Lower extremity injuries are ubiquitous in sports. Ankle sprains, anterior cruciate ligament (ACL) injuries, muscle strains, and a host of other acute and overuse issues plague athletes each year at every level of participation. Sport-specific rehabilitation programs are a necessary requirement for helping athletes return to their desired level of performance after injury. However, based on the high recurrence rates of many lower extremity injuries, the effectiveness of these programs for preparing athletes to return to performance with lower risk of injury needs to be questioned.
Sport performance is a combination of physical and perceptual-cognitive factors governing an athlete's ability to take appropriate actions to meet their goals in sport situations.1,2 It is important to keep in mind two essential principles related to performance. First, human performance is constrained by the context and conditions in which it takes place (the situation) and, second, the perceptual-cognitive processes related to performance center on decision-making based on goal-directed coordination of controlled actions.3 This means that athletes' ability to accomplish goals and coordinate movements is shaped by the circumstances of the situation in which they perform. Expert performance in sport is a combination of both physical and perceptual-cognitive skills that address the ability of an athlete to locate, identify, and process information in sport situations, and coordinate appropriate actions.4 Putting this in a context of injury mechanisms and rehabilitation, this indicates that performance deficits after injury may be linked to athletes' physical capacity and movement competence, as well as their perceptual-cognitive control within a given sport situation.5 Performance may change unfavorably when the athlete is required to reactively respond to unanticipated situations compared to anticipated ones.6 For example, it has been demonstrated that deficits in reaction time and processing speeds indicate a potential perceptual-cognitive predisposition to ACL injury.7 Therefore, athletic injuries may not only be associated with physical impairments and poor movement competence, but also perceptual-cognitive alterations that shape the coordination of movements.
Based on the high reinjury rates and the low rates of athletes to return to their pre-injury level after an ACL injury, it may be that the athletes with these injuries are inadequately prepared to meet the demands of their sport on return to participation. Both the physical capacity/movement competence of the athlete and perceptual-cognitive control of decision-making are modifiable through the rehabilitation process. The latter may be underrepresented in rehabilitation because there appears to be a predominant physical approach directed toward restoring range of motion, strength, power, and endurance; enhancing proximal stability and distal mobility; and progressing from simple to more complex movements. These goals primarily address physical capacity and movement competence. However, the perceptual-cognitive control of an athlete in the context of sport situations plays an important role in sports that require athletes to coordinate and adapt their movements in response to opponents and/or teammates.8 Athletes have to perceive essential information from rapidly changing playing situations, and must then interpret this information correctly to coordinate the most appropriate response based on their goals, the rules of the sport, and the interactions among their teammates and the opposing players.8
In this clinical commentary, we integrate elements of the dynamic systems theory and situational awareness to highlight the functional task environment that can be used as a rehabilitation tool to aid in restoring both physical and perceptual-cognitive aspects of sport performance. This theoretical framework will provide a model to manipulate the functional task environment during rehabilitation to enhance an athlete's ability to develop competence and regain control of performance after injury. To do this, we first discuss traditional rehabilitation strategies of sports injuries and then provide insights into how these strategies can be enhanced through manipulating the functional task environment. Table 1 lists terms and definitions that will be used within this model.
Changing the Rehabilitation Thought Process
As stated earlier, the moment-to-moment interaction between the athlete pursuing a particular goal in sport situations is defined as the functional task environment.9 Performance is constrained by the situation and the physical capacity and perceptual-cognitive control of the athlete.9 Traditional rehabilitation strategies are often performed within a predictable, fixed situation in which the athlete can fully anticipate the physical demands needed to perform the activities. Functional testing often grades an athlete's ability to perform specific tasks that the athlete already knows how to do. The physical demands of the athlete are typically manipulated (eg, adding changes in direction or increasing distance), but the perceptual-cognitive demands are fixed. However, real sport situations require high integration of physical capacity (eg, range of motion, strength, endurance, and power), movement competence (ie, appropriate movement patterns), and perceptual-cognitive control. In many circumstances, failure to challenge perceptual-cognitive control in functional testing may overestimate the readiness for return to sport from both performance and safety perspectives. How does performance on a triple hop for distance test translate to an athlete's ability to predict and appropriately act in real sport situations? Examining strategies to manipulate perceptual-cognitive demands into rehabilitation and functional testing may better prepare athletes to return to sports with pre-injury levels of skill and control.
