Increased temporal stride variability contributes to impaired gait coordination after stroke.

Heightened motor variability is a prominent impairment after stroke. During walking, stroke survivors show increased spatial and temporal variability; however, the functional implications of increased gait variability are not well understood. Here, we determine the effect of gait variability on the coordination between lower limbs during overground walking in stroke survivors. Ambulatory stroke survivors and controls walked at a preferred pace. We measured stride length and stride time variability, and accuracy and consistency of anti-phase gait coordination with phase coordination index (PCI). Stroke survivors showed increased stride length variability, stride time variability, and PCI compared with controls. Stride time variability but not stride length variability predicted 43% of the variance in PCI in the stroke group. Stride time variability emerged as a significant predictor of error and consistency of phase. Despite impaired spatial and temporal gait variability following stroke, increased temporal variability contributes to disrupted accuracy and consistency of gait coordination. We provide novel evidence that decline in gait coordination after stroke is associated with exacerbated stride time variability, but not stride length variability. Temporal gait variability may be a robust indicator of the decline in locomotor function and an ideal target for motor interventions that promote stable walking after stroke.

Motor Training After Stroke: A Novel Approach for Driving Rehabilitation.

Background: A key component of safe driving is a well-timed braking performance. Stroke-related decline in motor and cognitive processes slows braking response and puts individuals with stroke at a higher risk for car crashes. Although the impact of cognitive training on driving has been extensively investigated, the influence of motor interventions and their effectiveness in enhancing specific driving-related skills after stroke remains less understood. We compare the effectiveness of two motor interventions (force-control vs. strength training) to facilitate braking, an essential skill for safe driving. Methods: Twenty-two stroke survivors were randomized to force-control training or strength training. Before and after training, participants performed a braking task during car-following in a driving simulator. We quantified the cognitive and motor components of the braking task with cognitive processing time and movement execution time. Results: The cognitive processing time did not change for either training group. In contrast, the movement execution became significantly faster (14%) following force-control training but not strength training. In addition, task-specific effects of training were found in each group. The force-control group showed improved accuracy and steadiness of ankle movements, whereas the strength training group showed increased dorsiflexion strength following training. Conclusion: Motor intervention that trains ankle force control in stroke survivors improves the speed of movement execution during braking. Driving rehabilitation after stroke might benefit from incorporating force-control training to enhance the movement speed for a well-timed braking response.

Sex differences in cognitive-motor components of braking in older adults.

Fast and accurate braking is essential for safe driving and relies on efficient cognitive and motor processes. Despite the known sex differences in overall driving behavior, it is unclear whether sex differences exist in the objective assessment of driving-related tasks in older adults. Furthermore, it is unknown whether cognitive-motor processes are differentially affected in men and women with advancing age. We aimed to determine sex differences in the cognitive-motor components of the braking performance in older adults. Fourteen men (63.06 ± 8.53 years) and 14 women (67.89 ± 11.81 years) performed a braking task in a simulated driving environment. Participants followed a lead car and applied a quick and controlled braking force in response to the rear lights of the lead car. We quantified braking accuracy and response time. Importantly, we also decomposed response time in its cognitive (pre-motor response time) and motor (motor response time) components. Lastly, we examined whether sex differences in the activation and coordination of the involved muscles could explain differences in performance. We found sex differences in the cognitive-motor components of braking performance with advancing age. Specifically, the cognitive processing speed is 27.41% slower in women, while the motor execution speed is 24.31% slower in men during the braking task. The opposite directions of impairment in the cognitive and motor speeds contributed to comparable overall braking speed across sexes. The sex differences in the activation of the involved muscles did not relate to response time differences between men and women. The exponential increase in the number of older drivers raises concerns about potential effects on traffic and driver safety. We demonstrate the presence of sex differences in the cognitive-motor components of braking performance with advancing age. Driving rehabilitation should consider differential strategies for ameliorating sex-specific deficits in cognitive and motor speeds to enhance braking performance in older adults.

Does the contribution of the paretic hand to bimanual tasks change with grip strength capacity following stroke?

