It is important to view anatomy from a functional, integrated perspective. The health and fitness professional armed with a thorough understanding of functional anatomy will be better equipped to select exercises and design programs.
To produce movement the central nervous system (CNS) optimizes the selection of prime movers and muscle synergies. The CNS does not simply select an individual muscle to produce movement. The CNS coordinates deceleration, stabilization, and acceleration at every joint in the HMS in all three planes of motion. Muscles must also react proprioceptively to gravity, momentum, ground reaction forces, and forces created by other functioning muscles. Depending on the load, the direction of resistance, body position, and the movement being performed, muscles will participate as an agonist, antagonist, synergist, or stabiliser. Although they may have different characteristics, all muscles work together to produce efficient movement.
• Agonists are muscles that act as prime movers.
• Antagonists are muscles that act in direct opposition to prime movers.
• Synergists are muscles that assist prime movers during functional movement patterns.
• Stabiliser muscles support or stabilise the body while the prime movers and the synergists perform the movement patterns.
Muscles function synergistically in force-couples to produce force, reduce force, and dynamically stabilise the entire HMS; they function in integrated groups to provide control during functional movements. Understanding this allows one to view muscles functioning in all planes of motion throughout the full spectrum of muscle action (eccentric, concentric, isometric).
Current Concepts in Functional Anatomy
It has been proposed that there are two distinct, yet interdependent, muscular systems that enable our bodies to maintain proper stabilisation and ensure efficient distribution of forces for the production of movement. Muscles that are located more centrally to the spine provide support from vertebra to vertebra, whereas the more lateral muscles support the spine as a whole. Bergmark categorised these different systems in relation to the trunk into local and global muscular systems.
The Local Muscular System (Stabilisation System)
The local musculature system consists of muscles that are predominantly involved in joint support or stabilisation. It is important to understand that joint support systems are not confined to the spine and are evident in peripheral joints as well. Joint support systems consist of muscles that are not movement specific, rather they provide stability to allow movement of a joint. They are usually located in close proximity to the joint with a broad spectrum of attachments to the joint’s passive elements that make them ideal for increasing joint stiffness and stability. A common example of a peripheral joint support system is the rotator cuff that provides dynamic stabilization for the humeral head in relation to the glenoid fossa.
The joint support system of the core or LPHC includes muscles that either originate or insert (or both) into the lumbar spine. The major muscles include the transverse abdominis, multifidus, internal oblique, diaphragm and the muscles of the pelvic floor.
The Global Muscular Systems (Movement Systems)
The global muscular systems are responsible predominantly for movement and consist of more superficial musculature that originate from the pelvis to the rib cage, the lower extremities, or both. Examples include the rectus abdominis, external obliques, erector spinae, hamstring complex, gluteus maximus, latissimus dorsi, adductors, quadriceps, and gastrocnemius.
The movement system muscles are predominantly large muscles that are associated with movements of the trunk and limbs. These muscles are also important in transferring and absorbing forces from the upper and lower extremities to the pelvis.
The movement system muscles have been broken down and described as force-couples working in four distinct subsystems as follows:
The major soft tissue contributors to the deep longitudinal subsystem are the erector spinae, thoracolumbar fascia, sacrotuberous ligament biceps femoris, and peroneus longus. The DLS provides a longitudinal means of reciprocal force transmission from the trunk to the ground. The long head of the biceps femoris attaches in part to the sacrotuberous ligament at the ischium. The sacrotuberous ligament in turn attaches from the ischium to the sacrum. The erector spinae attach from the sacrum and ilium up the ribs to the cervical spine. Thus, activation of the biceps femoris increases tension in the sacrotuberous ligament, which in turn transmits force across the sacrum, stabilising the sacroiliac joint, then up the trunk through the erector spinae.
This transference of force is apparent during normal gait. Before heel strike, the biceps femoris activates to eccentrically decelerate hip flexion and knee extension. Just after heel strike, the biceps femoris is further loaded through the lower leg via posterior movement of the fibula. This tension from the lower leg, up through the biceps femoris, into the sacrotuberous ligament, and up the erector spinae creates a force that assists in stabilising the sacroiliac joint (SIJ).
Another force-couple in this subsystem consists of the superficial erector spinae, the psoas, and the intrinsic core stabilisers (transverses abdominus, multifidus). Although the erector spinae and psoas create lumbar extension and an anterior shear force at L4 through S1, during functional movements the local muscular system provides inter-segmental stabilisation and a posterior shear force. Dysfunction in any of these structures can lead to SIJ instability and low-back pain (LBP).
The posterior oblique subsystem works synergistically with the DLS. Both the gluteus maximus and latissimus dorsi have attachments to the thoracolumbar fascia, which connects to the sacrum, whose fibers run perpendicular to the SIJ. Thus, when the contralateral gluteus maximus and latissimus dorsi contract, a stabilising force is transmitted across the SIJ. Just before heel strike, the latissimus dorsi and the contralateral gluteus maximus are eccentrically loaded. At heel strike, each muscle accelerates its respective limb (through its concentric action) and creates tension across the thoracolumbar fascia. This tension also assists in stabilising the SIJ. Thus, when an individual walks or runs, the POS transfers forces that are summated from the muscle’s transverse plane orientation to propulsion in the sagittal plane.
The POS is also important for rotational activities such as swinging a golf club or throwing a ball. Dysfunction of any structure in the POS can lead to SIJ instability and LBP. The weakening of the gluteus maximus, the latissimus dorsi, or both can lead to increased tension in the hamstring complex. This is a factor in recurrent hamstring strains. If performed in isolation, squats for the gluteus maximus and pulldowns/pull-ups for the latissimus dorsi will not adequately prepare the POS to perform optimally during functional activities.
The anterior oblique subsystem is similar to the POS in that it also functions in a transverse plane orientation, mostly in the anterior portion of the body. The prime contributors are the internal and external oblique muscles, the adductor complex, and hip external rotators.
AOS muscles aid in pelvic stability and rotation as well as contributing to leg swing. The AOS is also a factor in the stabilisation of the SIJ. When we walk, our pelvis rotates in the transverse plane to create a swinging motion for the legs. The POS (posteriorly) and the AOS (anteriorly) contribute to this rotation. Knowing the fiber arrangements of the muscles involved (latissimus dorsi, gluteus maximus, internal and external obliques, adductors, and hip rotators) emphasises this point.
The AOS is also necessary for functional activities involving the trunk and upper and lower extremities. The obliques, working with the adductor complex, not only produce rotational and flexion movements, but are also instrumental in stabilising the lumbo-pelvic-hip complex.
The lateral subsystem is composed of the gluteus medius, tensor fascia latae, adductor complex, and the quadratus lumborum, all of which participate in frontal plane and pelvo-femoral stability.
The ipsilateral gluteus medius, tensor fascia latae, and adductors combine with the contralateral quadratus lumborum to control the pelvis and femur in the frontal plane during single leg functional movements such as in gait, lunges, or stair climbing.
Dysfunction in the LS is evident during increased subtalar joint pronation in conjunction with increased tibial and femoral adduction and internal rotation during functional activities.
Unwanted frontal plane movement is characterized by decreased strength and decreased neuromuscular control in the LS.
The descriptions of these four systems have been simplified, but it is important to understand that the human body simultaneously coordinates these subsystems during activity. Each system individually and collectively contributes to the production of efficient movement by accelerating, decelerating, and dynamically stabilizing the HMS during motion.