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Following completion of this chapter, the reader will be able to:

1. Define motor control, and discuss its relevance to the clinical treatment of patients with movement pathology.


2. Discuss how factors related to the individual, the task, and the environment affect the organization and control of movement.


3. Define what is meant by a theory of motor control, and describe the value of theory to clinical practice.


4. Compare and contrast the following theories of motor control: reflex, hierarchical, motor programming, systems, dynamic systems, and ecological, including the individu- als associated with each theory, critical elements used to explain the control of normal movement, limitations, and clinical applications.


5. Discuss the relationship between theories of motor control and the parallel development of clinical methods related to neurologic rehabilitation.


6. Compare and contrast the neurofacilitation approaches to the task-oriented approach with respect to assump- tions underlying normal and abnormal movement con- trol, recovery of function, and clinical practices related to assessment and treatment.
   INTRODUCTION What is Motor Control?
   Movement is a critical aspect of life. It is essential to our ability to walk, run, and play; to seek out and eat the food that nourishes us; to communicate with friends and family; to earn our living—in essence to survive. The field of motor control is directed at study- ing the nature of movement, and how movement is controlled. Motor control is defined as the ability to regulate or direct the mechanisms essential to move- ment. It addresses questions such as how does the central nervous system (CNS) organize the many indi- vidual muscles and joints into coordinated functional movements? How is sensory information from the environment and the body used to select and control movement? How do our perceptions of ourselves, the tasks we perform, and the environment in which we are moving influence our movement behavior? What is the best way to study movement, and how can movement problems be quantified in patients with motor control problems?
   Why Should Therapists Study Motor Control?
   Physical and occupational therapists have been referred to as “applied motor control physiologists” (Brooks, 1986). This is because therapists spend a considerable amount of time retraining patients who have motor
   3

4 PART I Theoretical Framework
control problems producing functional movement disorders. Therapeutic intervention is often directed at changing movement or increasing the capacity to move. Therapeutic strategies are designed to improve the quality and quantity of postures and movements essential to function. Thus, understanding motor con- trol and, specifically, the nature and control of move- ment is critical to clinical practice.
We will begin our study of motor control by dis- cussing important issues related to the nature and control of movement. Next, we will explore different theories of motor control, examining their underlying assumptions and clinical implications. Finally, we will review how theories of motor control relate to past and present clinical practices.
UNDERSTANDING THE NATURE OF MOVEMENT
Movement emerges from the interaction of three fac- tors: the individual, the task, and the environment. Movement is organized around both task and envi- ronmental demands. The individual generates move- ment to meet the demands of the task being performed within a specific environment. In this way, we say that the organization of movement is constrained by fac- tors within the individual, the task, and the environ- ment. The individual’s capacity to meet interacting task and environmental demands determines that person’s functional capability. Motor control research that focuses only on processes within the individual without taking into account the environment in which that individual moves or the task that he or she is per- forming will produce an incomplete picture. Thus, in this book our discussion of motor control will focus on the interactions of the individual, the task, and the environment. Figure 1.1 illustrates this concept.
Factors within the Individual That Constrain Movement
Within the individual, movement emerges through the cooperative effort of many brain structures and processes. The term “motor” control in itself is some- what misleading, since movement arises from the interaction of multiple processes, including those that are related to perception, cognition, and action.
Movement and Action
Movement is often described within the context of accomplishing a particular action. As a result, motor control is usually studied in relation to specific actions
Movement
T Task
M
IE Individual Environment
FIGURE 1.1 Movement emerges from interactions between the individual, the task, and the environment.
or activities. For example, motor control physiologists might ask: how do people walk, run, talk, smile, reach, or stand still? Researchers typically study movement control within the context of a specific activity, like walking, with the understanding that control pro- cesses related to this activity will provide insight into principles for how all of movement is controlled.
Understanding the control of action implies under- standing the motor output from the nervous system to the body’s effector systems, or muscles. The body is characterized by a high number of muscles and joints, all of which must be controlled during the execution of coordinated, functional movement. There are also multiple ways a movement can be carried out (multi- ple equivalent solutions). This problem of choosing among equivalent solutions and then coordinating the many muscles and joints involved in a movement has been referred to as the “degrees of freedom problem” (Bernstein, 1967). It is considered a major issue being studied by motor control researchers and will be dis- cussed in later chapters. So the study of motor control includes the study of the systems that control action.
Movement and Perception
Perception is essential to action, just as action is essen- tial to perception. Perception is the integration of sensory impressions into psychologically meaningful information. Perception includes both peripheral sen- sory mechanisms and higher-level processing that adds interpretation and meaning to incoming afferent infor- mation. Sensory/perceptual systems provide informa- tion about the state of the body (e.g., the position of different body parts in space) and features within the