INTRODUCTION: The majority of tasks we perform every day require coordinated use of both hands. Following a stroke, the paretic hand contribution to bimanual tasks is often impaired, leading to asymmetric hand use. Grip strength is a commonly used clinical indicator of progress towards stroke motor recovery. The extent to which the paretic hand's contribution to bimanual tasks improves with increasing grip strength is not known. The purpose of this study is to determine how grip strength capacity of the paretic hand influences its contribution to bimanual tasks. METHODS: Twenty-one chronic stroke participants and ten older control participants volunteered to take part in this study. The individuals with stroke were recruited in two distinct groups based on the grip strength capacity of paretic hand, i.e., paretic hand strength/non-paretic hand strength, expressed as a percentage. The low strength-capacity group was identified as individuals with grip strength capacity less than 60% and the high strength-capacity group was individuals with grip strength capacity greater than or equal to 60%. All groups performed isometric, grip force contractions in two bimanual tasks - a maximum force production (MVC) task and a submaximal force control task. We quantified the magnitude of force contributed by the paretic and non-paretic hands during both tasks. Additionally, in the force control task we quantified the amount and structure of force variability using coefficient of variation (CV) and approximate entropy (ApEn) for both hands. RESULTS: The amount of force contributed by the paretic hand increased in bimanual tasks with an increase in its grip strength capacity, (maximal force production: r = 0.85, p < 0.01; submaximal force control: r = 0.62, p < 0.01). In the bimanual MVC task and bimanual force control task, both hands contributed equal magnitudes of force in the high strength-capacity group but unequal forces in low strength-capacity group. Surprisingly, the amount and structure of force variability in bimanual force control tasks did not change with the increase in grip strength capacity, (CV of force: r = - 0.07, p = 0.77; ApEn: r = - 0.23, p = 0.31). Both low and high strength-capacity stroke groups showed significantly higher CV of force and heightened ApEn compared with the control group. CONCLUSION: With the increase in grip strength capacity, the paretic hand contributes greater magnitude of force but continues to show persistent deficits in force modulation in bimanual tasks. Therefore, stroke rehabilitation should emphasize retraining of the paretic hand for force modulation to maximize its use in bimanual tasks.

Force-Control vs. Strength Training: The Effect on Gait Variability in Stroke Survivors.

Purpose: Increased gait variability in stroke survivors indicates poor dynamic balance and poses a heightened risk of falling. Two primary motor impairments linked with impaired gait are declines in movement precision and strength. The purpose of the study is to determine whether force-control training or strength training is more effective in reducing gait variability in chronic stroke survivors. Methods: Twenty-two chronic stroke survivors were randomized to force-control training or strength training. Participants completed four training sessions over 2 weeks with increasing intensity. The force-control group practiced increasing and decreasing ankle forces while tracking a sinusoid. The strength group practiced fast ankle motor contractions at a percentage of their maximal force. Both forms of training involved unilateral, isometric contraction of the paretic, and non-paretic ankles in plantarflexion and dorsiflexion. Before and after the training, we assessed gait variability as stride length and stride time variability, and gait speed. To determine the task-specific effects of training, we measured strength, accuracy, and steadiness of ankle movements. Results: Stride length variability and stride time variability reduced significantly after force-control training, but not after strength training. Both groups showed modest improvements in gait speed. We found task-specific effects with strength training improving plantarflexion and dorsiflexion strength and force control training improving motor accuracy and steadiness. Conclusion: Force-control training is superior to strength training in reducing gait variability in chronic stroke survivors. Improving ankle force control may be a promising approach to rehabilitate gait variability and improve safe mobility post-stroke.

Cognitive and motor deficits contribute to longer braking time in stroke.

