Rehabilitation professionals think about the human body as a complex biological system with many interacting elements and subsystems (Figure 3-1). These components have an infinite number of ways to work together in accomplishing a goal-directed motor act.^47–49 Because the human body is a dynamic, adaptive, and inherently complex set of subsystems, motor behaviors and ways of moving become more efficient with practice and experience: motor control systems can consistently generate simple and well-organized movement from a complex array of movement possibilities.^50,51 The dynamic systems perspective of motor control is founded on understanding of behaviors that physical systems of various types have in common: the ability to change over time, the ability to be adaptive yet have preference for habitual tendencies, and the context of interaction with the environment in which movement occurs.^43,52–54 In the human movement system, there is great “motor abundance”; each person has a wide variety of ways to accomplish an intended movement goal (i.e., solve a functional movement problem) in whatever environmental conditions or circumstances that function occurs.^55,56

According to Bernstein’s model of motor control, individuals have the capacity “to make a choice within a multitude of accessible trajectories…of a most appropriate trajectory.”57 Dynamic systems theory suggests that there are both opportunities and challenges presented by interaction of the environment and the individual’s will to move.⁵⁷ Unlike systems that are purely physical, the human biological system is a smart, special-purpose machine able to instantaneously and efficiently work to meet the many parallel and serial functional demands.^58–60 In addition, biological systems such as the human body are self-organizing^59,61; the mutually dependent and complex processes among the body’s subsystems allow this wonderfully dynamic structure to enact efficient functional movement patterns. Even though it is an inherently multidimensional biological system, the human body prefers to be in a state of relative equilibrium.^62,63 This is likely to be the underlying reason that the gait cycle at self-selected (comfortable) walking speed tends to center around one cycle per second, and that most individuals transition from walk to run, as gait speed increases, at nearly the same velocity.⁶⁴ The human body, as a smart and dynamic biological system, is also intentional; there is a purposeful, goal-directed, and task-oriented nature in most motor behaviors.⁶⁵ The dynamic systems model defines an intention as a purposeful or desired act that influences (attracts) the human system to organize motor behavior toward the desired outcome, in the context of the environment in which the movement is occurring.⁶⁶ The organism and the environment are interdependent; each is defined with respect to the other.^58,65,66 Although the characteristics of the physical environment are the focus on many studies of goal-directed movement, the social-emotional environment can also influence the emergence of goal-directed movement.⁶⁷ The combination of resources available to the organism-environment interaction, in conjunction with the individual’s intention, shapes (constrains) how task-oriented motor behavior is organized.

Motor control has been defined by Shumway-Cook and Woollacott as “the ability to regulate or direct the mechanisms essential to movement.”³⁹ The interactive systems that provide resources that an individual uses to initiate and regulate goal-directed movement include the neurological, musculoskeletal, sensory/perceptual, cardiorespiratory, and cardiopulmonary, and the cognitive, learning, and memory systems. Human movement, or motor control, is a product of the interaction of the individual (with all of his or her subsystems), the characteristics of the environment, and the nature of the specific task or goal that the individual is involved in (Figure 3-2). Movement, then, is goal directed and purposeful; it makes use of the innate and learned resources available to the individual and is subject to the influences of the environment in which it is performed. By considering each of these essential contributors to functional movement, rehabilitation professionals can assess potential sources of movement dysfunction, explore alternative movement strategies, and adapt or alter the task or environment to improve movement outcomes.^68,69

Resources of the Individual

The first component to consider in this model of motor control is the individual, with his or her ability to think and reason, to sense and perceive, and to actively respond or initiate movement (Figure 3-3). An individual’s cognitive resources include the abilities to critically think and integrate concepts, organize and delay gratification, assign emotional meaning/significance to an activity or circumstance, problem solve, access and use memory, manage attention and focus (especially when engaged in concurrent tasks), and learn.^70–72 An individual’s perceptual resources are the products of the ability to receive and process many different types of sensory information (i.e., data) and to integrate and interpret these data at both subcortical and cortical levels of information processing.^73–77 An individual’s resources for action include the ability to motor plan and refine motion at cortical and subcortical levels; error control systems of the cerebellum; pyramidal and extrapyramidal motor systems; and the neuromuscular, musculoskeletal, and cardiopulmonary/cardiovascular contributors to “effector” systems.^78–93

