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Research Reports |
M.D. Lewek, PT, PhD, is Assistant Professor, Division of Physical Therapy, Department of Allied Health Sciences, University of North Carolina at Chapel Hill, 3043 Bondurant Hall, CB 7135, Chapel Hill, NC 27599-7135 (USA).
T.H. Cruz, MS, is a graduate student, Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois, and Department of Biomedical Engineering, Northwestern University, Chicago, Illinois.
J.L. Moore, PT, MPT, NCS, is Research Physical Therapist, Sensory Motor Performance Program, Rehabilitation Institute of Chicago.
H.R. Roth, PT, MSPT, NCS, is Research Physical Therapist, Sensory Motor Performance Program, Rehabilitation Institute of Chicago.
Y.Y. Dhaher, PhD, is Assistant Professor, Sensory Motor Performance Program, Rehabilitation Institute of Chicago, and Department of Biomedical Engineering, Northwestern University.
T.G. Hornby, PT, PhD, is Assistant Professor, Department of Physical Therapy, University of Illinois at Chicago, Chicago, Illinois, and Sensory Motor Performance Program, Rehabilitation Institute of Chicago.
Address all correspondence to Dr Lewek at: mlewek{at}med.unc.edu
Submitted June 17, 2008;
Accepted April 7, 2009
 | Abstract |
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Objective: The purpose of this study was to determine whether LT with physical assistance as needed was superior to guided, symmetrical, robotic-assisted LT for improving kinematic coordination during walking poststroke.
Design: This study was a randomized clinical trial.
Methods: Nineteen people with chronic stroke (>6 months’ duration) participating in a larger randomized control trial comparing therapist- versus robotic-assisted LT were recruited. Prior to and following 4 weeks of LT, gait analysis was performed at each participant's self-selected speed during overground walking. Kinematic coordination was defined as the consistency of intralimb hip and knee angular trajectories over repeated gait cycles and was compared before and after treatment for each group.
Results: Locomotor training with therapist assistance resulted in significant improvements in the consistency of intralimb movements of the impaired limb. Providing consistent kinematic assistance during robotic-assisted LT did not result in improvements in intralimb consistency. Only minimal changes in discrete kinematics were observed in either group.
Limitations: The limitations included a relatively small sample size and a lack of quantification regarding the extent of movement consistency during training sessions for both groups.
Conclusions: Coordination of intralimb kinematics appears to improve in response to LT with therapist assistance as needed. Fixed assistance, as provided by this form of robotic guidance during LT, however, did not alter intralimb coordination.
| Introduction |
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In contrast, the use of clinical robotic locomotor devices can relieve therapists of the physical effort often required during LT by providing consistent, repetitive guidance to the lower extremities.8–10 The ability of robotic devices to provide stable, repetitive LT is thought to supply many of the sensory-specific cues related to walking, which may strengthen neural pathways associated with the production of coordinated locomotion.10,11
Contrary to the notion that consistent sensory information during LT is critical to enhancing stepping, a long-standing body of research has indicated the importance of practice variability when learning a motor task.12 Recent data in experimental models of SCI indicate that variable, assist-as-needed step training improves the consistency of stepping compared with constrained guidance through a fixed trajectory.13 Furthermore, such fixed training paradigms are thought to reduce voluntary participation14 and the central nervous system's ability to fully explore various movement options.13 Thus, training with robotic devices that provide strict guidance of limb kinematics may limit improvements in the recovery of motor coordination by reducing movement variability, particularly compared with variable, compliant, assist-as-needed LT paradigms.13,15
Previous work investigating the effects of robotic- versus therapist-assisted training on recovery of walking function in subjects with hemiparesis poststroke focused on alterations in gait speed and symmetry and functional outcomes following training.16 In the present study, we sought to determine whether LT with therapist assistance as needed was superior to guided, symmetrical robotic-assisted LT at improving kinematic coordination during walking. An estimate of intralimb coordination has been quantified by other investigators6,17 as the repeatability or consistency of the coupling of hip and knee kinematics during multiple gait cycles. In the present study, gait kinematics were assessed in a subpopulation of individuals with chronic (>6 months’ duration) stroke from a larger randomized controlled study prior to and following 4 weeks of LT performed on a treadmill. Specific analyses were performed to determine alterations in intralimb coordination during overground walking and their relationship to functional improvements. Secondary analysis was performed to determine whether absolute joint angles and excursions were altered following LT with therapist or robotic assistance. Based on previous work,6,17 we hypothesized that therapist-assisted LT using variable assistance as needed would elicit greater improvements in intralimb coordination than robotic-assisted LT using fixed movement patterns.
