Abstract
Background and Purpose Stepping reactions are important for walking balance and community-level mobility. Stepping reactions of people with stroke are characterized by slow reaction times, poor coordination of motor responses, and low amplitude of movements, which may contribute to their decreased ability to recover their balance when challenged. An important aspect of rehabilitation of mobility after stroke is optimizing the motor learning associated with retraining effective stepping reactions. The Challenge Point Framework (CPF) is a model that can be used to promote motor learning through manipulation of conditions of practice to modify task difficulty, that is, the interaction of the skill of the learner and the difficulty of the task to be learned. This case series illustrates how the retraining of multidirectional stepping reactions may be informed by the CPF to improve balance function in people with stroke.
Case Description Four people (53–68 years of age) with chronic stroke (>1 year) and mild to moderate motor recovery received 4 weeks of multidirectional stepping reaction retraining. Important tenets of motor learning were optimized for each person during retraining in accordance with the CPF.
Outcomes Participants demonstrated improved community-level walking balance, as determined with the Community Balance and Mobility Scale. These improvements were evident 1 year later. Aspects of balance-related self-efficacy and movement kinematics also showed improvements during the course of the intervention.
Discussion The application of CPF motor learning principles in the retraining of stepping reactions to improve community-level walking balance in people with chronic stroke appears to be promising. The CPF provides a plausible theoretical framework for the progression of functional task training in neurorehabilitation.
When walking in the community, people experience balance challenges. Taking a step to regain balance, or a stepping reaction, in response to balance challenges is common.1 Stepping reactions of people with stroke are characterized by slow reaction times, poor coordination of motor responses, and low amplitude of movements, which may contribute to their decreased ability to recover their balance when challenged.2
A single-subject case study outlined 1 approach to the retraining of unidirectional stepping in subacute stroke rehabilitation.3 However, effective retraining of stepping reactions for safe community-level mobility must support the transfer of skill to responding to balance disturbances in a variety of directions. The use of motor learning principles, including the manipulation of information delivery (or augmented information), schedules of practice, and levels of physical assistance, may represent an optimal approach for motor skill retraining, retention, and transferability in people with stroke.
The Challenge Point Framework (CPF) suggests that motor learning is optimized when the learner is actively involved in problem solving during the process of finding movement solutions.4 The CPF focuses on the interaction of the skill of the learner and the difficulty of the task to be learned while important conditions of practice are manipulated to optimize motor learning. The CPF describes task difficulty as being “nominal” and “functional.” Nominal task difficulty includes only the characteristics of the task, regardless of who is performing the task and under what conditions.4 Functional task difficulty refers to the challenge of the task, taking into consideration the skill level of the person performing the task and the conditions under which it is performed,4 and can be manipulated readily by clinicians.
The CPF states that learning is influenced by the information available during performance in addition to the learner's ability to use this information.4 Information is derived from the nature of the task and the associated feedback the person may be provided. Therefore, too much or too little information may have a potentially negative effect on motor learning. The aim of designing skilled motor practice based on the principles of the CPF is to determine the appropriate level of functional task difficulty, or optimal challenge point, for a learner by controlling the level of information present within a task through manipulation of 2 practice variables—contextual interference and feedback.
Contextual interference is the level of interference resulting from the organization of practice (eg, blocked versus random practice) during motor skill learning.4 For example, practicing 3 different tasks, 1 at a time, would be considered blocked practice, whereas practicing the 3 tasks in a nonsystematic order would be considered random practice. Increased random practice, as a form of contextual interference, increases functional task difficulty because it challenges the learner to switch movement-related problem solving among the tasks.4 Providing information to the learner that assists in problem solving is called augmented feedback; importantly for optimized learning, this feedback must be balanced to enable the learner to experience error during practice and independent problem solving.5,6 The CPF predicts that a person who is earlier in the learning process may not interpret all of the information inherent in performance of the task and may benefit from blocked practice of motor skills together with simple immediate feedback to direct problem solving. As the learner becomes more proficient, he or she should be challenged at a higher level to promote motor learning processes.4 The CPF describes achieving progression to random practice with minimal augmented feedback as a practice design in which the learner is most likely to establish a new motor plan that is retained and transferable.
