Movement Variability — Connecting Strategies, Errors, and Interventions - SimpliFaster
- Updated on: 2024-03-22
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While the word “functional” may no longer be quite as popular, the term “movement variability” might be the new buzzword replacement for coaches. It seems I hear it in conversation every day, but I have yet to see someone really nail down the concept in practice, both scientifically and practically. When I ask a few benign questions, it seems that those that promote movement variability as the magic bullet to coaching don’t have a solid answer as to the real definition and have no exact sense of what to do with the information we do have. While movement variability is important, the extent that we need to actually focus on it is a different story.
The primary buzz over movement variability comes from motor learning or skill acquisition fans: “Movement” is all the rage and “variability” creates just the right amount of flavor while still being vague enough to stay unaccountable. Like circuits having very little “regulation” in program design, “movement variability” is the catchphrase when true solutions for developing an athlete are not available, and it’s easy to drop it when the challenge is high.
If you have heard of movement variability and want to know why it’s so important, don’t worry—I will go over that later. For now, the most important part of this article is knowing when to slow down and be cautious about information that is trendy. When a concept is overly promoted, don’t blame the subject matter or even those who promote its value. We should embrace education and progress to learn more information about training, but bringing up a concept without knowing how to use it waters down its value while creating too much overreaction from younger coaches. After a topic becomes overplayed, the next buzzword comes and the entire rise and fall starts again with another term. It’s time to break the cycle.
While this article is about movement variability in sport, nearly any buzzword or concept can be inserted as a lesson for all of us. As professionals, we can’t get too excited or too skeptical to the point that open discussions become like political debates heard at Thanksgiving between family members. To prevent the watering down of concepts that are important, including movement variability, we should all take a step back and evaluate how we can better use the information we have.
Obviously, the most important starting point is properly defining a term, but I knew it was more important to use movement variability as an example lesson first. Defining movement variability isn’t hard, but if it’s done by rehashing a textbook, it may lose the important connection to sport coaching because it may seem like a biomechanical term or rehabilitation concept.
Movement variability is the normal variation that occurs in motor performance across multiple repetitions of a task.
This definition from Stergiou and Decker is commonly accepted, and I like it because it uses the word “normal.” Yes, variation in movement with a task is typical with humans, and athletes, while special, share that commonality with regard to movement variability. Movement variability is perfectly normal, and may be part of health. For example, take another topic like heart rate variability, a monitoring metric originating from health and wellness. The changes in between beats in a beat-to-beat time period are a measure of health, but tasks such as sprinting and jumping are a little more complex and difficult to decipher.
The reason movement variability is complex is simple: There are interactions between so many variables internally with the body and externally with the environment. The prime reason I am cautious in artificially strumming up more complexity for athletes is simply that activities are challenges. How many people have tripped over very minimal interference or practically nothing?
It’s easy to go into a deep dive with movement variability and regurgitate some very fascinating components of the literature, but applying that information requires a far different grasp of the subject. Movement variability must be understood and evaluated for its potential use in training and teaching—the core of coaching in sport.
Most of the focus of this article will not be on origin history or new developments in motor learning. As coaches, most of you have enough on your plate, so I will cut to the core of what will likely be the bulk of the need for those working with age groups from 12-22, the years that move away from youth games and physical education foundations to competitive sport. The end of middle school and the beginning of high school are the years that seem to drastically shift from movement education to movement competition, thus causing an array of problems. Not only do coaches need to teach skills and tactics, but also prepare young athletes physically for the rigors of sports so they stay healthy and perform better.
The evaluation of a movement strategy depends highly on what success looks like with a task, and this is the heart of the difference between variability and error. If an athlete sets a world record in the high jump with a strange new style, like Dick Fosbury, that’s a variation of technique, not movement variability. An error is a combination of conscious and unconscious factors that usually create a subpar result, and clear consequences in a movement pattern. Usually, errors are less efficient and less effective, while movement variability maintains enough of the essential needs of the task to perform at the same or higher level.
The most common challenge with coaching is seeing the acceptable and subtle differences in movement variability and knowing when an athlete is struggling with errors. Determining when to speak up and when to shut up is hard, as athletes’ intentions are not easily seen in full speed, and sometimes coaching bias and ego ruin natural development. The lure to be part of a process sometimes interrupts the natural and more effective route to learning. Therefore, the art is to identify less-effective movement strategies and the inability to perform either with the naked eye or during video sessions.