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Participants randomly assigned to the robotic-assisted LT group used the Lokomat,* a robotic gait trainer, to assist the lower extremities in a consistent, symmetrical walking pattern during treadmill stepping. The design and control of this device have been described previously.11 Participants were fixed to the device with adjustable cloth straps placed around the trunk, pelvis, and lower extremities, with hip and knee joints aligned with computer-controlled actuators. Spring-loaded cloth straps were attached around the participants’ forefoot to ensure toe clearance during swing on the paretic side. The robotic device provided continuous assistance in kinematic trajectories approximating "normal" gait. Participants were given continuous visual feedback of bilateral hip and knee torques during walking and were encouraged to generate maximal effort in the paretic limb.
Participants randomly assigned to the therapist-assisted LT group received manual assistance from a single therapist for limb advancement or pelvic control. An ankle-foot orthosis (AFO) was used only if an individual was unable to step safely without it. Manual facilitation was provided only if a participant could not step continuously at the required treadmill speed (ie, an assist-as-needed paradigm) and was not provided to normalize kinematics between limbs.
Gait Analysis
Gait analysis was performed for all participants less than 1 week prior to the initiation of LT and was repeated less than 1 week following the last LT session. Eight participants (4 in each group) required some form of ankle bracing (7 AFOs, 1 ankle stirrup brace), and use of orthoses and assistive devices was consistent during testing sessions. Participants ambulated at least 5 times across a 10-m walkway at their comfortable, self-selected speed, while an 8-camera motion capture system
recorded the 3-dimensional (3D) movement of 25.4-mm (1-in) retroreflective markers affixed to the pelvis, thighs, shanks, and feet. Specifically, markers were placed on the posterior sacrum, bilateral anterior-superior iliac spine, medial and lateral femoral condyles, medial and lateral malleoli, and posterior heel counter of the shoe and dorsally over the second metatarsal head to identify segment ends. The motion of the thighs and shanks was tracked by 3 markers rigidly affixed to thermoplastic shells, which, in turn, were wrapped securely around each limb segment.
Data Management
The marker trajectories were identified and low-pass filtered (6 Hz) to track the 3D motion of the pelvis and lower-limb segments using EvaRT software. Relative positions and intersegmental joint angles (eg, hip, knee, and ankle angles) were calculated using a rigid body analysis19 and normalized to a stride cycle using OrthoTrak 6.2.4.
The consistency of intralimb coordination between the hip and knee joints was quantified by calculating the average coefficient of correspondence (ACC) as described by Field-Fote and Tepavac.17 The ankle joint was not assessed because some participants used AFOs to restrict ankle kinematics. The ACC uses a vector coding technique to analyze the sagittal-plane hip and knee angles on an angle-angle plot. The difference between successive frames (one frame equals 1% of the gait cycle) on the phase plane is represented by a vector whose length is calculated by:
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) and sin() for a given frame over multiple steps was calculated. The mean vector angle for each frame can then be evaluated by:
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i and sin i are the mean cos() and sin() for each i frame. The ai values are a measure of dispersion across strides of the hip and knee angle pair at each percent of the gait cycle. Values equal to 1 would indicate that there is perfect consistency across all steps for that given frame. To represent all the ai values as a single variable, the mean of the a values for all i frames was calculated to represent the hip and knee ACC. Individuals who are unimpaired walking at their self-selected speeds exhibit a hip and knee ACC of .9417 to .97.6 A representative example of the hip and knee angle-angle plot and the steps involved in the calculation of hip and knee ACC in an individual poststroke is shown in Figure 2. Overall, an average of 15 strides (SD=8) on the involved side and an average of 16 strides (SD=9) on the uninvolved side per participant were analyzed.
