Recovery of walking in nonambulatory children with chronic spinal cord injuries: Case series.

The immature central nervous system is recognized as having substantial neuroplastic capacity. In this study, we explored the hypothesis that rehabilitation can exploit that potential and elicit reciprocal walking in nonambulatory children with chronic, severe (i.e., lower extremity motor score < 10/50) spinal cord injuries (SCIs). Seven male subjects (3-12 years of age) who were at least 1-year post-SCI and incapable of discrete leg movements believed to be required for walking, enrolled in activity-based locomotor training (ABLT; clinicaltrials.gov NCT00488280). Six children completed the study. Following a minimum of 49 sessions of ABLT, three of the six children achieved walking with reverse rolling walkers. Stepping development, however, was not accompanied by improvement in discrete leg movements as underscored by the persistence of synergistic movements and little change in lower extremity motor scores. Interestingly, acoustic startle responses exhibited by the three responding children suggested preserved reticulospinal inputs to circuitry below the level of injury capable of mediating leg movements. On the other hand, no indication of corticospinal integrity was obtained with transcranial magnetic stimulation evoked responses in the same individuals. These findings suggest some children who are not predicted to improve motor and locomotor function may have a reserve of adaptive plasticity that can emerge in response to rehabilitative strategies such as ABLT. Further studies are warranted to determine whether a critical need exists to re-examine rehabilitation approaches for pediatric SCI with poor prognosis for any ambulatory recovery.

Acute intermittent hypercapnic-hypoxia elicits central neural respiratory motor plasticity in humans.

Acute intermittent hypoxia (AIH) elicits long-term facilitation (LTF) of respiration. Although LTF is observed when CO2 is elevated during AIH in awake humans, the influence of CO2 on corticospinal respiratory motor plasticity is unknown. Thus, we tested the hypotheses that acute intermittent hypercapnic-hypoxia (AIHH): (1) enhances cortico-phrenic neurotransmission (reflecting volitional respiratory control); and (2) elicits ventilatory LTF (reflecting automatic respiratory control). Eighteen healthy adults completed four study visits. Day 1 consisted of anthropometry and pulmonary function testing. On Days 2, 3 and 4, in a balanced alternating sequence, participants received: AIHH, poikilocapnic AIH, and normocapnic-normoxia (Sham). Protocols consisted of 15, 60 s exposures with 90 s normoxic intervals. Transcranial (TMS) and cervical (CMS) magnetic stimulation were used to induce diaphragmatic motor-evoked potentials and compound muscle action potentials, respectively. Respiratory drive was assessed via mouth occlusion pressure (P0.1 ), and minute ventilation measured at rest. Dependent variables were assessed at baseline and 30-60 min after exposures. Increases in TMS-evoked diaphragm potential amplitudes were observed following AIHH vs. Sham (+28 ± 41%, P = 0.003), but not after AIH. No changes were observed in CMS-evoked diaphragm potential amplitudes. Mouth occlusion pressure also increased after AIHH (+21 ± 34%, P = 0.033), but not after AIH. Ventilatory LTF was not observed after any treatment. We demonstrate that AIHH elicits central neural mechanisms of respiratory motor plasticity and increases resting respiratory drive in awake humans. These findings may have important implications for neurorehabilitation after spinal cord injury and other neuromuscular disorders compromising breathing. KEY POINTS: The occurrence of respiratory long-term facilitation following acute exposure to intermittent hypoxia is believed to be dependent upon CO2 regulation - mechanisms governing the critical role of CO2 have seldom been explored. We tested the hypothesis that acute intermittent hypercapnic-hypoxia (AIHH) enhances cortico-phrenic neurotransmission in awake healthy humans. The amplitude of diaphragmatic motor-evoked potentials induced by transcranial magnetic stimulation was increased after AIHH, but not the amplitude of compound muscle action potentials evoked by cervical magnetic stimulation. Mouth occlusion pressure (P0.1 , an indicator of neural respiratory drive) was also increased after AIHH, but not tidal volume or minute ventilation. Thus, moderate AIHH elicits central neural mechanisms of respiratory motor plasticity, without measurable ventilatory long-term facilitation in awake humans.