To illustrate how individual resources influence movement, consider two individuals who are walking to their cars after a major-league baseball game. Their pathway moves across a gravel-surfaced parking area with a slightly sloped and slightly unstable support surface. One person has the “stocking-glove” sensory and motor impairment typical of diabetic polyneuropathy. The other has consumed a few too many servings of beer in cheering his team to victory, making his thinking and motor behavior less efficient than normal. Both are likely to exhibit less efficient postural response and unsteady gait patterns as they return to their vehicles, but for very different reasons. The quality of the sensory data that the individual with diabetic neuropathy can collect may not be sufficient for accurate perception of environmental conditions, and, complicated by distal weakness, her patterns of movement may not meet the challenges presented by the sloped and slightly movable ground surface. The individual who is tipsy has normal data collection ability; however, the temporary impairment in cognitive function (judgment and perception) and less efficient “error control” associated with alcohol consumption lead to motor behaviors that are not matched to environmental demands. Both baseball fans may stumble, walk with a wide base of support, or reach for the support of solid objects as they make their way toward their cars, but the underlying individual contributors to this motor outcome are quite different.

Nature of the Task

The task is the second essential component to the overall outcome or motor behavior performed. A functional task may require an individual to organize goal-directed movement to address one or more of the following motor control goals (Figure 3-4):

• Maintaining or adjusting antigravity posture (static, anticipatory, or reactionary postural control)94–96

• Transitioning from one stable position to another (quasimobility; e.g., moving from sitting to standing)97–99

• Moving a limb or the whole body through space (e.g., reaching, lifting, carrying, walking, stair climbing, walking on inclines, avoiding obstacles, hopping, running)100–102

• Using or manipulating tools appropriate to the task (e.g., assistive devices, objects needed for ADLs)103^,104

Any task can be described along a number of different dimensions or continua: it can have discrete beginning and endpoints (e.g., transferring from bed to chair) or be continuous (e.g., walking or running over large distances). They can involve stability or require mobility, occur at various speeds, require different levels of accuracy or precision, and demand different levels of attention or focus (Box 3-1). Repetitive and overlearned tasks performed in predictable (closed or fixed) environments are often executed on a nearly automatic level, requiring little attention; this allows the individual to focus attentional resources on other prioriteis.¹⁰⁵ Tasks occurring in a changing (dynamic or open) environment must be flexible or adaptable to be successful and require a higher degree of attention during performance.^106,107 Finally, the complexity of the task and the attentional requirements for effective task performance must be considered.¹⁰⁸

Box 3-1

Descriptors of Movements Based on the Attributes/Nature of a Task

• Discrete: The beginning or end point of movement, or both, as determined by the task itself (e.g., stepping onto a curb, donning a prosthesis, catching a ball).

• Serial: An ordered sequence of discrete movements, defined by the task itself (e.g., climbing a flight of stairs).

• Continuous: The beginning and end points of the task are determined and controlled by the individual (e.g., riding a bicycle, deciding when to start or stop).

• Stability: The primary task goal is to maintain position of body segments (often against gravity or in response to perturbation) or to keep the body’s center of mass within the available base of support during functional activity (e.g., to provide a secure base in sitting or standing for subsequent skilled use of extremities).

• Transitional (quasimobility): The primary task goal is to move the body from a starting position of stability to a different ending position of stability (e.g., moving from sitting to standing, rolling from supine to prone, getting up from the floor).

• Mobility: The primary task goal is to move a body part, or the entire body, through physical space (e.g., rolling over in bed, walking or running, reaching for an object on a shelf or on the floor).

• Manipulation continuum: The degree to which a task requires the individual to use (manipulate) or interact with one or more external objects in order to complete the activity successfully (e.g., fastening buttons or handling clothes during dressing, donning/doffing a prosthesis or orthosis, opening doors during mobility, locking the brakes on a wheelchair).