Interventions aimed to enhance performance and reduce the risk of reinjury should reflect the elements of a complex sport-specific functional task environment because most injuries occur in sport-specific situations.10 To target skill acquisition, clinicians should be cognizant of the constant interaction among the athlete, task, and environmental constraints of the functional task environment in the situations where decisions and movements are made.11 For example, among the goals in current ACL rehabilitation programs is that the athlete learns movement competence such as jumping and landing with “knees over toes” and “hips in plane.”12 Any deviation is deemed an error and is corrected. In many sports, although basic movement competence needs to be acquired, there is no ideal movement pattern because relatively unique functional movement solutions emerge from the interaction of task and environmental constraints in the sport situation.13 Hence, movement variability increases the adaptability of athletes to handle complex situations as they emerge on the field.2 In rehabilitation, rather than pushing an athlete toward an “ideal” movement pattern, it is important to consider how the task and environment constraints can be manipulated to optimize movement solutions.14–17 The concept that an athlete can self-organize actions into a wide variety of potential solutions for a given movement goal in a sport situation is referred to as functional variability.15
Stemming from the dynamic systems theory of motor control, functional variability is recognized as a beneficial mechanism for coping with change, preventing injury, and attaining higher skill levels.2 The foundation of the dynamic systems theory is that coordination is shaped and constantly changing based on the circumstances of the situation.18 Moment-to-moment interactions of the athlete in sport situations require athletes to (1) effectively search for information about the situation, (2) direct their attention to the most relevant information related to the movement goal in the context of the sport situation, and (3) coordinate movements to successfully react or anticipate their changing functional task environment.4,5,9,14 Their movements then change how they perceive themselves, the situation, and the new movement goals. This complex process requires athletes to make predictions of how they need to move, anticipate movements of others, and develop contingency plans for their actions. Real time sport situations are embedded with uncertainty and it is critically important to incorporate coping strategies for dealing with uncertainty within the functional task environment. Uncertainty within the functional task environment can dramatically affect an athlete's ability to effectively perceive and act within a sport situation.19 Consider the disconnect between the complex process of navigating real sport situations and the current functional performance testing. Do functional performance tests that emphasize only physical performance really help clinicians to gauge the readiness of an athlete to engage in real sport situations?
Coping With Uncertainty in the Functional Task Environment: A Physical and Perceptual-Cognitive Continuum
An important perceptual-cognitive skill is anticipation, the capability of an athlete to perceive and predict relevant features of the functional task environment (eg, an opponent's movement) before changes take place. Control signifies the ability to plan, select, and execute an action based on the perception of a situation and the anticipation of how it might change.4 In situational awareness theory, there are three types of control: strategic, tactical, and reactive.3,5,20
Strategic control is used when decisions are not time-dependent. The athlete has plenty of time to explore and coordinate potential movement solutions to enhance functional variability. This is typically the type of control used in the rehabilitation setting. Athletes are afforded the time to become familiar with a specific activity, progress at their own pace, and refine their movement patterns in a safe and certain functional task environment.
Tactical control takes place when perceptual-cognitive and physical performance demands are compressed into a time-dependent situation with increasing uncertainty. The ability to fully explore the functional task environment is constrained and the athlete is required to rely on sport rules and previous experiences. Previous knowledge and experiences help the athlete form a range of movement solutions to pull from when uncertainty in the functional task environment increases. Tactical control is typically incorporated into sport drills and maneuvers in which athletes work on their performance during changing sport situations in a relatively controlled functional task environment. Tactical control in rehabilitation centers on the time-dependent demands in which athletes learn to rely on their ability to rapidly assess the situation within the functional task environment and use the skills honed from the strategic control phase. The tactical control phase shifts the focus of rehabilitation from simply physical performance to time-dependent decision-making and physical performance.
