Brain Spill #2: Thoughts on Movement Variability, Pain Science, and Overuse Injury

For the first part of this Brain Spill by Dr. Dave Tilley, click here! Now onto part 2!

For some reason my reading has taken me a lot into the concepts of movement variability, the role of coordinative and elemental variability, and how this all plays into in skill performance.  I’ve always been curious about how athletes like gymnasts learn and perform such highly complex skills. Closely related to this, it’s also incredible to read pain neuroscience and compare that to motor control/ movement variability research. By reading from a few different sources, I’ve been trying to connect the dots on how it relates to pain science, overuse injury, and the the neurological map the brain has over the body guiding learning of a sport specific skill.

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For anyone interested, here are 5 fantastic articles and a few other things I’ve been learning from.

• The Effect of Practice on Coordination 
• Coordinative Variability and Overuse Injury
• Optimal Loading – Key Variables and Mechanisms
• Human Movement Variability, Nonlinear Dynamics, and Pathology: Is There A Connection?
• Movements That Are Both Variable and Optimal
• This great audio lecture by Guido Van Ryssegem on Movement Variability 
• Paul Hodges Spinal Control Book (Scroll Down on Left)
• Schmidt’s Motor Control and Learning Book (Scroll Down on Left)
• Adrian Louw’s MedBridge Courses and Pain Science Text (Scroll Down on left)

Similar to my “brain spill” post on pain science and motor control, these are just a few thoughts floating around in my brain as I work with people. Here goes, again a lot nerdy and a little long (I’m not offended if you revisit this in chunks).

Types of Movement Variability

• “Coordinative” Variability reflects the amount of variance in sequencing parts together. Take for example the variability in sequencing intersegemental coordination of the trunk, hips, knees, ankles, and feet when decelerating for a jump landing. Coordinative variability ideally decreases with practice as the person learns to be more efficient controlling degrees of freedom to perform a discrete task. This makes sense as we use drills, cueing, and environment set up to help foster better sequencing of a movement pattern. With practice of a new skill someone theoretically is able to demonstrate synergy to continuously recognize and use the important performance variables (load the posterior chain, feet about here) that lead to successful movement performance. The process of strengthening the movement synergy is through repetitive synaptic firing of neurons. This repetitive firing creates a better, more efficient pathway through increased myelination/long term potentiation.
• “Elemental” Variability reflects the amount of variance within the global movements, due to the the infinite changing conditions that occur before and during the movement task. It also deals with ability to handle errors and make real time adjustments that occur with movement. Having more elemental variability theoretically allows more movement options to be available to the system for use during real time patterning. This also makes sense as even though globally a movement pattern may look consistent, it is really never the exact same thing happening each time. “Repetition without repetition” is a famous quote by Bernstein. Even the highest level of athletes have a ton of variability in their repetition of skill. It is thought this is what makes them such great athletes. The super talented ones have more strategies to figure out and respond to errors, and can “get the job done” so to speak.
• With movement practice, it is believed by some that coordinative variability decreases (better able to synergies motor patterns for general movement planning) while elemental variability increases (more strategies to generate real time adjustments or handle different conditions while still successfully completing the given task or skill).
• It also has been suggested that there is an optimal amount of variability for skills. Too little variability in their skill, and the person is stuck with an inflexible system that has very limited adaptability. Too much variability (especially coordinative) in their skill and the person may be all over the place unable to narrow in on the important performance components that lead to skill success. This is often referred to as a “noisey” or “chaotic” system.