environment critical to the regulation of movement. Sensory/perceptual information is clearly integral to the ability to act effectively within an environment (Rosenbaum, 1991). Thus, understanding movement requires the study of systems controlling perception and the role of perception in determining our actions.
Movement and Cognition
Since movement is not usually performed in the absence of intent, cognitive processes are essential to motor con- trol. In this book, we define cognitive processes broadly to include attention, planning, problem solving, moti- vation, and emotional aspects of motor control that underlie the establishment of intent or goals. Motor control includes perception and action systems that are organized to achieve specific goals or intents. Thus, the study of motor control must include the study of cogni- tive processes as they relate to perception and action.
So within the individual, many systems inter- act in the production of functional movement. While each of these components of motor control— perception, action, and cognition—can be studied in isolation, we believe a true picture of the nature of motor control cannot be achieved without a synthesis of information from all three. This concept is shown in Figure 1.2.
Mobility
CHAPTER 1 Motor Control: Issues and Theories 5 Task Constraints on Movement
In addition to constraints related to the individual, tasks can also impose constraints on the neural orga- nization of movement. In everyday life, we perform a tremendous variety of functional tasks requiring movement. The nature of the task being performed in part determines the type of movement needed. Thus, understanding motor control requires an awareness of how tasks regulate neural mechanisms controlling movement.
Recovery of function following CNS damage requires that a patient develop movement patterns that meet the demands of functional tasks in the face of sensory/perceptual, motor, and cognitive impair- ments. Thus, therapeutic strategies that help the patient (re)learn to perform functional tasks, taking into consideration underlying impairments, are essen- tial to maximizing the recovery of functional indepen- dence. But what tasks should be taught, in what order, and at what time? An understanding of task attributes can provide a framework for structuring tasks. Tasks can be sequenced from least to most difficult based on their relationship to a shared attribute.
The concept of grouping tasks is not new to clini- cians. Within the clinical environment, tasks are rou- tinely grouped into functional categories. Examples of
Stability
Manipulation
T
M IE
C
Cognition
PA
Regulatory
Nonregulatory
FIGURE 1.2
Perception
Action
Factors within the individual, the task, and the environment affect the organiza- tion of movement. Factors within the individual include the interaction of perception, cognition, and action (motor) systems. Environmental con- straints on movement are divided into regulatory and nonregulatory factors. Finally, attributes of the task contribute to the organization of func-
tional movement.

