ABC of Football Medicine® Lesson 9: The role of motor control in the muscle injury prevention – Part 1

Navigating through the pillars of muscle injury prevention, here’s a recap:

-> chapter 4 presented a introduction to load monitorization, diving into the means of monitoring and the impact that the monitored load volumes may have in increasing the risk of injury;

->we covered mobility in chapter 7, where we presented the principles of how mobility has an impact on the body, how this impact affects prevention and a proposal of how to implement it in the training plan;

->in chapter 8, the topic has been the athletic training of the athlete, presenting the modalities that “gym work” may follow in building the strength domains as well as the energy systems (how the muscle and cardiovascular system adapt to different intensities of sustained/paused training).

This brings us to the last chapter dedicated to another pillar of muscle injury prevention : motor control. You may think of motor control as the skill to control movement but the implications of this concept are broader than just during movement, occurring both after and before any movement has occurred. Besides understanding the concept, we’ll go into the practical side of it (as we’ve done in previous chapters) and there we’ll discuss how to develop and include this in the training session. Spoiler alert: it’s not by simply adding unstable surface exercises into the warm up routine.

Well, here we go.

Sports science research has been booming in the last decades, which allows for the surrounding agents involved (coaches and their technical teams, team managers and even the clinical teams) to know more about the determinant factors on performance development and, with an even greater degree of complexity, injury influencing factors: both the ones that increase risk as well as the ones that may decrease it. Taking this knowledge into consideration, it is quite understandable that the main agent involved – the player – has also been getting aware of the role of his own physical skills as well as aware of the impact that these skills play on individual performance.

These developments in the “Science of Training” made it possible to increase the individual player’s responsibility and adaptability and therefore, respond to modern football demands; which would be impossible if, all of a sudden, we imposed this on an athlete 20/30 years ago.

This increase in demand means that the athlete has to have a constant reading and interpretation of his/her surrounding environment (we’ll call these the constraints from now on) and, in the light of his/her knowledge of the game and the possible combination of actions, decide to respond with the execution that has the highest chance of success to result in what he/she idealizes.

This may be simply passing the ball to the side, creating a pass line, or accelerating and heading a ball that has just been crossed over.  It is demanded that the athlete has both the connection and comprehension of the game so that he/she, autonomously, is able to make the best decisions and execute them with high efficiency. These are some practical examples of the importance of motor control in football, which gather the perception and analysis of the surrounding environment, the creation/conception of an adequate motor program and its execution (as close as possible to what was idealized).

The relationship between motor control and muscle injury has been explored by several distinct points of view.

One of these focuses on running technique and hamstring injury, as seen in a study by Schermans et al. Although a topic of debate for many years, the majority of the literature suggests that the timing of the hamstring injury during high-speed running has been associated with the late swing phase. Therefore, it isn’t farfetched to consider the hypothesis that both the sprinting technique and the kinematic and kinetic characteristics may be variables to take into account.

Besides running, another domain of motor control that has been claimed to impact the injury risk is the core/trunk stability. Here, (Hides & Stanton, 2014) found a positive relation between trunk motor control training –aka core training- (focusing on body self-recognition, posture and its natural curves) and a decrease in hamstring injuries (in this particular study, in australian football). This finding is consonant  with the wider beliefs in the sports medicine scientific community regarding these injuries, in which the lumbopelvic control plays an important role in rehabilitation as well as in prevention. However, it is not clear how this factors in, since the mechanism of primary injury is – as we’ve stated and seen throughout this book – related to high velocity sprints (HVS). 

Hypothesis: Could it be that core training reduces the tissue vulnerability towards a primary injury? Or does it impact on proximal stability and therefore exposure to load? 

As we’ve been building, both the running technique and the core stability are suspected to play a role but they look, at a first glance, completely unrelated. In order to maximize the profit from taking this into account, we’ll need to dive further into the science behind this hypothesis. 

Running technique

When analysing high velocity running patterns, we see that they are characterized by the high acceleration horizontal displacement of the center of mass, in which the role of the “core” is to facilitate the movement economy, the sustainability of the effort and execution and safety. The absence of this core control could, perhaps, lead to an altered running technique, hence increasing the risk of injury? This topic is yet to be clear, as it has not been fully explored in the literature. Schuermans et al (2017) studied a group of athletes finding no significative differences in the kinematics of the ankle, knee, hip, pelvis or torax upon the initial assessment. However, upon a 1 year follow-up assessment, the athletes that showed a primary injury also showed pelvis and thorax differences, specifically, an increase in the anterior pelvic tilt during the entire stride, with emphasis on the backswing phase as well as an increase in lateralization of the thorax in the front-swing phase. In conclusion, the lumbopelvic kinematics of the athletes with a previous injury, pointed towards an increase in fluctuation/movement (as some would call, an unstable movement*).

