Supporting Post Stroke Motor Recovery
by Julia E. Bryson, MD, MPH;
Board-certified in physical medicine and rehabilitation, subspecialty certified in neurorehabilitation
Novel therapeutic interventions aimed at post stroke motor recovery have evolved at a steady pace.
The new training paradigms were sparked by animal studies in the 1990s, which demonstrated activity- induced cortical reorganization and provided promise for restorative strategies, as opposed to compensatory strategies, to address hemiparesis. Active interventions have included constraint-induced movement therapy (CIMT), massed practice and locomotor training (body- weight supported ambulation).
Additionally, adjunctive therapies have developed to prime the brain with application of sensory stimulation or an electromagnetic field to the central nervous system (CNS) and peripheral nervous system (PNS). Clinical research to evaluate therapeutic effectiveness has been difficult to perform due to heterogeneous clinical profiles and lack of uniform interventions and outcome measures. In the last decade, however, multiple sites have coordinated efforts to produce a small number of sufficiently powered and randomized-controlled trials to study functional outcomes. Lastly, advanced neuroimaging studies on humans have offered insights into the experience-induced restructuring of residual neural tissue that confers motor learning. The sum of this research points towards the importance of repetitive, task-specific practice to remediate motor deficits following CNS damage.
Clinical trials to date overwhelmingly point to the importance of practice intensity to promote motor learning. The largest (multicenter) RCT of post-stroke ambulation, the Locomotor Experience Applied Post Stroke (LEAPS) trial, examined walking speed recovery after stoke. The gait speed of study participants receiving "usual" care at 6 months improved only half as much as those involved in an intensive structured activity of either locomotor training with body weight-supported treadmill training (BWSTT) or a home exercise program (.13 vs ~0.25 m/s). Given that the study's mobility entry criteria were modest, specifically the capacity to ambulate only 10 feet with no more than 1 person assisting, the generalizability of these findings are broad.
Most studies measure intensity of practice by duration of therapy, but level of exertion is another way to promote intensity. Dobkin, et al., showed that simply a daily verbal encouragement and knowledge of performance on a short walk trial can achieve that end. In this international, multicenter study, stroke patients in rehabilitation units were asked to increase their walking speed on beyond their comfortable walking speed but still within a speed that could be safely performed. At discharge, gait speed had doubled to 0.46m/s (exceeding the minimal clinically important change in gait speed of >0.16 m/s) and had exceeded that of the control group's by 0.19 m/s. The functional implication, based on the well-accepted threshold of 0.4 m/s as predictive of a functional ambulation class (FAC) beyond household-level distances, is that the experimental group achieved the ability to ambulate short distances in the community whereas the control group did not.
Intensity of practice alone, however, appears insufficient for optimal motor learning; skill acquisition also requires task-specific practice. Body-weight supported treadmill training (BWSTT) and robotic- assisted step training (RAST), for example, are task- oriented therapies which were presumed to confer an advantage over over-ground training (OGT) by offering the opportunity for massed practice (for persons who could not otherwise support their own weight to walk). However, despite similar intensity of practice, lower limb advancement on a treadmill, facilitated by a robot or a therapist, has not yet proved superior to OGT. One reason that the anticipated benefits of intensive practice have not borne fruit is that errorless performance of an activity does not place the same demands on networks devoted to attention and/or motor planning. One might deduce, therefore, that performance errors-which demand changes in sequencing, timing and scaling of movements-are necessary to promote the encoding of information which confers motor learning.
Further evidence for the necessity of task-based practice comes from functional neuroimaging. In functional MRI (fMRI) studies of controlled limb movements, healthy controls show lateralized motor cortex activity, which results from the inter-hemispheric inhibition. However, following stroke, the damaged motor cortex can no longer inhibit the contralateral motor cortex, and the patients show bilateral activation. Boyd, et al. (see Figure) demonstrated that on a post-training fMRI of a learned motor task, the general-use training showed no effect on the degree of bilateral activity, but that task-specific training (SP) was able to restore laterality to near that of the healthy brain. Moreover, the SP demonstrated greater improvement in reaction times as compared to GP therapy (p=.004).
While intense, task-specific practice is important to achieve motor recovery, capacity for improvement appears to be influenced by the initial severity of disability. In the LEAPS trial, for example, only half of study participants transitioned to a higher FAC (from household to limited community or from limited community to slow, unlimited community levels of ambulation) and these subjects were more likely to have started with a higher level of initial gait speed. Nevertheless, even if the effect size of therapeutic interventions for highly disabled individuals is modest, such a transition, especially the progression beyond household-level ambulation, is correlated with improved quality of life (QOL) measures (Schmid).
In summary, animal and clinical research has unmasked the essential ingredient of motor learning: intensive task-specific practice. Unfortunately, the allotted dose of therapy in acute and subacute rehabilitation settings does not appear to meet the anticipated sufficient dose required for optimal motor learning. Furthermore, observational data suggest that actual practice intensity is low and is frequently not task-specific (Lang). Feasibility studies on interventions such as accelerating the progression of tasks and reducing the number of rest breaks, as well as provision of recreational therapists to provide practice during non-scheduled therapy hours, deserve consideration.
Additionally, since to date expensive robotic approaches have not conferred an advantage over comparable and less costly home-based therapies, wide implementation of practical, low-cost technologies should be a priority. For example, knowledge of performance provided by personalized-accelerometry devices or gaming software show promise as a pragmatic and effective means of achieving increased intensity and engagement in practice to achieve motor learning. Finding ways to continue to incentivize and harness the power of intense task-based specific practice is critical to improve functional outcomes and QOL through the continuum of recovery.