If uncertainty continues to increase and time for decision-making decreases, the athlete may shift to reactive control where there is limited or no time to explore the functional task environment. In reactive control, an athlete may enter a “panic” style of coordination. Panic in this context represents the breakdown in the ability to meaningfully link the perceptual-cognitive (anticipation and control) and physical (movement competence and functional variability) factors for successfully attaining a particular goal, which ultimately increases the risk for compromised performance. This is typically when we may see an athlete freeze up or perform dangerous movements that are not linked to safe performance in sport situations. Panic control may result in high risk behavior for injury because the movements are no longer connected to the situation in a meaningful way.
Injury Alters Anticipation, Control, and Coordination
Anticipation, control, and coordination of movement goals are heavily dependent on the health of the athlete in the context of the situation and the functional task environment.16 Lower extremity injuries substantially impact performance. Increased sensory-detection thresholds, diminished balance ability, alterations in coordination, reduced self-reported function, increased fear, and avoidance are consistent manifestations of disability in those with lower extremity injuries.21–24 There is also emerging evidence to suggest that, although these injuries are physical in nature, they also have the ability to negatively impact perceptual-cognitive performance25 and vice versa; added perceptual-cognitive load further impairs performance in injured athletes.26
We propose that the perceptual-cognitive and physical alterations associated with lower extremity injury may result in a shifting in the ability of an athlete to cope with uncertainty within the functional task environment. Due to the injury, athletes may have a decreased ability to anticipate relevant features within the functional task environment and subsequently have a reduced ability to coordinate movements to accomplish their goals in sport situations. This then leads to a reduction in their coping threshold for uncertainty before panic sets in. Panic may then predispose athletes to further injury because their actions are no longer connected to the functional task environment, resulting in disorganized and dangerous movement strategies. Although traditional rehabilitation strategies focus on restoring damaged physical components (reducing pain and edema, improving range of motion and strength, and restoring movement competence), there may be little done to address the altered perceptual-cognitive components and the coping threshold for uncertainty. This coping threshold is not something that is easily assessed on physical examination or the typical performance assessments (eg, single-limb hop, postural stability tests, or agility tests). To do this, a systematic approach shaping the functional task environment is necessary.
Constraint-led Approach to Shaping the Functional Task Environment
Coordination of movement arises from the complex interplay of individual, task, and environment constraints that shape movement solutions. In rehabilitation, these constraints can be manipulated to shape the functional task environment. To highlight how the functional task environment can be shaped through rehabilitation, it is first important to consider task and environment constraints.
Sport-related tasks typically focus on skills through which movement goals are accomplished (playing basketball involves dribbling, running, cutting, landing, and rebounding). The regulatory conditions of the task serve to shape how an individual self-organizes to accomplish a movement goal (eg, scoring points or defending against them). The dynamics of a task can be manipulated through constraints such as object manipulation (sprinting vs sprinting while dribbling a ball) or body manipulation (whether the athlete is stationary while performing the skill or the task regulatory conditions call for moving to different places). In this framework, the manipulation of task constraints serves to help the athlete seek out relevant perceptual features of performance as they relate to the execution of movement goals.16
Task performance is highly influenced by the predictability and relevance of information from the environment.3,9 Because of this interdependence, the nature of the task helps to highlight the relevance of important features within the environment for coordinating movement strategies. The predictability of the information flow between the person performing the task and the environment shapes coordination. Manipulation of environmental regulatory conditions for skill acquisition often takes on the form of stationary versus moving objects/people, the predictability of the surface in which a task is performed, and the amount of shared variance between these conditions.15,16
Together, the task and environmental constraints and their regulatory conditions combined with the physical capacity, movement competence, and perceptual-cognitive control of the individual form the functional task environment. Key to this concept is the athlete's ability to deliberately search for, interpret, and predict relevant, moment-to-moment information pertaining to the current and future dynamics of the functional task environment.3,5,9,27 This requires the athlete to direct attention toward the goal (goal-directed attention) and the situation.9,14,16,28 Physical and perceptual-cognitive alterations from an injury may affect the athlete's ability to maintain goal-directed attention. This then may result in a shift to a reactive control strategy when uncertainty increases in the functional task environment. The panic that comes from reactive control then reduces the ability to maintain goal-directed attention. Although there is limited research evidence to support this theoretical model right now, this seems to be a common clinical conversation among athletic trainers about athletes who can maintain good form in the clinic, but fall apart when returned to live sport situations. Rather than being a physical factor (eg, the athlete lacks conditioning or movement competence), it may be that the athlete cannot cope with that level of uncertainty in the situation.