Errors or faults are a combination of intent, environment, task, and ability. Progressions and regressions are loved because they are exercise-driven, but corrections also need to take into account how the central nervous system (CNS) works and how it can be used better. Sport science, specifically biomechanics, addressed movement variability long ago because data analysis must take movement variability into consideration. In addition to biomechanical evaluation, monitoring movement variabilityis another difficult task, especially with the limitations of EMG and IMU systems.
It is an emerging challenge to know for sure what is truly variability that matters and what is just noise—not just because you think you “see” something in practice or in competition. Don’t be afraid to say that you don’t know if an error is happening or the aberration is just part of movement variability during practice. Positive outcomes and consistency in reaching the task’s goal successfully, in various reasonable environments, are enough to demonstrate progress. Making tasks unrealistically complex or foreign is just self-sabotage, so learn that just enough change can work wonders. Don’t create motor skill obstacle courses that are just busy work for PE youth programs, and inappropriate for sports performance.
Create checklists for the learning session, and include basic exposure to mastering a very finite need for elite performance. Practice doesn’t make perfect or permanent—it simply provides a dress rehearsal for athletes. When I was a rookie high school coach, my ego was shattered after several All-Americans in swimming changed their strokes in college. The changes were barely perceptible, but they occurred because the swimmers were not overcoached. What was clear was that the better coaches knew how to get the most out of an athlete versus putting the best of themselves into their technique. Again, this is more evidence that athlete-centric models are better than leadership or coaching hierarchies.
Looking at the work of Piasenta, the French master of athletic development, cyclograms with stride analysis are now the new normal. In fact, Nikolai Bernstein is credited for being the father of biomechanics and the driver of movement variability because his amazing cyclographic techniques resonated with coaches. Most of what Bernstein shared decades ago still rings true today, and coaches can use his translated work as a guide in how they perceive motor learning and expression of movement.
The core issue outside of error detection, fatigue management, and return to play is increasing the environment and task connection so athletes can learn better. Clearly, performance is beyond this one section, specifically teaching and training, but movement variability is not just adding different exercises or playing with surfaces—it’s knowing when to progress an athlete and when to come back and refine techniques.
I wish I had spent more time on central pattern generators in my core training article, but Frans Bosch brought up the topic in his book on resistance training. To me, Frans’ concepts stand far above his tactical solutions. His motor learning and advanced anatomy knowledge is very provocative, but to actually solve development methods, conventional training has proven to work more than his exercise selection. I do think we need the same line of thought as Frans advocates, such as challenges that don’t purely replicate competition: grass hills; other forms of locomotion, like skipping for distance; and even weight training modifications that are not as static.
Too much tinkering with training and adding variation to the process are not directly related to movement variability. Movement variability is a response of the nervous system, not about purposely training elements to teach new movement strategies or refine existing ones. I think Frans spent too much time trying to recreate and expand the demands on the nervous system instead of looking at the constraints and determining the amount of environmental challenge necessary to keep the body learning. With too much demand on the system, movement variability ceases because it’s in a protected learning environment. Like overloading the body with weight, environment can be one of those factors that reduces movement variability because the nervous system is threatened.
Movement variability in athletic development is similar to nature conservation—if you leave it alone, things tend to take care of themselves. The extension of the analogy is also true: The right intervention may help accelerate growth if done properly.
Without distilling the process too much, coaches will want to replicate the physical education model of exposing athletes to the right tasks in the right environment, in addition to ensuring they have the physical capacity to do so. Motor learning should never be viewed separately from conditioning, even though it can be done sometimes in a near vacuum if needed. Coaches tend to separate biomotor abilities instead of seeing how each element interacts or when they are impaired.
Movement variability increases and decreases under fatigue. Why and when varies between athlete and task, because variability is often consciously overridden when an athlete is aware they are tired based on either perceptual feedback or objective clues from the activity, such as time and distance. Two of the theories with injury from overload are that, if movement variability exceeds the normal boundaries, the body isn’t prepared for it, or if it the movement pattern is too monotonous, the soft and hard tissues are at risk of degeneration. Knowing that fatigue can create two distinct patterns of motion, either being more variable or ceasing fluctuation, coaches have a responsibility to know what to look for and have some working idea of what is acceptable.