• Automaticity: The degree to which the task is well understood and can be carried out automatically or requires attention because of high task demand (level of preciseness, consequence of error) or the changing nature of the task or environmental conditions (e.g., threading a sewing needle, walking down an icy sloping walkway, catching a thrown object).

• Variability in performance: The degree to which an individual is able to adapt the performance of a learned task in response to differences in environmental conditions or changes in task constraints; the flexibility to apply what has been learned to similar or novel situations.

One way to understand the nature of a task (either broken into components or as a whole) is to examine or classify the task using Gentile’s Taxonomy of Movement Tasks (Figure 3-5).⁴⁰ The first component considered in the taxonomy is the movement task’s outcome goals: does the task primarily focus on stability of the body, transition between stable positions, or on transport (movement) of the body through space? As an example of a body stability task, consider the ability of an individual learning to use a transfemoral prosthesis to control hip and pelvic position while in single-limb stance on the prosthetic side, while slowly lifting the “intact” limb to place it on a stool or step placed in front of him or her. A transitional (quasimobile) task for this person might be practicing moving between sitting and standing position from various seating surfaces or heights.⁴ A body mobility task for the same individual might be to learn to use a cadence-responsive prosthetic knee unit by altering gait speed, changing direction, or navigating through a crowded public space.

The next consideration is whether the task involves use of, or interaction with, a tool or object (i.e., is object manipulation part of the task?). In working with persons with spinal cord injuries to develop postural control in sitting, for example, therapists often use catching and throwing activities with balloons and balls of various weights, thrown at different speeds and in varying directions, to provide opportunity to master this body stability skill.109–111 Managing assistive devices (e.g., cane, crutches) during transfers or operating orthotic knee locks or prosthetic knee units during transfers are examples of object manipulation during transitional motor tasks. Learning to use an ambulatory assistive device (e.g., crutch walking in a four-point reciprocal pattern; managing crutches when ascending or descending stairs) is a prime example of a body mobility task that requires object manipulation.^112,113

Characteristics of the Environment

The final component of the Shumway-Cook and Woollacott’s model of motor control is the setting, environmental context, or conditions in which the goal-directed movement takes place (Figure 3-6). The physical therapist must examine (and, during intervention, purposefully manipulate) the environmental context in which functional movement occurs. Is the physical environment comfortable to be in while taking part in exercise and other rehabilitation interventions? Is it visually interesting and stimulating but not too distracting or challenging? Is the motor task occurring in an environment that is predictable (i.e., in a closed environment), or is there a degree of variability and possibility of change external to the individual (i.e., an open environment) that will require the individual to monitor and respond more carefully while performing the task?^114–116 Therapists must also consider the social-emotional context of the environment that is rooted in the interpersonal interaction: will the individual feel supported and encouraged as he takes risks and makes errors as part of the development of skill in salient activities? Or does the emotional environment contribute to anxiety about receiving negative criticism or a fear of failure?^117,118

For the therapeutic application of environmental variables, therapists can consider both macroenvironmental influences (e.g., actual physical conditions that influence task demand, the therapeutic setting, or the involvement of family members), as well as microenvironmental influences (e.g., the level of visual and auditory “noise” present in the therapy room or variations in surfaces over which a client may be sitting or walking). Mastery of a motor task within a single, simple environment does not directly translate into safe performance of the same task under more complex and demanding environmental conditions. Navigating up and down a set of training steps in the physical therapy gym does not mean that the individual with stroke or paraplegic-level spinal cord injury will be functional and safe on a wet, leaf-covered, uneven brick staircase (with no railings) when entering or leaving his best friend’s house or favorite neighborhood hangout.119^,120

When working with persons with acquired brain injury functioning at the Rancho Los Amigos cognitive continuum of 4 (confused and agitated), 5 (confused inappropriate), or 6 (confused appropriate), therapists must provide a structured and predictable environment for functional and rehabilitative activities, so that the demands of the environment do not exceed the individual’s ability to monitor and respond to the challenges that the environment presents.^121–123 A complex environment can be overwhelming to the individual recovering from brain injury; the structured environment provides opportunity to complete key tasks with minimal frustration and behavioral complications. However, the complexity of the environment must be gradually increased as the individual prepares for discharge. Being able to cross the street safely at a crosswalk with real traffic is a more complex task than managing curbs and walking over a distance in the rehabilitation gym.