This excessive pelvic and trunk movement during the aerial phases (also the ones in which injury occurs) may be due to insufficient control or, looking at it from another point of view, from a lack in “experiencing this pattern” (which is a High Velocity Sprint pattern). This non-existence of a primal pattern could therefore be responsible for the high variability/low consistency in the movements observed.

One other study, by Preece et al (2016), studied the coordination between these segments (pelvis and trunk) in the three different planes of movement: it found movements occuring in opposing directions in both the sagittal and frontal plane, which suggests that this may be the consequence of mechanisms aiming to diminish the movement of the center of mass in the anterioposterior direction (anti-extension) and lateral movements. In specific, on the transverse plane, some lagging in the pelvic movement following the trunk movement was found; the explanation found was that the this transverse plane movement did not happen passively has a consequence of the pelvic movement but, happened instead as a mechanism needed to facilitate trunk rotation (associated to the arm movement)

Zouhal et al (2018) studied the impact of fatigue on a protocol of sprinting series, through different kinetic and kinematic variables. They found that changes in the muscle pattern and the horizontal force production and, particularly that: 1) the role of the hamstrings changes with the onset of fatigue; 2) Due to this fatigue, the hip extension function becomes dependent on the hip extensors, namely, glut max.

Based on these findings, the authors consider that these changes may be a compensatory/adaptative strategy to maintain performance and protect the muscular limitations of the hamstrings. However, if faced with poor/inefficient hip extensors, this protection of the hamstrings wouldn’t be possible and would, in theory, put them at a higher risk of injury (Zouhal et al., 2018). 

Core training

Although we see these higher levels of anterior pelvic tilt and lateral inclination of the trunk during sprints being associated with hamstring injuries, assuming the origin (or, even worse but more important, the solution) would be a logical leap.

Exercises such as the frontal and lateral plank, as well as other variations, are largely accepted as part of the lumbopelvic training (aka core training). However, the evidence to support that these low intensity exercises in ranges of motion/postures fully unrelated to the causative ones of hamstring injury, may have a modelling effect on the motor behaviour and therefore reduce the risk of injury, is scarce. (Shield & Bourne, 2018)

The relation between proximal (lumbopelvic) stability and the occurrence of muscle injury has been seen by several authors but quantifying the relation or looking for a causality component is a challenge. 

The current literature points that the core training should be aimed to maximize the transfer towards the known injury mechanism – sprinting. Therefore, exercises related to sprints, with proper joint angulation and specific movement timings will develop the muscle recruitment and harmonizing the syncrony needed. These can be achieved through maximum sprinting exercises and explosive agility, both exposing the hamstrings and requiring ideal core firing, needed to provide proximal stability to enhance the movement performance.

This does not mean that core stability exercises, such as the ones commonly used in the fitness context, are forbidden. They may be used, especially during an initial phase of improving the pattern. Nevertheless, these exercises should not be simply used in isolation or with a rationale of being the solution towards the “core” needs, and they shouldn’t take up training time from other evidence-based practices. The core needs to be trained at what the core will be required to do.

In summary, both the running technique and the core control appear to play a role in the prevention and should, therefore, be addressed, taking into account the injury mechanism. The single observation of changes in the core control, which the literature does show, shouldn’t guide you towards isolating the core training. One way of correcting these changes should be by training the sprinting pattern and demanding this pattern at high intensities.  

After understanding what the changes in movement seem to be and the influence this may have in the injury risk, we are yet to clearly define the one key concept:

After all, what is motor control?

To answer this, we’ll briefly give some context and present to you the development of these concepts throughout the years.

The theory of movement by Bernstein is one of the most known in the study of motor learning and is, consequently, a good starting point. In this theory, Bernstein presents a four level hierarchical model: tonus, synergy, spatial and action. While tonus (the resting muscle tension), space and action may be self-explanatory, the concept of synergy here is important to define: it is the adaptation between units of a motor system and their changes towards changes in external forces . The adaptation and the external forces mean that the system takes into account the centripetal force and inertia along the movement, as well as the force of gravity and the continued influence in the forces, depending on their direction.

This means that this theory rejects the idea of the existence of an exclusive relationship between the neural movement codes and the movement output, bringing advances in the kinematic study and human movement description, leaving behind the preconceived traditional ideas of a top-down model that is purely based on neural activity.

Later, and taking the concepts above as a base, an adaptation has been proposed by Kelso, the Dynamic System Theory. In this school of thought, the human behaviour is seen through a self-organizatory point of view, with the spontaneous formation of patterns surging as the answer towards motor problems and resulting in one output out of many combinations that arrive from the following Triad: athlete, environment and task. In this perspective, the central nervous system isn’t the exclusive responsible for movement; movement is a product of diverse biomechanical and energy properties of the tissue, the environment and the specific needs of the task, in a non-hierarchical and non linear relation, with properties such as self-organization and flexibility. 

