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.

The influence of backward versus forward locomotor training on gait speed and balance control post-stroke: Recovery or compensation?

Backward walking training has been reported to improve gait speed and balance post-stroke. However, it is not known if gains are achieved through recovery of the paretic limb or compensations from the nonparetic limb. The purpose of this study was to compare the influence of backward locomotor training (BLT) versus forward locomotor training (FLT) on gait speed and dynamic balance control, and to quantify the underlying mechanisms used to achieve any gains. Eighteen participants post chronic stroke were randomly assigned to receive 18 sessions of either FLT (n = 8) or BLT (n = 10). Pre- and post-intervention outcomes included gait speed (10-meter Walk Test) and forward propulsion (time integral of anterior-posterior ground-reaction-forces during late stance for each limb). Dynamic balance control was assessed using clinical (Functional Gait Assessment) and biomechanical (peak-to-peak range of whole-body angular-momentum in the frontal plane) measures. Balance confidence was assessed using the Activities-Specific Balance Confidence scale. While gait speed and balance confidence improved significantly within the BLT group, these improvements were associated with an increased nonparetic limb propulsion generation, suggesting use of compensatory mechanisms. Although there were no improvements in gait speed within the FLT group, paretic limb propulsion generation significantly improved post-FLT, suggesting recovery of the paretic limb. Neither training group improved in dynamic balance control, implying the need of balance specific training along with locomotor training to improve balance control post-stroke. Despite the within-group differences, there were no significant differences between the FLT and BLT groups in the achieved gains in any of the outcomes.

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.

Differences in balance control between healthy younger and older adults during steady-state walking.

Each year approximately one third of older adults fall and experience extensive musculoskeletal injuries and functional disabilities. An important element in maintaining dynamic balance is the regulation of whole-body angular momentum, which is achieved by proper foot placement with respect to the body center-of-mass as well as generation of appropriate ground reaction forces. Analyzing these quantities in younger and older adults may provide insight into differences in their underlying mechanics for maintaining dynamic balance. This study examined three-dimensional whole-body angular momentum in 13 healthy older (71.8 ± 8.3 years) and 9 younger (23.2 ± 2.8 years) adults walking at their self-selected and fastest-comfortable speeds. The older adults had a significantly higher range of frontal-plane angular momentum compared to the younger adults at both speeds, suggesting poorer mediolateral balance control. This difference was related to the older adults having a wider foot placement with respect to the body center-of-mass, which when combined with the vertical ground reaction force, created a higher destabilizing external moment during single-limb stance that acts to rotate the body towards the contralateral swing leg. To counteract this destabilizing moment, the older adults generated a higher hip abduction moment. There were no differences in the range of sagittal- and transverse-plane angular momentum between age groups at either speed. These results suggest that control of dynamic balance in the frontal-plane is more challenging than in the sagittal-plane for older adults and highlight the importance of proper weight transfer mechanisms and hip abductor force production for maintaining mediolateral balance during walking.

Assessment of backward walking unmasks mobility impairments in post-stroke community ambulators.

Background: While over half of stroke survivors recover the ability to walk without assistance, deficits persist in the performance of walking adaptations necessary for safe home and community mobility. One such adaptation is the ability to walk or step backward. Post-stroke rehabilitation rarely includes backward walking (BW) assessment and BW deficits have not been quantified in post-stroke community ambulators. Objective: To quantify spatiotemporal and kinematic BW characteristics in post-stroke community ambulators and compare their performance to controls. Methods: Individuals post-stroke (n = 15, 60.1 ± 12.9 years, forward speed: 1.13 ± 0.23 m/s) and healthy adults (n = 12, 61.2 ± 16.2 years, forward speed: 1.40 ± 0.13 m/s) performed forward walking (FW) and BW during a single session. Step characteristics and peak lower extremity joint angles were extracted using 3D motion analysis and analyzed with mixed-method ANOVAs (group, walking condition). Results: The stroke group demonstrated greater reductions in speed, step length and cadence and a greater increase in double-support time during BW compared to FW (p < .01). Compared to FW, the post-stroke group demonstrated greater reductions in hip extension and knee flexion during BW (p < .05). The control group demonstrated decreased plantarflexion and increased dorsiflexion during BW, but these increases were attenuated in the post-stroke group (p < .05). Conclusions: Assessment of BW can unmask post-stroke walking impairments not detected during typical FW. BW impairments may contribute to the mobility difficulties reported by adults post-stroke. Therefore, BW should be assessed when determining readiness for home and community ambulation.