Responding to multidirectional stimuli with effective stepping reactions is highly challenging after stroke. Asymmetrical weakness, altered sensation and coordination,7 and decreased self-efficacy for tasks requiring a higher level of mobility8 combine to increase the relative difficulty of stepping reactions. The CPF has been demonstrated to be an effective approach to neurorehabilitation for people with Parkinson disease (PD).9 The CPF has not been applied directly in stroke rehabilitation research; however, some investigators used a similar motor learning theory in stroke rehabilitation.10–15 The CPF relies on the effects of practice scheduling or contextual interference to manipulate the functional difficulty of a new motor task. Past work demonstrated that manipulating contextual interference is an effective means of altering functional task difficulty, cortical excitability, and rates of change associated with motor learning.15–17 Given these effects, contextual interference is an ideal principle to use in the study of CPF, which involves the manipulation of practice schedules relative to functional task difficulty for each person. The purpose of this case series is to illustrate the use of the CPF in the retraining of multidirectional stepping reactions to improve community-level walking balance, the motor performance of stepping reactions, and participants' confidence when performing challenging walking tasks.
Participants
Four community-dwelling participants in the chronic phase of stroke recovery were recruited. The inclusion criteria included: independent ambulation with or without an assistive device and at least a stage 3 level of motor recovery, as measured using the foot and leg components of the Chedoke-McMaster Stroke Assessment (CMSA), with each component graded out of a score of 7.18 Participants were excluded if they had any comorbidities that seriously affected mobility (eg, severe osteoarthritis). The study conformed to the standards set by the latest revision of the Declaration of Helsinki and was approved by the University of British Columbia Clinical Research Ethics Board.
Intervention
Protective Stepping Reaction Retraining Protocol
The stimulus used to provoke protective stepping reactions was self-initiated leaning in different directions. Participants were instructed to stand straight and to lean, pivoting from the ankles, in 1 of 4 directions: forward, backward, or laterally to the right or left. Participants were instructed to perform this activity without trying to control their lean and to simply “let themselves fall like a tree” until they felt the need to step to keep from falling. The aim of this balance challenge was not to replicate a real-life scenario but rather was to use the sensation of the movement of the center of mass outside the base of support (past the perceived limits of stability) as a stimulus to produce a stepping reaction in multiple directions to prevent a fall. To reduce the potential fear of falling, participants were encouraged to focus on increasing the speed and length of the stepping reaction rather than their limits of stability. Participants had equal practice performing steps with both legs as the initial stepping leg. Participants were able to follow the initial step with as many additional steps as required to regain their balance; however, they were encouraged to try to come to a stop in 2 to 3 steps. When performing lateral leaning stimuli, no lead leg was specified, and either a cross-step or a same-side strategy was permitted.1
Training involved 45-minute sessions 3 times per week for 4 weeks. Testing was conducted during 3 of the 12 sessions, leaving 9 practice sessions. During training, participants completed 2 sets of 60 stepping reactions (10 repetitions with each leg in each direction), with brief rest periods in a standing position between repetitions and seated rest periods of approximately 5 minutes between sets. The number and length of training sessions were determined from a previous efficacy study.2 No training was included on testing days. Testing took place before the initiation of training after 2 weeks and 4 weeks of the intervention. Finally, a long-term retention test was completed 1 year later.
Practice Design
Contextual interference and progression of functional task difficulty.
The first training week started as blocked practice of stepping reactions in each direction to optimize the initial acquisition of the motor skill (Fig. 1A) and progressed to random practice to optimize motor learning (Figs. 1B and 1C; see below for progression criteria). Physical assistance was decreased from wearing a harness (which was attached to a ceiling track, secured with a tether, and held by a physical therapist), to a walking belt, to spotting by the physical therapist in each progression of the task (Fig. 1).
Stepping reaction training protocol (A–C). As the participant becomes more skilled at performing stepping reactions (the participant is able to perform a single set without reliance on the associated level of assistance [eg, the overhead harness]) and reports confidence to progress to next level of task, the functional task difficulty is increased through the introduction of random practice (B) for increased contextual interference, decreased physical support, and decreased augmented feedback. The final progression (C) of functional task difficulty increases the amount of information to which the learner must attend while performing the task. Bkwd=backward, Fwd=forward, Lat=lateral.
The final progression of functional task difficulty during forward and backward leaning blocks involved increased information for the learner to attend to during practice (Fig. 1C). Participants were instructed to wait for a verbal command as to the leg with which to step; this command was provided randomly after the lean was initiated. Ten trials with the paretic leg were performed in both forward and backward leaning blocks. The aim of this progression was to increase functional task difficulty by combining random practice with increased cognitive load. The random practice of this task increased functional task difficulty by requiring a fast reaction time in response to variable movement commands, thereby decreasing the time to plan the movement strategy. Progression of the task was determined by the treating physical therapist in conjunction with the participant. Progression was suggested by the therapist when a full set could be performed without reliance on the overhead harness or the walking belt to regain standing balance. If the participant expressed concern over progression to the next level of the task, he or she repeated an additional set with the current level of physical assistance. One additional set was always sufficient for the participant to achieve readiness to progress to the next level.