BACKGROUND: Braking is a critical determinant of safe driving that depends on the integrity of cognitive and motor processes. Following stroke, both cognitive and motor capabilities are impaired to varying degrees. The current study examines the combined impact of cognitive and motor impairments on braking time in chronic stroke. METHODS: Twenty stroke survivors and 20 aged-matched healthy controls performed cognitive, motor, and simulator driving assessments. Cognitive abilities were assessed with processing speed, divided attention, and selective attention. Motor abilities were assessed with maximum voluntary contraction (MVC) and motor accuracy of the paretic ankle. Driving performance was examined with the braking time in a driving simulator and self-reported driving behavior. RESULTS: Braking time was 16% longer in the stroke group compared with the control group. The self-reported driving behavior in stroke group was correlated with braking time (r = - 0.53, p = 0.02). The stroke group required significantly longer time for divided and selective attention tasks and showed significant decrease in motor accuracy. Together, selective attention time and motor accuracy contributed to braking time (R2 = 0.40, p = 0.01) in stroke survivors. CONCLUSIONS: This study provides novel evidence that decline in selective attention and motor accuracy together contribute to slowed braking in stroke survivors. Driving rehabilitation after stroke may benefit from the assessment and training of attentional and motor skills to improve braking during driving.

Impaired force control contributes to car steering dysfunction in chronic stroke.

PURPOSE: Precise control of a car steering wheel requires adequate motor capability. Deficits in grip strength and force control after stroke could influence the ability steer a car. Our study aimed to determine the impact of stroke on car steering and identify the relative contribution of grip strength and grip force control to steering performance. METHODS: Twelve chronic stroke survivors and 12 controls performed three gripping tasks with each hand: maximum voluntary contraction, dynamic force tracking, and steering a car on a winding road in a simulated driving environment. We quantified grip strength, grip force variability, and deviation of the car from the center of the lane. RESULTS: The paretic hand exhibited reduced grip strength, increased grip force variability, and increased lane deviation compared with the non-dominant hand in controls. Grip force variability, but not grip strength, significantly predicted (R2 = 0.49, p < 0.05) lane deviation with the paretic hand. CONCLUSION: Stroke impairs the steering ability of the paretic hand. Although grip strength and force control of the paretic hand are diminished after stroke, only grip force control predicts steering accuracy. Deficits in grip force control after stroke contribute to functional limitations in performing skilled tasks with the paretic hand.Implications for rehabilitationDriving is an important goal for independent mobility after stroke that requires motor capability to manipulate hand and foot controls.Two prominent stroke-related motor impairments that may impact precise car steering are reduced grip strength and grip force control.In individuals with mild-moderate impairments, deficits in grip force modulation rather than grip strength contribute to compromised steering performance with the paretic hand.We recommend that driving rehabilitation should consider re-educating grip force modulation for successful driving outcomes post stroke.

Functional implications of impaired bimanual force coordination in chronic stroke.

BACKGROUND: The ability to coordinate forces with both hands is crucial for manipulating objects in bimanual tasks. The purpose of this study was to determine the influence of bimanual force coordination on collaborative hand use for dexterous tasks in chronic stroke survivors. METHODS: Fourteen stroke survivors (63.03 ±â€¯15.33 years) and 14 healthy controls (68.85 ±â€¯8.16) performed two bimanual tasks: 1) Pegboard assembly task, and 2) dynamic force tracking task using bilateral index fingers. The Pegboard assembly task required collaborative use of both hands to construct a structure with pins, collars, and washers. We quantified bimanual dexterity with Pegboard assembly score as the total number of pins, collars, and washers assembled in one minute. The force tracking task involved controlled force increment and decrement while tracking a trapezoid trajectory. The task goal was to match the target force with the total force, i.e., sum of forces produced by both hands as accurately as possible. We quantified bimanual force coordination by computing time-series cross-correlation coefficient, time-lag, amplitude of coherence in 0 - 0.5 Hz, and 0.5-1 Hz for force increment and decrement phases. RESULTS: In the Pegboard assembly task, the stroke group assembled fewer items relative to the control group (p = 0.004). In the bimanual force tracking task, the stroke group showed reduced cross-correlation coefficient (p = 0.01), increased time-lag (p = 0.00), and reduced amplitude of coherence in 0-0.5 Hz (p = 0.03) and in 0.5-1 Hz (p = 0.00). Multiple regression analysis in the stroke group revealed that performance on Pegboard assembly task was explained by cross-correlation coefficient and coherence in 0.5-1 Hz during force increment (R2 = 0.52, p = 0.00). CONCLUSIONS: Individuals with stroke show impaired bimanual dexterity and diminished bimanual force coordination. Importantly, stroke-related deterioration in bimanual force coordination was associated with poor performance on dexterous bimanual tasks that require collaboration between hands. Re-training bimanual force coordination in stroke survivors could facilitate a higher degree of participation in daily activities through improved bimanual dexterity.

