Background Previous data suggest the amount and aerobic intensity of stepping training may improve walking post-stroke. Recent animal and human studies suggest training in challenging and variable contexts can also improve locomotor function. Such practice may elicit substantial stepping errors, although alterations in locomotor strategies to correct these errors could lead to improved walking ability. Objective This un-blinded, pretest-posttest pilot study was designed to evaluate the feasibility and preliminary efficacy of providing stepping practice in variable, challenging contexts (tasks and environments) at high aerobic intensities in participants with chronic (< 6 months) and subacute (1–6 months) stroke. Methods Twenty-five participants with stroke (gait speeds < 0.9 m/s with no more than moderate assistance) participated in ≤ 40 1-hr training sessions within 10 weeks. Stepping training in variable, challenging contexts was performed at 70–80% heart rate reserve, with feasibility measures of total steps/session, ability to achieve targeted intensities, patient tolerance, dropouts, and adverse events. Measures of daily stepping, gait speed, symmetry, and 6-min walk were performed every 4–5 weeks or 20 sessions with a 3 month follow-up. Results Twenty-two participants completed ≥ 4 weeks of training, averaging 2887±780 steps/session over 36±5.8 sessions. Self-selected and fastest speed, paretic single limb stance, and 6-min walk improved significantly at post-training and follow-up. Conclusions This preliminary study suggests stepping training at high aerobic intensity in variable contexts was tolerated by participants post-stroke, with significant locomotor improvements. Future trials should delineate the relative contributions of amount, intensity and variability of stepping training to maximize outcomes.

BackgroundSensory augmentation has been shown to improve postural stability during real-time balance applications. Limited long-term controlled studies have examined retention of balance improvements in healthy older adults after training with sensory augmentation has ceased. This pilot study aimed to assess the efficacy of long-term balance training with and without sensory augmentation among community-dwelling healthy older adults.MethodsTwelve participants (four males, eight females; 75.6 ± 4.9 yrs) were randomly assigned to the experimental group (n = 6) or control group (n = 6). Participants trained in their homes for eight weeks, completing three 45-min exercise sessions per week using smart phone balance trainers that provided written, graphic, and video guidance, and monitored trunk sway. During each session, participants performed six repetitions of six exercises selected from five categories (static standing, compliant surface standing, weight shifting, modified center of gravity, and gait). The experimental group received vibrotactile sensory augmentation for four of the six repetitions per exercise via the smart phone balance trainers, while the control group performed exercises without sensory augmentation. The smart phone balance trainers sent exercise performance data to a physical therapist, who recommended exercises on a weekly basis. Balance performance was assessed using a battery of clinical balance tests (Activity Balance Confidence Scale, Sensory Organization Test, Mini Balance Evaluation Systems Test, Five Times Sit to Stand Test, Four Square Step Test, Functional Reach Test, Gait Speed Test, Timed Up and Go, and Timed Up and Go with Cognitive Task) before training, after four weeks of training, and after eight weeks of training.ResultsParticipants in the experimental group were able to use vibrotactile sensory augmentation independently in their homes. After training, the experimental group had significantly greater improvements in Sensory Organization Test and Mini Balance Evaluation Systems Test scores than the control group. Significant improvement was also observed for Five Times Sit to Stand Test duration within the experimental group, but not in the control group. No significant improvements between the two groups were observed in the remaining clinical outcome measures.ConclusionThe findings of this study support the use of sensory augmentation devices by community-dwelling healthy older adults as balance rehabilitation tools, and indicate feasibility of telerehabilitation therapy with reduced input from clinicians.

A previous study from our laboratory showed that when soleus electromyography was used to control the amount of plantar flexion assistance from a robotic ankle exoskeleton, subjects significantly reduced their soleus activity to quickly return to normal gait kinematics. We speculated that subjects were primarily responding to the local mechanical assistance of the exoskeleton rather than directly attempting to reduce exoskeleton mechanical power via decreases in soleus activity. To test this observation we studied ten healthy subjects walking on a treadmill at 1.25 m/s while wearing a robotic exoskeleton proportionally controlled by medial gastrocnemius activation. We hypothesized that subjects would primarily decrease soleus activity due to its synergistic mechanics with the exoskeleton. Subjects decreased medial gastrocnemius recruitment by 12% (p<0.05) but decreased soleus recruitment by 27% (p<0.05). In agreement with our hypothesis, the primary reduction in muscle activity was not for the control muscle (medial gastrocnemius) but for the anatomical synergist to the exoskeleton (soleus). These findings indicate that anatomical morphology needs to be considered carefully when designing software and hardware for robotic exoskeletons.

When humans hop or run on different surfaces, they adjust their effective leg stiffness to offset changes in surface stiffness. As a result, the overall stiffness of the leg-surface series combination remains independent of surface stiffness. The purpose of this study was to determine whether humans make a similar adjustment when springs are placed in parallel with the leg via a lower limb orthosis. We studied seven human subjects hopping in place on one leg while wearing an ankle-foot orthosis. We used an ankle-foot orthosis because the ankle joint is primarily responsible for leg stiffness during hopping. A spring was added to the ankle-foot orthosis so that it increased orthosis stiffness by providing plantar flexor torque during ankle dorsiflexion. We hypothesized that subjects would decrease their biological ankle stiffness when the spring was added to the orthosis, keeping total ankle stiffness constant. We collected kinematic, kinetic, and electromyographic data during hopping with and without the spring on the orthosis. We found that total ankle stiffness and leg stiffness did not change across the two orthosis conditions (ANOVA, P > 0.05). This was possible because subjects decreased their biological ankle stiffness to offset the orthosis spring stiffness (P < 0.0001). The reduction in biological ankle stiffness was accompanied by decreases in soleus, medial gastrocnemius, and lateral gastrocnemius muscle activation (P < 0.0002). These results suggest that an elastic exoskeleton might improve human running performance by reducing muscle recruitment.

The majority of individuals poststroke recover the ability to walk overground, although residual impairments contribute to reduced walking speed, spatiotemporal asymmetries, inefficient gait, and limited walking activity in the home and community. A substantial number of studies have investigated the effects of various interventions on locomotor function in individuals poststroke; these studies vary widely in types of tasks practiced, the amount of practiced activities, and the intensity or workload during the intervention. In contrast, basic and applied studies have identified specific parameters of training that could be applied towards treatment of patients poststroke. More directly, the specificity, amount, and intensity of walking practice are thought to be critical variables of rehabilitation interventions that can facilitate plasticity of neuromuscular and cardiopulmonary systems and result in improved locomotor function. In the present commentary, we delineate the evidence and physiological rationale for providing large amounts of high-intensity locomotor training to improve ambulatory function in individuals poststroke. Additional evidence is presented to indicate that improvements in non-walking tasks, such as static balance and performance of transfers, may also occur following locomotor training. We further evaluate previous and more recent studies in the context of these parameters and provide suggestions for providing locomotor training for patients with stroke in the clinical setting.