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Data Analysis
All statistical analyses were performed with SPSS, version 15.0.
The effect of LT on the consistency of intralimb coordination was evaluated with a 2-group (robotic-assisted LT and therapist-assisted LT) x 2-session (pretraining and posttraining) analysis of variance (ANOVA) for repeated measures for session. Post hoc testing of within-group differences for comparison of pretraining and posttraining values was performed using paired t tests. Group data are reported as mean (SD), with 
=.05. The relationship between gait speed and intralimb coordination was assessed with Pearson correlation coefficients. Secondary measures of peak joint angle and excursions are presented using descriptive statistics (ie, mean and SD), but pretraining and posttraining values were not compared, as these were not primary outcomes. In addition, a stepwise linear regression analysis was used to determine the relative contributions of cadence and stride length to changes in walking speed. Cadence and stride length for each group were compared before and after training with paired t tests.
| Results |
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TopAbstractIntroductionMethodResultsDiscussionConclusionReferences |
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2=2.10, P=.147). In addition, data collection procedures on 1 participant in the therapist-assisted LT group resulted in unusable kinematic data, yielding a total of 10 participants in the robotic-assisted LT group and 9 participants in the therapist-assisted LT group for data analysis. Demographic characteristics of these 19 participants are provided in Table 1.
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| Discussion |
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TopAbstractIntroductionMethodResultsDiscussionConclusionReferences |
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Investigations of improvements in acquisition and retention of novel motor tasks following variable and consistent practice have been performed in subjects who were neurologically intact. In general, variable practice conditions appear to decrease motor performance during learning compared with constant task practice, although better retention or transfer is observed with more-variable practice.21,22 In contrast, few data are available regarding the effects of variable or consistent practice conditions for improving locomotor function in individuals poststroke.
Significant between-group differences in robotic- versus therapist-assisted LT were not revealed, further indicating the general efficacy of locomotor training. Nevertheless, robotic-assisted LT did not elicit improvements in hip and knee ACC. Instead, intralimb coordination as quantified using the hip and knee ACC, was improved with therapist-assisted training and might suggest that mechanically imposed practice of movement consistency during training does not, by itself, improve intralimb coordination (ie, consistency of hip and knee trajectories). The extent of error allowed by the patient during training may influence changes in intralimb coordination. During robotic-assisted LT, hip and knee joints were rigidly "guided" through a given movement trajectory, thereby minimizing movement errors. In contrast, although therapists can encourage consistent kinematic movements associated with locomotion, they cannot minimize error to the same extent. The resultant variability in lower-limb trajectories with therapist assistance may allow the patient to explore various solutions to accomplish the locomotor task and adapt to a more consistent locomotor trajectory.13
Although the paretic-side hip and knee ACC of the therapist-assisted LT group increased significantly, there was no significant change in hip and knee ACC for the nonparetic limb of either group. The nonparetic limb exhibited somewhat less-consistent movements than what has been reported for individuals who were unimpaired (eg, ACC values=.94–.97).6,17 Nevertheless, the hip and knee ACC for the nonparetic limb was similar to values reported by Daly and colleagues6 for the nonparetic limb of their participants. Unfortunately, they did not report training-induced changes to the nonparetic limb, although it appears from our data that LT with either robotic or therapist assistance is unable to significantly alter the nonparetic limb's hip and knee ACC.