Feasibility of transcutaneous spinal direct current stimulation combined with locomotor training after spinal cord injury.

STUDY DESIGN: Feasibility study, consisting of random-order, cross-over study of a single intervention session, followed by a parallel-arm study of 16 sessions. OBJECTIVES: To investigate the feasibility of a novel combinatorial approach with simultaneous delivery of transcutaneous spinal direct current stimulation (tsDCS) and locomotor training (tsDCS + LT) after spinal cord injury, compared to sham stimulation and locomotor training (sham + LT), and examine preliminary effects on walking function. SETTING: Clinical research center in the southeastern United States. METHODS: Eight individuals with chronic incomplete spinal cord injury (ISCI) completed the two-part protocol. Feasibility was assessed based on safety (adverse responses), tolerability (pain, spasticity, skin integrity), and protocol achievement (session duration, intensity). Walking function was assessed with the 10 m and 6 min walk tests. RESULTS: There were no major adverse responses. Minimal reports of skin irritation and musculoskeletal pain were consistent between groups. Average training peak heart rate as percent of maximum (mean(SD); tsDCS + LT: 66 (4)%, sham + LT: 69 (10)%) and Borg ratings of perceived exertion (tsDCS + LT: 17.5 (1.2), sham + LT: 14.4 (1.8)) indicate both groups trained at high intensities. Walking speed gains exceeded the minimal clinically important difference (MCID) in three of four who received tsDCS + LT (0.18 (0.29) m/s) and one of four in sham + LT (-0.05 (0.23) m/s). Gains in walking endurance exceeded the MCID in one of four in each group (tsDCS + LT: 36.4 (69.0) m, sham + LT: 4.9 (56.9) m). CONCLUSIONS: Combinatorial tsDCS and locomotor training is safe and feasible for individuals with chronic ISCI, even those with considerable walking impairment. Study outcomes support the need to investigate the efficacy of this approach.

Diaphragm Pacing and a Model for Respiratory Rehabilitation After Spinal Cord Injury.

BACKGROUND AND PURPOSE: Cervical spinal cord injury (CSCI) can cause severe respiratory impairment. Although mechanical ventilation (MV) is a lifesaving standard of care for these patients, it is associated with diaphragm atrophy and dysfunction. Diaphragm pacing (DP) is a strategy now used acutely to promote MV weaning and to combat the associated negative effects. Initial reports indicate that DP also may promote neuromuscular plasticity and lead to improvements in spontaneous diaphragm activation and respiratory function. These outcomes suggest the need for reevaluation of respiratory rehabilitation for patients with CSCI using DP and consideration of new rehabilitation models for these patients and their unique care needs. SUMMARY OF KEY POINTS: This article discusses the rationale for consideration of DP as a rehabilitative strategy, particularly when used in combination with established respiratory interventions. In addition, a model of respiratory rehabilitation and recovery (RRR) is presented, providing a framework for rehabilitation and consideration of DP as an adjuvant rehabilitation approach. The model promotes goals such as respiratory recovery and independence, and lifelong respiratory health, via interdisciplinary care, respiratory training, quantitative measurement, and use of adjuvant strategies such as DP. Application of the model is demonstrated through a description of an inpatient rehabilitation program that applies model components to patients with CSCI who require DP. RECOMMENDATIONS FOR CLINICAL PRACTICE: As DP use increases for patients with acute CSCI, so does the need and opportunity to advance rehabilitation approaches for these patients. This perspective article is a critical step in addressing this need and motivating the advancement of rehabilitation strategies for CSCI patients. (See Video Abstract, Supplemental Digital Content, available at: http://links.lww.com/JNPT/A348).

Rehabilitation with accurate adaptability walking tasks or steady state walking: A randomized clinical trial in adults post-stroke.