6 PART I Theoretical Framework
functional task groupings include bed mobility tasks (e.g., moving from a supine to a sitting position, mov- ing to the edge of the bed and back, as well as changing positions within the bed); transfer tasks (e.g., moving from sitting to standing and back, moving from chair to bed and back, moving onto and off of a toilet), and activities of daily living (ADLs) (e.g., dressing, toilet- ing, grooming, and feeding).
An alternative to classifying tasks functionally is to categorize them according to the critical attributes that regulate neural control mechanisms. For example, movement tasks can be classified as discrete or continu- ous. Discrete movement tasks, such as kicking a ball or moving from sitting to standing or lying down, have a recognizable beginning and end. In continuous move- ments such as walking or running, the end point of the task is not an inherent characteristic of the task but is decided arbitrarily by the performer (Schmidt, 1988b).
Movement tasks have also been classified accord- ing to whether the base of support is still or in motion (Gentile, 1987). “Stability” tasks such as sitting or standing are performed with a nonmoving base of support, while “mobility” tasks such as walking and running have a moving base of support. In the clinic, tasks involving a nonmoving base of support (e.g., sitting and standing) are often practiced prior to mobility tasks such as walking, on the premise that stability requirements are less demanding in the tasks that have a nonmoving base of support. Support for this type of hierarchical ordering of postural tasks comes from research demonstrating that attentional resources increase as stability demands increase. For example, tasks that have the lowest attentional demand are those with a nonmoving base of support (often called “static postural control tasks”) such as sitting and standing; attentional demands increase in mobility tasks such as walking and obstacle clearance (Chen et al., 1996; LaJoie et al., 1993).
The presence of a manipulation component has also been used to classify tasks (Gentile, 1987). The addition of a manipulation task increases the demand for stability beyond that demanded for the same task
lacking the manipulation component. Thus, tasks might be sequenced in accordance with the hierarchy of stability demands (e.g., standing, standing and lift- ing a light load, standing and lifting a heavy load).
Finally, tasks have been classified according to movement variability (Gentile, 1987; Schmidt, 1988b). Open movement tasks such as playing soccer or ten- nis require performers to adapt their behavior within a constantly changing and often unpredictable envi- ronment. In contrast, closed movement tasks are rela- tively stereotyped, showing little variation, and they are performed in relatively fixed or predictable envi- ronments. The training for closed movement tasks is often performed prior to that for open movement tasks, which require adapting movements to chang- ing environmental features. Figure 1.2 shows three of the task components we are concerned with in this book.
Understanding important attributes of tasks allows a therapist to develop a taxonomy of tasks that can provide a useful framework for functional examination; it allows a therapist to identify the spe- cific kinds of tasks that are difficult for the patient to accomplish. In addition, the set of tasks can serve as a progression for retraining functional movement in the patient with a neurologic disorder. An example of a taxonomy of tasks using two attributes, stability– mobility and environmental predictability is shown in Table 1.1. However, as discussed above, a taxon- omy of tasks can be developed using other attributes as well. Lab Activity 1-1 offers you an opportunity to develop your own taxonomy of tasks. The answers to this activity may be found at the end of this chapter.
Environmental Constraints on Movement
Tasks are performed in a wide range of environments. Thus, in addition to attributes of the task, movement is also constrained by features within the environ- ment. In order to be functional, the CNS must take into consideration attributes of the environment when
TABLE 1.1
A Taxonomy of Tasks Combining the Stability−Mobility and Closed−Open Task Continua
Stability
Quasimobile
Mobility
Walk/nonmoving surface
Walk on uneven or moving surface
Sit/stand/ nonmoving surface
Sit to stand/kitchen chair w/arms
Stand/rocker board
Sit to stand/Rocking chair
Closed predictable environment
Open unpredictable environment

planning task-specific movements. As shown in Figure 1.2, attributes of the environment that affect movement have been divided into regulatory and nonregulatory features (Gordon, 1987). Regulatory features specify aspects of the environment that shape the movement itself. Task-specific movements must conform to regu- latory features of the environment in order to achieve the goal of the task. Examples of regulatory features of the environment include the size, shape, and weight of a cup to be picked up and the type of surface on which we walk (Gordon, 1997). Nonregulatory fea- tures of the environment may affect performance, but movement does not have to conform to these features. Examples of nonregulatory features of the environ- ment include background noise and the presence of distractions.
Features of the environment can in some instances enable or support performance, or alternatively, they may disable or hinder performance. For example, walking in a well-lit environment is much easier than walking in low light conditions or in the dark because the ability to detect edges, sizes of small obstacles, and other surface properties is compromised when the light level is low (Patla & Shumway-Cook, 1999).
Thus, understanding features within the environ- ment that both regulate and affect the performance of movement tasks is essential to planning effective inter- vention. Preparing patients to perform in a wide vari- ety of environments requires that we understand the features of the environment that will affect move- ment performance and that we adequately prepare our patients to meet the demands in different types of environments.
We have explored how the nature of movement is determined by the interaction of three factors, the individual, the task, and the environment. Thus, the movement we observe in patients is shaped not just by factors within the individual, such as sensory, motor,
and cognitive impairments, but also by attributes of the task being performed and the environment in which the individual is moving. We now turn our attention to examining the control of movement from a number of different theoretical views.
THE CONTROL OF MOVEMENT: THEORIES OF MOTOR CONTROL
Theories of motor control describe viewpoints regarding how movement is controlled. A theory of motor control is a group of abstract ideas about the control of movement. A theory is a set of intercon- nected statements that describe unobservable struc- tures or processes and relate them to each other and to observable events. Jules Henri Poincare (1908) said, “Science is built up of facts, as a house is built of stone; but an accumulation of facts is no more a science than a heap of stones is a house.” A theory gives meaning to facts, just as a blueprint provides the structure that transforms stones into a house (Miller, 2002).
However, just as the same stones can be used to make different houses, the same facts are given differ- ent meaning and interpretation by different theories of motor control. Different theories of motor control reflect philosophically varied views about how the brain controls movement. These theories often reflect differences in opinion about the relative importance of various neural components of movement. For exam- ple, some theories stress peripheral influences, others may stress central influences, while still others may stress the role of information from the environment in controlling behavior. Thus, motor control theories are more than just an approach to explaining action. Often they stress different aspects of the organization of the underlying neurophysiology and neuroanatomy of
CHAPTER 1 Motor Control: Issues and Theories 7
LAB ACTIVITY 1-1
Objective: To develop your own taxonomy of move- ment tasks.
Procedure: Make a graph like the one illustrated
in Table 1.1. Identify two continua you would like to combine. You can begin by using one or more of the continua described above, or alternatively you can create your own continuum based on attributes of movement tasks we have not discussed. In our example, we combined the stability—mobility continuum with the open—closed continuum.

