Synchronous Systems Development Model Excerpt

Structures, Functions, Actions, and Patterns 

The human body is comprised of bones, organs, connective tissue, fat, muscle, and nerve tissue. This is a reductionist summary with the point being that the vessel of the body is made of liquid, solid, elastic, and gaseous materials which compress, expand, and move around each other. The intention of this section is not to repeat what many kinesiology and biomechanics books have already done. That is to say that this will not be a complete referent of joints, attachments, standard ranges of motion, or a physics compendium. Rather, this section will provide greater commentary on how movement occurs in the system of the body, different ways to conceptualize assessing and prescribing movement in a training environment, and how exercises can be categorized and chosen based on the desired body structure, muscle, or joint function or action, or the movement pattern one desires to train. 

Discovering better answers begins with asking better questions. By first categorizing the needs of the athlete, the demands of the task or skill they desire to improve, and selecting exercises or drills that will address those needs and meet the demands of the task in incrementally challenging ways, substantial performance improvements can be garnered. Having the wisdom to use varying methods of exercise selection and prescription in different contexts takes time however with an eclectic tool kit and practice a whole world of problem-solving is available to the coach that would otherwise be off-limits to those chained to one model or approach.


While the body is composed of many “structures”, the structural elements this section will be referring to specifically will be the skeletal system in the form of joints and their associated ranges of motion. The muscular system and its actions of shortening and lengthening tissues around joints, and the muscular system’s function in yielding and overcoming forces to create stability in patterns of movement. Shape change occurs for the athlete as a byproduct of the interaction between the internal environment and external environment and the structures of the body permit or inhibits this shape change. Before getting too far into more complex ideas about shape change it is important to define some common terms related to movement and anatomy. 

Range of motion 

Any standard kinesiology or biomechanics textbook will list standard joint ranges of motion and muscular attachment points. Range of motion can be measured via passive table tests and may tell the practitioner useful information, for example, if an athlete has full access to the bony ranges of their hip in a passive setting without pain. What these table tests won’t tell the practitioner is what ranges of motion the athlete has control over in an active setting or throughout different joint angles under stress or situations which demand particular quantities of force, speed, or coordination to be produced. Nonetheless, table tests can be a useful way to assess what movements may be more or less suited to an athlete and if the athlete has any history of pain, restriction, or injury may serve as a clearance assessment about if it is wise to continue to train or refer out to a clinician. 

Aside from the measurable joint range of motion, other manifestations of ROM are observable. Passive stretching may immediately yield improvements in range of motion if only temporarily and an athlete may be able to passively stretch into a position or movement but not have the muscular control or strength to access it through muscular efforts alone. This presents three situations for the expression of the range of motion which will be referred to and defined as follows:

  • Joint ROM 
      • The skeletal and capsular range of motion available to an individual. 
  • Flexibility
      • The muscular and tendinous tissue’s ability to be passively moved into a position provided the underlying joint ROM is available.
  • Mobility
      • The muscular ability to control the body through ranges of joint  motion and varying positions.
  • Active vs. Passive Deficit
      • Garnering access to as much of a joint ROM as possible is, in many cases, desirable for performance. Assessing an athlete’s passive joint ROM and flexibility will yield information about positions they may be able to access but training through those positions to ensure access at will through strength is the ultimate display of mobility. 
      • Some athletes will show varying degrees of ROM or asymmetry that are considered positive or necessary adaptations to their sport. For example, baseball pitchers will often display altered shoulder internal and external rotation on their pitching arm. An attempt to “correct” this or create symmetry in these athletes may cause detrimental adaptations to their sporting performance. Symmetry in this context shouldn’t’ be an end goal so much as ensuring as much pain-free and powerful physical capacity as possible through training interventions regardless of minor asymmetries. 
  • Internal Rotation
      • Also referred to as medial rotation, where a joint or limb rotates towards the midline. When referring to the wrists and ankles rotating inwards is referred to as pronation. (overhand grip)
  • External Rotation
      • Also referred to as lateral rotation, where a joint or limb rotates away from the midline. When referring to the wrists and ankles rotations outwards are referred to as supination (palm up in anatomical position, underhand grip) 
  • Abduction
      • Movement away from the midline of the body.
    • Adduction
      • Movement towards the midline of the body
  • Extension
      • Straightening movement that increases the joint angle of a body part. Straightening the knees for example. When referencing the head, neck, and spine extension refers to moving posteriorly. 
  • Flexion
    • Bending or closing the angle of a joint. When referencing the head, neck, and spine flexion refers to moving anteriorly or laterally as in forward folding or side bending. 

Muscle Function vs Action

In order to produce or resist movement, the muscles around a joint generate tension at varying muscular lengths. When determining exercise selection, considering the difference between the function vs the action of a muscle can assist in making quality choices. The actions of the latissimus dorsi are adduction, medial rotation, and extension of the glenohumeral (shoulder) joint. The function of the latissimus dorsi is to stabilize the trunk rotationally as it connects to the lumbar spine through the thoracolumbar fascia, iliac crest, lowermost ribs (9-12), and the spinous princesses of T7-T12. The function vs the action of any muscle can be considered when determining what type of training outcome is desired. When looking to train localized strength or hypertrophy, focusing on movements that address the various actions of a muscle is likely the optimal choice. When looking to integrate a muscle into a larger movement for the generation of stability training the function of a muscle is likely the superior route.

