Hyosok Lim

Crouch gait is one of the most frequently observed gait abnormalities in children with cerebral palsy (CP). These findings suggest that applying a targeted downward pulling force during the mid-stance phase, compared with a constant condition, may facilitate motor adaptation for improving crouch gait in children with CP, whereas applying a force during the early-stance may be less effective. These findings may be used to develop new interventions to improve crouch gait in children with CP.

We examined the effect of providing lateral perturbation force at the trunk during walking on improving trunk control in children with cerebral palsy (CP). We found that repeated motor adaptation to trunk perturbation force during walking may promote motor learning of improved trunk control in children with CP. In particular, we found that motor variability of trunk movement can predict motor learning ability of trunk postural control in children with CP.

Many children with cerebral palsy (CP) exhibit impairments in trunk postural control, particularly the second level of postural control. Results from this study suggest that applying repeated pelvis perturbations during sitting astride may induce an improvement in reactive trunk postural control in children with CP. Further, increasing motor variability by applying repeated VARIED force perturbations may be more effective than the CONSTANT perturbations in promoting motor learning of improved head stability and reactive trunk postural control in children with CP.

The goal of this study was to determine whether increasing motor variability by applying varied perturbation forces to the pelvis during sitting astride would facilitate motor learning of improved trunk postural control in children with cerebral palsy (CP). Fourteen children with spastic CP were tested in two conditions: CONSTANT and VARIED force perturbations in two training sessions with each session lasted for 15 minutes. A custom robotic system was used to deliver repetitive perturbation forces to the pelvis while participants sat astride. Postural reactions to the unpredicted perturbations in the anterior and posterior directions were tested before and after each training session. Kinematics of head, trunk, and pelvis movement, and muscle electromyography signals were recorded. One session of pelvis perturbation training with either the CONSTANT (P = 0.028) or VARIED force magnitudes (P = 0.009) induced an earlier onset of trunk extensor under unpredicted perturbations. In addition, one session of pelvis perturbation training with VARIED force magnitudes induced a significant decrease in peak angle of head extension (P = 0.016), and an improvement in recruitment order of the neck and trunk muscles under unpredicted perturbations (P = 0.020). These results suggest that repeated pelvis perturbations during sitting astride may induce improvement in muscle activation onset under unpredicted perturbations in children with CP. Moreover, repeated pelvis perturbations with varied force magnitudes, which may increase motor variability, may lead to improvements in head stability and muscle activation sequence of trunk and neck muscles in response to unpredicted perturbations in children with CP.

Motor interference, where new skill acquisition disrupts the performance of a previously learned skill, is a critical yet underexplored factor in gait rehabilitation post‐stroke. This study investigates the interference effects of two different practice schedules, applying interleaved (ABA condition) and intermittent (A‐A condition) pulling force to the pelvis during treadmill walking, on lateral pelvis shifting towards the paretic leg in individuals with stroke. Task A involved applying resistive pelvis force (pulling towards the non‐paretic side), and Task B applied assistive force (pulling towards the paretic side) at the stance phase of the paretic leg during walking. Sixteen individuals with chronic stroke were tested for gait pattern changes, including lateral pelvis shifting and spatiotemporal gait parameters, and neurophysiological changes, including muscle activity in the paretic leg and beta band absolute power in the lesioned cortical areas. A‐A condition demonstrated increased lateral pelvis shifting towards the paretic side, extended paretic stance time and longer non‐paretic step length after force release while ABA condition did not show any changes. These changes in gait pattern after A‐A condition were accompanied by increased muscle activities of the ankle plantarflexors, and hip adductors/abductors. A‐A condition demonstrated greater changes in beta band power in the sensorimotor regions compared to ABA condition. These findings suggest that while walking practice with external force to the pelvis can improve lateral pelvis shifting towards the paretic leg post‐stroke, practicing a new pelvis shifting task in close succession may hinder the performance of a previously obtained lateral pelvis shifting pattern during walking.