Assignment
Fill in the boxes with examples of tasks that reflect the demands of each of the continua.
Think about ways you could “progress” a patient through your taxonomy. What assumptions do you have about which tasks are easiest and which the hardest? Is there a “right” way to move through your taxonomy? How will you decide what tasks to use and in what order?

8 PART I Theoretical Framework
that action. Some theories of motor control look at the brain as a black box and simply study the rules by which this black box interacts with changing environ- ments as a variety of tasks are performed. As you will see, there is no one theory of motor control that every- one accepts.
Value of Theory to Practice
Do theories really influence what therapists do with their patients? Yes! Rehabilitation practices reflect the theories, or basic ideas, we have about the cause and nature of function and dysfunction (Shepard, 1991). In general, then, the actions of therapists are based on assumptions that are derived from theories. The specific practices related to examination and interven- tion used with the patient who has motor dyscontrol are determined by underlying assumptions about the nature and cause of movement. Thus, motor control theory is part of the theoretical basis for clinical prac- tice. This will be discussed in more detail in the last section of this chapter.
What are the advantages and disadvantages of using theories in clinical practice? Theories provide:
• a framework for interpreting behavior;
• a guide for clinical action;
• new ideas; and
• working hypotheses for examination and
intervention.
Framework for Interpreting Behavior
Theory can help therapists to interpret the behavior or actions of patients with whom they work. Theory allows the therapist to go beyond the behavior of one patient and broaden the application to a much larger number of cases (Shepard, 1991).
Theories can be more or less helpful depending on their ability to predict or explain the behavior of an individual patient. When a theory and its associ- ated assumptions does not provide an accurate inter- pretation of a patient’s behavior, it loses its usefulness to the therapist. Thus, theories can potentially limit a therapist’s ability to observe and interpret movement problems in patients.
Guide for Clinical Action
Theories provide therapists with a possible guide for action (Miller, 2002; Shepard, 1991). Clinical interven- tions designed to improve motor control in the patient with neurologic dysfunction are based on an under- standing of the nature and cause of normal movement,
as well as an understanding of the basis for abnormal movement. Therapeutic strategies aimed at retraining motor control reflect this basic understanding.
New Ideas: Dynamic and Evolving
Theories are dynamic, changing to reflect greater knowledge relating to the theory. How does this affect clinical practices related to retraining the patient with motor dyscontrol? Changing and expanding theories of motor control need not be a source of frustration to clinicians. Expanding theories can broaden and enrich the possibilities for clinical practice. New ideas related to examination and intervention will evolve to reflect new ideas about the nature and cause of movement.
Working Hypotheses for Examination and Intervention
A theory is not directly testable, since it is abstract. Rather, theories generate hypotheses, which are test- able. Information gained through hypothesis test- ing is used to validate or invalidate a theory. This same approach is useful in clinical practice. So-called hypothesis-driven clinical practice transforms the therapist into an active problem solver (Rothstein & Echternach, 1986; Rothstein et al., 2003). Using this approach to retrain the patient with motor dyscontrol calls for the therapist to generate multiple hypotheses (explanations) for why patients move (or do not move) in ways to achieve functional independence. Dur- ing the course of therapy therapists will test various hypotheses, discard some, and generate new explana- tions that are more consistent with their results.
Each of the many theories that will be discussed in this chapter has made specific contributions to the field of motor control, and each has implications for clinicians retraining patients with motor dyscontrol. It is important to understand that all models are unified by the desire to understand the nature and control of movement. The difference is in the approach.
Reflex Theory
Sir Charles Sherrington, a neurophysiologist in the late 1800s and early 1900s, wrote the book The Integra- tive Action of the Nervous System in 1906. His research formed the experimental foundation for a classic reflex theory of motor control. The basic structure of a reflex is shown in Figure 1.3. For Sherrington, reflexes were the building blocks of complex behavior. He believed that complex behavior could be explained through the combined action of individual reflexes that were chained together (Sherrington, 1947). Sherrington’s view of a reflexive basis for movement persisted