OBJECTIVE: To assess changes in walking function and walking-related prefrontal cortical activity following two post-stroke rehabilitation interventions: an accurate adaptability (ACC) walking intervention and a steady state (SS) walking intervention. DESIGN: Randomized, single blind, parallel group clinical trial. SETTING: Hospital research setting. SUBJECTS: Adults with chronic post-stroke hemiparesis and walking deficits. INTERVENTIONS: ACC emphasized stepping accuracy and walking adaptability, while SS emphasized steady state, symmetrical stepping. Both included 36 sessions led by a licensed physical therapist. ACC walking tasks recruit cortical regions that increase corticospinal tract activation, while SS walking activates the corticospinal tract less intensely. MAIN MEASURES: The primary functional outcome measure was preferred steady state walking speed. Prefrontal brain activity during walking was measured with functional near infrared spectroscopy to assess executive control demands. Assessments were conducted at baseline, post-intervention (three months), and follow-up (six months). RESULTS: Thirty-eight participants were randomized to the study interventions (mean age 59.6 ± 9.1 years; mean months post-stroke 18.0 ± 10.5). Preferred walking speed increased from baseline to post-intervention by 0.13 ± 0.11 m/s in the ACC group and by 0.14 ± 0.13 m/s in the SS group. The Time × Group interaction was not statistically significant (P = 0.86). Prefrontal fNIRS during walking decreased from baseline to post-intervention, with a marginally larger effect in the ACC group (P = 0.05). CONCLUSIONS: The ACC and SS interventions produced similar changes in walking function. fNIRS suggested a potential benefit of ACC training for reducing demand on prefrontal (executive) resources during walking.

Synergy between Acute Intermittent Hypoxia and Task-Specific Training.

Acute intermittent hypoxia (AIH) and task-specific training (TST) synergistically improve motor function after spinal cord injury; however, mechanisms underlying this synergistic relation are unknown. We propose a hypothetical working model of neural network and cellular elements to explain AIH-TST synergy. Our goal is to forecast experiments necessary to advance our understanding and optimize the neurotherapeutic potential of AIH-TST.

Clinical Practice Guideline to Improve Locomotor Function Following Chronic Stroke, Incomplete Spinal Cord Injury, and Brain Injury.

BACKGROUND: Individuals with acute-onset central nervous system (CNS) injury, including stroke, motor incomplete spinal cord injury, or traumatic brain injury, often experience lasting locomotor deficits, as quantified by decreases in gait speed and distance walked over a specific duration (timed distance). The goal of the present clinical practice guideline was to delineate the relative efficacy of various interventions to improve walking speed and timed distance in ambulatory individuals greater than 6 months following these specific diagnoses. METHODS: A systematic review of the literature published between 1995 and 2016 was performed in 4 databases for randomized controlled clinical trials focused on these specific patient populations, at least 6 months postinjury and with specific outcomes of walking speed and timed distance. For all studies, specific parameters of training interventions including frequency, intensity, time, and type were detailed as possible. Recommendations were determined on the basis of the strength of the evidence and the potential harm, risks, or costs of providing a specific training paradigm, particularly when another intervention may be available and can provide greater benefit. RESULTS: Strong evidence indicates that clinicians should offer walking training at moderate to high intensities or virtual reality-based training to ambulatory individuals greater than 6 months following acute-onset CNS injury to improve walking speed or distance. In contrast, weak evidence suggests that strength training, circuit (ie, combined) training or cycling training at moderate to high intensities, and virtual reality-based balance training may improve walking speed and distance in these patient groups. Finally, strong evidence suggests that body weight-supported treadmill training, robotic-assisted training, or sitting/standing balance training without virtual reality should not be performed to improve walking speed or distance in ambulatory individuals greater than 6 months following acute-onset CNS injury to improve walking speed or distance. DISCUSSION: The collective findings suggest that large amounts of task-specific (ie, locomotor) practice may be critical for improvements in walking function, although only at higher cardiovascular intensities or with augmented feedback to increase patient's engagement. Lower-intensity walking interventions or impairment-based training strategies demonstrated equivocal or limited efficacy. LIMITATIONS: As walking speed and distance were primary outcomes, the research participants included in the studies walked without substantial physical assistance. This guideline may not apply to patients with limited ambulatory function, where provision of walking training may require substantial physical assistance. SUMMARY: The guideline suggests that task-specific walking training should be performed to improve walking speed and distance in those with acute-onset CNS injury although only at higher intensities or with augmented feedback. Future studies should clarify the potential utility of specific training parameters that lead to improved walking speed and distance in these populations in both chronic and subacute stages following injury. DISCLAIMER: These recommendations are intended as a guide for clinicians to optimize rehabilitation outcomes for persons with chronic stroke, incomplete spinal cord injury, and traumatic brain injury to improve walking speed and distance.

