S B Coaches College - Motor Learning Part I




		Motor Learning, Part I *John Pallof, PT, CSCS*

Motor learning is a term that has become increasingly popular in the performance enhancement and rehabilitation fields. Clearly, much of what we do as professionals in these fields focuses on encouraging proper motor learning to improve performance and rehabilitate from injury or surgery. A basic understanding of what motor learning is can aid in effective implementation of sound treatment and conditioning strategies.

Movement

Having a working definition of the term movement is useful when discussing how the process of motor learning takes place. Movement can be defined as the ability to manipulate/control one’s center of gravity within or over a given base of support, in a given sensory environment. An average person’s center of gravity is located just anterior to the spinal segment S2 at rest. Of course, the center of gravity changes with different movements and positions, and conceptually moving in and out of the person’s physical body. The base of support is the athlete’s contact points with a surface – whether upper extremity (an offensive lineman utilizing his hands while blocking a defender) or lower extremity. This surface is what provides the counterforce to the athlete’s force – hence generating movement and/or stability.

Given sensory environment is an important concept to grasp, as it is the one that enables us to apply our trade, as rehabilitation/conditioning professionals. We manipulate the given sensory environment in order to produce the desired results: efficient and powerful movement patterns. The “given sensory environment” is the set of conditions that exist (or are perceived to exist) - in the external and internal environments - that will affect motor execution. It collectively refers to the entire volume of data the brain has available when making decisions about motor planning and execution. There are various processes through which this data travels on its way to the end result of motor execution; we’ll examine these processes later. External data is collected via the external receptors: the eyes, pressure sensors (e.g. on the plantar surface of the foot), Golgi Tendon Organs (GTOs), spindles, and vestibular organs (to name a few). This data provides information on the athlete’s body position in relation to the physical environment, body segment positions in relation to self, and orientation within the environment (am I upright or on my butt?). This can also be affected by the subject’s emotional and psychological status, the so-called sympathetic/parasympathetic nervous system influences. Is the athlete focused, hyped up, or somewhat relaxed? Moreover, in what state do they perform best?

Environmental conditions can also vary considerably. Gravity is a constant environmental condition (but is also one that we can manipulate via height or weight). Surface and visual conditions can be stable or unstable (with stable, controlled conditions being easier situations under which to perform). An unstable visual environment would be one that requires frequent and rapid changes in visual tracking and depth perception or focus; think of a running back picking his way through a crowd of defenders. Contrast that to the very stable visual environment a golfer experiences while swinging a club.

We manipulate the aforementioned variables to shape the stimulus for the athlete/patient to perform sound motor patterns. We modify and alter an athlete’s given sensory environment in order to stimulate the desired physiological adaptations and movement patterns. A therapist mobilizing a spinal facet joint is an example of a change in the given sensory environment; after the adjustment, the body needs to learn to perform movement patterns with increased range of motion. For instance, increased thoracic mobility would certainly affect how a shoulder functions with a throwing athlete suffering impingement-type symptoms. Exercise selection presents numerous variables to manipulate; these variables include speed of movement, direction of movement, gravity’s influence (can be emphasized or de-emphasized by adding resistance, changing the height and direction of a box jump), sensory cues (verbal cuing, utilizing a mirror), joint dominance, and a host of other subtleties. This is the essence of what makes these fields interesting; there are endless combinations of stimuli/variables that can be employed to attain the desired results. One cannot help but wonder if certain combinations more effective than others. It seems so. Why is this?

Peripheral Sensory Reception

As mentioned previously, external sensory receptors are where the body obtains its “raw data.” There are three primary sensory inputs: somatosensory, visual, and vestibular inputs. Collectively, these inputs combine to provide the central nervous system with real time data on what’s taking place in the athlete’s given sensory environment. Generally, with athletic movement, each of these systems is active. However, each unique athlete may rely on these three systems in varying ratios; this varying reliance dictates whether an athlete is so-called visually dominant, or perhaps vestibular dominant. This means that an individual relies on one particular sensory input more than the others when formulating motor patterns. Sensory Organization Tests can determine what particular sensory data an individual relies more heavily upon by measuring (via force plate and computer imagery) changes in postural sway in response to specific, controlled disturbances in visual, somatosensory, and vestibular input. An understanding of these concepts can be important when selecting the stimuli to elicit improved motor execution; perhaps an athlete will learn better with an emphasis on a particular sensory input, or from a challenge that involves purposely de-emphasizing or removing a particular input. It is generally easier to attain a desired result using a specific sensory system in a structured, progressive fashion – think of performing a movement pattern slowly, progressing to more rapid movements.