Gentile’s taxonomy provides an organizational strategy for intervention planning by rehabilitation professions working with individuals with musculoskeletal or neuromuscular impairments and limitations in performing functional activities. The primary goal of a man who has had a recent stroke may be to climb stairs so that he can return to his home, where the bedroom and bathroom are upstairs. In the early stages of rehabilitation, it may be necessary to first concentrate on static postural control and controlled weight shifting in sitting and standing on a firm support surface (body stability, no object manipulation, predictable environment). As the quality and control of these motor tasks become more consistent, intervention expands to include ambulation in the parallel bars (body mobility, no object manipulation, unvarying environment), then with an assistive device in a quiet hallway (body mobility, object manipulation, predictable environment), and finally in a busy rehabilitation gym in which the individual must anticipate and react to others in the environment (body mobility, object manipulation, changing environment). As postural control becomes more efficient on level surfaces, task demand is increased by increasing speed or attempting more challenging surfaces such as stairs, inclines, and stepping over obstacles; this may initially occur in a relatively predictable environment but must eventually occur in an “open” situation in which the individual must dynamically react to or navigate around other persons and objects.

Initial models of motor learning were published in the early 1970s, the most prominent being Adams’ closed-loop theory and Schmidt’s schema theory.134^,135 Both models assume that, as a result of the motor learning process, the brain develops generalized motor programs: rules for timing and sequencing of muscle activity for key tasks.¹³² The closed-loop theory proposes that sensory information generated from movements occurring during performance of functional tasks provides feedback necessary to build the memory and perceptual traces that guide and refine subsequent performance of the task.¹³⁴ In contrast, schema theory suggests that an open-loop process occurs, in which a general set of rules for a particular movement is developed (motor recall and sensory recognition schema) over time. Such schemas allow the individual to continuously compare actual outcomes of movement with anticipated (feedforward)/predicted outcomes via error detection and correction mechanism.^135,136 According to schema models, variability of practice must occur to establish and strengthen the movement schema over time.^137,138

In the 1990s, Newell proposed an alternative ecological model of motor learning (resonant with Bernstein’s dynamic systems model of motor control) that suggests individuals use a problem-solving approach to discover the optimal strategy to produce the task (performance) given both environmental and task influences.^139,140 By exploring the perceptual motor workspace during practice, individuals begin to recognize salient sensory/perceptual cues as they explore movement options that might lead to successful task completion. In viewing a demonstration, perceptual information helps the learner better understand the nature of the task and task-related movements that need to be mastered. Perception during (knowledge of performance) and perception after (knowledge of results) task-related movement provides intrinsic feedback that assists the problem solving process in the development of optimal strategies for the task at hand. Therapists can provide augmented information (explicit cues and extrinsic feedback) to facilitate an individual’s search for optimal strategies. In this way, the perception (salient cues about the task and the environmental) and action (adaptive motor performance of the task.) are linked so that task-relevant connection is established.¹⁴⁵

Refer to Shumway-Cook and Woollacott¹³² and Schmidt and Lee¹²⁸ for a more detailed discussion of these theoretical models.

Motor learning has also been explained through a temporal perspective in which learning occurs in stages over time. Various three- and two-stage models have been proposed to describe the process for acquisition of a skill and for adaptability or generalization/transfer of the skill (Table 3-1).

Three-stage models generally describe the earliest stage as the discovery stage, in which an understanding of the nature of a task is developed through trial and error, sometimes with guidance.54^{,128,137–144} In this initial stage of motor learning, the need for attention is high, and there is significant trial and error-related variability in task performance early on, with an eventual understanding or selection of the best plan for the task for that individual. Once a plan has been settled on, the second stage of motor learning focuses on refinement of the performance; error during performance decreases while efficiency of performance increases, but attention is still required and distraction is often problematic, interfering with performance.¹⁴⁵ In the third and final stage of motor learning, the individual can generalize or adapt the learned skill to changing environmental demands; much less attention to task is required, and the task can be performed effectively in various ways under multiple environmental demands.