The influence of locomotor training on dynamic balance during steady-state walking post-stroke.

Slow walking speed and lack of balance control are common impairments post-stroke. While locomotor training often improves walking speed, its influence on dynamic balance is unclear. The goal of this study was to assess the influence of a locomotor training program on dynamic balance in individuals post-stroke during steady-state walking and determine if improvements in walking speed are associated with improved balance control. Kinematic and kinetic data were collected pre- and post-training from seventeen participants who completed a 12-week locomotor training program. Dynamic balance was quantified biomechanically (peak-to-peak range of frontal plane whole-body angular-momentum) and clinically (Berg-Balance-Scale and Dynamic-Gait-Index). To understand the underlying biomechanical mechanisms associated with changes in angular-momentum, foot placement and ground-reaction-forces were quantified. As a group, biomechanical assessments of dynamic balance did not reveal any improvements after locomotor training. However, improved dynamic balance post-training, observed in a sub-group of 10 participants (i.e., Responders), was associated with a narrowed paretic foot placement and higher paretic leg vertical ground-reaction-force impulse during late stance. Dynamic balance was not improved post-training in the remaining seven participants (i.e., Non-responders), who did not alter their foot placement and had an increased reliance on their nonparetic leg during weight-bearing. As a group, increased walking speed was not correlated with improved dynamic balance. However, a higher pre-training walking speed was associated with higher gains in dynamic balance post-training. These findings highlight the importance of the paretic leg weight bearing and mediolateral foot placement in improving frontal plane dynamic balance post-stroke.

Dynamic Balance during Human Movement: Measurement and Control Mechanisms.

Walking can be exceedingly complex to analyze due to highly nonlinear multi-body dynamics, nonlinear relationships between muscle excitations and resulting muscle forces, dynamic coupling that allows muscles to accelerate joints and segments they do not span, and redundant muscle control. Walking requires the successful execution of a number of biomechanical functions such as providing body support, forward propulsion and balance control, with specific muscle groups contributing to their execution. Thus, muscle injury or neurological impairment that affects muscle output can alter the successful execution of these functions and impair walking performance. The loss of balance control in particular can result in falls and subsequent injuries that lead to the loss of mobility and functional independence. Thus, it is important to assess the mechanisms used to control balance in clinical populations using reliable methods with the ultimate goal of improving rehabilitation outcomes. In this review, we highlight common clinical and laboratory-based measures used to assess balance control and their potential limitations, show how these measures have been used to analyze balance in several clinical populations, and consider the translation of specific laboratory-based measures from the research laboratory to the clinic.

Dynamic balance during walking adaptability tasks in individuals post-stroke.

Maintaining dynamic balance during community ambulation is a major challenge post-stroke. Community ambulation requires performance of steady-state level walking as well as tasks that require walking adaptability. Prior studies on balance control post-stroke have mainly focused on steady-state walking, but walking adaptability tasks have received little attention. The purpose of this study was to quantify and compare dynamic balance requirements during common walking adaptability tasks post-stroke and in healthy adults and identify differences in underlying mechanisms used for maintaining dynamic balance. Kinematic data were collected from fifteen individuals with post-stroke hemiparesis during steady-state forward and backward walking, obstacle negotiation, and step-up tasks. In addition, data from ten healthy adults provided the basis for comparison. Dynamic balance was quantified using the peak-to-peak range of whole-body angular-momentum in each anatomical plane during the paretic, nonparetic and healthy control single-leg-stance phase of the gait cycle. To understand differences in some of the key underlying mechanisms for maintaining dynamic balance, foot placement and plantarflexor muscle activation were examined. Individuals post-stroke had significant dynamic balance deficits in the frontal plane across most tasks, particularly during the paretic single-leg-stance. Frontal plane balance deficits were associated with wider paretic foot placement, elevated body center-of-mass, and lower soleus activity. Further, the obstacle negotiation task imposed a higher balance requirement, particularly during the trailing leg single-stance. Thus, improving paretic foot placement and ankle plantarflexor activity, particularly during obstacle negotiation, may be important rehabilitation targets to enhance dynamic balance during post-stroke community ambulation.