The Strange Loop of Movement and Bill Hartman’s Propulsion Model

In A Coach’s Guide to Optimizing Movement Dr. Pat Davidson discusses how natural systems represent repeating patterns of a fractal nature. Much like Fibonacci numbers dictate the spiral of a sunflower, nautilus shell, or fern frond so the body’s systems repeat patterns from the smallest cell to the larger manifestations of structures and movement. In his book I am Strange Loop Douglas Hoffstadter said “The Strange Loop phenomenon occurs whenever, by moving upwards (or downwards) through levels of some hierarchical system, we unexpectedly find ourselves right back where we started.” In his book, Pat Davidson brilliantly notes that the body is built from helical structures from the smallest level of the DNA double helix to the largest levels of movement through spiraling actions where compression and coiling occur in one direction and expansion and uncoiling occurs in a complementary fashion.

Bodies get through space by creating a propulsive force. Propulsion, according to Websters, can be defined as “the action of propelling, to drive forward utilizing a force that produces motion.” By fluxing through shape change, compression, expansion, overcoming, yielding, etc bodies create a cycle of propulsion. The gait cycle can be found in many anatomy textbooks however Bill Hartman has conceived of a unique propulsion arc that appears as follows:

In Hartman’s propulsion model, at the beginning of a squat, the hip passes from external rotation in Zone 1 on an inhaled pelvis, it momentarily internally rotates on an exhaled pelvis through the Zone 2 midway point of 60-120 degrees of hip flexion before passing back through Zone 3 in an externally rotated hip position again from 120-180 degrees of hip flexion on an inhaled pelvis. Just like in Hoffstadter’s strange loop, the body’s orientations find themselves right back where they started. Individual bodies will manifest slightly different versions of the arc and the exact moments may change, but this model can be used when assessing movement and assigning exercises for individuals with ease. Furthermore, the propulsion arc doesn’t apply purely to the hips, it can be interpreted through the shoulders in a similar fashion and through a broad range of movements around the pelvis and ribcage. 

In the above model, the terms yielding and overcoming actions are referenced. It is not difficult to imagine yielding and overcoming actions occurring in real movements. After all, when landing in a jump tissues yield to the forces of the landing action only to be reversed into an overcoming action against the force of gravity to generate another jump. Furthermore, in the above model, the idea of concentric or eccentric orientations can be ascertained. Muscles in a lengthened position in a given movement are said to be utilizing an eccentric orientation and those which are in a shortened position to be using a concentric orientation. While a muscle can produce yielding or overcoming action from either orientation muscular range of motion will be affected. For example, an individual could execute an overcoming isometric bench press from the bottom position where the pecs and triceps are lengthened and eccentrically oriented but by driving the bar against a fixed surface the muscles are producing an overcoming force against an immovable object. However, to complete a full bench press rep the pecs and triceps must move from a concentric orientation around the shoulder to an eccentric orientation. Being unable to create the full expression of either orientation in a region may present issues. Imagine now that an athlete presents with a chronically eccentrically oriented pelvic floor, this individual is going to have a hard time moving through an optimal squat pattern unless their pelvic floor can fully concentrically orient as well. 


Respiration breathes life into movement. By connecting the pelvic and ribcage structures through movement, and by providing the gas exchange that keeps the body alive, respiration serves a tremendous function in the body. In the propulsion arc, inhaled and exhaled pelvic positions are referred to. In respiratory mechanics, the pelvis opens at the top to receive the downward pressure of inhalation through the counternutation of the sacrum. Conversely, during exhalation, the sacrum will nutate creating upwards pressure to assist in exhalation. In the image below, the motion of sacral nutation is displayed in red and the motion of sacral counternutation is in blue. The two innominate bones of the pelvis, the wing-like structures, move in a complementary fashion to the sacrum. During inhalation, counternutation of the sacrum occurs and an externally rotated “inhaled” pelvis shape change occurs, during exhalation an internally rotated “exhaled” pelvis shape occurs. These motions are illustrated below with inhalation and counternutation in blue and exhalation and nutation in red. When the pelvis is inhaled, the sacrum is in counternutation, and the innominate bones are externally rotated. This allows for retroversion of the hip. In layman’s terms, more external rotation of the hip joint becomes available to the athlete as the pelvic bones open up more space externally to the hip when they are internally rotated. Likewise, on an exhaled pelvis the innominate bones internally rotate creating retroversion of the hip and permitting a greater excursion of internal rotation availability. When assessing clients the practitioner will likely notice that some individuals tend to bias towards some compensation strategies more than others in particular movements. Training should be designed to help athletes move through shape change and exercises can be assigned to address the individual’s biases in a nuanced fashion. This concept will be elaborated on further on in the book.