Movement Variability Linking To Pain Output and Overuse Injuries

• Theoretically, if someone has excessively high coordinative variability and has too little elemental variability, acute tissue overload may occur when a large unexpected error of force is presented that the system can not handle. This could then possibly lead to pain out and sensitization if the nervous system deems it large enough of a threat.
• This may also be true if a lack of elemental variability exists with commonly used movements, the person may only have a hand full of movement strategies to use during repetitions. This could create situations where the same tissue may become constantly loaded or used, again possibly leading to overuse, threat, and potential pain output from the CNS. Thinking from a training point of view, increasing elemental motor variability may be crucial to help reduce potential overuse injury situations. This may be especially true for sports that are placing high force on the body under high volume. A person who lacks of neurological flexibility and has an inability to use different strategies may be at risk for both acute and overuse injuries. Building movement variability in the system and also having global training variability may be a big key here. Not to mention the potential role of cross training, and allowing athlete’s to not always train just their sport specific patterns. This could not only de-load certain areas subject to repetitive strain but also create more variability in the system. Taking it one step further (but a discussion for another time) this is closely related to why there is so much buzz about the risk of early specialization , the role of youth multisport participation, and why so many elite level athlete’s are multisport athletes before specialists.
• (If you’ve stuck around this long, thanks I appreciate your interest.)
• Even though I do think there is connection between optimal movement variability and potential tissue overload triggering threat, even with the athlete we have to remember there is a lot to why pain is being perceived by the individual. I think that the concept of variability related to motor skill does factor into the biomechanical/anatomy department. But as Adrian Louw talks about in his fantastic MedBridge course there is a ton more we have to consider when discussing injuries with athletes. The environment, beliefs, social roles related to a team/performance, fear, and anxiety about injury all can amplify a pain experience and motor learning potential. This can have a very significant impacts on chemical/neurological function, but also the rehabilitation process as a whole.
• One of the biggest ideas that has stuck with me from Louw’s work is how the pain neurosignature map has pre-frontal/cerebellar/parietal cortex involvement (not one “pain center” in the brain). In my mind, I think there may be a huge interaction that persistent pain in the athlete may be having a negative effect on the neural flexibility and the persons ability to regain movement variability in a rehab setting. I’d have to spend a lot more time learning on it, but it seems possible that ongoing pain neurotag ignition can be heavily tied to a lack of regaining movement variability. I think this is even more so the case especially in the athlete that is chronically under stress or high sympathetic drive. Like noted above fear, anxiety, perceived beliefs, and social roles can play a big role into high sympathetic drive that may be a factor we need to address. Lack of variability from a movement, autonomic regulation, and global training perspective all seem to be tied together as markers of a problem.
• As my man Seth Oberst has talked about, the ability to understand variability in the autonomic system is crucial, especially when trying to build an optimal learning environment for motor learning. A great amount of work discusses the role of neuroscience education, stress regulation techniques, breathing, and aerobic exercise (continuing upper light cardio for a patient with ACL reconstruction) for inducing positive neurochemical and psychological changes related to pain. This may be a huge first step in rehab to help maintain motor/sensory maps that will later be needed to rebuild neural flexibility and movement variability.
• This is being explored in ACL reconstruction research. I think the concept of building variability to shift tissue stress, as well as needing to fully restore movement variability in the athlete being rehabbed is key. This is especially true for those looking to return to high level sporting activity. A small quote section from Stergiou and Decker was lighting up this thought train for me when they write,
• “It has been proposed that the loss of proprioceptive input from the mechanoreceptors that exist in the ACL may lead to changes in the CNS which, in turn, leads to the development of altered muscle patterns and postural synergies. This suggests that this kind of injury might be regarded as a neurophysiological dysfunction, not a simple musculoskelatal injury. ACL deficiency can lead to altered somatosensory input which results in decline in the system’s flexibility and narrowed functional responsiveness reflected as rigidity. Therefore, it is possible that the increased behavioral rigidity found in these patients could lead to continuous systematic loading of the same areas on the articulating surfaces of the bones resulting over time in pathological results”
• Maybe the key for injury rehab, prevention, and combatting threat is to find the best way to optimize the motor synergy, but at the same time build variability within the nervous system.  This is so the nervous system will
  1. Resist becoming stagnant, preventing the same tissues being overloaded
  2. Have optimal motor variability to handle error preventing acute overload and
  3. Have optimal somatosensory and motor cortex recovery to build high level skill
• We have to remember pain distorts motor control, and a short term adaptation to deal with threat may become a long term problem in movement mechanics. As Mosely’s new work has proposed, the neurological system may individually reorganize to help deal with acute threat. The system may instinctively reduce it’s variability and lock down degrees of freedom to constrain movement and protect the area under threat. As clinicians, we really have to make sure we re-introduce movement variability when appropriate, safely stress the system/structures being rehabbed, and help the nervous system learn about the huge degrees of freedom arsenal it has.
• I think manual therapy, mobility exercises, or motor control drills might be a way to re-introduce certain areas of the body to potentially be utilized for motor variability during motor patterns. I think these interventions give the opportunity for the CNS to regain awareness of the area, or the potentially use those areas of the body that were protected during the threat response. For example, say someone lacks left hip mobility into closed chain flexion or has FAI related symptoms during a squat. The CNS will likely not attempt to engage that range during the movement due to the lack of motion or the potential threat. It will make an in the moment adjustment to complete the pattern because the “left hip” involvement strategy is not available for use. One possible alternate movement strategy would be to lean slightly more into the right lower extremity chain and recruit that extension motor synergy more during the squat. This shift may increase the amount of stress that will be on the right side of the body during squatting, possibly creating mechanical overload and pain output. So this lack of left hip accessibility is reducing the variability the person has to shift tissue stress over reps.  I can get behind the idea that if we correct the left hip mobility restriction and build the new range into a useful squat pattern, we may be able to foster an environment that increases movement variability. If we give the person a left hip to use with manual therapy or exercise selections, I think we have opened the door for the system to become more variable during squatting reps.
• There is a ton of buzz around dynamic systems theory where there is “control without the controller”. From what I have read it seems very appealing knowing that there is so much variation in movement and that so many real time adjustments have been made. There is a ton of the systems theory and self organization concepts that goes into how we work with any patient, athlete, or client (see the audio lecture above for more). Sometimes it’s better just to set up the environment (safely) and cue the right thing appropriately, then let movement emerge through practice spontaneously. I will admit that I’m still continuing to dive into the dynamic systems theory research, but Todd Hargrove has a great post on it here, and another great post on a systems approach to chronic pain. As a side note it’s amazing the brain can do so much below the level of conscious control.

As I stated last time, I’m not expert an in this field. I’m just trying to wrap my head around what I read and can use to help people improve their movement.  I hope some nerdy people out there thought some of this was interesting, I’m sure there is more of this stuff coming down the road for me. Take care,

via Dr. Dave Tilley, DPT of The Hybrid Perspective!

Interested in live cases where I apply this approach and integrate it with manual therapy and repeated motions? Check it out on The OMPT Channel!

Keeping it Eclectic...