Somatosensory input is generated within the body, from structures such as GTOs, muscle spindles, cutaneous sensory receptors, and other mechanoreceptors (most any receptor that responds to some form of mechanical stress). These structures give information about muscle length, stretch, rate of length change, pain, temperature, pressure, and joint position. They are present almost everywhere in the musculoskeletal system, including joint capsules, ligaments, muscles, and tendons (among other areas). These receptors provide information for both spinal level motor responses (reflexive actions that occur too fast to have any sort of higher level CNS influence) and for processing higher in the CNS, where the cognitive information and parasympathetic/sympathetic influences are blended with the external sensory information. The central nervous system utilizes this information to develop information on spatial awareness, kinesthesia, and proprioception. Consider the different somatosensory input generated with an isometric hold versus a plyometric exercise; in CNS terms, an isometric hold will “look” significantly different than a plyometric action. Further examination of concentric and eccentric contractions in this context reveals their differences in neurological terms; eccentric muscle contractions will probably generate more tension (more “sensory rich?”), as the musculoskeletal system is resisting both gravity and momentum, versus just resisting gravity. The squat is an excellent example. In the eccentric phase, the body is resisting both the force of gravity pulling the barbell to the ground (or any free weight for that matter – gravity is one thing that is generally constant) and the momentum of the bar traveling downward. In the concentric phase, the body is simply working against gravity pulling the barbell to the ground - and sometimes gravity wins! The musculoskeletal sensory receptors are going to register a difference in tension that may be clinically significant enough to lead to increased motor unit recruitment, which is certainly a powerful tool, especially with rehabilitation.

Visual input is obviously first received in the eyes and their associated nerves. Initially this information is registered in the occipital lobe, and is then utilized in other areas of the brain for higher level processing in motor learning/movement generation. Vision can be divided into two components: central, or focal vision; and peripheral, or ambient vision. Central vision provides information about environmental orientation, verticality, object motion, and identification of hazards or opportunities. Peripheral vision detects motion of self in relation to the environment - including head movements and postural sway – and also acceleration or rate of speed through the environment. Information received from peripheral vision can be cross-referenced with vestibular data to get a concise register of acceleration and change of direction. When attempting to teach a particular exercise or movement pattern, consider the difference in CNS input in utilizing a mirror and not utilizing a mirror, especially if the athlete is a visually dominant learner. Identifying this, and utilizing this information could certainly lead to improved acquisition of motor skills. Something as simple as stabilizing an athlete’s visual field while learning a new task can enhance performance; pick a point and focus on it while executing particular movements. To enhance learning, and increase difficulty, create more unstable, or even absent (eyes closed) conditions. Progressive application of differing stimuli will be discussed in more depth in Part Two.

Vestibular input is received from the vestibular organs, one of the most unique structures in the body. These organs are much like gyroscopes in that they’re fluid filled chambers lined with small cilia, with stones (otoliths) resting on top of them. These cilia are attached to nerves; when the head moves, these cilia bend, either facilitating or inhibiting its individual nerve. From these organs, the CNS determines the position of the head in relation to gravity, and both linear and angular accelerations of the head during movement. Pathological functioning of these organs generates vertigo (also known as “the spins”). A depth jump from a box and a slowly executed eccentric one-legged squat will produce distinctly different movement of the cilia inside of the cochlea, and correspondingly different reflexive responses. An interesting (yet anecdotal) example of vestibular-rich movement can be seen with many children – children love this type of sensory input – jumping up and down on a bed, rapidly rocking back and forth, and swinging. They crave this type of input during a crucial period of their motor development, as it provides their CNS with plenty of data for formulation of motor patterns. Vestibular displacement reflexively generates “anti-gravity” muscle activation in neck, trunk, thigh, and ankle musculature, taking between 45 and 90 milliseconds – below the threshold of voluntary activation. This is an extremely powerful tool when trying to facilitate certain movement patterns to generate stability or movement. This will be discussed in much more detail in Part Two of this article, where I’ll review important concepts such as automatic postural responses, and vestibulo-ocular and vestibulospinal reflexes.