  • Inhalation
    • Counter Nutation of Sacrum
    • External Rotation of Innominate Pelvic Bones
    • Descended Pelvic Floor
    • Retroverted hip 
  • Exhalation
    • Nutated Sacrum
    • Internal Rotation of Innominate Pelvic Bones
    • Ascended Pelvic Floor
    • Anteverted hip

These concepts can feel tremendously difficult and frustrating at first, but with time spent dissecting movement and considering skeletal motion, the practitioner will begin to knit the pieces together. For further information, it is recommended that those interested seek out Bill Hartman’s website and youtube where he elaborates on these concepts in-depth as well as information from Pat Davidson, the Postural Restoration Institute, Connor Harris, and Katie St Claire. 

Ribcage and Infrasternal Angle

Now that the concepts of respiration at the pelvis and the relationship to the propulsion arc have been introduced it is time to cover respiration and shape change at the ribcage. When inhalation occurs, the diaphragm descends to draw air into the lungs. This descending motion creates gas and fluid pressure which presses down into the organ cavity and is received by an inhaled pelvis and descended pelvic floor shape. On exhalation, the pelvic floor ascends, the sacrum nutates, the innominate bones internally rotate, and the diaphragm ascends up into the ribcage pressing the air out of the lungs. Much like the pelvis changes shape so does the ribcage. The ribcage manifests pump handle and bucket handle style motion. The pump handle motion of the uppermost ribs creates a rocking pump motion (left picture). The bucket handle ribs create lateral – side to side – expansion where the lowermost ribs rock upwards like a handle rotates up and down on the side of a bucket (right picture)

Upon inhalation, the pump and bucket handles will move upwards allowing for expansion. Upon exhalation, the pump and bucket handles will move downwards creating compression. Much like individuals can be biased towards a particularly inhaled or exhaled pelvic shape so they can be biased towards a wide or narrow ribcage shape. Likewise, much like pelvic shape affects hip motion, so ribcage shape affects shoulder motion. In many ways, the pelvic innominate bones and hip joint are analogous structures to the scapula and shoulder joint. In this context, rather than referring to inhaled or exhaled ribcage shape, the practitioner can assess infrasternal angle or ISA. In layman’s terms, the practitioner can “type” athletes based upon how wide or narrow the resting angle of the ribs under the sternum bone is. A wide infrasternal angle position is characterized by expansion of the bucket handle lower ribs. Because these individuals are exhalation biased at their axial skeleton, they struggle to expand their ribcage. In order to overcome this bias towards skeletal exhalatoon, they utilize a compensation strategy wherein they flare the lowermost anterior ribs to attempt to source inhalation and expansion.

  • Wide ISA Characterizations
    • Flared infrasternal angle
    • Exhaled bias axial skeleton – “stuck” in exhalation
    • Appear squeezed front to back (wider from the front, narrower from the side)
    • Internally Rotated Ribcage 
    • Exhale biased pelvis
      • Nutated Sacrum
      • Internal Rotation of Innominate Pelvic Bones
      • Ascended Pelvic Floor
      • Anteverted hip
      • Pronated foot

The narrow ISA presentation is characterized with a bias towards inhalation of the axial skeleton and external rotation of the ribcage. Because they struggle to fully drive air out of the ribcage, they compensate through the mobile bucket handle ribs through excessive compression leading to the presentation of the narrow infrasternal and compressed lower ribcage. These individuals are globally biased towards external rotation skeletally and thus external rotation. Narrow ISA individuals are characterized as follows:

  • Narrow ISA characerizations
    • Compressed infrasternal angle
    • Inhalation biased skeleton – “stuck” in inhalation
    • Appear narrower, squeezed side to side
    • Externally rotated ribcage
    • Inhalation biased pelvis
      • Counternutated sacrum
      • External rotation of innominate pelvic bones
      • Descended pelcic floor
      • Supinated foot 

Being able to move in and out of expansion and compression is a fundamental need and being able to do this shape-changing optimally is the goal. However, because bodies are variable athletes often tend to swing towards one strategy more than another. Wide ISA folks often struggle to expand elsewhere and thus attempt to drive expansion throughout the malleable lower ribs whereas narrow ISA folks often struggle to compress elsewhere and will thus attempt to drive compression through the malleable lower ribs. Training individuals who compensate through the ribcage how to compress or expand elsewhere can be tremendously helpful at assisting these athletes to execute the needed shape changes for other movements. 

Addressing Compensation Layers

A critical point of the compression expansion and infrasteral angle model is to understand that the widening and narrowing of the infrasternal angle are first order compensations that fight the initial bias of the skeleton. For example if an individual is internal rotated and biased towards exhalation their skeleton will compensate for this compressed skeleton shape by creating extra flare and expansion at the mobile lower ribs. Second order compensations spring from this initial respiration and skeletal compensation. Due to the internal rotation bias and exhalation bias the larger muscles of the wise ISA individual will also trend towards certain strategies. Addressing second order compensations in movement prep and primary compensations with training is paramount to opening up options for these athletes. The next chapter will address more programming in depth but the following compensation flow charts can be used as a “cheat sheet” for understanding compensation patterns and exercise prescription.

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