These characteristics become the constraints to action (not in a negative meaning), influencing directly the perception/attention of the central nervous system and affecting the degrees of freedom of the body during the motor learning.

Figure 1 – Motor Control Triad: Constraints that guide the human motor action

These constraints aren’t the action starters; their role is to limit the solutions (decisions/motor patterns) that are not possible given the full situation assessment. The real action starter is still the individual’s own intention, his goal. However, this does not mean that he will formulate a “motor program” that completely predicts what is going to happen (the “movement” or  “skill”) as well as when (the “timing”). 

The relationship between improvements in motor control and decreases in muscular injury risk is far from straightforward due to the broadness of the definition of motor control.

To make this more practical and looking at the athlete from an holistic training approach, the first question to ask is:

“Does the athlete have a wide range of motor programs to choose from, allowing him to choose the one that better fits to the constraints he has assessed, resulting in a broader set of options towards the game situation, whether anticipated or not?”

Comparing the question to a cooking situation, consider a chef that’s brilliant at preparing one single dish; this chef will never be able to adapt to a different setting of ingredients, client requests or kitchen changes. The reason for his failures wouldn’t be that he is technically limited but that the technique is “closed” and not adjusted to the changing surroundings. 

Besides the “wideness” of his saved motor programs, it should be noted if an athlete performs the same programs on a controlled variability setting and is able to maintain a constant execution for the whole duration of the effort. (Or if the chef can maintain the performance of his known dishes through the entire night)

Finally, it should be looked if the athlete is able to, unconsciously, have these motor programs engaged in the decision taking process.

These three steps (a wide range of motor programs, consistency in performance and cognitive ease in choosing from the motor programs) take a central role when we’re talking about the athletes recovering from an injury. Nevertheless, they also play a role during the secondary or primary prevention, being the base point to assess the influence of the injury in the adaptability capacity of the athlete and if he is ready to resume to the increasing demand of unpredictability which characterizes the regular match.

Not having a quantitative nature such as the exercise prescription for physical qualities, it requires a big amount of attention in order to explain and understand that even if the numbers add up (and by “numbers”, we mean things like ranges of motion as seen in chapter 7 or velocities/maximum strength as seen in chapter 8), the athlete still can’t properly transfer the isolated actions towards the game, where the environment and task constraints are different.

There is no ultimate formula that allows to teach/develop solutions for all the possible situations the athlete will face; hopefully, this reasoning of motor learning as a process guided by constraints does increase the coaches’ perception that motor training will harvest both from the science of motor learning and from the art of using the evidence. This is seen in processes such as reintegrating/relearning the mechanism that lead to the previously injury (running, shooting, sprinting, changing direction), not simply by correcting it (as if it was wrong before) but optimizing the individual, taking into account its characteristics, the movements of the task and the environment in which the task will happen, progressing towards a dynamic harmony. This is the path (not necessarily an end result) that consists of the capacitation of the athlete towards being adaptable to variable constraints – the bulletproof rehabilitation.

Authors: Bruno Rodrigues  e Lucas Brink Carvalho 
Special thanks for the bullet proof reading by: Tomás Correia e Marcos Agostinho

Read what we read:

Schuermans J, Danneels L, Van Tiggelen D, Palmans T, Witvrouw E. Proximal Neuromuscular Control Protects Against Hamstring Injuries in Male Soccer Players: A Prospective Study with Electromyography Time-Series Analysis during Maximal Sprinting. Am J Sports Med 2017; 45(6): 1315-1325. doi:10.1177/0363546516687750.

Preece S, Mason D, Bramah C. The coordinated movement of the spine and pelvis during running. Hum Mov Sci 2016; 45: 110-118. doi:10.1016/j.humov.2015.11.014.

de Visser HM, Reijman M, Heijboer MP, Bos PK. Risk factors of recurrent hamstring injuries: a systematic review. Br J Sports Med 2012; 46(2): 124-130. doi:10.1136/bjsports-2011-090317.

Sherry MA, Best TM. A comparison of 2 rehabilitation programs in the treatment of acute hamstring  strains. J Orthop Sports Phys Ther 2004; 34(3): 116-125. doi:10.2519/jospt.2004.34.3.116.

Freckleton G, Cook J, Pizzari T. The predictive validity of a single leg bridge test for hamstring injuries in  Australian Rules Football Players. Br J Sports Med 2014; 48(8): 713-717. doi:10.1136/bjsports-2013-092356.

Profeta V, Turvey M. Bernstein’s levels of movement construction: A contemporary perspective. Hum Mov Sci 2017; 57: 111-133. doi:10.1016/j.humov.2017.11.013.

Renshaw I, Chow JY, Davids K, Hammond J. A constraints-led perspective to understanding skill acquisition and game play: a basis for integration of motor learning theory and physical education praxis? Phys Educ Sport Pedagog 2010; 15(2): 117-137. doi:10.1080/17408980902791586.