A Backward Walking Training Program to Improve Balance and Mobility in Acute Stroke: A Pilot Randomized Controlled Trial.

BACKGROUND AND PURPOSE: Strategies to address gait and balance deficits early poststroke are minimal. The postural and motor control requirements of Backward Walking Training (BWT) may provide benefits to improve balance and walking speed in this population. This pilot study (1) determined the feasibility of administering BWT during inpatient rehabilitation and (2) compared the effectiveness of BWT to Standing Balance Training (SBT) on walking speed, balance, and balance-related efficacy in acute stroke. METHODS: Eighteen individuals 1-week poststroke were randomized to eight, 30-minute sessions of BWT or SBT in addition to scheduled therapy. Five-Meter Walk Test, 3-Meter Backward Walk Test, Activities-Specific Balance Confidence Scale, Berg Balance Scale, Sensory Organization Test, and Function Independence Measure-Mobility were assessed pre- and postintervention and at 3 months poststroke. RESULTS: Forward gait speed change (BWT: 0.75 m/s; SBT: 0.41 m/s), assessed by the 5-Meter Walk Test, and backward gait speed change (BWT: 0.53 m/s; SBT: 0.23 m/s), assessed by the 3-Meter Backward Walk Test, preintervention to 1-month retention were greater for BWT than for SBT (P < 0.05). Group difference effect size from preintervention to 1-month retention was large for Activities-Specific Balance Confidence Scale, moderate for Berg Balance Scale and Function Independence Measure-Mobility, and small for Sensory Organization Test. DISCUSSION AND CONCLUSIONS: Individuals 1-week poststroke tolerated 30 min/d of additional therapy. At 1-month postintervention, BWT resulted in greater improvements in both forward and backward walking speed than SBT. Backward walking training is a feasible important addition to acute stroke rehabilitation. Future areas of inquiry should examine BWT as a preventative modality for future fall incidence.Video Abstract available for more insights from the authors (see Video, Supplemental Digital Content 1, http://links.lww.com/JNPT/A193).

Mobility Function and Recovery After Stroke: Preliminary Insights From Sympathetic Nervous System Activity.

BACKGROUND AND PURPOSE: Poststroke hemiparesis increases the perceived challenge of walking. Perceived challenge is commonly measured by self-report, which is susceptible to measurement bias. A promising approach to objectively assess perceived challenge is measuring sympathetic nervous system (SNS) activity with skin conductance to detect the physiological stress response. We investigated the feasibility of using skin conductance measurements to detect task-related differences in the challenge posed by complex walking tasks in adults poststroke. METHODS: Adults poststroke (n = 31) and healthy young adults (n = 8) performed walking tasks including typical walking, walking in dim lighting, walking over obstacles, and dual-task walking. Measures of skin conductance and spatiotemporal gait parameters were recorded. Continuous decomposition analysis was conducted to assess changes in skin conductance level (ΔSCL) and skin conductance response (ΔSCR). A subset of participants poststroke also underwent a 12-week rehabilitation intervention. RESULTS: SNS activity measured by skin conductance (both ΔSCL and ΔSCR) was significantly greater for the obstacles task and dual-task walking than for typical walking in the stroke group. Participants also exhibited "cautious" gait behaviors of slower speed, shorter step length, and wider step width during the challenging tasks. Following the rehabilitation intervention, SNS activity decreased significantly for the obstacles task and dual-task walking. DISCUSSION AND CONCLUSIONS: SNS activity measured by skin conductance is a feasible approach for quantifying task-related differences in the perceived challenge of walking tasks in people poststroke. Furthermore, reduced SNS activity during walking following a rehabilitation intervention suggests a beneficial reduction in the physiological stress response evoked by complex walking tasks.Video Abstract available for more insights from the authors (See Video, Supplemental Digital Content 1, http://links.lww.com/JNPT/A234).

