The Idea of Variability in Sport and Movement Practice (Part 2, The Purpose, Relevance & Importance of Variability and Attractors)

Now you may be wondering what is the importance and relevance of having this so called “bandwidth” (as Harry Simington refers to) or wiggle room in the availability of our movement solutions and attractors? The second part of this article will explore two main reasons as to why a degree of variability may be beneficial in terms of our movement options, but also one reason where we also see variability benefit the structure of our training. 

James (2004) "variability-overuse hypothesis"

Firstly, having adequate variability in movement solutions has been linked to potentially reducing injury risk. This thought is based largely on the work of James (2004) and his “variability-overuse hypothesis” where he believed that “variability might play a positive role in preventing overuse injury by providing a broader distribution of stresses among different tissues." Looking back to the first part of this article, we can easily relate this to Bernstein’s Degrees of Freedom problem, where simply having limited Degrees of Freedom in the completion of a task will repeatedly stress the same tissues and structures over and over again, possibly leading to injury. Multiple studies by Bonacci and colleagues (2018 & 2020) concluded that runners suffering with patellarfemoral pain (PFP) saw reductions in their symptoms by either increasing joint variability at the hips, knees, and ankles or by running at varied cadences. However, these are recent studies, and I definitely think more studies can and will be carried out on other parts of the body in various sports skills such as throwing, swinging, etc. The list is endless really! But Bonacci and colleagues have given us a flavour of the possible benefits of having multiple movement solutions to access when completing the same task. 

Secondly, variability plays a crucial role in our ability to adapt to what is presented in front of us in the form of movement tasks. During my onsite induction for my MSc, I was introduced to Newell’s Model of Constraints (1986), which explains how our movement patterns and solutions are based off of these three different constraints: individual, environmental, and task orientated. With all three of these constraints constantly changing during the chaos of sport, it is also key to take into consideration that no matter how organised and orderly you may think a sport skill or movement task may be, the constraints are always changing. For example, the movement task of a tennis serve, some may think is very organised and controlled from one game to the next. However, even a tennis serve has constraints that are ever changing. Has that athlete changed height over the course of a year or two and potentially developed greater physical strength? How does losing affect the confidence levels, or even as we age, how does this change our coordination? These are all examples of individual constraints that must be managed constantly. Additionally, environmental constraints such as moving from clay to grass to hard courts—how does this impact the speed of the ball and consequently the athlete's placement of the ball in the opponent's service box to be most effective? We need to have the ability to adapt to these changing constraints; as Rob Gray (2021) rightly put, “if the problems of movement are always changing, then we need to have multiple solutions." I think it is pretty obvious here, but if we are to be successful at anything, especially sport, we have to have as many options as possible to allow us to be successful so that no matter what we are constrained by, we have the movement solutions and patterns available to us to succeed more often than not. In Gray’s (2017) own study with baseball players, he found that adding variation and variability into practice sessions for batsmen through the use of virtual reality significantly increased the adaptability when it came to batting test scores compared to other groups who did not. Simply adding this task orientated constraint in the form variation in batting practice meant those batsmen were far more well equipped with movement solutions to do better in the batting tests. This study provides the basis for many more studies to come, where increasing an individual's movement solutions available to them equates to improved results in a given sport skill or movement task. 

How would both John Isner and Diego Schwartzman need to adapt to receive each other's serves?

Furthermore, the addition of variability in our general physical preparedness (GPP) aspect of training serves (no tennis pun intended!) yet another purpose. If we are to continually keep striving towards adaptations, say in muscle cross-sectional area (CSA) or maximal strength qualities, it is crucial that we provide the system with a stimulus great enough to promote those adaptations we set out to achieve. Fundamentally, our goal of training away from the sport itself is to create adaptation. Improving limiting physical capacities along with access to efficient, fluid, and stable attractors will likely enhance our ability to perform sport skills to the best of our ability. The only way we achieve this is through stressing our system in the right way with the right doses to promote supercompensatory effects on the body (Yakovlev, 1955). Too little stress will create no adaptation, and too much stress will lead to overtraining. 

Fortunately, our bodies are incredibly efficient when it comes to learning and adapting to new stimuli, so much so that if we continually give the same stimulus that once created adaptation, our system will actually start becoming numb to it. So a stimulus that once created adaptation no longer has the same potent effect. One could argue that it is of paramount importance that we continually change the stimuli so adaptation does not stagnate. Steffan Jones has a great metaphor that states that “when you walk into a room of flowers, you smell them immediately. After time, the smell goes away. Senses are tuned out to it”. This is one of the main reasons why strength coaches such as Cal Dietz utilise his undulating block system method to continually create supercompensatory effects when peaking his athletes. This ensures his athletes continually receive stimuli great enough to promote adaptation on whichever system is being stressed. As Hans Seyle (1950) discovered, stress is the ultimate driver of change. 