Building on the work of Lereijken and colleagues, Shumway-Cook and Woollacott describe a system-oriented three-stage model, integrating principles of dynamic systems motor control, human development, and the ecological model of motor learning.^132,144 Early in motor learning, individuals constrain (freeze) the degrees of freedom among limb segments (joints) involved in the task as a means of reducing task difficulty; this freezing cocontraction around joints results in relatively accurate movement, although the movment typcially has a high energy cost.¹⁴⁶ As learning occurs, there is a tendency to “unfreeze” joints sequentially such that movement becomes more fluid and energy-efficient. With mastery, the individual employs freedom of movement to fluidly perform the task and can adapt to changing characteristics of the environment.¹⁴⁷

Two-stage models of motor learning focus on (1) acquisition of the skill and (2) adaptation or application of the skilled motor behavior.¹⁴⁸ The initial phase consolidates the first two components of the three-stage models: Acquisition and refinement of performance occur within the same stage. Variability of performance occurs through internal demands within the individual’s attempts to find and select a preferred action/strategy before refinement. In the second stage performance is variable due to external demands of the environment: The person must adapt the task accordingly; this is quite similar to the final component of each of the three-stage models.¹⁴⁹

To understand the process of motor learning, it is important to consider the principles underlying all learning processes: how new information is translated into memory to become useful. One can think about learning as the process of acquiring new information and new skills; memory then is the product or outcome of the learning process.150 Learning is one of the major drivers of plasticity within the CNS, stimulating formation of new synapses as well as refinement of existing neural connections throughout the brain.^151,152 This plasticity is evident as information is moved from our short term (working) memory into initial long term memory stores which become better established, and more resistant to disruption, with practice and experience (Figure 3-7).¹⁵³

Learning theorists describe two major categories of learning: implicit (nondeclarative) and explicit (declarative) learning (Figure 3-8).¹⁵⁴ Both categories lead to functional and physiological changes in synapses of involved areas of the spinal cord, brainstem, and forebrain.¹⁵⁵ One aspect of motor learning falls into the category of implicit procedural learning: it requires trial and error (discovery) in a relevant and functional context.¹⁵⁵ Consistently improved task performance over time and situation provide evidence of effective procedural learning. Neural structures thought to be necessary for implicit procedural learning include cortex of the frontal and parietal lobes, nuclei of the basal ganglia, and cerebellar cortex and nuclie.^156–158 Recent work has also identified that the hippocampus in involved in perceptual components of procedural learning.¹⁵⁹ Explicit (declarative) learning is founded on attention and conscious thought and can be described or demonstrated by the learner.¹⁶⁰ Neural structures involved with explicit learning include prefrontal cortex, cingulate gyrus (limbic system), head of the caudate nucleus, medial temporal lobes, and hippocampus.¹⁶¹ The hippocampus plays a key role in motor learning because it contains a cognitive-spatial map of the typical areas in which humans function.¹⁶⁶ Early motor learning is strengthened, as evidenced by changes in output of the primary motor cortex, when explicit learning of sequences is associated with implicit learning.^162–164

Once sequential aspects of the task are well understood, the need to pay close attention during motor performance diminishes, and the skill becomes less effortful as it transitions toward automaticity.165 As automaticity increases, the ability to attend to simultaneous tasks also increases.^166,167 There is growing evidence that the transition from early motor learning of complex, sequentially organized tasks to automaticity requires more time and practice as a person ages.^168–171 Encouragement and feedback that focus on building perceptions of capability (self-efficacy) with respect to better performance than peers appears to enhance motor learning in both young and older adults.^172,173

Key motor learning concepts that physical therapists working with individuals new to prosthetic or orthotic use include practice conditions and schedule; the role of variability, contextual interference, and feedback on skill acquisition; development of automaticity of performance; as well as retention and transfer of the newly learned motor skill (Box 3-2).^128,132 Each is discussed in the following section.