Anatomy and physiology of phrenic afferent neurons.

Large-diameter myelinated phrenic afferents discharge in phase with diaphragm contraction, and smaller diameter fibers discharge across the respiratory cycle. In this article, we review the phrenic afferent literature and highlight areas in need of further study. We conclude that 1) activation of both myelinated and nonmyelinated phrenic sensory afferents can influence respiratory motor output on a breath-by-breath basis; 2) the relative impact of phrenic afferents substantially increases with diaphragm work and fatigue; 3) activation of phrenic afferents has a powerful impact on sympathetic motor outflow, and 4) phrenic afferents contribute to diaphragm somatosensation and the conscious perception of breathing. Much remains to be learned regarding the spinal and supraspinal distribution and synaptic contacts of myelinated and nonmyelinated phrenic afferents. Similarly, very little is known regarding the potential role of phrenic afferent neurons in triggering or modulating expression of respiratory neuroplasticity.

Sex differences in spatial accuracy relate to the neural activation of antagonistic muscles in young adults.

Sex is an important physiological variable of behavior, but its effect on motor control remains poorly understood. Some evidence suggests that women exhibit greater variability during constant contractions and poorer accuracy during goal-directed tasks. However, it remains unclear whether motor output variability or altered muscle activation impairs accuracy in women. Here, we examine sex differences in endpoint accuracy during ankle goal-directed movements and the activity of the antagonistic muscles. Ten women (23.1 ± 5.1 years) and 10 men (23 ± 3.7 years) aimed to match a target (9° in 180 ms) with ankle dorsiflexion. Participants performed 50 trials and we recorded the endpoint accuracy and the electromyographic (EMG) activity of the primary agonist (Tibialis Anterior; TA) and antagonist (Soleus; SOL) muscles. Women exhibited greater spatial inaccuracy (Position error: t = -2.65, P = 0.016) but not temporal inaccuracy relative to men. The motor output variability was similar for the two sexes (P > 0.2). The spatial inaccuracy in women was related to greater variability in the coordination of the antagonistic muscles (R 2 0.19, P = 0.03). These findings suggest that women are spatially less accurate than men during fast goal-directed movements likely due to an altered activation of the antagonistic muscles.

Altered activation of the antagonist muscle during practice compromises motor learning in older adults.

Aging impairs the activation of muscle; however, it remains unclear whether it contributes to deficits in motor learning in older adults. The purpose of this study was to determine whether altered activation of antagonistic muscles in older adults during practice inhibits their ability to transfer a motor task ipsilaterally. Twenty young (25.1 ± 3.9 yr; 10 men, 10 women) and twenty older adults (71.5 ± 4.8 yr; 10 men, 10 women) participated. Half of the subjects practiced 100 trials of a rapid goal-directed task with ankle dorsiflexion and were tested 1 day later with elbow flexion (transfer). The rest did not perform any ankle practice and only performed the task with elbow flexion. The goal-directed task consisted of rapid movement (180 ms) to match a spatiotemporal target. For each limb, we recorded the EMG burst activity of the primary agonist and antagonist muscles. The rate of improvement during task acquisition (practice) was similar for young and older adults (P > 0.3). In contrast, only young adults were able to transfer the task to the upper limb. Specifically, young adults who practiced ankle dorsiflexion exhibited ∼30% (P < 0.05) lower movement error and ∼60% (P < 0.05) lower antagonist EMG burst activity compared with older adults who received equal practice and young adults who did not receive any ankle dorsiflexion practice. These results provide novel evidence that the deficient motor learning in older adults may be related to a differential activation of the antagonist muscle, which compromises their ability to acquire the task during practice.

Aging and limb alter the neuromuscular control of goal-directed movements.