An important feature of these sensory systems is the fact that they are all bilateral. Because they are present on both sides of the body, “cross referencing” between sides can take place to assure the CNS an accurate register of the external sensory environment. Common sense seems to dictate that in order to “program” a motor pattern/ movement, one should progress from movements that do not challenge this system significantly to those with less congruent sensory data. In theory, one must “challenge” the CNS in order to ingrain efficient movement patterns/muscle activation in varied “given sensory environments.” This concept is important when considering injury prevention; after all, many injuries occur as a result of the athlete’s failure to execute a sound motor pattern while in an abnormal sensory environment. You need not look any further than non-contact ACL injuries. This will prove important later when we discuss motor learning.

Proper functioning of these systems is crucial for motor learning. Orientation to the given sensory environment allows efficient “feed forward” and anticipatory motion/actions. Detection of head movements and body sway provides feedback for responsive actions. These systems provide the data essential for efficient, powerful movement.

Sensory Integration and Organization

Sensory integration, the first level of CNS processing, takes the peripheral sensory information and organizes it so that proper motor planning can take place. The athlete’s given sensory environment is registered here and organized into data useful to motor planning. A very important function that takes place with sensory organization is verification of the given sensory environment. This function illustrates the beautiful design of the human nervous system in the way it accomplishes this task. As previously mentioned, the fact that the somatosensory system is organized in a bilateral fashion allows the CNS to compare data from side to side within each given sensory system, allowing a “cross-check” of data, or a perceived sensory environment. This explains why we have two vestibular organs, two eyes, and sensory regions of the brain are organized bilaterally. This feature’s importance is evident in the consideration of an injured athlete, or even an athlete who displays asymmetrical movement patterns. An injured athlete will present with asymmetrical movement patterns due to various unilateral factors, including pain, strength deficits, flexibility/range of motion deficits, and faulty motor patterns (e.g. a limp). Now consider what this does to the sensory data the CNS relies upon for motor planning; sensory conflict now exists. The bilateral data is now asynchronous, and the CNS must first recognize this, and then select what it deems to be accurate inputs upon which to base motor planning. Which situation produces more efficient movement patterns: synchronous or asynchronous data? If an athlete can master particular movement patterns with intentionally asynchronous data, it may ultimately lead to improved motor execution under more “normal,” synchronous conditions. Perhaps the CNS’ ability to process bilateral data can be improved with carefully applied stimuli – manipulation of the given sensory environment through exercise/intervention technique selection. Consider the difference between a barbell slide board split squat and a standard front squat. The split squat presents significant opposing forces from one leg to the other (hip flexion synergy vs. hip extension synergistic movements), placing significantly different demands on the body.

The second means of data verification the CNS utilizes relies upon the fact that it gathers data from three separate systems: the vestibular, somatosensory, and visual systems. It can compare data among these three systems - plus bilaterally within each - to verify a particular sensory environment. For example, the CNS can refer to both the vestibular and visual systems to gauge acceleration and movement though the external environment. This provides the therapist/coach with another means of manipulating the given sensory environment via careful selection of specific training/rehabilitation stimuli.

Central Motor Planning

Central motor planning is an important phase for motor planning, as it is where the interaction between the individual and the chosen task takes place. This is where goal directed movement begins its formation. It isn’t just about the registration of sensory data; the powerful descending influence of higher levels of the CNS is entered into the equation: what is my objective? Do I want to kick a ball, run, jump, or throw? Central motor planning is where the CNS formulates motor plans to accomplish these goals. Ultimately, this is the area we would like to affect with our interventions, in order to facilitate improved motor execution, whether the athlete is training or rehabilitating.

The first step in central motor planning is when the athlete chooses their objective; what is the athletic endeavor they are looking to accomplish? Whether it’s performing a technically perfect clean or shooting a three pointer, there are common steps that take place in this process. First, the athlete chooses their goal. An optimal motor pattern must then be chosen in order to accomplish this. At this point, the athlete will choose from a motor pattern or a combination of motor patterns of which he already has knowledge from previous “memory folders,” or locations within the CNS where this data is stored. If he has no experience in this movement, the athlete will draw from the motor patterns most likely to produce success, based on their chosen goal. Our job is to give the athlete the best possible motor patterns - via our selected interventions - that should carefully manipulate the various facets of the motor learning process in order to ensure that particular individual can best learn. The emphasis is on the unique nature of each individual athlete; each athlete will have particular preferred movement patterns (e.g. hip vs. ankle balance strategies), and preferred sensory mediums (e.g. visual dominant vs. vestibular dominant motor learners). It is our job to evaluate individual differences and manipulate them through our selection of interventions. This is a very important point to remember when we discuss intervention selection a bit later.