Zatsiorsky & Kraemer (2006)

Now, Grays’ 2017 study introduced us to a more sport-specific training method where exposing baseball batsmen to a wider range of stimuli during practice led to improved batting test scores, but how are we seeing this same concept of variability being implemented into our training in less sport-specific settings? If we take Bernstein’s “repetition without repetition” concept, rather simply put, we need to find ways of doing the same things slightly differently, and one really easy way to go about this is adding perturbations to movements. Bernstein (1967), Newell (1986) and Haken and colleagues (1985) all built upon Henri Poincaré’s early 19th-century work to later coin the term perturbations as disturbances used to promote adaptability, deepen attractor valleys, and allow for exploration of an individual's perceptual-motor landscape in the development of a new movement solution or skill. The likes of Frans Bosch have popularised perturbations in modern training settings through his use of aquabags and weights attached to bars by bands to cause these disturbances, or perturbations in a Constraints Led Approach (CLA) to coaching (Bosch, 2015). The sloshing movement of the water in the bags or bounce from the weights dangling from bars results in a system having to continually adapt to these ever changing stimuli to find stability. We see this method implemented into sports like cricket (Steffan Jones), baseball, and athletics, but will we continue to see further use of this style of training in more sports? Who knows!

Overall, we have seen how variability can benefit an individual in multiple scenarios, from injury risk prevention to improved adaptability in both motor learning and the development of physical capacities. However, I believe it is crucial to continue exploring ways in which we can assess coordination better to gain deeper insight into what an individual's limitations are. Whether that is an inability to access a movement solution due to a lack of a particular physical capacity or for more neurological reasons, and this is where I would question the nature of some overuse injuries. For example, look at a tennis player who is suffering from knee pain around change of direction on court. You may have established that the individual is severely down in their eccentric braking force capacity, which is impacting their movement solutions they opt to use to decelerate as they change direction. Consequently, their knee may be experiencing forces exceeding the current tissue tolerance, resulting in the pain. Now it is fine to say you then improved the physical capacity and tolerance at a tissue level of eccentric braking forces, which was assessed through a countermovement jump (CMJ) on force decks or an isometric knee flexion test with a dynamometer. However, if that individual is still continually displaying poor, sub-optimal movement solutions to decelerate their leg when changing direction, then I would really question these approaches that solely focus on physical capacities. Questions need to be asked around how does whatever we are working on actually change the pattern or movement solution you want to see transferred onto the tennis court, which would result in less pain as they change direction repeatedly? Of course this is a very brief and small example looking at it from one lens (kinetics), and others may look from more kinematic or coachable changes or even from a more nutritional perspective with changes to bodyweight lessening the loads on joints—I am digressing!

The point is, we must understand, to best of our abilities, what an individual needs to enhance the transferability of our training to performance and competitive settings. This is problem solving at its finest! Utilising variability as a tool in my opinion has a huge place in sport and movement practice, but further knowledge is required to understand the intentions and adaptations such a tool sets out to achieve as well as how we can integrate this type of varied practice into structured programmes. Above everything motor learning is incredibly complex and multifaceted and this was further highlighted when listening to an incredible insightful lecture recently by Jon Goodwin. I was reminded that although you may change an individuals physiology with the intensions of altering a movement solution. We may not actually see the athlete express the desired outcome or movement solution we believed that giving access to the right physical capacities would allow. Jon mentioned that if an individual learnt a movement solution at a specific stage under certain circumstances, perhaps either weak or strong as one example, then no amount of physiological adaptation would alter their brains decision to choose to express a learnt sub-optimal movement solution. Fundamentally, this boils down to the exact neurology of that individual and I think it is fair to say even with huge advancements in our understandings of the brain due the technology we have available, we are still very far off from understanding everything there is to know about the brain. 

References / Sources:

Bernstein, N. (1967). The Co-ordination and Regulation of Movements. United Kingdom: Pergamon Press.

Bosch, F. (2015). Strength Training and Coordination: An Integrative Approach. Netherlands: 2010 Publishers.

Calvin Dietz - Strength & Conditioning Coach & Author of ‘Triphasic Training’ 

Gray, R. (2017). Transfer of training from virtual to real baseball batting. Frontiers in psychology, 8, 2183.

Gray, R. (2021). How We Learn to Move: A Revolution in the Way We Coach & Practice Sports Skills. United States: Rob Gray.

Haken, H., Kelso, J. S., & Bunz, H. (1985). A theoretical model of phase transitions in human hand movements. Biological cybernetics, 51(5), 347-356.

James, C.R. (2004) Considerations of Movement Variability in Biomechanics Research. Innovative Analyses of Human Movement, United Kingdom: Human Kinetics., 29-62. 

Jon Goodwin - ex Academy Head of Sports Science at Fulham FC & Director of High Performance Services at the Saudi Olympic Training Centre & current Head of Performance and Medical at Wycombe Wanderers FC. 

Newell, K. M. (1986). Constraints on the Development of Coordination. In M. G. Wade, & H. T. A. Whiting (Eds.), Motor Development in Children: Aspects of Coordination and Control 341-360. The Netherlands: Martinus Nijhoff, Dordrecht.

Seley, H. (1950). Stress and the general adaptation syndrome. British medical journal, 1(4667), 1383–1392.

Steffan Jones - Pace Lab 

Yakovlev N. N. (1955). Survey on Sport Biochemistry (in Russian). Moscow: FiS. 

Zatsiorsky, V.M., and Kraemer, W.J. (2006). Science and practice of strength training. Champaign (Il): Human Kinetics, Cop.