Short-term Performance-based Error-augmentation versus Error-reduction Robotic Gait Training for Individuals with Chronic Stroke: A Pilot Study

Special Article – Gait Rehabilitation

Phys Med Rehabil Int. 2015; 2(9): 1066.

Short-term Performance-based Error-augmentation versus Error-reduction Robotic Gait Training for Individuals with Chronic Stroke: A Pilot Study

Kao PC¹*, Srivastava S², Higginson JS³, Agrawal SK4 and Scholz JP5

¹Department of Physical Therapy, University of Massachusetts Lowell, USA

²Department of Health Sciences and Research, Medical University of South Carolina, USA

³Department of Mechanical Engineering, University of Delaware, USA

4Department of Mechanical Engineering, Columbia University, USA

5Biomechanics and Movement Science Program, University of Delaware, USA

*Corresponding author: Pei-Chun Kao, Department of Physical Therapy, University of Massachusetts Lowell, USA

Received: September 15, 2015; Accepted: November 09, 2015; Published: November 12, 2015


The success of locomotion training with robotic exoskeletons requires identifying control algorithms that effectively retrain gait patterns in neurologically impaired individuals. Here we report how the two training paradigms, performancebased error-augmentation versus error-reduction, modified walking patterns in four chronic post-stroke individuals as a proof-of-concept for future locomotion training following stroke. Stroke subjects were instructed to match a prescribed walking pattern template derived from neurologically intact individuals. Target templates based on the spatial paths of lateral ankle malleolus positions during walking were created for each subject. Robotic forces were applied that either decreased (error-reduction) or increased (error-augmentation) the deviation between subjects’ instantaneous malleolus positions and their target template. Subjects’ performance was quantified by the amount of deviation between their actual and target malleolus paths. After the error-reduction training, S1 showed a malleolus path with reduced deviation from the target template by 16%. In contrast, S4 had a malleolus path further away from the template with increased deviation by 12%. After the error-augmentation training, S2 had a malleolus path greatly approximating the template with reduced deviation by 58% whereas S3 walked with higher steps than his baseline with increased deviation by 37%. These findings suggest that an error-reduction force field has minimal effects on modifying subject’s gait patterns whereas an error-augmentation force field may promote a malleolus path either approximating or exceeding the target walking template. Future investigation will need to evaluate the long-term training effects on over-ground walking and functional capacity.

Keywords: Force field; Gait rehabilitation; Rehabilitation robotics; Stroke; Walking


Robotic leg exoskeletons have been developed to assist gait rehabilitation for individuals with neurological disorders [1]. Incorporating robotic devices into training can substantially reduce physical demands on therapists and provide more precise guidance than conventional therapist-assisted training [2]. However, recent large-scale randomized controlled trials demonstrated that robotassisted locomotion training was worse than or not superior to the conventional physical therapy or therapist-assisted treadmill training [3-6]. It is possible that the excessive guidance and stabilization provided by the robotic exoskeleton interferes with learning and reduces subjects’ effort [7].

One way to ensure the success of gait rehabilitation with robotic exoskeletons is to identify robotic control algorithms that facilitate motor learning in people with neurological disorders [8]. An assistas- needed paradigm, providing guidance only when needed, is employed in some current leg exoskeletons [9-12]. Generally, the assist-as-needed guidance reduces the deviation between subject’s movement pattern and a prescribed pattern. We refer to this paradigm as performance-based error-reduction. The nature of this paradigm would minimize subject’s performance errors [13] which are important for motor learning [14]. This is potentially problematic for chronic stroke survivors since they do not recognize errors in their performance and enhancing those errors may enhance motor learning [15].

A performance-based error-augmentation paradigm may have the potential to better engage subject’s in the training. Because the performance-based error-augmentation paradigm amplifies subjects’ movement errors, this type of protocol would favour motor learning principles such as encouraging active participation [16] and physical effort [17], preserving movement variability [18, 19] and allowing subjects to discover normal movement patterns. Here we report how four chronic post-stroke individuals responded to the performancebased error-augmentation versus error-reduction training as a proofof- concept for future locomotion training following stroke.

Device Description

Training was performed using a unilateral robotic leg exoskeleton (Figure 1). Details of the exoskeleton’s design and algorithms of force field are documented elsewhere [11, 20, 21]. Briefly, when the force field is active, motors mounted at the hip and knee joints of the exoskeleton provide a pattern of torques with a resulting force applied to the ankle. Target walking templates based on the spatial paths of neurologically intact volunteers’ lateral malleolus positions (i.e., malleolus path) during walking were created for each subject (Figure 2). The performance-based force field was programmed as a non-linear virtual spring [11, 20, 22-24], applying a normal force towards (error-reduction) or away from (error-augmentation) the prescribed template (Figure 2). The amount and direction of the normal force varied depending on the deviation between subjects’ instantaneous malleolus position and their prescribed template.