Neha Lodha

Bilateral movement training and stroke motor recovery progress: a structured review and meta-analysis.

The purpose was to conduct a structured review and meta-analysis to determine the cumulative effect of bilateral arm training on motor capabilities post stroke. Forty-eight stroke studies were selected from three databases with 25 comparisons qualifying for inclusion in our meta-analysis. We identified and coded four types of bilateral arm interventions with 366 stroke patients. A random effects model using the standardized mean difference technique determined a large and significant effect size (0.734; SE=0.125), high fail-safe N (532), and medium variability in the studies (I(2)=63%). Moderator variable analysis on the type of bilateral training revealed two large and significant effects: (a) BATRAC (0.842; SE=0.155) and (b) coupled bilateral and EMG-triggered neuromuscular stimulation (1.142; SE=0.176). These novel findings provide strong evidence supporting bilateral arm training with the caveat that two coupled protocols, rhythmic alternating movements and active stimulation, are most effective.

Force control and degree of motor impairments in chronic stroke

OBJECTIVE This study determined the variability and regularity of force production in impaired upper extremities of chronic stroke survivors. Two hypotheses included: (1) stroke will increase the variability and regularity of force output in comparison to age-matched controls and (2) degree of motor impairments will be positively correlated with the variability and regularity of force output. METHODS Nine chronic stroke and nine age-matched controls performed unimanual isometric wrist and finger extension movements for 20s to three different target force levels. Force output was indexed by magnitude, accuracy, variability, and regularity. Stroke motor impairment levels were determined by Fugl-Meyer upper extremity assessment. RESULTS The stroke group demonstrated increased variability and regularity of the force output. Further, motor impairments scaled with increase in variability and regularity of force output. CONCLUSIONS The variability and regularity of force differentiated isometric contractions performed by chronic stroke survivors from age-matched controls. Moreover, in clinical settings an objective assessment of force control on variability and regularity appears to be most meaningful at 25% of MVC. SIGNIFICANCE Increased variability contributes to reduced steadiness in force output. Increased regularity characterizes the adaptability losses in motor capabilities following stroke. This knowledge may facilitate planning and evaluating rehabilitation protocols.

Upper extremity improvements in chronic stroke: Coupled bilateral load training

BACKGROUND The current treatment intervention study determined the effect of coupled bilateral training (i.e., bilateral movements and EMG-triggered neuromuscular stimulation) and resistive load (mass) on upper extremity motor recovery in chronic stroke. METHODS Thirty chronic stroke subjects were randomly assigned to one of three behavioral treatment groups and completed 6 hours of rehabilitation in 4 days: (1) coupled bilateral training with a load on the unimpaired hand, (2) coupled bilateral training with no load on the unimpaired hand, and (3) control (no stimulation assistance or load). RESULTS Separate mixed design ANOVAs revealed improved motor capabilities by the coupled bilateral groups. From the pretest to the posttest, both the coupled bilateral no load and load groups moved a higher number of blocks and demonstrated more regularity in the sustained contraction task. Faster motor reaction times across test sessions for the coupled bilateral load group provided additional evidence for improved motor capabilities. CONCLUSIONS Together these behavioral findings lend support to the contribution of coupled bilateral training with a load on the unimpaired arm to improved motor capabilities on the impaired arm. This evidence supports a neural explanation in that simultaneously moving both limbs during stroke rehabilitation training appears to activate balanced interhemispheric interactions while an extra load on the unimpaired limb provides stability to the system.

Force control deficits in chronic stroke: grip formation and release phases

The aim of the study was to develop a novel approach for quantifying stair-stepping in a trajectory tracking task with the goal of understanding how age and stroke-related differences in motor control contribute to force control deficits. Nine stroke participants, nine age-matched controls, and nine young healthy adults performed an isometric gripping task while squeezing, holding, and releasing a cylindrical device. The visual tracking task involved three different rates of force production (5, 10, and 20% maximal force/s). Four outcome measures determined force control deficits: (a) root mean square error, (b) standard deviation, (c) step number, and (d) mean pause duration. Our findings indicate that step number, and especially mean pause duration, differentiated force control deficits in the three groups more effectively than the traditional root mean square error. Moreover, stroke participants showed the largest force control deficits during the grip release phase compared to age-matched and young healthy controls. Importantly, step number and mean pause duration quantified stair-stepping while measuring different constructs than root mean square error. Distinct step and duration interruptions in force modulation by persons post-stroke during the grip release phase provide new information with implications for motor recovery during rehabilitation.