Force control predicts fine motor dexterity in high-functioning stroke survivors.

BACKGROUND AND PURPOSE: High-functioning stroke survivors with mild to moderate motor impairments show greater functional autonomy in activities of daily living, and often return to work or prior activities. Increased functional independence necessitates dexterous use of hands to execute tasks such as typing, using a phone, and driving. Despite the absence of any pronounced motor impairments, high-functioning individuals with stroke report challenges in performing skilled manual tasks. Two prominent motor deficits that limit functional performance after stroke are decline in strength and force control. Here, we quantify the deficits in fine motor dexterity in high-functioning stroke survivors and determine the relative contribution of strength and force control to fine motor dexterity. METHODS: Fifteen high-functioning participants with stroke (upper-limb Fugl-Meyer score ≥43/66) and 15 controls performed following tasks with the paretic and non-dominant hands respectively: i) Nine-hole peg pest, ii) maximum voluntary contraction and iii) dynamic force tracking with isometric finger flexion. RESULTS: High-functioning stroke participants required greater time to complete the pegboard task, showed reduced finger strength, and increased force variability relative to the controls. Importantly, the time to complete pegboard task in high-functioning stroke participants was explained by finger force variability, not strength. DISCUSSION AND CONCLUSIONS: High-functioning stroke survivors show persistent deficits in fine motor dexterity, finger strength, and force control. The ability to modulate forces (control) contributes to fine motor dexterity in high-functioning stroke survivors. Interventions to improve fine motor dexterity in these individuals should include the assessment and training of force control.

Motor impairments in transient ischemic attack increase the odds of a positive diffusion-weighted imaging: A meta-analysis.

BACKGROUND: Unilateral motor impairment is a key symptom used in the diagnosis of transient ischemic attack (TIA). Diffusion-weighted imaging (DWI) is a promising diagnostic tool for detecting ischemic lesions. While both motor impairments and DWI abnormalities are linked to the diagnosis of TIA, the association between these prognostic factors is not well understood. OBJECTIVE: To examine the association between unilateral motor impairments and the odds of a positive DWI in TIA. Further, to determine whether the time between symptom onset and neuroimaging (delay to scan) influences the odds of a positive DWI. METHODS: We used PRISMA guidelines to conduct a systematic search from 1989 to 2018. We included studies that reported number of individuals with/without unilateral motor symptoms and a positive/negative DWI. RESULTS: Twenty-four studies from North America, Australia, Asia, and Europe were submitted to a meta-analysis. A pooled odds ratio of 1.80 (95% CI, 1.45-2.24, p = 0.00; I2 = 57.38) suggested that the odds of a positive DWI are greater in TIA individuals who experience motor symptoms as compared with those who experience no motor symptoms. Further, increasing the time delay to scan from the symptom onset (>2 days) did not influence the odds of a positive DWI as compared with an earlier scan (≤2 days). CONCLUSIONS: The current meta-analysis provides cumulative evidence from 6710 individuals with TIA that the presence of motor symptoms increases the odds of a positive DWI by two-folds. These findings transform the clinical perception into evidence-based knowledge that motor impairments elevate the risk for brain tissue damage. Unilateral motor impairments in a cerebrovascular event should increase a physician's suspicion of detecting brain infarctions. These findings may influence the clinical management of TIA by generating faster response to motor impairments in TIA and accelerating referral to specialized stroke clinic.

Is simulator-based driver rehabilitation missing motion feedback?