Enhancing Perceptual-Cognitive Control and Coordination in Sport Rehabilitation
In traditional sport rehabilitation, rehabilitation programs are designed to enhance the physical capacity of athletes to meet the demands of their sport. In this context, therapeutic exercises are often trained repetitively with progressive difficulty. Once clinicians are satisfied with performance at a particular level of physical difficulty, the athlete progresses to next level.4,10,14 This progressive overload model capitalizes on the purposeful manipulation of task and environment constraints, but may limit the restoration of perceptual-cognitive control. By preparing the athlete where only physical conditions are practiced, rehabilitation progressions lack the perceptual-cognitive overload required for returning to sport situations.19,29 Increasing the complexity of the functional task environment with graded uncertainty may help restore both the physical and perceptual-cognitive aspects of performance and prepare athletes for participation in real-world sport situations.19,29
The Importance of Goal-Directed Attention
Attention is a key perceptual-cognitive factor in performance. By directing attention to the goal and the situation, athletes can then actively engage with their functional task environment. Throughout the rehabilitation process, it is important to help the athlete promote goal-directed attention. This refers to guiding the athlete to actively seek out relevant information from the functional task environment for shaping coordination and control.3,9 This involves the athlete paying attention to external and internal information that help to shape coordination. Due to injury, athletes may develop “self-directed” attention in which their attention is directed toward only their bodies rather than the functional task environment. In this case, athletes may be more concerned with the pain felt in their injured limb rather than how to effectively move in the situation. We believe the terms “goal-directed” versus “self-directed” are helpful for both the clinician and the athlete when talking about the functional task environment because they emphasize the relevant features of the situation (goal-directed attention) or a lack of engagement in the situation (self-directed attention). Most importantly, goal-directed attention centers on the ability to engage both the perceptual-cognitive and physical performance factors in the functional task environment.3,9,14
The Necessity of Variety
Sport rehabilitation should include a variety of activities that represent typical situations associated with the athlete's functional task environment. In dynamic systems theory, optimal performance requires functional variability. The more potentially equivalent strategies, the greater the probability of successfully accomplishing a goal.1,2,30 There also needs to be variety in the functional task environment and movement goals to ensure that goal-directed attention can be honed under a variety of conditions. Adding various task constraints (without increasing the difficulty level) poses new exercise conditions that the athlete must cope with to find new solutions for successful execution. An example of increasing task constraint complexity would be incorporating ball tosses using balls of different sizes and weights. The movement goal remains the same, but the information provided from varied balls requires the athletes to anticipate changes in their movement strategies to accomplish their goal. The size, color, and shape of the ball then become potentially more relevant to the athletes as they engage in their functional task environment. It is a misconception that adding constraints always increases the task complexity. In fact, adding a constraint may make an exercise easier because there are fewer movement options to choose from.