Cross‐education, a phenomenon where unilateral strength (or skill) training enhances strength (or skill) in the contralateral untrained limb, has been well studied in able‐bodied individuals. Cross‐education effect accompanies bilateral changes of corticomotor activity in the motor cortex (M1). Recent reports demonstrated greater cross‐education effect in stroke survivors compared to healthy individuals, however, corticomotor responses to cross‐education in stroke remains unclear. This study aimed to determine the effects of non‐paretic leg movements on corticomotor excitability (CME) and reaction time of the paretic leg in severely impaired stroke survivors. Seventeen post stroke individuals with severe leg motor impairment (Fugl‐Meyer lower extremity score less than 21 and absence of motor evoked potential in the paretic leg) performed three 20‐min motor trainings using their non‐paretic ankle: skill (targeted dynamic movements), strength (isometric resistance) and sham (sub‐threshold electrical nerve stimulation). During training, verbal instructions were given to the participants to limit their movement to the non‐paretic leg and this was confirmed with visual observation of the paretic leg. Transcranial magnetic stimulation measured CME of the contralateral pathways from the non‐lesioned M1 to the non‐paretic tibialis anterior (TA) muscle, ipsilateral pathways to the paretic TA and transcallosal inhibition (TCI) from the non‐lesioned to lesioned M1. Paretic ankle reaction time was measured using a reaction time paradigm. All outcomes were measured before, immediately post, 30‐min post and 60‐min post priming. CME of the non‐paretic TA increased after skill (.08 ± .10 mV) and strength (.06 ± .05 mV) training (p < .01). Ipsilateral CME of the paretic TA (.02 ± .01 mV) and TCI (.01 ± .01 s, ipsilateral silent period; more inhibition to the lesioned M1) increased after skill (p < .05) but not strength training. Reaction time of the paretic ankle improved after skill and strength training (−.11 ± .2 and −.13 ± .20 s, respectively; p < .05) and was sustained at 60 min. No changes were observed during the sham condition. Our findings may inform future studies for using non‐paretic leg movements as a priming modality, especially for those who are contraindicated to other priming paradigms (e.g., brain stimulation) or unable to perform paretic leg movements. Conclusion: Non‐paretic leg movements can be used as a priming modality, especially for those who are contraindicated to other priming paradigms (e.g., brain stimulation) or unable to perform paretic leg movements.

Background: Cross-education, a phenomenon where unilateral strength (or skill) training enhances strength (or skill) in the contralateral untrained limb, has been well studied in able-bodied individuals. However, whether non-paretic leg movements can modulate corticomotor excitability (CME) and improve motor control of the paretic leg in stroke remains unclear. Objective: To determine the effects of non-paretic leg movements on corticomotor responses and motor control of the paretic leg in persons with severe stroke. Methods: Seventeen post stroke individuals with severe leg motor impairment performed three 20-min motor trainings using their non-paretic ankle: skill (targeted dynamic movements), strength (isometric resistance), and sham (sub-threshold electrical nerve stimulation). Transcranial magnetic stimulation measured CME of the contralateral pathways from the non-lesioned motor cortex (M1) to the non-paretic tibialis anterior (TA) muscle, ipsilateral pathways to the paretic TA, and transcallosal inhibition (TCI) from the non-lesioned to lesioned M1. Paretic ankle motor control was measured using a reaction time paradigm. Results: CME of the non-paretic TA increased after skill (23%) and strength (19%) training (p<0.01). Ipsilateral CME of the paretic TA (23%) and TCI (36%) increased after skill (p<0.05) but not strength training. Reaction time of the paretic ankle improved after skill and strength training (~12%; p<0.05) and was sustained at 60 minutes. No changes were observed during the sham condition. Conclusion: Our findings may inform future studies for using non-paretic leg movements as a priming modality, especially for those who are contraindicated to other priming paradigms (e.g., brain stimulation) or unable to perform paretic leg movements.

Current stroke rehabilitation interventions focus on intensive task specific training of the paretic limb, which may not be feasible for individuals with higher levels of impairment or in the early phase of stroke. Cross-education, a mechanism that improves strength or skill of the untrained limb following unilateral motor training, has high clinical relevance for stroke rehabilitation. Despite its potential benefits, our knowledge on the application and efficacy of cross-education in stroke is limited. We performed a scoping review to synthesize the current evidence regarding neurophysiological and motor effects of cross-education training in stroke. Low to strong evidence from five studies demonstrated strength gains ranging from 31–200% in the untrained paretic limb following non-paretic muscle training. Neurophysiological mechanisms underlying cross-education were unclear as the three studies that used transcranial magnetic stimulation to probe functional connectivity demonstrated mixed results in low sample size. Our review suggests that cross-education is a promising clinical approach in stroke, however high quality studies focusing on neurophysiological mechanisms are required to establish the efficacy and underlying mechanisms of cross-education in stroke. Recommendations regarding future directions and clinical utility are provided.

Cortical priming is an emerging strategy to enhance motor recovery after stroke, however, limited information exists on the neuromodulatory effects of lower limb movement-based priming to facilitat...