Currently, driver rehabilitation involves use of fixed-base simulators. Such simulators are used infrequently and with little success. We hypothesize that the absence of motion feedback may be limiting the therapeutic effectiveness of driving simulation. During real, motor vehicle driving, the driver receives motion feedback that provides rich and real-time information about acceleration, deceleration and turning of the vehicle. Thus, motion feedback may be a key missing component that could dramatically increase the clinical pragmatism of simulator-based driver rehabilitation. In this pilot study, six young adult drivers participated in simulated driving tasks with or without motion feedback. Participants who received motion feedback completed faster laps on a racetrack and committed fewer driving infractions on a highway. They reported being more motivated and aware of the pressure of high speed driving. Particularly, they experienced substantially fewer symptoms of simulator sickness, a primary impedient to widespread use of driving simulators for driver rehabilitation. These preliminary finding motivate a full investigation of the impacts of motion feedback during simulated driving, and of the efficacy of lower cost, two degree of freedom driving simulators for clinical use.

Dynamic bimanual force control in chronic stroke: contribution of non-paretic and paretic hands.

Dynamic force modulation is critical for performing skilled bimanual tasks. Unilateral motor impairments after stroke contribute to asymmetric hand function. Here, we investigate the impact of stroke on dynamic bimanual force control and compare the contribution of each hand to a bimanual task. Thirteen chronic stroke and thirteen healthy control participants performed bimanual, isometric finger flexion during visually guided, force tracking of a trapezoidal trajectory with force increment and decrement phases. We quantified the accuracy and variability of total force from both hands. Individual hand contribution was quantified with the proportion of force contributed to total force and force variability of each hand. The total force output was 53.10% less accurate and 56% more variable in the stroke compared with the control group. The variability of total force was 91.10% greater in force decrement than increment phase. In stroke group, the proportion of force and force variability contributed by each hand differed across the two phases. During force decrement, the proportion of force contributed by the non-paretic hand reduced and force variability of the non-paretic hand increased, compared with the increment phase. The control group showed no differences in each hand's contribution across the two force phases. In conclusion, dynamic bimanual force modulation is impaired after stroke, with greater deficits in force decrement than force increment. The non-paretic and paretic hands adapt differentially to dynamic bimanual task constraints. During force decrement, the non-paretic hand preferentially assumes force modulation, while the paretic hand produces steady force to meet the force requirements.

Endpoint accuracy of goal-directed ankle movements correlates to over-ground walking in stroke.

OBJECTIVES: Goal-directed movements are essential for voluntary motor control. The inability to execute precise goal-directed movements after stroke can impair the ability to perform voluntary functions, learn new skills, and hinder rehabilitation. However, little is known about how the accuracy of single-joint, goal-directed ankle movements relates to multi-joint, lower limb function in stroke. Here, we determined the impact of stroke on the accuracy of goal-directed ankle movements and its relation to over-ground walking. METHODS: Stroke (N = 28) and control (N = 28) participants performed (1) goal-directed ankle dorsiflexion movements to accurately match 9 degrees in 180 ms and (2) over-ground walking. During goal-directed ankle movements, we measured the endpoint error, position error, time error and the activation of the agonist and antagonist muscles. During over-ground walking, we measured the walking speed, paretic stride length, and cadence. RESULTS: The stroke group demonstrated increased endpoint error than the controls. Increased endpoint error was associated with increased co-activation between agonist-antagonist muscles. Endpoint error was a significant predictor of walking speed and paretic stride length in stroke. CONCLUSIONS: Impaired accuracy of goal-directed, ankle movements is correlated to over-ground walking in stroke. SIGNIFICANCE: Quantifying accuracy of goal-directed ankle movements may provide insights into walking function post-stroke.

Bimanual force control differs between increment and decrement.