In a complex and variable world, there are innumerable ways to respond to challenges that are encountered. Over the life span, typically developing individuals explore many movement options to accomplish salient task goals, developing a set of action plans that demonstrate both automaticity in performance and adaptability to variations in task or environmental constraints (i.e., the mastery of bipedal locomotion, over different surfaces, at various speeds, in closed versus open environments).175^,176 Discovery learning and the feedback/feedforward provided by error during repeated practice across conditions with differing constraints allows the individual to develop an understanding (perception) of the common elements of the task wherever and whenever it is performed.^174,177,178 This perception provides the flexibility to select from a range of task-specific options and adapt movement in response to variations encountered in daily life; variability in skilled movement is an adaptive resource responsive to variation in environmental demands.¹⁷⁹

The movement patterns of individuals with neurological or neuromuscular dysfunction, however, often demonstrate hypervariability or hypovariability.^176,180 Too much or too little variability is problematic: Perception of the nature of the task and of interaction between task and environment may be limited or altered, and acquisition of skill may be challenged by the constraints associated with altered muscle performance and motor control.^181–183 Functionally, this contributes to a reduced ability to adapt (vary) performance in response to changing environmental conditions. The rigidity characteristic of Parkinson disease, for example, creates “super stability” of the trunk and extremities that interferes with mobility (locomotion) and postural control when task conditions change (i.e., the need to increase speed, walk through doorways, or to walk on inclines).^181,184 In persons with stroke, impaired ability to move the involved upper extremity was accompanied by difficulty recognizing action of the corresponding limb when observing others or a computer model.¹⁸⁵ In persons with right hemisphere stroke, impairments of attention and perception challenge the ability to develop the set of task-specific movement options necessary for adaptive function in response to variations in environment and context.^186,187 While implicit motor learning can be successful after a stroke, movement during acquisition stages is often slower and more variable in both blocked and random practice conditions.¹⁸⁸ Variability in movement is also altered in children with hypertonic and dyskinetic cerebral palsy, and in those with developmental coordination disorder.^179,182,189

In rehabilitation, therapists set up opportunities for discovery motor learning for patients that are designed to enhance the likelihood of discovering, from among all possible movement options, the set of movements most likely to result in successful task performance.^175,176 This is accomplished by manipulating the environmental and task constraints in relevant and meaningful ways to actively engage the individual in iterations of the task, with the goal of promoting both perceptual understanding and a usable set of action options for completing the task.^175,190,191

One way to describe practice is by whether it occurs in a blocked or random sequence. Blocked practice (also known as constant practice) is characterized by separate but subsequent repeated trials of the same task.132^,174 For blocked practice, the task is repeated under consistent environmental conditions. Modified blocked practice involves repeating the motor task three or more times in one condition before altering conditions or context in which practice of the same task is repeated. During blocked practice, the individual concentrates on performance of a single task; this focus reduces overall demand on working memory. As a result, quality of performance tends to improve substantially over successive bouts of blocked practice. In healthy adults, acquisition of skill appears to be effective (performance becomes more accurate over a single practice session) with blocked practice, however retention of the skill over time and transfer of the skill to differing conditions is not as strong.¹⁹² Blocked practice appears to have a positive impact on retention of skill for children younger than 10 years; this is thought to be a function of emergence of information processing capability in late childhood and early adolescence.^193,194

For the individual with transfemoral amputation working on stance control on the prosthetic limb, a blocked practice session might include stepping up onto a stool with the intact limb for 10 trials (repetitions), while standing in the parallel bars. The level of difficulty of the activity could be advanced by setting up an additional practice session, asking the individual to perform a similar task while supporting himself or herself with a straight cane to a practice curb or step outside the parallel bars. Theoretically, practice in the parallel bars would provide a model to use when performing a similar activity outside the parallel bars.