The purpose of this study was to determine whether the neuromuscular control of goal-directed movements is different for young and older adults with the upper and lower limbs. Twenty young (25.1 ± 3.9 years) and twenty older adults (71.5 ± 4.8 years) attempted to accurately match the displacement of their limb to a spatiotemporal target during ankle dorsiflexion or elbow flexion movements. We quantified neuromuscular control by examining the movement endpoint accuracy and variability, and the antagonistic muscle activity using surface electromyography (EMG). Our results indicate that older adults exhibit impaired endpoint accuracy with both limbs due to greater time variability. In addition, older adults exhibit greater EMG burst and lower EMG burst variability as well as lower coactivation of the antagonistic muscles. The impaired accuracy of older adults during upper limb movements was related to lower coactivation of the antagonistic muscles, whereas their impaired accuracy during lower limb movements was related to the amplified EMG bursts. The upper limb exhibited greater movement control than the lower limb, and different neuromuscular parameters were related to the accuracy and consistency for each limb. Greater endpoint error during upper limb movements was related to lower coactivation of the antagonistic muscles, whereas greater endpoint error during lower limb movements was related to the amplified EMG bursts. These findings indicate that the age-associated impairments in movement control are associated with altered activation of the involved antagonistic muscles. In addition, independent of age, the neuromuscular control of goal-directed movements is different for the upper and lower limbs.

Neuromuscular control of goal-directed ankle movements differs for healthy children and adults.

PURPOSE: The purpose was to compare neuromuscular control of rapid ankle goal-directed movements in healthy preadolescent children and young adults. METHODS: Ten young adults (20.0 ± 0.9 years) and ten children (9.5 ± 0.7 years) attempted to accurately match the peak displacement of the foot to a spatiotemporal target with an ankle dorsiflexion movement. The targeted displacement was 9° of ankle dorsiflexion, and the targeted time was 180 ms. Surface electromyograms (EMGs) were recorded from the tibialis anterior (TA; agonist) and soleus (SOL; antagonist) muscles. Ankle movement control was quantified with endpoint accuracy and variability. The activation of the involved muscles was quantified with an EMG burst analysis. RESULTS: Children exhibited decreased endpoint accuracy and control compared with young adults, as indicated by greater endpoint errors (47.6 ± 15.2 vs. 25.8 ± 9.0%) and position variability (29.5 ± 5.7 vs. 15.2 ± 6.1 %). In addition, children exhibited differences in muscle activation, as evidenced by greater TA (53.2 ± 19.1 vs. 33.0 ± 19.0%) and SOL (19.9 ± 12.0 vs. 9.6 ± 5.4%) amplitudes of EMG burst, shorter TA duration (251.3 ± 43.6 vs. 296.1 ± 27.6%), and greater variability in the activation of these muscles. The endpoint error (R (2) = 0.7) and position variability (R (2) = 0.67) were predicted from the TA burst amplitude variability and TA burst duration. CONCLUSION: The differences in muscle activation and deficient control of rapid goal-directed ankle movements exhibited by children are likely due to their incomplete development of higher centers.

Speed- and Endurance-Based Classifications of Community Ambulation Post-Stroke Revisited: The Importance of Location in Walking Performance Measurement.

BACKGROUND: Gait speed or 6-minute walk test are frequently used to project community ambulation abilities post-stroke by categorizing individuals as household ambulators, limited, or unlimited community ambulators. However, whether improved clinically-assessed gait outcomes truly translate into enhanced real-world community ambulation remains uncertain. OBJECTIVE: This cross-sectional study aimed to examine differences in home and community ambulation between established categories of speed- and endurance-based classification systems of community ambulation post-stroke and compare these with healthy controls. METHODS: Sixty stroke survivors and 18 healthy controls participated. Stroke survivors were categorized into low-speed, medium-speed, or high-speed groups based on speed-based classifications and into low-endurance, medium-endurance, or high-endurance groups based on the endurance-based classification. Home and community steps/day were quantified using Global Positioning System and accelerometer devices over 7 days. RESULTS: The low-speed groups exhibited fewer home and community steps/day than their medium- and high-speed counterparts (P < .05). The low-endurance group took fewer community steps/day than the high-endurance group (P < .05). Despite vast differences in clinical measures of gait speed and endurance, the medium-speed/endurance groups did not differ in their home and community steps/day from the high-speed/endurance groups, respectively. Stroke survivors took 48% fewer home steps/day and 77% fewer community steps/day than healthy controls. CONCLUSIONS: Clinical classification systems may only distinguish home ambulators from community ambulators, but not between levels of community ambulation, especially beyond certain thresholds of gait speed and endurance. Clinicians should use caution when predicting community ambulation status through clinical measures, due to the limited translation of these classification systems into the real world.