After the athlete chooses a motor pattern, it is then delivered to the peripheral motor system, which is located in the cerebellum. Movement is then initiated, as the CNS compares incoming sensory information (from the sources previously discussed) with the intended movements and performance outcome. The CNS then works to detect movement and performance errors – plans for correction are then formed and transmitted. This process of error detection and error correction is the foundation of motor learning!!!! It is how an athlete gets better at what they do. How we affect this will be discussed in Part Two.

Optimal Motor Patterns

An optimal motor pattern has a few key requirements:

1.) Knowledge of self – Athletes must know their own unique abilities and limitations, which can be significantly altered via our chosen interventions. When they become more “athletic”, their limitations will change/decrease while their abilities will improve/increase. An excellent example would be how training improves the athlete’s ability to eccentrically dissipate forces; this will certainly improve their ability to move.

2.) Knowledge of the chosen task – What are the characteristics of successful execution of this particular movement pattern or task? Have I performed this task/movement pattern before? Often, practice does make perfect; in our case, we are trying to get the athlete to “practice” key movement patterns in various sensory environments, with the ultimate goal of improving performance.

3.) Knowledge of the given sensory environment – What risks and opportunities are present? Frame by frame (so called “real time data”) information regarding the instantaneous sensory environment must be present in order to form effective motor plans.

Figure One. Motor Learning – cognitive influences and error detection/correction

Why is this important?

One may ask, “How is this pertinent to what I do?” When considering what takes place when the conditioning specialist/ therapist chooses different interventions, significant attention should be given to how the prescribed technique/exercise will affect motor learning processes. This may be where one technique/philosophy is more effective than another; can the athlete learn optimal motor patterns, and how quickly? Depending on the athlete, varying approaches can be taken to ensure orderly, effective motor learning, in a systematic fashion. Taking advantage of how a particular athlete prefers to move and learn new motor skills can speed improvement and allow the athlete/patient to acquire new skills. When first trying to teach a motor pattern, the athlete should ideally be given a “sensory-rich” environment. What really fires up the nervous system? Adequate visual feedback/cues, significant somatosensory input (e.g. slow eccentric phases of movement), movement through space to stimulate the vestibular system (consider the vestibular activity of a squat vs. a plyometric movement), and concise verbal cuing all aid motor learning. As the athlete acquires skill, the sensory environment should be manipulated to further refine these patterns – emphasizing and de-emphasizing various sensory modalities. In theory, if the athlete can perform the motor pattern optimally in a sensory-manipulated environment, their skill level should be that much better in their “normal” sensory environment.

A look ahead to Part Two

So what does all this mean? Where does the science meet practice? A helpful model is the World Health Organization (WHO) model of disability and impairment. Basically, impairment is the physical disability, while the disability is the inability to perform a task. Hmmm…very applicable to training. Consider this:

1. Impairment is the lack of specific physical qualities that we look to affect. This would include normal range of motion/flexibility, normalized muscular/fascial tone, strength, joint mobility, form/force closures (e.g. the ability to combine explosive hip extension with a stable lumbo-pelvic region), emotional/affective influences, and energy systems. A convenient term for these qualities is physiological substrates – physiological qualities that enable us to execute efficient motor patterns. It does not, however, include the motor patterns themselves…

2. Disability is the inability to execute particular motor patterns with exceptional efficiency and power. Think about an injured athlete, or the untrained athlete.

So, we should keep these two categories in mind when designing programs for training and rehabilitation; programs should address both areas, not just one. In Part Two, we’ll discuss motor planning considerations with respect to selecting various exercises or interventions, and how the different sensory systems affect motor learning.

John Pallof, PT, C.S.C.S. is a physical therapist in Worcester, Massachusetts. He specializes in rehabilitating and training athletes of all levels and sports.