Random practice (also described as variable practice) is characterized as practicing a set of tasks in which order and perhaps difficulty of tasks varies across bouts of practice.^132,174 Because of the variation encountered during random practice, there is less improvement of performance in a given practice session (compared with blocked practice); however, there is greater retention of what has been learned over time. Theoretically, random practice creates contextual interference (the work of keeping many options available in working memory over time) that actually enhances learning and mastery over time despite poorer immediate performance.^174,192 While this may be counterintuitive, the efficacy of contextual interference on mastery of complex movement tasks is well supported.^195–199 One of the proposed mechanisms for enhanced retention in random practice is increased attentional demand that results in better use of perceptual understanding to prepare for movement.^197,199 The degree of similarity of tasks (distraction) undertaken during a practice session can also be a source of contextual interference; greater attention is required to discriminate between tasks with similar but distinct characteristics.¹⁹⁸ The improvement of retention occurs even when the context or characteristics of the task are somewhat altered; thus random variable practice may enhance transfer of learning.¹⁷⁴

To practice the primary task of stance phase stability using a random practice order, the individual with a transfemoral prosthesis would be involved in an ongoing session of gait training. As this person walked the length of the parallel bars (or across the gym), he or she might be asked to step up onto a stool or over an obstacle at a different point in the walk and to change direction or speed on randomly delivered commands. The walk itself might be repeated 10 times (practice trials), with a step up onto or over the stool and changing speed and direction at a different point in each of the 10 trials of walking. These trials of stepping up or over and altering speed and direction do not occur sequentially but instead are interspersed throughout the entire ambulation event.

A third practice condition called serial practice can be thought of as a blending of the blocked and random practice order. Serial practice is a collection of different tasks performed sequentially, from a designated starting point to a defined ending point, always occurring in the same order, and repeated as a whole set of movement tasks.^132,174

In a serial practice session for an individual learning to use a transfemoral prosthesis, the therapist may instruct him or her to repeat a specific sequence of movements such as the following:

Another way to classify practice is by the relative period of time spent in active practice versus rest time between practice sessions. In conditions of massed practice, there is more time spent over a practice trial than there is rest time between trials. Fatigue may be a factor in decreases in performance over repeated practice sessions if rest periods are insufficient. In conditions of distributed practice, the amount of practice time is less than or equal to the amount of rest time between trials.132^,174 Given evidence of better retention and transfer of skills with longer rest periods between practice trials (i.e., distributed practice), rest appears to be more than a period of physical recovery; it may also enhance consolidation of perceptual schemas and action rules associated with the skill that has been practiced into memory.²⁰⁰ What is not yet understood is how much practice time and how much rest is optimal for tasks of different complexity or learners with various resources or impairments.

Many functional tasks have sequential, recognizable subcomponents. The task of rising from a chair, for example, may require moving forward toward the edge of the seat, changing foot position, leaning forward to shift body weight from the ischial tuberosities toward the feet, lifting off the seat, accelerating quickly upward into standing, and then establishing postural control in the upright position.201 The task of walking can be divided into stages including weight acceptance in early stance, stability during single limb stance, preparation for swing at the end of stance, and initiation through completion of limb advancement during swing phase.²⁰² When working with individuals who have neurological, neuromuscular, or musculoskeletal related movement dysfunction, therapists often use task analysis to determine what subcomponents of the task are problematic. The therapist might opt to practice the problematic components of the task to build skill before attempting the entire task (part to whole training) or to practice the entire task repeatedly (whole task training). In partial task training, the task is divided into separate parts, and each part is explained or modeled as distinct components of the task, while in whole task training the entire task is explained verbally or modeled (demonstrated) in entirety from beginning to end. The decision to structure training as part versus whole is influenced by level of difficulty of the task; the degree that the individual has already mastered some of the task components; the individual’s ability to attend to the task, his or her level of motivation and frustration; and safety considerations as the task is attempted. Tasks that are serial in nature lend themselves in part to whole training; spending time practicing complex or difficult task components (ending the session by putting all of the components together to perform the whole task) often leads to better retention and transfer than the same amount of time spent practicing the entire task.^174,202,203 Tasks that are continuous, such as carrying a tray while walking through the cafeteria, are not as easily separated into components because of the degree of coordination and interplay necessary among task components. When coordination, timing, and interaction must be learned, whole task training appears to be more efficacious.^174,203,204