Articulated ankle-foot-orthosis improves inter-limb propulsion symmetry during walking adaptability task post-stroke.

BACKGROUND: Community ambulation involves complex walking adaptability tasks such as stepping over obstacles or taking long steps, which require adequate propulsion generation by the trailing leg. Individuals post-stroke often have an increased reliance on their trailing nonparetic leg and favor leading with their paretic leg, which can limit mobility. Ankle-foot-orthoses are prescribed to address common deficits post-stroke such as foot drop and ankle instability. However, it is not clear if walking with an ankle-foot-orthosis improves inter-limb propulsion symmetry during adaptability tasks. This study sought to examine this hypothesis. METHODS: Individuals post-stroke (n = 9) that were previously prescribed a custom fabricated plantarflexion-stop articulated ankle-foot-orthosis participated. Participants performed steady-state walking and adaptability tasks overground with and without their orthosis. The adaptability tasks included obstacle crossing and long-step tasks, leading with both their paretic and nonparetic leg. Inter-limb propulsion symmetry was calculated using trailing limb ground-reaction-forces. FINDINGS: During the obstacle crossing task, ankle-foot-orthosis use resulted in a significant improvement in inter-limb propulsion symmetry. The orthosis also improved ankle dorsiflexion during stance, reduced knee hyperextension, increased gastrocnemius muscle activity, and increased peak paretic leg ankle plantarflexor moment. In contrast, there were no differences in propulsion symmetry during steady-state walking and taking a long-step when using the orthosis. INTERPRETATION: Plantarflexion-stop articulated ankle-foot-orthoses can improve propulsion symmetry during obstacle crossing tasks in individuals post-stroke, promoting paretic leg use and reduced reliance on the nonparetic leg.

Visuospatial cognition predicts performance on an obstructed vision obstacle walking task in older adults.

Walking performance and cognitive function demonstrate strong associations in older adults, with both declining with advancing age. Walking requires the use of cognitive resources, particularly in complex environments like stepping over obstacles. A commonly implemented approach for measuring the cognitive control of walking is a dual-task walking assessment, in which walking is combined with a second task. However, dual-task assessments have shortcomings, including issues with scaling the task difficulty and controlling for task prioritization. Here we present a new assessment designed to be less susceptible to these shortcomings while still challenging cognitive control of walking: the Obstructed Vision Obstacle (OBVIO) task. During the task, participants hold a lightweight tray at waist level obstructing their view of upcoming foam blocks, which are intermittently spaced along a 10 m walkway. This forces the participants to use cognitive resources (e.g., attention and working memory) to remember the exact placement of upcoming obstacles to facilitate successful crossing. The results demonstrate that adding the obstructed vision board significantly slowed walking speed by an average of 0.26 m/s and increased the number of obstacle strikes by 8-fold in healthy older adults (n = 74). Additionally, OBVIO walking performance (a score based on both speed and number of obstacle strikes) significantly correlated with computer-based assessments of visuospatial working memory, attention, and verbal working memory. These results provide initial support that the OBVIO task is a feasible walking test that demands cognitive resources. This study lays the groundwork for using the OBVIO task in future assessment and intervention studies.

Cardiorespiratory Responses to Acute Intermittent Hypoxia in Humans With Chronic Spinal Cord Injury.