Increasing Complexity and Uncertainty in the Functional Task Environment
Rehabilitation progressions should gradually increase the complexity of the perceptual-cognitive and physical performance load. Activities should be representative of the functional task environment that the athletes will most likely return to. For example, in basketball, dribbling and passing are essential skills within the functional task environment. Early in the rehabilitation process, including dribbling as part of balance training for basketball players helps to shape goal-directed attention related to the functional task environment. The athlete needs to be able to work through the typical rehabilitation exercises while also shifting goal-directed attention to dribbling to meet the demands of basketball situations. The athlete can explore the functional task environment without uncertainty at the strategic level. To shift to the tactical level in the same exercise, the athlete might perform the same balance training task while dribbling, but now defending against an opponent who is attempting to steal the ball. Uncertainty ramps up by integrating more complex decisions about how to maintain single-limb balance, dribbling, and anticipating what the other person might do to steal the ball. When both the clinician and athlete perceive that movement competence can be maintained without panic, it would then be an opportunity to change the activity to something new.
This contextual control model3,5,19 for movement goal execution can be applied to any rehabilitation activity. The key elements are that the athlete needs to be challenged by reducing the certainty in perception or the available time to make decisions for action execution.14 Initial exercises should afford a full catalog of perceptual information with no time constraint for movement execution. These conditions allow the athlete to perform at a strategic level by gathering the maximum amount of information, forming strategies on how to accomplish the movement goal, and identifying optimal movement solutions.14 By adding uncertainty through increasing decision-making demands, removing information about the functional task environment (eg, performance with eyes closed), and/or increasing the complexity of the task and unpredictability of opponents in the functional task environment, the athlete will be forced to work at a tactical level by relying on past experiences for adopting and implementing movement solutions.14 Final stages of progression require athletes to perform under high uncertainty by providing minimal information coupled with rapid decision-making requirements with an increasing number of choices to induce a reactive level for pursuing the performance goal.14 This level of uncertainty will require the athletes to impulsively formulate movement solutions in a manner that is closest to their real-world sport situations where they are closest to the panic threshold. It is in this phase where the athlete can see the value of the goal-directed constructs built through training. Panic then becomes an outcome tool for the clinician to evaluate the athlete's ability to cope with uncertainty. Through this process, at any level of rehabilitation, athletes can carefully monitor their perception of panic, ability to maintain goal-directed attention, and movement competence.
We can use this contextual control model to progress balance and coordination training exercises in the functional task environment through the purposeful manipulation of constraints and uncertainty to enhance decision-making capacity.14 The goal of this constraint-led approach to shaping the functional task environment is to gradually ramp up the physical and perceptual-cognitive capacity of rehabilitation programs to meet or exceed the contextual demands of sport situations.
What Have We Changed? Functional Task Environment Outcome Assessments
Many of the contemporary functional assessments used to monitor recovery or make return to sport decisions examine the athlete's physical ability to perform at the strategic level rather than the tactical or reactive level, which may be needed for sport situations. For example, hop tests have been commonly used as a return to sport functional test following ACL injury.31 The traditional method for administering these tests assesses athletes at the strategic level by affording them a closed task environment, minimal uncertainty, and clear affordances to generate an optimal movement solution. These testing parameters allow the athlete to coordinate movements in a manner that hides impairments (ie, quad strength) and lacks the perceptual-cognitive load, stressors, and demands of performing in the actual functional task environment. Therefore, the primary outcome of hop distance may seem satisfactory under these testing parameters; however, when released to the sport environment it may become clear that the athlete remains at a deficit.32
Integrating perceptual-cognitive or motor dual tasks, spatial and temporal uncertainty, and elements of the functional task environment may provide an indication of performance capability at the tactical level that is more representative of the demands of sport situations. The addition of uncertainty may add additional levels of demand to functional assessments and provides the opportunity to concurrently examine physical performance characteristics (ie, hop distance, balance errors, and bio-mechanics) and also perceptual-cognitive performance (ie, decision-making, attention, working memory, and control).19 Under this model, we propose that athletes who can perform functional assessments and do not exhibit a breakdown in physical performance while demonstrating levels of perceptual-cognitive control without panic are more capable of performing in sport situations. Athletes who move to panic style while others are still tactically performing might be more at risk for physical performance detriments and injury. For these athletes, a clinician may need to scale down the time-dependent demands in their tactical control training before progressing to more challenging levels of uncertainty. Therefore, the goal of this new rehabilitation model is to expand the bandwidth for performing at the tactical level by continuing to stress the higher end of the ability to cope with uncertainty and rapidly make decisions.