BACKGROUND: Everyday bimanual tasks require increasing and decreasing forces to manipulate objects. Optimal bimanual coordination during force increment and decrement is essential to complete a bimanual task. However, little is known about the differences in bimanual control during force increment and decrement. The purpose of this study was to 1) investigate whether task performance and bimanual coordination differ between force increment and force decrement in a bimanual task, and 2) determine the contribution of bimanual coordination to task performance during force increment and force decrement. METHODS: Seventeen right-handed young adults (24.10 ± 3.09 years) performed following tasks involving bimanual isometric index finger flexion: 1) maximum voluntary contractions and 2) visually-guided force tracking involving gradual force increment and decrement. The force tracking task involved controlled force increment and decrement while tracking a trapezoid trajectory. The task goal was to match the target force with the total force, i.e., sum of forces produced by both hands as accurately as possible. We quantified bimanual task performance with the accuracy and variability of total force in force increment and decrement phases. We measured bimanual coordination between two hand forces by computing time-series cross-correlation coefficient and amplitude of coherence in 0-1 Hz. RESULTS: We found decreased accuracy and increased variability of the total force in decrement compared with increment phase. Further, the cross-correlation coefficient and coherence amplitude were greater during force decrement than force increment phase. Finally, cross-correlation coefficient and coherence in 0.5-1 Hz predicted the accuracy and variability of total force. CONCLUSIONS: We provide evidence that task performance is reduced during force decrement as compared with force increment, suggesting that force release is more challenging than force generation in bimanual tasks. Further, bimanual coupling of the forces was better during force decrement than force increment. Overall, the coordination of forces from both hands influences the task performance across combined increment and decrement phases. Specifically, decoupling of forces produced by both hands facilitates error compensation strategy to reach the task goal. Together, these findings highlight that the bimanual control of forces is task-dependent and emphasize the importance of collaboration between hands in achieving a common task goal. These results may have implications for understanding changes in bimanual control with aging and neurological disorders.

Strength or Motor Control: What Matters in High-Functioning Stroke?

Background: The two primary motor impairments that hinder function after stroke are declines in strength and motor control. The impact of motor impairments on functional capacity may vary with the severity of stroke motor impairments. In this study, we focus on high-functioning stroke individuals who experience mild to moderate motor impairments and often resume prior activities or return to work. These tasks require the ability to move independently, placing high demands on their functional mobility. Therefore, the purpose of this study was to quantify impairments in strength and motor control and their contribution to functional mobility in high-functioning stroke. Methods:Twenty-one high-functioning stroke individuals (Fugl Meyer Lower Extremity Score = 28.67 ± 4.85; Functional Activity Index = 28.47 ± 7.04) and 21 age-matched healthy controls participated in this study. To examine motor impairments in strength and motor control, participants performed the following tasks with the paretic ankle (1) maximum voluntary contractions (MVC) and (2) visuomotor tracking of a sinusoidal trajectory. Strength was quantified as the maximum force produced during ankle plantarflexion and dorsiflexion. Motor control was quantified as (a) the accuracy and (b) variability of ankle movement during the visuomotor tracking task. For functional mobility, participants performed (1) overground walking for 7 meters and (2) simulated driving task. Functional mobility was determined by walking speed, stride length variability, and braking reaction time. Results: Compared with the controls, the stroke group showed decreased plantarflexion strength, decreased accuracy, and increased variability of ankle movement. In addition, the stroke group demonstrated decreased walking speed, increased stride length variability, and increased braking reaction time. The multiple-linear regression model revealed that motor accuracy was a significant predictor of the walking speed and braking reaction time. Further, motor variability was a significant predictor of stride length variability. Finally, the dorsiflexion or plantarflexion strength did not predict walking speed, stride length variability or braking reaction time. Conclusions: The impairments in motor control but not strength predict functional deficits in walking and driving in high-functioning stroke individuals. Therefore, rehabilitation interventions assessing and improving motor control will potentially enhance functional outcomes in high-functioning stroke survivors.

EMG synchrony to assess impaired corticomotor control of locomotion after stroke.