Bimanual isometric force control: Asymmetry and coordination evidence post stroke

OBJECTIVE This study determined the nature of bimanual deficits during visually-guided isometric force production in chronic stroke. METHODS Stroke survivors and age-matched controls performed bimanual isometric wrist/finger extension contractions for 20s to target submaximal force levels. Force asymmetry was indexed by the proportion of force contributed by the impaired hand to total force. Force coordination was determined by computing time-series cross-correlations and time-lag between force outputs of both hands. RESULTS The stroke group demonstrated greater asymmetry and reduced coordination in force produced by each hand. The extent of asymmetry in the force magnitude remained constant across the three submaximal force levels in both groups. Bimanual force coordination increased at higher forces in controls but not in stroke. Finally, the less-impaired hand forces time-lagged the impaired hand. CONCLUSIONS Bimanual motor impairments in chronic stroke are characterized by increased asymmetry and reduced coordination between individual hand forces. Distinct control mechanisms are involved in the production and coordination of forces following stroke. SIGNIFICANCE An implication involves rehabilitation protocols that emphasize bimanual coordination for training the hands to produce symmetric forces that are temporally coordinated.

Increased force variability in chronic stroke: contributions of force modulation below 1 Hz.

Increased force variability constitutes a hallmark of arm disabilities following stroke. Force variability is related to the modulation of force below 1 Hz in healthy young and older adults. However, whether the increased force variability observed post stroke is related to the modulation of force below 1 Hz remains unknown. Thus, the purpose of this study was to compare force modulation below 1 Hz in chronic stroke and age-matched healthy individuals. Both stroke and control individuals (N = 26) performed an isometric grip task to submaximal force levels. Coefficient of variation quantified force variability, and power spectrum density of force quantified force modulation below 1 Hz with a high resolution (0.07 Hz). Analyses indicated that force variability was greater for the stroke group compared with to healthy controls and for the paretic hand compared with the non-paretic hand. Force modulation below 1 Hz differentiated the stroke individuals and healthy controls, as well as the paretic and non-paretic hands. Specifically, stroke individuals (paretic hand) exhibited greater power ∼0.2 Hz (0.07–0.35 Hz) and lesser power ∼0.6 Hz (0.49–0.77 Hz) compared to healthy controls (non-dominant hand). Similarly, the paretic hand exhibited greater power ∼0.2 Hz, and lesser power ∼0.6 Hz than the non-paretic hand. Moreover, variability of force was strongly predicted from the modulation of specific frequencies below 1 Hz (R 2 = 0.80). Together, these findings indicate that the modulation of force below 1 Hz provides significant insight into changes in motor control after stroke.

Bimanual force control strategies in chronic stroke: finger extension versus power grip.

Stroke leads to motor asymmetries in the flexor and extensor muscles of the hand. Typically, the strength deficits in the extensors are greater than the flexors. The impact of differential motor abilities of these muscle groups on the execution of bimanual force control tasks in individuals with stroke is unknown. The primary purpose of this study was to determine the influence of task constraints on visually guided bimanual force control in chronic stroke. Stroke survivors and age-matched individuals performed bimanual isometric contractions for 20s to match target submaximal force levels. Online visual feedback of the total force (sum of the forces produced by both hands) was provided. The task constraints were manipulated by (a) finger extension, and (b) finger flexion (power grip). Force asymmetry was indexed by the proportion of force contributed by the paretic hand to the total force. The stroke group demonstrated task-specific asymmetry in bimanual force control. Specifically, the paretic hand contributed less force than the non-paretic hand in finger extension whereas this relationship was reversed in power grip. Importantly, regardless of the nature of the task, reduction in motor impairments was associated with increased symmetry and coordination in bimanual tasks. Further, bimanual submaximal grip force control revealed asymmetry and coordination deficits that are not identified by investigating bimanual maximal force production alone. The motor control strategy adopted to optimize performance on bimanual tasks revealed the altered force production of the paretic hand due to the combined effect of extensor weakness and enhanced flexor bias following stroke. Bimanual asymmetries in stroke survivors highlight the need for identifying and treating the task-specific impairments for maximizing motor recovery post stroke.