CHAPTER 1 Motor Control: Issues and Theories 9
} Stimulus
unchallenged by many clinicians for 50 years, and it continues to influence thinking about motor control today.
Limitations
There are a number of limitations of a reflex theory of motor control (Rosenbaum, 1991). First, the reflex cannot be considered the basic unit of behavior if both spontaneous and voluntary movements are recog- nized as acceptable classes of behavior, because the reflex must be activated by an outside agent.
Second, the reflex theory of motor control does not adequately explain and predict movement that occurs in the absence of a sensory stimulus. More recently, it has been shown that animals can move in a relatively coordinated fashion in the absence of sensory input (Taub & Berman, 1968).
Third, the theory does not explain fast move- ments, that is, sequences of movements that occur too rapidly to allow for sensory feedback from the pre- ceding movement to trigger the next. For example, an experienced and proficient typist moves from one key to the next so rapidly that there is no time for sensory information from one keystroke to activate the next.
Fourth, the concept that a chain of reflexes can create complex behaviors fails to explain the fact that a single stimulus can result in varying responses depending on context and descending commands. For example, there are times when we need to over- ride reflexes to achieve a goal. Thus, normally touch- ing something hot results in the reflexive withdrawal of the hand. However, if our child is in a fire, we may override the reflexive withdrawal in order to pull the child from the fire.
Finally, reflex chaining does not explain the abil- ity to produce novel movements. Novel movements put together unique combinations of stimuli and responses according to rules previously learned. A violinist who has learned a piece on the violin and also knows the technique of playing the cello can play that piece on the cello without necessarily having
practiced it on the cello. The violinist has learned the rules for playing the piece and has applied them to a novel situation.
Clinical Implications
How might a reflex theory of motor control be used to interpret a patient’s behavior and serve as a guide for the therapist’s actions? If chained or compounded reflexes are the basis for functional movement, clini- cal strategies designed to test reflexes should allow therapists to predict function. In addition, a patient’s movement behaviors would be interpreted in terms of the presence or absence of controlling reflexes. Finally, retraining motor control for functional skills would focus on enhancing or reducing the effect of various reflexes during motor tasks.
Hierarchical Theory
Many researchers have contributed to the view that the nervous system is organized as a hierarchy. Among them, Hughlings Jackson, an English physi- cian, argued that the brain has higher, middle, and lower levels of control, equated with higher associa- tion areas, the motor cortex, and spinal levels of motor function (Foerster, 1977).
Hierarchical control in general has been defined as organizational control that is top down. That is, each successively higher level exerts control over the level below it, as shown in Figure 1.4. In a strict verti- cal hierarchy, lines of control do not cross and there is never bottom-up control.
In the 1920s, Rudolf Magnus began to explore the function of different reflexes within different parts of the nervous system. He found that reflexes controlled by lower levels of the neural hierarchy are present only when cortical centers are damaged. These results were later interpreted to imply that reflexes are part of a hierarchy of motor control, in which higher centers normally inhibit these lower reflex centers (Magnus, 1925; 1926)
Top
Down
The hierarchical control model is character- ized by a top-down structure, in which higher centers are