A limitation to the present study is that we did not quantify the extent of movement consistency during training sessions for either group, and we are unsure of the extent of error allowance or consistency achieved with therapist assistance. However, the lower-limb trajectories during robotic-assisted treadmill stepping are extremely consistent, with very little error in kinematic trajectories.23 It is unlikely that therapist-assisted LT provides consistency of movement similar to that of robotic-assisted treadmill stepping, where joint kinematic trajectories are so tightly controlled.11
Although the allowance of errors during training may facilitate improvements in locomotor consistency in animal models of SCI13 and in the current data in individuals with hemiparesis poststroke, the type of feedback that facilitates improvement in coordination still is uncertain. Specifically, participants who received robotic-assisted LT were provided visual feedback of their relative hip and knee torques during walking (eg, kinetics) to increase volitional effort during stepping,14,24 but they did not improve their hip and knee ACC. A previous study in individuals without neurological injury indicated that continuous physical guidance with visual feedback during learning of a novel task may limit retention and transfer,25 particularly compared with subjects who received no guidance and a reduced schedule of feedback. More-recent data obtained during learning of a novel 3D upper-limb task indicate that mechanical guidance through the required trajectory that combined proprioceptive and visual input was slightly inferior to a simple visual demonstration that involved no limb movement.26 Comparative data of the effect of visual, kinematic, or kinetic feedback and error in improving locomotor function in individuals poststroke are lacking, however, and further investigation is needed.27
As a secondary measure, gait speed also improved significantly following LT, but only in the therapist-assisted LT group by an average of 0.06 m/s. Results from the regression analysis indicated that gait speed increases were determined by changes in stride length, although stride length did not increase significantly after training. The magnitudes of changes in gait speed in both groups were lower than those observed in the larger randomized training trial, although relative differences in gait speed improvements between groups were consistent between studies.16 Although this change in gait speed in the therapist-assisted LT group may be relatively small, such an improvement is thought to constitute a "small meaningful change"28 according to recently established estimates obtained, in part, in subjects with subacute (1–5 months’ duration) stroke (see Fulk and Echternach,29 however, for changes in acute stroke). The relatively smaller sample size may have contributed to nonsignificant differences between LT groups, and studies with larger sample sizes are needed to reveal differences in walking speed16 as well as kinematic coordination between groups.
Additional secondary measures of joint kinematic data indicate very little changes in joint angle kinematics on the paretic extremity. Importantly, kinematic parameters of interest were peak angles during specific gait phases and net joint excursions and did not take into account alterations in angular velocities, which may be present with changes in gait speed, particularly in the therapist-assisted LT group. Accordingly, although increased hip and knee ACC values were observed in the therapist-assisted LT group, it is unclear whether this response to training is beneficial or detrimental. Increasing movement consistency has traditionally been viewed as a favorable outcome, as excessive movement variability has been purported to indicate inappropriate motor control and decreased movement efficiency.30–32 In the therapist-assisted LT group, however, the relative lack of changes in discrete kinematic data points suggests that although the movements became more similar after training, individuals were not repeating "correct" patterns. Therefore, the therapist-assisted training may reinforce impaired gait patterns that have been ingrained in the chronic stages poststroke.
Possible reasons for the relative lack of changes in absolute joint angular excursions in both groups may be multifactorial. To begin, it is possible that training intensities were not high enough to elicit alterations in kinematic variables. This is particularly relevant for the robotic-assisted LT group, which may have allowed participants to walk more "passively" than those in the therapist-assisted LT group due to the continuous physical guidance from the Lokomat. Walking with robotic assistance has been shown in ambulatory subjects with incomplete SCI to reduce metabolic costs of stepping compared with therapist-assisted stepping.14 Reduced volitional effort during training may limit the possibility of enhanced learning of skilled movements.33 Providing feedback during training, as performed in our study, however, mitigates these effects.14 Nevertheless, as we did not measure "effort" during LT, it is possible that the capacity for passive walking in the robotic-assisted LT group contributed to a lack of improvements in hip and knee ACC and gait speed. Furthermore, the protocol used for the present study required the treadmill speed during LT to be limited by the device used, with maximal speeds of 3.0 km/h used in the present study. Although training speeds were greater than the self-selected speed of all participants and similar to those of previous studies of LT in individuals poststroke,34 our inability to further increase stepping speed during training may have reduced walking intensity, even during therapist-assisted LT, when passive assistance was limited. Stepping at higher speeds may have required greater joint excursions35 and has been shown to elicit greater changes in locomotor ability (ie, walking speed, spatiotemporal parameters) than walking at slower speeds.34,36 There is, however, little evidence to support improvements in kinematic patterns as a result of increased training speeds, although we cannot exclude this possibility.