Force Control Is Related to Low-Frequency Oscillations in Force and Surface EMG

Force variability during constant force tasks is directly related to oscillations below 0.5 Hz in force. However, it is unknown whether such oscillations exist in muscle activity. The purpose of this paper, therefore, was to determine whether oscillations below 0.5 Hz in force are evident in the activation of muscle. Fourteen young adults (21.07±2.76 years, 7 women) performed constant isometric force tasks at 5% and 30% MVC by abducting the left index finger. We recorded the force output from the index finger and surface EMG from the first dorsal interosseous (FDI) muscle and quantified the following outcomes: 1) variability of force using the SD of force; 2) power spectrum of force below 2 Hz; 3) EMG bursts; 4) power spectrum of EMG bursts below 2 Hz; and 5) power spectrum of the interference EMG from 10–300 Hz. The SD of force increased significantly from 5 to 30% MVC and this increase was significantly related to the increase in force oscillations below 0.5 Hz (R 2 = 0.82). For both force levels, the power spectrum for force and EMG burst was similar and contained most of the power from 0–0.5 Hz. Force and EMG burst oscillations below 0.5 Hz were highly coherent (coherence = 0.68). The increase in force oscillations below 0.5 Hz from 5 to 30% MVC was related to an increase in EMG burst oscillations below 0.5 Hz (R 2 = 0.51). Finally, there was a strong association between the increase in EMG burst oscillations below 0.5 Hz and the interference EMG from 35–60 Hz (R 2 = 0.95). In conclusion, this finding demonstrates that bursting of the EMG signal contains low-frequency oscillations below 0.5 Hz, which are associated with oscillations in force below 0.5 Hz.

Long-term rehabilitation for chronic stroke arm movements: a randomized controlled trial:

Objective: We investigated the effect of long-term practice on motor improvements in chronic stroke patients. Design: Randomized parallel group controlled study. Setting: Motor Behavior Laboratory, University of Florida. Subjects: Eighteen individuals who experienced a stroke more than nine months prior to enrolling. Interventions: The treatment interventions were bilateral arm movements coupled with active neuromuscular stimulation on the impaired arm for both practice duration groups. The short-term group received one treatment protocol, whereas, over 16 months, the long-term practice group completed 10 treatment protocols. All protocol sessions were 6 hours long (90 minutes 1 day/week/4 weeks) and were separated by 22 days. Main outcome measures: Repeated data collection on three primary outcome measures (i.e. Box and Block test, fractionated reaction times, and sustained force production) evaluated motor capabilities across rehabilitation times. Results: Mixed design ANOVAs (Group × Retention Test: 2 × 4; Group × Retention Test × Arm Condition: 2 × 4 × 2) revealed improved motor capabilities for the long-term practice duration group on each primary measure. At the 16-month delayed retention test, when compared to the short-term group, the long-term group demonstrated: (a) more blocks moved (43 v 32), (b) faster premotor reaction times (158 v 208 ms), and (c) higher force production (75 v 45 N). Conclusion: Sixty hours of rehabilitation over 16 months provided by various bilateral arm movements and coupled active stimulation improved motor capabilities in chronic stroke.

Low-Frequency Oscillations and Control of the Motor Output

A less precise force output impairs our ability to perform movements, learn new motor tasks, and use tools. Here we show that low-frequency oscillations in force are detrimental to force precision. We summarize the recent evidence that low-frequency oscillations in force output represent oscillations of the spinal motor neuron pool from the voluntary drive, and can be modulated by shifting power to higher frequencies. Further, force oscillations below 0.5 Hz impair force precision with increased voluntary drive, aging, and neurological disease. We argue that the low-frequency oscillations are (1) embedded in the descending drive as shown by the activation of multiple spinal motor neurons, (2) are altered with force intensity and brain pathology, and (3) can be modulated by visual feedback and motor training to enhance force precision. Thus, low-frequency oscillations in force provide insight into how the human brain regulates force precision.