Brief exposure to repeated episodes of low inspired oxygen, or acute intermittent hypoxia (AIH), is a promising therapeutic modality to improve motor function after chronic, incomplete spinal cord injury (SCI). Although therapeutic AIH is under extensive investigation in persons with SCI, limited data are available concerning cardiorespiratory responses during and after AIH exposure despite implications for AIH safety and tolerability. Thus, we recorded immediate (during treatment) and enduring (up to 30 min post-treatment) cardiorespiratory responses to AIH in 19 participants with chronic SCI (>1 year post-injury; injury levels C1 to T6; American Spinal Injury Association Impairment Scale A to D; mean age = 33.8 ± 14.1 years; 18 males). Participants completed a single AIH (15, 60-sec episodes, inspired O2 ≈ 10%; 90-sec intervals breathing room air) and Sham (inspired O2 ≈ 21%) treatment, in random order. During hypoxic episodes: (1) arterial oxyhemoglobin saturation decreased to 82.1 ± 2.9% (p < 0.001); (2) minute ventilation increased 3.83 ± 2.29 L/min (p = 0.008); and (3) heart rate increased 4.77 ± 6.82 bpm (p = 0.010). Considerable variability in cardiorespiratory responses was found among subjects; some individuals exhibited large hypoxic ventilatory responses (≥0.20 L/min/%, n = 11), whereas others responded minimally (<0.20 L/min/%, n = 8). Apneas occurred frequently during AIH and/or Sham protocols in multiple participants. All participants completed AIH treatment without difficulty. No significant changes in ventilation, heart rate, or arterial blood pressure were found 30 min post-AIH p > 0.05). In conclusion, therapeutic AIH is well tolerated, elicits variable chemoreflex activation, and does not cause persistent changes in cardiorespiratory control/function 30 min post-treatment in persons with chronic SCI.

Modular control of varied locomotor tasks in children with incomplete spinal cord injuries.

A module is a functional unit of the nervous system that specifies functionally relevant patterns of muscle activation. In adults, four to five modules account for muscle activation during walking. Neurological injury alters modular control and is associated with walking impairments. The effect of neurological injury on modular control in children is unknown and may differ from adults due to their immature and developing nervous systems. We examined modular control of locomotor tasks in children with incomplete spinal cord injuries (ISCIs) and control children. Five controls (8.6 ± 2.7 yr of age) and five children with ISCIs (8.6 ± 3.7 yr of age performed treadmill walking, overground walking, pedaling, supine lower extremity flexion/extension, stair climbing, and crawling. Electromyograms (EMGs) were recorded in bilateral leg muscles. Nonnegative matrix factorization was applied, and the minimum number of modules required to achieve 90% of the "variance accounted for" (VAF) was calculated. On average, 3.5 modules explained muscle activation in the controls, whereas 2.4 modules were required in the children with ISCIs. To determine if control is similar across tasks, the module weightings identified from treadmill walking were used to reconstruct the EMGs from each of the other tasks. This resulted in VAF values exceeding 86% for each child and each locomotor task. Our results suggest that 1) modularity is constrained in children with ISCIs and 2) for each child, similar neural control mechanisms are used across locomotor tasks. These findings suggest that interventions that activate the neuromuscular system to enhance walking also may influence the control of other locomotor tasks.

Sympathetic nervous system responses during complex walking tasks and community ambulation post-stroke.

Stroke survivors frequently report increased perceived challenge of walking (PCW) in complex environments, restricting their daily ambulation. PCW is conventionally measured through subjective questionnaires or, more recently, through objective quantification of sympathetic nervous system activity during walking tasks. However, how these measurements of PCW reflect daily walking activity post-stroke is unknown. We aimed to compare the subjective and objective assessments of PCW in predicting home and community ambulation. In 29 participants post-stroke, we measured PCW subjectively with the Activities-specific Balance Confidence (ABC) Scale and objectively through electrodermal activity, quantified by change in skin conductance levels (SCL) and skin conductance responses (SCR) between outdoor-complex and indoor-steady-state walking. High-PCW participants were categorized into high-change SCL (ΔSCL ≥ 1.7 µs), high-change SCR (ΔSCR ≥ 0.2 µs) and low ABC (ABC < 72%) groups, while low-PCW participants were categorized into low-change SCL (ΔSCL < 1.7 µs), low-change SCR (ΔSCR < 0.2 µs) and high-ABC (ABC ≥ 72%) groups. Number and location of daily steps were quantified with accelerometry and Global Positioning System devices. Compared to low-change SCL group, the high-change SCL group took fewer steps in home and community (p = 0.04). Neither ABC nor SCR groups differed in home or community steps/day. Objective measurement of PCW via electrodermal sensing more accurately represents home and community ambulation compared to the subjective questionnaire.