Alternatively, our data may suggest that the ambulatory individuals with chronic stroke recruited for this training program had well-established abnormal gait patterns that could not be modified in 4 weeks of treadmill training with therapist or robotic assistance. Altering these persistent, learned gait deviations may require training programs that begin more acutely,37 consist of longer, more-frequent sessions, continue for a longer period of time,38 or offer a different training method. Other researchers, however, have used LT for a 12-week period (eg, control group described by Daly et al39) and also did not show a change in gait kinematics. These data, therefore, may indicate that much-longer training is necessary to elicit changes poststroke or that simply providing appropriate repetitions for task practice may be an insufficient stimulus for evoking substantial changes in kinematic trajectories during walking. Perhaps additional sensorimotor stimuli may be necessary to elicit changes during walking in individuals with chronic stroke. An enhanced physical stimulus, such as the addition of neuromuscular or reflex electrical stimulation during locomotor training, for instance, may evoke substantial changes to joint kinematics in individuals poststroke39 and those with incomplete SCI.17
Another potential limitation of this study is the relatively small sample size tested. Although we were able to document changes in intralimb coordination following therapist-assisted LT, we did not find differences between groups. Additionally, it appeared that kinematic changes were not appreciably altered. Nevertheless, other researchers34,39,40 have used equivalent or even smaller sample sizes to demonstrate that LT with specific modalities or protocols has the ability to elicit changes following stroke. Recruitment of substantially larger sample sizes may reveal significant differences in relative hip-knee coordination between groups, although the differences in the observed magnitude of altered gait kinematics may not be clinically meaningful.
| Conclusion |
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TopAbstractIntroductionMethodResultsDiscussionConclusionReferences |
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It is unclear whether there is a positive effect on functional outcomes from improving intralimb coordination without eliciting substantial alterations in discrete joint kinematics. Further research is needed to determine more-optimal training parameters, including duration, intensity, and timing, following stroke to optimize both outcomes related to impairments and functional limitations. In addition, the efficacy of additional physical (eg, electrical stimulation)6 or other therapeutic interventions to "normalize" kinematic patterns needs to be more thoroughly investigated.
| Footnotes |
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This study was approved by the Northwestern University Institutional Review Board.
Portions of these results were presented at the Combined Sections Meeting of the American Physical Therapy Association; February 14–18, 2007; Boston, Massachusetts.
Funding for this project was provided by the National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health (grant F32AR053447), and the National Institute on Disability and Rehabilitation Research (grants H133G040065 and H133B031127).
* Hocoma AG, Industriestrasse 4, CH-8604 Volketswil, Switzerland. 
Motion Analysis Corp, 3617 Westwind Blvd, Santa Rosa, CA 95403.
SPSS Inc, 233 S Wacker Dr, Chicago, IL 60606.
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  C. Patten, E. J. Gonzalez-Rothi, V. L. Little, and S. A. Kautz Invited Commentary on "Allowing Intralimb Kinematic Variability During Locomotor Training Poststroke Improves Kinematic Consistency: A Subgroup Analysis From a Randomized Clinical Trial" Physical Therapy, August 1, 2009; 89(8): e7 - e8. [Full Text] [PDF]
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