Movement variability transitioning from small natural changes to larger pathological risk is likely when the actual overall load is too high. Spotting this requires a keen eye, as well as secondary ways to measure such changes. If the coach’s eye was perfect, nobody would get hurt at any level during training or competition. For example, look at jumping and the stretch shortening cycle research, specifically under fatigue. Athletes who decrease their compliance and become rigid are likely at a point where they need to stop and rest rather than increase risk. Targeting narrow risk might be possible in the future, as specific joints and loading patterns have unique patterns of decay and deterioration of movement variability.
Fatigue sometimes forces athletes to rely too much on technique to be efficient, thus posing potential risk to the body. Athletes may go to movement strategies they simply can’t use effectively or require muscles not accustomed to compensating, causing overload from unprepared exposure. Currently, all of the monitoring of fatigue and movement variability research is very early and inconclusive, as simple gait analysis and cutting tasks for the ACL are grossly incomplete, but promising. I do think the art is knowing when to anticipate fatigue and communicate what the coach perceives and what the athlete believes. Data always keeps both parties honest, of course, but it will take more time to make sure the small subtle patterns barely seen by the naked eye (if at all) are a part of coaching practice versus coaching belief.
Disease models and reconstructive surgery research lead the charge with movement variability research. We know that rehabilitation (return to play) is not the same as disease management (fighting decline in performance), but both offer similar learning opportunities. In sports medicine, most of the need is reloading carefully to allow for biomaterial healing. Even after going through a great rehabilitation program, the research hints that an injured athlete’s “scars” are still there in the nervous system, specifically the CNS. Many athletes don’t come back from major injuries, but we tend to see more of the success stories than the athletes that don’t return.
Coupled with emotional or psychological factors, movement variability during rehab is tricky. While change is expected, the complications of primary and secondary injuries make it a hard juggle for therapists to determine what is typical and what is a potential problem that could lead to re-injury. Progress in sensor technology, along with clinical research trials, revealed this important point: Without knowing the compensation strategy of athletes, some athletes are progressed too fast. Conversely, athletes often struggle with motor tasks because the wrong mindset is managed, and the rehab fails because either the athlete is overconfident or not confident enough in their abilities during training.
Even the term “load” gets tossed around too freely, since just training progressively is loading and rest—something any athlete can do with little guidance. If I was to develop a practical “ratio” for therapy, it would be the success and failure ratio, to determine how much of an overload challenge exists in a program, whether coordination or resistance. Athletes are sometimes exposed to such mild volumes and intensities to be “pain free” or “confident” that when the real competition comes, they look ill-prepared.
Movement variability restoration may be a sign of readiness to play after injury. If an athlete is successful but too robotic, they are artificially prepared and are likely unable to handle chaos at higher speeds and more demanding environments. A simple example of this is in ACL injuries, where side-step forces are lower than controls with regard to movement variability. In addition to lateral deceleration profiles, center of pressure analysis also shows ACL risk after concussion, thus creating a problem for coaches outside of the obvious brain considerations.
Most of the research with post-injury data is very crude and poorly conducted, because higher subject numbers tend to give the findings inflated confidence, rather than depth of evidence. I would prefer to follow 30 athletes over a period of years than do a systematic review of hundreds of athletes and look for re-injury rates without knowing anything about the rehabilitation process. We need outcomes (re-injury) from both large cohort studies and specific case studies to give confidence to how ideal movement variability is restored to injured athletes, if it is restored at all.
My intention was to get to the core of the needs for most coaches and even sports medicine professionals, and not push a concept so far that it’s not practical for those in the trenches with youth development. It’s easy to get too excited about something new or popular, but it’s responsible to make sure we tease out what is necessary and useful from what is fascinating and intellectually shiny.
Movement variability is an important factor in coaching and rehabilitation, and knowing the necessary subtleties can make a big difference between getting results and getting frustrated. Invest in practical corrections and wise advice based on expert evidence when looking at movement development, and you will be able to better manage the element of variability.
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