Augmented feedback.
The content and scheduling of augmented verbal feedback from the physical therapist were designed to assist in initial problem solving and then faded to avoid the possibility that they might interfere with motor learning as skill level progressed.5,6,19 In the first week of practice, information was provided to the participants regarding an effective stepping reaction requiring sufficient speed and length to control the momentum of the body.20 This information set the parameters for the content of feedback during the remainder of practice.
Participants were provided information regarding 2 aspects of the stepping reaction. The first was knowledge of the results of the stepping reaction (the occurrence of a fall or not) through information inherent in the task (the pull of the harness) and verbal feedback regarding the level of assistance required. The second was knowledge of the performance of the stepping reaction through qualitative verbal feedback about the speed and amplitude of the initial and follow-up steps observed by the treating physical therapist; for example, “steps need to be faster” or “try stepping further” (no absolute values of distance or speed were provided). Because participants had different levels of motor recovery and progressed through training at different rates, individualized augmented feedback was provided to adjust the optimal challenge for each learner. For example, participant 3 had spasticity (Chedoke-McMaster Stroke Assessment score=leg 3 and foot 3) and required feedback to use a wider step with the paretic leg to minimize the impact of the movement pattern (adduction at the hip together with inversion and plantar flexion at the ankle).
Additionally, the provision of verbal feedback during the task was guided by the principle of the “value of error estimation” combined with knowledge of the results to enhance motor learning.21 Feedback was added after each participant was asked to provide an opinion about the quality of the performance of the stepping reaction. The therapist initiated discussion with the participant if progression appeared to be hampered by repetition of errors. At each level of functional task difficulty, feedback was faded by the therapist (approximate progression: following 5 then 10 repetitions during blocked practice and following 6 then 30 then 60 repetitions during random practice) until there was little discussion after the trials and only feedback inherent to the task was available for problem solving and learning. During blocked practice, verbal feedback was provided as summary feedback after the performance of a single-direction block; during random practice, summary feedback included information for each direction after the performance of a random multidirectional block.
Outcome Measures
Walking balance.
Walking balance was measured with the Community Balance and Mobility Scale (CB&M). The CB&M contains high-level balance tasks that reflect the balance requirements for community-level walking.18,22 Item scoring contains components of timing and quality of movement, including protective reactions, during tasks such as walking and turning, walking backward, and tandem walking. The total score is 96 points, indicating maximum performance.
Confidence performing walking tasks.
Because self-efficacy regarding falls has been linked to the occurrence of falls in people with stroke,8 the Activities-specific Balance Confidence Scale (ABC) was administered.23 The ABC is a self-report measure of the confidence that people have in performing activities in the home and the community (eg, reaching for an item on a shelf, walking on a slippery surface, or using an escalator). The scale is expressed as a percentage. People are asked to rate their confidence that they will not lose their balance while performing the tasks. Complete confidence in their abilities would result in a score of 100. The ABC self-efficacy assessment was supplemented with a qualitative inquiry asking participants to identify community-based ambulatory activities that they were not undertaking as a result of their balance impairment after stroke; resumption of these activities served as a treatment goal, similar to a clinical subjective assessment before a balance intervention.
Kinematics.
Participants performed 5 trials in each direction, with each leg as the lead stepping leg for forward and backward stepping but not specified for lateral stepping to the left or right. Unlike practice sessions, all testing sessions involved the use of the overhead harness. Reflective markers were affixed to the heel and great toe area of the shoes of participants, and a single video camera was positioned perpendicular to the plane of movement to record movement of the reflective markers. Video gait analysis with an automated digitization program (Peak Motus, Centennial, Colorado) was used to measure step length and average velocity of the paretic leg (average of 3 trials). Feedback on the first day included only enough information to establish a level of comfort with “letting your body go” in a leaning action until feeling the need to step and assurance that the therapist and harness system could stop a fall.
Outcome
Descriptions of the participants are shown in the Table. Each participant reported that at least 1 fall occurred during the 6 months before the intervention and resulted in a soft tissue injury.
Participant Descriptiona
Figure 2 shows each participant's scores on the CB&M. All participants showed improvements in their scores, from a range of 20 to 81 before the intervention to 26 to 88 at 2 weeks and 39 to 92 at 4 weeks (completion of the intervention). Scores at the 1-year follow-up (41–88), although lower than those at the fourth week, remained higher than those before the intervention.