Correlations between measures of dynamic balance in individuals with post-stroke hemiparesis.

Mediolateral balance control during walking is a challenging task in post-stroke hemiparetic individuals. To detect and treat dynamic balance disorders, it is important to assess balance using reliable methods. The Berg Balance Scale (BBS), Dynamic Gait Index (DGI), margin-of-stability (MoS), and peak-to-peak range of angular-momentum (H) are some of the most commonly used measures to assess dynamic balance and fall risk in clinical and laboratory settings. However, it is not clear if these measures lead to similar conclusions. Thus, the purpose of this study was to assess dynamic balance in post-stroke hemiparetic individuals using BBS, DGI, MoS and the range of H and determine if these measure are correlated. BBS and DGI were collected from 19 individuals post-stroke. Additionally, kinematic and kinetic data were collected while the same individuals walked at their self-selected speed. MoS and the range of H were calculated in the mediolateral direction for each participant. Correlation analyses revealed moderate associations between all measures. Overall, a higher range of angular-momentum was associated with a higher MoS, wider step width and lower BBS and DGI scores, indicating poor balance control. Further, only the MoS from the paretic foot placement, but not the nonparetic foot, correlated with the other balance measures. Although moderate correlations existed between all the balance measures, these findings do not necessarily advocate the use of a single measure as each test may assess different constructs of dynamic balance. These findings have important implications for the use and interpretation of dynamic balance assessments.

The influence of solid ankle-foot-orthoses on forward propulsion and dynamic balance in healthy adults during walking.

BACKGROUND: In post-stroke hemiparetic subjects, solid polypropylene ankle-foot-orthoses are commonly prescribed to assist in foot clearance during swing while bracing the ankle during stance. Mobility demands, such as changing walking speed and direction, are accomplished by accelerating or decelerating the body and maintaining dynamic balance. Previous studies have shown that the ankle plantarflexors are primary contributors to these essential biomechanical functions. Thus, with ankle-foot-orthoses limiting ankle motion and plantarflexor output during stance, execution of these walking subtasks may be compromised. This study examined the influence of a solid polypropylene ankle-foot-orthosis on forward propulsion and dynamic balance in healthy adults. METHODS: Kinematic and kinetic data were recorded from 10 healthy adults walking with and without a unilateral ankle-foot-orthosis at steady-state slow (0.6m/s) and moderate (1.2m/s) speeds, and during accelerated (0-1.8m/s at 0.06m/s(2)) and decelerated (1.8-0m/s at -0.06m/s(2)) walking. Propulsion was quantified by propulsive and braking impulses (i.e., time integral of the anterior-posterior ground reaction force) while dynamic balance was quantified by the peak-to-peak range of whole-body angular momentum. FINDINGS: The propulsive impulses decreased in the leg with ankle-foot-orthosis compared to the contralateral leg and no ankle-foot-orthosis condition. Further, the ankle-foot-orthosis resulted in a greater range of angular momentum in both the frontal and sagittal planes, which were correlated with the reduced peak hip abduction and reduced ankle plantarflexor moments, respectively. INTERPRETATION: Solid ankle-foot-orthoses limit the successful execution of important mobility subtasks in healthy adults and that the prescription of ankle-foot-orthosis should be carefully considered.