Assessments designed to evaluate athletes along the perceptual-cognitive continuum following lower extremity injury require further study and development. However, a feasible starting point is to build on hop, drop landing, and agility tests that are already commonly used to assess readiness for sport. Several single-limb hop tests, including the hop for distance, triple hop for distance, crossover hop, and 6-m hop, have been modified to add perceptual-cognitive components that provide more ecological validity to test sport activity demands.33 For these assessments, lighted LED discs created go/no-go conditions based on reaction time that were unique for each of the four hop assessments. Simon et al34 reported that single-hop performance deficits were amplified by the addition of perceptual-cognitive challenges. Similarly, athletes have demonstrated alterations in lower extremity biomechanics with drop landing trials that incorporated time constraints on decision-making when compared to standard drop landing trials.35,36 These studies have created dual tasks by using the Stroop task to dictate the correct landing location36 or illuminating one of two different stimuli that dictated whether the athlete landed or landed and vertically jumped.35 Finally, a series of upper and lower extremity reaction and agility tests have been proposed by Wilke et al,37 which provides a range of reliable assessment strategies to engage the perceptual-cognitive continuum in functional testing. Therefore, the addition of perceptual-cognitive components to traditional hop or drop landing tasks may allow clinicians to assess athletes at the initial tactical or reactive levels. Nonetheless, in athletic environments, athletes have to comprehend and respond to uncertain, constantly and quickly changing sport situations. For this reason, assessment of performance and/or risk for recurrent injuries should reflect the elements of these complex sport-specific situations.10
It is important to take into account athletes' perceptual-cognitive control, physical capacity, and movement competence in their goal execution within the functional task environment. Performance should be viewed as a measure of an athlete's ability to flexibly adapt to changing situations within the functional task environment. In this context, performance purposefully links the physical and perceptual-cognitive components in the functional task environment. Clinicians can use competence and control (strategic, tactical, or reactive) as outcomes to assess whether the athlete demonstrates satisfactory performance within the functional task environment. We propose that evaluating competence and control can manifest in various situations:
The athlete performs well from both the competence in movement strategies and perceptual-cognitive control in accomplishing goals within the functional task environment. In this case, uncertainty demands can continue to be ramped up.
The athlete demonstrates satisfactory competence in movement strategies, but with diminished sense of perceptual-cognitive control (eg, starts to panic) as uncertainty increases in the functional task environment. In this case, the time-dependent demands may need to be scaled down in the tactical control phase, allowing the athlete to enhance perceptual-cognitive decision-making before progressing to more uncertainty.
The athlete does not demonstrate full competence in movement strategies but maintains good perceptual-cognitive control in accomplishing goals with increased uncertainty in the functional task environment. In this case, athletes may need to spend more time in the strategic phase on specific skills in which they need to increase their movement competence (ie, more opportunity to explore the task and environmental constraints to restore functional variability).
The athlete demonstrates both unsatisfactory competence and control in the functional task environment. In this case, the athlete may require greater focus on strategic control phase honing goal-directed attention for all rehabilitation activities due to a reduced ability to combine physical performance with perceptual-cognitive decision-making.
By evaluating competence and control as uncertainty increases, it may be possible to develop better predictions for when athletes are prepared to progress in their functional task environment. Incorporating a social support system and intrinsic motivation have been suggested as important factors for enhancing rehabilitation adherence and decreasing negative affective responses.38 Therefore, if athletes are experiencing difficulty coping with increased uncertainty within their functional task environment, the clinician should also consider other contextual factors. Psychological, social, and contextual factors play a critical role in recovery and factors such as fear-avoidance and self-efficacy have emerged as important factors for lower extremity injury rehabilitation.39–46 The role of specific impairments and psychosocial factors in the ability to progress along the perceptual-cognitive continuum and ultimately return to sport requires further investigation; however, it is evident that this multifactorial approach to monitoring recovery is warranted to optimize return to participation, sport, and performance decision-making.