Community Balance and Mobility Scale scores before intervention (Base), after 2 weeks of the intervention, at the end of the 4-week intervention, and at 1 year after completion of the intervention. Data for participants 1, 2, 3, and 4 are represented by black squares, black circles, white squares, and white circles, respectively.
Kinematic data for the paretic leg are shown in Figure 3. All participants showed increases in the length and velocity of the initial step taken with the paretic leg in both forward and backward directions upon completion of the intervention (4 weeks). At the 1-year follow-up, the kinematic results were variable, with values for forward and backward stepping remaining above preintervention values in participants 2 and 3, respectively.
Step velocity and step length (mean and standard deviation) of the paretic leg as the lead leg in the protective stepping reaction in response to forward-leaning stimulus (A) and backward-leaning stimulus (B). Measurements were obtained before the intervention (Base), after 2 weeks of the intervention, at the end of the 4-week intervention, and at 1 year after completion of the intervention. Data for participants 1, 2, 3, and 4 are represented by black squares, black circles, white squares, and white circles, respectively.
Little change on the ABC (Fig. 4) was demonstrated. However, 3 of 4 participants reported that during the intervention period, they expanded their activity levels to include activities that they had not resumed after stroke because of fear of falling. For example, participant 2 began trail walking with a friend, participant 3 began to run short distances, and participant 4 began walking outdoors without a cane. At the 1-year follow-up, participants 2 and 3 had maintained their increased level of activity; however, participant 4 had returned to using a cane outdoors.
Activities-specific Balance Confidence Scale scores before intervention (Base), after 2 weeks of the intervention, at the end of the 4-week intervention, and at 1 year after completion of the intervention. Data for participants 1, 2, 3, and 4 are represented by black squares, black circles, white squares, and white circles, respectively.
No falls were reported during the 4-week intervention. At the 1 year follow-up, participant 1 reported a fall that occurred while he was carrying an object in both hands and tripped on the uneven surface of the patio; no injury occurred.
All participants completed each phase of the training progression. No adverse events that resulted in missed treatment sessions occurred. The first participant asked to perform a third set (for a total of 180 repetitions) during the first week of training but experienced knee pain after the treatment. The additional set was not repeated, and all subsequent treatment sessions were maintained at the previously planned total of 120 repetitions. All participants progressed to the walking belt by the second week of practice (Fig. 1B). All participants progressed to performing the stepping reaction with an increased cognitive load, using a walking belt in the second set performed during practice sessions at the beginning of the final week (Fig. 1C).
Discussion
The balance intervention reported here focused specifically on retraining multidirectional stepping reactions in people with stroke. Progression involved increasing levels of functional task difficulty requiring fast stepping reactions to prevent a fall. The intervention was tolerated by participants, who were able to ambulate independently, dwelled in the community, were 53 to 68 years of age, had different lesion locations, had a moderate to high level of motor recovery of the lower extremity (Chedoke-McMaster Stroke Assessment scores of 3–7), and had a wide range of initial community-level walking balance scores (20–81, as measured with the CB&M). All participants were able to progress to the highest level of functional task difficulty, with only 1 report of posttreatment knee pain, when 3 sets were performed instead of 2.
Positive results were demonstrated in the area of walking balance, with higher scores on the CB&M. Contrary to our expectation, the quality of the stepping reaction, as indicated by the kinematic data, did not necessarily coincide with higher scores on the CB&M. For instance, patient 2 had the lowest CB&M scores throughout the program but had the second longest and fastest stepping reactions. Patient 4 had 1 of the 2 lowest values for stepping amplitude and velocity but had the second best performance on the CB&M. Perhaps step length and velocity are not kinematic measurements that are most reflective of a change in stepping reaction performance. The relationship between stepping reaction performance and functional community-level balance abilities requires further investigation.
The CPF was applied in a neurorehabilitation intervention study for people with PD.9 This work showed that the level of nominal difficulty of the “to-be-learned-task” and demands of information processing inherent in the practice conditions interact and play an important role in the motor learning of people with PD.9 Although the present case series does not enable conclusions on the effectiveness of the CPF to be drawn, the positive outcomes in community-level walking balance supported the predictions of the CPF. Like previous work,14 the present case series suggested that people with stroke may benefit from increased contextual interference in random practice.
