reducing force or acting in an eccentric manner. Therefore, the description of hip flexion, adduction and/or internal rotation as a separate action is merely for simplicity. With a fixed foot, they will all occur together.
In everyday functioning, the GM works eccentrically both with the foot unfixed as well as fixed. As mentioned above, this can be demonstrated during walking or running. As the leg swings forward, the GM assists the biceps femoris in deceleration of hip flexion prior to the foot making contact with the ground. By slowing the forward swing of the femur, the tibia will continue to swing forward, extending the knee and allowing for a proper foot placement on the ground in relation to the body.
Once the foot is in contact with the ground and pronation begins, the GM must then help to decelerate the forward momentum of the trunk (hip flexion) in the sagittal plane, hip adduction in the frontal plane and internal rotation of the femur and tibia in the transverse plane. Thus the GM has a direct influence on the knee and foot/ankle complex as well as the hip.
An example of a sagittal plane dominant eccentric action of the GM includes the deceleration of the lower extremity (pronation) with every step a sprinter or jogger takes. A frontal plane dominant example would include decelerating the lead leg during the lateral shuffling of an offensive lineman down the line of scrimmage or side stepping through a crowd. A transverse plane dominant example would include decelerating the internal rotation of the front leg (hip) of a batter swinging the bat or a person rinsing dishes and turning to put them on the sink to dry.
In a stabilization capacity, the GM assists in dynamically stabilizing the knee via the IT band as well as the sacroiliac joint (SI joint) via the latissimus dorsi and the sacrotuberous ligament.
As previously mentioned, the GM provides frontal and transverse plane control of the knee by decelerating internal rotation and adduction of the femur and tibia. Dynamically, it stabilizes the knee by preventing increased internal rotation during the transition from pronation (eccentric) to supination (concentric).
This is achieved in part by the insertion of the GM into the extensive fascial network of the IT band that allows for increased tension and stability at the hip and knee. Stabilization at the knee as a result of GM activity is also attributed to the synergistic function of its upper fibers with those of the gluteus medius assisting in the deceleration of femoral adduction.
With respect to the SI joint, the GM provides stabilization in concert with its interconnection to the latissimus dorsi and the sacrotuberous ligament.
Again, using the walking cycle to illustrate this action, as the foot strikes the ground and proceeds into the mid-stance phase, the GM increases in activation (tension). This is the transition from pronation (eccentric deceleration) into supination (concentric acceleration), which is the motion necessary to accelerate the leg and propel the body forward. The increase in GM activation coupled with the activation of the contralateral latissimus dorsi from the back swing of the arm (shoulder extension), create an increased tension in the thoracolumbar fascia and sustained tension in the sacrotuberous ligament that act to stabilize the SI joint. This has also been termed the posterior oblique system.
Synergists and Antagonists
The central nervous system (CNS) is designed to produce movement through the selection of muscles in groups. Simply stated, no muscle works alone to produce movement. Thus the main muscle or agonist (prime mover) must rely on help from other assistant muscles. These assistant muscles are termed synergists.
Muscles that are synergists to the GM include the hamstring, erector spinae and adductor magnus predominantly in the sagittal plane, the gluteus medius and minimus predominantly in the frontal plane and the hip external rotators and latissimus dorsi predominantly in the transverse plane.
In order to properly accelerate and decelerate joint motion in all directions, it is necessary to have opposing prime movers or muscles that act opposite of each other. These muscles are termed antagonists. This is much like a giant two-man saw used by lumberjacks to cut down a tree. In order to make the saw move properly, there must be opposing forces (people) working with one another. Person #1 pushes the saw (concentric action) while person #2 must allow the saw to be pushed (eccentric action) in order to move the saw into a position that it can then be pushed back by person #2.
Muscles that are antagonists to the GM include the iliopsoas and rectus femoris predominantly in the sagittal plane and the adductors predominantly in the frontal and transverse planes. Comparing muscles to the lumberjack example, the GM and the iliopsoas are the two people maneuvering the saw and the hip joint is the tree. This concept will become more important when reviewing common causes of disruption in neuromuscular efficiency and how to correct them in the second and third parts of this series.
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