Adapting one's gait pattern requires a contribution from cortical motor commands. Evidence suggests that frequency-based analysis of electromyography (EMG) can be used to detect this cortical contribution. Specifically, increased EMG synchrony between synergistic muscles in the Piper frequency band has been linked to heightened corticomotor contribution to EMG. Stroke-related damage to cerebral motor pathways would be expected to diminish EMG Piper synchrony. The objective of this study is therefore to test the hypothesis that EMG Piper synchrony is diminished in the paretic leg relative to nonparetic and control legs, particularly during a long-step task of walking adaptability. Twenty adults with post-stroke hemiparesis and seventeen healthy controls participated in this study. EMG Piper synchrony increased more for the control legs compare to the paretic legs when taking a non-paretic long step (5.02±3.22% versus 0.86±2.62%), p<0.01) and when taking a paretic long step (2.04±1.98% versus 0.70±2.34%, p<0.05). A similar but non-significant trend was evident when comparing non-paretic and paretic legs. No statistically significant differences in EMG Piper synchrony were found between legs for typical walking. EMG Piper synchrony was positively associated with walking speed and step length within the stroke group. These findings support the assertion that EMG Piper synchrony indicates corticomotor contribution to walking.

Motor Impairments in Transient Ischemic Attack Increase the Odds of a Subsequent Stroke: A Meta-Analysis.

BACKGROUND AND PURPOSE: Transient ischemic attack (TIA) increases the risk for a subsequent stroke. Typical symptoms include motor weakness, gait disturbance, and loss of coordination. The association between the presence of motor impairments during a TIA and the chances of a subsequent stroke has not been examined. In the current meta-analysis, we examine whether the odds of a stroke are greater in TIA individuals who experience motor impairments as compared with those who do not experience motor impairments. METHODS: We conducted a systematic search of electronic databases as well as manual searches of the reference lists of retrieved articles. The meta-analysis included studies that reported an odds ratio relating motor impairments to a subsequent stroke, or the number of individuals with or without motor impairments who experienced a subsequent stroke. We examined these studies using rigorous meta-analysis techniques including random effects model, forest and funnel plots, I2, publication bias, and fail-safe analysis. RESULTS: Twenty-four studies with 15,129 participants from North America, Australia, Asia, and Europe qualified for inclusion. An odds ratio of 2.11 (95% CI, 1.67-2.65, p = 0.000) suggested that the chances of a subsequent stroke are increased by twofolds in individuals who experience motor impairments during a TIA compared with those individuals who have no motor impairments. CONCLUSION: The presence of motor impairments during TIA is a significantly high-risk clinical characteristic for a subsequent stroke. The current evidence for motor impairments following TIA relies exclusively on the clinical reports of unilateral motor weakness. A comprehensive examination of motor impairments in TIA will enhance TIA prognosis and restoration of residual motor impairments.

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.

Motor plan differs for young and older adults during similar movements.

Older adults exhibit altered activation of the agonist and antagonist muscles during goal-directed movements compared with young adults. However, it remains unclear whether the differential activation of the antagonistic muscles in older adults results from an impaired motor plan or an altered ability of the muscle to contract. The purpose of this study, therefore, was to determine whether the motor plan differs for young and older adults. Ten young (26.1 ± 4.3 yr, 4 women) and 16 older adults (71.9 ± 6.9 yr, 9 women) participated in the study. Participants performed 100 trials of fast goal directed movements with ankle dorsiflexion while we recorded the electromyographic activity of the primary agonist (tibialis anterior; TA) and antagonist (soleus; SOL) muscles. From those 100 trials we selected 5 trials in each of 3 movement end-point categories (fast, accurate, and slow). We investigated age-associated differences in the motor plan by quantifying the individual activity and coordination of the agonist and antagonist muscles. During similar movement end points, older adults exhibited similar activation of the agonist (TA) and antagonist (SOL) muscles compared with young adults. In addition, the coordination of the agonist and antagonist muscles (TA and SOL) was different between the two age groups. Specifically, older adults exhibited lower TA-SOL overlap (F1,23 = 41.2, P < 0.001) and greater TA-SOL peak EMG delay (F1,25 = 35.5, P < 0.001). This finding suggests that although subjects in both age groups displayed similar movement end points, they exhibited a different motor plan, as demonstrated by altered coordination between the agonist and antagonist muscles.NEW & NOTEWORTHY We aimed to determine whether the altered activation of muscles in older adults compared with young adults during fast goal-directed movements is related to an altered motor plan. For matched movements, there were differences in the coordination of antagonistic muscles but no differences in the individual activation of muscles. We provide novel evidence that the differential activation of muscles in older adults is related to an altered motor plan.