Despite little change on the ABC, the final qualitative reports from the participants indicated that 2 participants had returned to meaningful activities in which they initially reported they had not taken part since their stroke because of fear of falling during the activities. It is possible that the ABC was not responsive enough to detect any improved levels of self-efficacy with regard to walking balance in community-level ambulators following stroke. By engaging in activities that challenged walking balance for each participant, important consolidation and progression of further motor learning toward walking balance likely occurred outside the planned intervention. These 2 participants showed maintenance of to slight improvement in CB&M scores at the 1-year follow-up. Improving self-efficacy in conjunction with regaining motor skills associated with dynamic balance is an important concept in recovery from stroke.8,10 People with low self-efficacy regarding falls are more likely to avoid activity and experience a further decline in walking balance as a result of this activity avoidance.8,10 Future research should include outcome measures that may be more sensitive in community-dwelling people who have stroke.
The use of physical assistance during task progression was an important element facilitating practice, ensuring that retraining of stepping reactions allowed for progression of the skill concurrent with risk of the loss of balance. This is consistent with studies supporting the adjustment of functional task difficulty to a learner's skill level in accordance with the CPF.24,25 Furthermore, the participants' ability to assist in decision making regarding their readiness for task progression (specifically with respect to physical assistance) may have contributed to improved motor learning24,26 and has been suggested to lead to a deeper processing of information during the learning of more complex motor skills.26 Only 1 fall was reported by a participant at 1 year after training, perhaps indicating the retention of an effective stepping reaction when a loss of balance occurred.
According to the CPF, the impact of externally provided, augmented feedback on motor skill acquisition is dependent on the type, timing, and meaningfulness of the information provided.4 Boyd and Winstein12 showed that people with chronic stroke (>6 months) demonstrated impaired implicit learning during a serial reaction time task performed with the limb ipsilateral to the lesion. The impaired motor learning was attenuated somewhat by the provision of explicit information regarding the sequential pattern that was being learned.12 The authors suggested that the improvement noted in their study may have been due to the simplicity of the rules governing the “to-be-learned” serial motor task.12 The requirement to take faster or longer steps in the present case series may be easier than sequential instruction with precise, kinematic information (eg, description of how to move the joints of the limb specifically). Thus, it is possible that the simplistic nature of the feedback in the present case series contributed positively to motor learning.
Motor learning from error has been found to be an important concept; however, it is likely best used when functional task difficulty is controlled to keep the learner in an optimal state, as suggested by the CPF.4 In the present case series, the progression of functional task difficulty and physical assistance, together with the direction of focus provided by feedback, were planned to counterbalance a potential cognitive preoccupation with falling. Orrell et al10 proposed a strategy to enhance implicit motor learning of a balancing task after stroke—learning without error to the decrease cognitive load associated with a heightened fear of falling. The authors hypothesized that, when people with stroke attempted to consciously control their motor actions, their motor skills were impaired.10
The present case series implemented a somewhat modified approach to the use of error. Error in the protective stepping task is equivalent to a fall. Participants were prevented from experiencing a fall by the use of progressively decreasing levels of physical assistance. However, error detection was possible and was experienced by a participant with the sensation of a pull from the harness or from the walking belt. Participants were asked to comment on their performance of an effective (or ineffective) stepping reaction before the physical therapist provided augmented feedback. In this way, participants focused on task components that they might change in their action plan to improve stepping reactions rather than on the risk of falling. As suggested by the CPF, this feedback was faded with improvement of skill, allowing for more self-directed problem solving, which is associated with better motor learning.
This case series must be interpreted with caution. It included a small number of participants, and all of the participants were motivated. Additionally, interpretation is limited because this case series did not include a control intervention and a masked assessor did not perform a participant evaluation. The therapist did not review the previous outcome measure scores before performing each successive evaluation.
This case series demonstrates the clinical application of information delivery, practice schedules, and physical assistance to optimally challenge participants' learning, as described in the CPF, to direct practice conditions to retrain stepping reactions in people with chronic stroke with the goal of improving walking balance. The positive outcomes associated with the intervention design may offer important insight into the planning of clinical intervention studies to achieve greater community-level mobility in people after stroke. Further investigation of the application of the CPF to stroke rehabilitation interventions is warranted.
Footnotes
All authors provided concept/idea/project design and writing. Ms Pollock and Dr Hunt provided data collection and project management. Ms Pollock, Dr Boyd, and Dr Hunt provided data analysis. Dr Garland provided fund procurement and consultation (including review of manuscript before submission). Dr Boyd provided participants. Dr Hunt and Dr Garland provided facilities/equipment.
This project was approved by the University of British Columbia Clinical Research Ethics Board.
- Received February 7, 2013.
- Accepted December 12, 2013.
- © 2014 American Physical Therapy Association
References
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